System for prevention of paroxysmal supraventricular tachycardia

• US 4,572,192 A
• Filed: 09/21/1983
• Issued: 02/25/1986
• Est. Priority Date: 09/21/1983
• Status: Expired due to Fees

• Current Assignee: The Board of Regents of the University of Colorado (University of Colorado System)
• Original Assignee: The Board of Regents of the University of Colorado (University of Colorado System)
• Inventors: Lazzara, Ralph, Jackman, Warren M.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US06/534,367
• Time in Patent Office: 888 Days
• Field of Search: 128/419 PG, 128/419 PT
• US Class Current: 607/14
• CPC Class Codes: A61N 1/3621 for treating or preventing abnormally high heart rate
• CPC Class Codes: A61N 1/3622 comprising two or more electrodes co-operating with different heart regions

Abstract

A system for aborting the dual pathway tachycardias in a heart comprising the syndrome of paroxysmal supraventricular tachycardia (due generally to atrioventricular nodal reentry or atrioventricular reentry using an anomalous atrioventricular connection for retrograde conduction) by sensing cardiac impulses and, with respect to each sensed cardiac impulse, determining if such sensed cardiac impulse is an inciting cardiac impulse, a cardiac impulse which occurs at a time with respect to the last received cardiac impulse which falls within a predetermined echo zone and which will result in the initiation of a dual pathway tachycardia, and inducing an aborting cardiac impulse in response to a sensed inciting cardiac impulse in the cardiac muscle at a time within the predetermined aborting zone for aborting the initiation of the dual pathway tachycardia. The system also contemplates sensing cardiac impulses and delivering aborting electrical stimuli at a particular position on the cardiac muscle to allow more accurate recognition of inciting cardiac impulses and for more effectively delivering the aborting electrical stimulus, inducing the aborting cardiac impulse in sufficient time to abort the onset of dual pathway tachycardia.

Claims

1. A system for aborting the initiation of a dual pathway tachycardia in a heart producing cardiac impulses induced as a result of an inciting cardiac impulse, comprising the steps of:

determining at least one time range, each time range being an echo zone, following a cardiac impulse within which an inciting cardiac impulse may occur resulting in a dual pathway tachycardia;

determining at least one time range, each time range being an aborting zone, following an inciting cardiac impulse within which an aborting cardiac impulse may be induced in the cardiac muscle for aborting the dual pathway tachycardia which otherwise would have occurred as a result of the inciting cardiac impulse;

sensing cardiac impulses in a heart;

determining a sensed inciting cardiac impulse as a sensed cardiac impulse sensed at a time within the echo zone; and

inducing an aborting cardiac impulse at a time within the aborting zone in response to sensing an inciting cardiac impulse.

2. The system of claim 1 wherein the heart'"'"'s cardiac impulses have cardiac cycle lengths (the time between maximum amplitudes of adjacent cardiac impulses, the cardiac cycles occurring in varying lengths which are referred to as ranges of cardiac cycle lengths);

and wherein the step of determining at least one echo zone is defined further to include determining a plurality of echo zones, each echo zone being determined for each of a plurality of predetermined ranges of cardiac cycle lengths; and

wherein the step of determining at least one aborting zone is defined further to include determining a plurality of aborting zones, each aborting zone being determined for each of a plurality of the predetermined ranges of cardiac cycle lengths; and

wherein the step of sensing the cardiac impulses is defined further to include the period of time lapsed between the sensed cardiac impulse and the last sensed cardiac impulse; and

wherein the system is defined further to include the steps of;

continuously determining the cardiac cycle length;

continuously determining an average cardiac cycle length for a predetermined time period or a predetermined number of sensed cardiac impulses prior to the last sensed cardiac impulse;

determining the lapse of time between each sensed cardiac impulse and the last sensed cardiac impulse;

determining, for each sensed cardiac impulse, the echo zone and the aborting zone corresponding to the last determined average cardiac cycle length; and

comparing the determined lapse of time between each sensed cardiac impulse and the last sensed cardiac impulse with the echo zone determined from the last determined average cardiac cycle length to determine if the sensed cardiac impulse occurred at a time within such determined echo zone thereby determining if the sensed cardiac impulse is an inciting cardiac impulse; and

wherein the step of inducing the aborting cardiac impulse is defined further as delivering an aborting electrical stimulus to the cardiac muscle at a time within the aborting zone determined from the last determined average cardiac cycle length to induce aborting cardiac impulse.

3. The system of claim 2 wherein the aborting zone has a start time and a stop time, and wherein the step of inducing the aborting cardiac impulse is defined further as inducing the aborting cardiac impulse at a time within the aborting zone determined from the last determined average cardiac cycle length and at a time relatively close in time to the start time of the aborting zone.

4. The system of claim 2 wherein the echo zone is defined further as having a start time spaced in time a predetermined time period from the last sensed cardiac impulse signal and a stop time spaced in time a predetermined time period from the last sensed cardiac impulse signal.

5. The system of claim 4 wherein the aborting zone is defined further to include a start time and a stop time, the start time of the aborting zone being spaced in time a predetermined time period from the inciting cardiac impulse and the stop time of the aborting zone being spaced a predetermined time period from the inciting cardiac impulse.

6. The system of claim 5 wherein the heart includes a first pathway for conducting an electrical impulse generally between the atria and the ventricles and a second pathway for conducting an electrical impulse generally between the atria and the ventricles, the first and second pathway each having conducting cells which will function to conduct an electrical impulse when reconditioned (including repolarization) and which require a period of time after being depolarized to be reconditioned for conducting a subsequently received electrical impulse and the period of time for reconditioning after being depolarized is referred to as the refractory period, and wherein the start time of the echo zone is defined further as being a time after the last sensed cardiac impulse signal when the conducting cells in one of the first and second pathways are reconditioned and the conducting cells in the other one of the first and second pathways are not yet reconditioned.

7. The system of claim 6 wherein the echo zone is defined further as being a period of time after a last sensed cardiac impulse during which an inciting cardiac impulse conducted through one of the first and second pathways can be conducted back through the other one of the first and second pathways to produce a cardiac echo impulse, the conducting cells in the last mentioned other one of the first and second pathways being reconditioned for conducting such a returning impulse.

8. The system of claim 1 wherein the dual pathway tachycardia is defined further as being due to atrioventricular nodal reentry wherein the atrioventricular node in the heart includes a first pathway adapted for conducting an electrical impulse generally between the atria and the ventricles and a second pathway adapted for conducting an electrical impulse generally between the atria and the ventricles;

and wherein the step of determining the echo zone is defined further as determining the A₂ echo zone following a sensed atrial impulse A₁ within which an inciting atrial impulse A₂ may occur resulting in dual pathway tachycardia; and

wherein the step of determining the aborting zone is defined further as determining the A₃ aborting zone following an inciting atrial impulse A₂ within which an aborting atrial impulse A₃ may be induced in the atria for aborting the dual pathway tachycardia which otherwise would have occurred as a result of the inciting atrial impulse A₂ ; and

wherein the step of sensing cardiac impulses is defined further as sensing atrial impulses A₁ '"'"'s in a heart (an inciting atrial impulse A.sub. 2 being an atrial impulse A₁ which occurs at a time within the A₂ echo zone) and wherein the step of inducing an aborting cardiac impulse is defined further as inducing an aborting atrial impulse A₃ at a time within the A₃ aborting zone in response to sensing an inciting atrial impulse A₂.

9. The system of claim 8 wherein the heart'"'"'s cardiac impulses have cardiac cycle lengths (the time between maximum amplitudes of adjacent cardiac impulses, the cardiac cycles occurring in varying lengths which are referred to as ranges of cardiac cycle lengths);

and wherein the step of determining at least one echo zone is defined further to include determining an A₂ echo zone for each of a plurality of predetermined ranges of atrial cycle lengths; and

wherein the step of determining at least one aborting zone is defined further to include determining an A₃ aborting zone for each of a plurality of the predetermined ranges of atrial cycle lengths; and

wherein the step of sensing the atrial impulses A₁ '"'"'s is defined further as determining the period of time lapsed between the sensed atrial impulse A₁ and the last sensed atrial impulse A₁ ; and

wherein the system is defined further to include the steps of;

continouously determining the atrial cycle length;

continuously determining an average atrial cycle length for a predetermined time period or a predetermined number of sensed atrial impulses A₁ '"'"'s prior to the last sensed atrial impulse;

determining the lapse of time between each sensed atrial impulse A₁ and the last sensed atrial impulse A₁ ;

determining, for each sensed atrial impulse A₁, the A₂ echo zone and the A₃ aborting zone corresponding to the last determined average atrial cycle length; and

comparing the determined lapse of time between each sensed atrial impulse A₁ and the last sensed atrial impulse A₁ with the A₂ echo zone determined from the last determined average atrial cycle length to determine if the sensed atrial impulse A₁ occurred at a time within such determined A₂ echo zone thereby determining if the sensed atrial impulse A₁ is an inciting atrial impulse A₂ ; and

wherein the step of inducing the aborting atrial impulse A₃ is defined further as delivering an aborting electrical stimulus S_A.sbsb.3 to the atrial cardiac muscle at a time within the A₃ aborting zone determined from the last determined average atrial cycle length.

10. The system of claim 9 wherein the A₃ aborting zone includes a start time and a stop time, and wherein the step of inducing the aborting atrial impulse A₃ is defined further as inducing the aborting atrial impulse A₃ at a time within the A₃ aborting zone determined from the last determined average atrial cycle length and at a time relatively close in time to the start time of the A₃ aborting zone.

11. The system of claim 9 wherein the steps of sensing the artial impulses A₁ '"'"'s and inducing the atrial aborting impulse A₃ are defined further as sensing the atrial impulses A₁ and delivering an aborting electrical stimulus S_A.sbsb.3 at a position on the atrial cardiac muscle generally near the atrioventricular node to:

(1) allow the system to define accurately whether a sensed atrial impulse A₁ occurs in the A₂ echo zone since the ability of an inciting atrial impulse A₂ to induce the form of dual pathway tachycardia referred to as atrioventricular nodal reentry, is in general dependent on the time of the arrival of the inciting atrial impulse A₂ at the atrioventricular node rather than the time of the arrival of the inciting atrial impulse A₂ elsewhere in the atrial cardiac muscle; and

(2) allow the aborting atrial impulse A₃ to be induced and conducted to the atrioventricular node in sufficient time to effectively abort the initiation of the dual pathway tachycardia.

12. The system of claim 8 wherein the A₂ echo zone is defined further as having a start time spaced in time a predetermined time period from the last sensed atrial impulse A₁ and a stop time spaced in time a predetermined time period from the last sensed atrial impulse A₁, for each of the predetermined ranges of average atrial cycle length.

13. The system of claim 12 wherein the A₃ aborting zone is defined further to include a start time and a stop time, the start time of the A₃ aborting zone being spaced in time a predetermined time period from the sensed inciting atrial impulse A₂ and the stop time of the A₃ aborting zone being spaced a predetermined time period from the sensed inciting atrial impulse A₂.

14. The system of claim 13 wherein an inciting atrial impulse A₂ is defined further as a atrial impulse received at the atrioventricular node under the following conditions:

(1) when the conducting cells in one of the first and second pathways are excitable (receptive);

(2) when the conducting cells in the other of the first and second pathways are still refractory (unreceptive) and block any received impulse;

(3) when the initially refractory conducting cells in the first or second pathway will be reconditioned (become excitable) in time to receive and conduct the impulse arriving at the junction of the first and second pathways near the ventricles, as a result of conduction of the inciting atrial impulse A₂ towards the ventricles through the initially conducting first or second pathway, back towards the atria to produce an atrial echo impulse A_e ; and

(4) when the conducting cells in the initially conducting first or second pathway will be reconditioned in time to receive and conduct the impulse arriving at the junction of the first and second pathways near the atria, as a result of conduction of the impulse towards the atria over the initially refractory first or second pathway, back towards the ventricles, forming a repetitive circuit.

15. The system of claim 14 wherein there is a period of time between a received atrial impulse A₁ and a time when an inciting atrial impulse A₂ might occur (start time of the A₂ echo zone) and this period of time is defined (among other factors) as being the longer of the atrial refractory period (period of time following the prior atrial impulse A₁ during which the atria cannot be reexcited) and the period of time following the last sensed atrial impulse A₁ during which the conducting cells in both the first and the second pathways still are refractory (not yet reconditioned to receive and conduct the atrial impulse) and an atrial impulse received during this period of time will be blocked in both first and second pathways.

16. The system of claim 15 wherein there is a time (the stop time of the A₂ echo zone) after the sensing of an atrial impulse A₁ after which another received atrial impulse A₁ will not constitute an inciting atrial impulse A₂ because (among other factors) either:

(1) the conducting cells in both the first and second pathways are reconditioned (receptive) and an atrial impulse received within this period of time will be conducted towards the ventricles through both the first and second pathways;

or (2) the atrial impulse A₁ is received sufficiently early in time with respect to the preceding atrial impulse A₁ that the cells in the first pathway still are refractory to excitation and the cells in the second pathway have recovered excitability (been reconditioned) allowing conduction to the ventricles only through the second pathway, but not sufficiently early to produce the degree of conduction delay in the second pathway (dampening effect) necessary to allow the cells in the first pathway to recover excitability to allow the impulse initially conducted through the second pathway to be conducted back towards the atria through the first pathway.

17. The system of claim 1 wherein the dual pathway tachycardia is defined further as being due to the presence of an anomalous atrioventricular connection wherein the heart includes an anomalous strand of conductive cells which extend around or through the annulus fibrosa to form a first pathway adapted for conducting an electrical impulse generally between the atria and the ventricles and the atrioventricular node provides a second pathway adapted for conducting an electrical impulse generally between the atria and the ventricles;

and wherein the step of determining the echo zone is defined further as determining the A₂ echo zone following a sensed atrial impulse A₁ within which an inciting atrial impulse A₂ may occur resulting in dual pathway tachycardia; and

wherein the step of determining the aborting zone is defined further as determining the A₃ aborting zone following an inciting atrial impulse A₂ within which an aborting atrial impulse A₃ may be induced in the atria for aborting the dual pathway tachycardia which otherwise would have occurred as a result of the inciting atrial impulse A₂ ; and

wherein the step of sensing cardiac impulses is defined further as sensing atrial impulses A₁ '"'"'s in a heart (an inciting atrial impulse A₂ being an atrial impulse A₁ which occurs at a time in the A₂ echo zone); and

wherein the step of inducing an aborting cardiac impulse is defined further as inducing an aborting atrial impulse A₃ at a time within the A₃ aborting zone in response to sensing an inciting atrial impulse A₂.

18. The system of claim 17 wherein the heart'"'"'s cardiac impulses have cardiac cycle lengths (the time between maximum amplitudes of adjacent cardiac impulses, the cardiac cycles occurring in varying lengths which are referred to as ranges of cardiac cycle lengths);

and wherein the step of determining at least one echo zone is defined further to include determining an A₂ echo zone for each of a plurality of predetermined ranges of atrial cycle lengths; and

wherein the step of determining at least one aborting zone is defined further to include determining an A₃ aborting zone for each of a plurality of the predetermined ranges of atrial cycle lengths; and

wherein the step of sensing the atrial impulses A₁ '"'"'s is defined further as determining the period to time lapsed between the sensed atrial impulse A₁ and the last sensed atrial impulse A₁ ; and

wherein the system is defined further to include the steps of;

continuously determining the atrial cycle length;

continuously determining an average atrial cycle length for a predetermined time period or a predetermined number of sensed atrial impulses A₁ '"'"'s prior to the last sensed atrial impulse A₁ ;

determining the lapse of time between each sensed atrial impulse A₁ and the last sensed atrial impulse A₁ ;

determining, for each sensed atrial impulse A₁, the A₂ echo zone and the A₃ aborting zone corresponding to the last determined average atrial cycle length; and

comparing the determined lapse of time between each sensed atrial impulse A₁ and the last sensed atrial impulse A₁ with the A₂ echo zone determined from the last determined average atrial cycle length to determine if the sensed atrial impulse A₁ occurred at a time within such determined A₂ echo zone thereby determining if the sensed atrial impulse A₁ is an inciting atrial impulse A₂ ; and

wherein the step of inducing the aborting atrial impulse A₃ is defined further as delivering an aborting electrical stimulus S_A.sbsb.3 to the atrial cardiac muscle at a time within the A₃ aborting zone determined from the last determined average atrial cycle length.

19. The system of claim 18 wherein the steps of sensing the atrial impulses A₁ '"'"'s and inducing the atrial aborting impulse A₃ are defined further as sensing the atrial impulses A₁ '"'"'s and delivering the aborting electrical stimuli S_A.sbsb.3 '"'"'s at a position on the atrial cardiac muscle generally near the atrioventricular node (second pathway), and when practical between the atrioventricular node and the atrial insertion site of the anomalous atrioventricular connection (first pathway) to:

(1) allow the system to define accurately whether an atrial impulse A₁ occurs within the A₂ echo zone because the ability of an atrial impulse A₁ to induce the form of dual pathway tachycardia referred to as atrioventricular nodal reentry using an anomalous atrioventricular connection for retrograde conduction is in general dependent on the time of its arrival at the first and second pathways; and

(2) allow the aborting atrial impulse A₃ to be induced and conducted to the second pathway (atrioventricular node) in sufficient time to effectively abort the initiation of the dual pathway tachycardia.

20. The system of claim 17 wherein the A₃ aborting zone includes a start time and stop time, and wherein the step of inducing the aborting atrial impulse A₃ is defined further as inducing the aborting atrial impulse A₃ at a time within the A₃ aborting zone determined from the last determined average atrial cycle length and at a time relatively close in time to the start time of the A₃ aborting zone.

21. The system of claim 17 wherein the A₂ echo zone is defined further as having a start time spaced in time a predetermined time period from the last sensed atrial impulse A₁ and a stop time spaced in time a predetermined time period from the last sensed atrial impulse A₁.

22. The system of claim 21 wherein the A₃ aborting zone is defined further to include a start time and a stop time, the start time of the A₃ aborting zone being spaced in time a predetermined time period from the sensed inciting atrial impulse A₂ and the stop time of the A₃ aborting zone being spaced a predetermined time period from the sensed inciting atrial impulse A₂.

23. The system of claim 17 wherein an inciting atrial impulse A₂ is received at the first and second pathways under the following conditions:

(1) when the conducting cells in one of the first and second pathways are excitable (receptive);

(2) when the conducting cells in the other one of the first and second pathways are still refractory (unreceptive);

(3) when the initially refractory conducting cells in the first or second pathway will be reconditioned (become excitable) in time to receive and conduct the impulse arriving at the junction of the first and second pathways near the ventricles, as a result of conduction of the inciting atrial impulse A₂ through the initially conducting first or second pathway, back to the atria to produce an atrial echo impulse A_e ; and

(4) when the conducting cells in the initially conducting first or second pathway will be reconditioned in time to receive and conduct the atrial echo impulse A_e back to the ventricles forming a repetitive circuit.

24. The system of claim 23 wherein there is a period of time between a received atrial impulse signal A₁ and a time when an inciting atrial impulse A₂ might occur (start time of the A₂ echo zone) and this period of time is defined as being the longer of the atrial refractory period (period of time following the prior atrial impulse A₁ during which the atria cannot be reexcited) and the period of time following the last sensed atrial impulse A₁ during which the conducting cells in both the first and the second pathways still are refractory (not yet reconditioned to receive and conduct the atrial impulse) and an atrial impulse received during this period of time will be blocked in both first and second pathways.

25. The system of claim 24 wherein there is a time (the stop time of the A₂ echo zone) after the sensing of an atrial impulse signal A₁ after which another sensed atrial impulse A₁ will not constitute an inciting atrial impulse A₂ because either:

(1) the conducting cells in both the first and second pathways are reconditioned (receptive) and an atrial impulse A₁ received within this period of time will be conducted towards the ventricles through both the first and second pathways;

or (2) the atrial impulse A₁ is received sufficiently early in time with respect to the preceding atrial impulse A₁ that the cells in the first pathway still are refractory to excitation and the cells in the second pathway have recovered excitability (been reconditioned) allowing conduction to the ventricles only through the second pathway, but not sufficiently early to produce the degree of conduction delay in the second pathway (dampening effect) necessary to allow the cells in the first pathway to recover excitability to allow the impulse initially conducted through the second pathway to be conducted back towards the atria through the first pathway.

26. The system of claim 17 wherein the accessory (anomalous) pathway (the first pathway) is defined further as being capable of conduction only in the retrograde direction (from the ventricles to the atria) and wherein an inciting atrial impulse A₂ is defined further as being an atrial impulse A₁ which occurs at a time after the conducting cells in the second pathway (atrioventricular node) have been reconditioned to conduct an impulse and at a time such that, when the inciting atrial impulse A₂ is conducted through the second pathway to the junction of the first and second pathways near the ventricles, the conducting cells in the first pathway have been reconditioned to receive and conduct this impulse back towards the atria thereby producing an atrial echo impulse A_e and at such a time so that, when the atrial echo impulse A_e is received by the conducting cells in the second pathway, the conducting cells in the second pathway have had sufficient time to be reconditioned for receiving and conducting this atrial echo impulse A_e back towards the ventricles initiating a condition of sustained reentering of the second pathway in the antegrade direction (atria to ventricles) and the first pathway in the retrograde direction (ventricles to atria).

27. The system of claim 1 wherein the dual pathway tachycardia is defined as being induced by an inciting ventricular impulse (V₂)_x originating in the ventricles and resulting in an inciting atrial impulse (A₂)_x, and wherein the heart includes a first pathway adapted for conducting an electrical impulse generally between the atria and the ventricles and a second pathway adapted for conducting an electrical impulse generally between the atria and the ventricles;

and wherein the step of determining the echo zone is defined further as determining the (A₂)_x echo zone following a sensed atrial impulse A₁ within which an inciting atrial impulse (A₂)_x may occur as a result of conduction of the inciting ventricular impulse (V₂)_x to the atria through the initially conducting first or second pathway and which result in dual pathway tachycardia; and

wherein the step of determining the aborting zone is defined further as determining the (A₃)_x aborting zone following a sensed inciting atrial impulse (A₂)_x within which an aborting atrial impulse (A₃).sub. x may be induced in the atrial cardiac muscle for aborting the dual pathway tachycardia which otherwise would have occurred as a result of the inciting ventricular impulse (V₂)_x and the subsequent inciting atrial impulse (A₂)_x ; and

wherein the step of sensing cardiac impulses is defined further as sensing atrial impulses A₁ '"'"'s in a heart; and

wherein the step of inducing an aborting cardiac impulse is defined further as inducing an aborting atrial impulse (A₃)_x at a time within the (A₃)_x aborting zone in response to sensing an inciting atrial impulse (A₂)_x.

28. The system of claim 27 wherein the inciting ventricular impulse (V₂)_x is defined further as occuring at a time in which one of the first or second pathways has been reconditioned to accept and conduct the inciting ventricular impulse (V₂)_x towards the atria while the other one of the first and second pathways has not been reconditioned (still refractory to excitation) to accept and conduct the inciting ventricular impulse (V₂)_x towards the atria, thereby resulting in:

(1) conduction of the inciting ventricular impulse (V₂)_x towards the atria through the initially conducting first or second pathway; and

(2) block of the inciting ventricular impulse (V₂)_x in the pathway other than the initially conducting first or second pathway, and the inciting ventricular impulse (V₂)_x being further defined as being conducted through the initially conducting first or second pathway and arriving at the junction of the first and second pathways near the atria at a time in which the pathway other than the initially conducting first or second pathway has been reconditioned, that impulse being conducted towards the ventricles through the pathway other than the initially conducting first or second pathway producing another ventricular impulse (ventricular echo impulse V_e), and the reconduction of the ventricular echo impulse V_e back toward the atria resulting in a repetitive reentering of the conducted impulse between the first and second pathways (dual pathway tachycardia).

29. The system of claim 28 wherein the inciting ventricular impulse (V₂)_x is defined further as being a ventricular impulse V₁ occuring within a (V₂)_x echo zone having a start time and a stop time, the period of time between the last ventricular impulse V₁ and a time when an inciting ventricular impulse (V₂)_x might occur being the start time of the (V₂)_x echo zone, this period of time being the longer of the ventricular refractory period (period of time following the last ventricular impulse V₁ during which the ventricles cannot be reexcited) and the period of time following the last ventricular impulse V₁ during which the conducting cells in both the first and second pathways still are refractory to excitation (not yet reconditioned to receive and conduct the ventricular impulse towards the atria) and a ventricular impulse V₁ received during this period of time being blocked in both the first and second pathways.

30. The system of claim 29 wherein the stop time of the (V₂)_x echo zone is defined as being a time after a ventricular impulse V₁ after which another received ventricular impulse V₁ will not constitute an inciting ventricular impulse (V₂)_x because either:

(1) the conducting cells of both the first and second pathways are reconditioned (receptive) and a ventricular impulse received within this period of time simply will be conducted towards the atria through both the first and second pathways resulting only in a single atrial impulse;

or (2) the ventricular impulse is received sufficiently early in time with respect to the last received ventricular impulse V₁ that the conducting cells in one of the first or second pathways still are refractory to excitation and the cells in the other first or second pathway have been reconditioned to receive and conduct the ventricular impulse towards the atria, but not sufficiently early to either prevent enough penetration of the ventricular impulse into the initially blocking first or second pathway or to produce sufficient conduction delay through the initially conducting first or second pathway such that when the impulse traveling toward the atria through the initially conducting first or second pathway penetrates the initially blocking first or second pathway and attempts to conduct through that pathway back toward the ventricles, that impulse encounters cells which have not yet become reconditioned to accept and conduct the impulse, extinguishing the impulse and preventing the initiation of a dual pathway tachycardia.

31. The system of claim 27 wherein the (A₂)_x echo zone is defined further as having a start time and a stop time, the start time of the (A₂)_x echo zone being the earliest time when an inciting atrial impulse (A₂)_x can occur following an inciting ventricular impulse (V₂)_x and the stop time of the (A₂)_x echo zone being the latest time when an inciting atrial impulse (A₂)_x can occur following an inciting ventricular impulse (V₂)_x.

32. The system of claim 31 wherein the heart'"'"'s cardiac impulses have cardiac cycle lengths (the time between maximum amplitudes of adjacent cardiac impulses, the cardiac cycles occurring in varying lengths which are referred to as ranges of cardiac cycle lengths);

and wherein the step of determining at least one echo zone is defined further to include determining an (A₂)_x echo zone for each of a plurality of predetermined ranges of atrial cycle lengths; and

determining an (A₃)_x aborting zone for each of a plurality of the predetermined ranges of atrial cycle lengths; and

wherein the step of sensing the atrial impulses A₁ '"'"'s is defined further as determining the period of time lapsed between the sensed atrial impulse A₁ and the last sensed atrial impulse signal A₁ ; and

wherein the system is defined further to include the steps of;

continuously determining the atrial cycle length;

continuously determining an average atrial cycle length for a predetermined time period or a predetermined number of sensed atrial impulses A₁ '"'"'s prior to the last sensed atrial impulse signal A₁ ;

determining the lapse of time between each sensed atrial impulse A₁ and the last sensed atrial impulse signal A₁ ;

determining, for each sensed atrial impulse A₁, the (A₂)_x echo zone and the (A₃)_x aborting zone corresponding to the last determined average atrial cycle length; and

comparing the determined lapse of time between each sensed atrial impulse A₁ and the last sensed atrial impulse A₁ with the (A₂)_x echo zone determined from the last determined average atrial cycle length to determine if the sensed atrial impulse A₁ occurred at a time within such determined (A₂)_x echo zone thereby determining if the sensed atrial impulse A₁ is an inciting atrial impulse (A₂)_x ; and

wherein the step of inducing the aborting atrial impulse (A₃)_x is defined further as delivering an aborting electrical stimulus S(_A.sbsb.3)_x to the atrial cardiac muscle at a time within the (A₃)_x aborting zone determined from the last determined average atrial cycle length.

33. The system of claim 32 wherein the step of inducing the aborting atrial impulse (A₃)_x is defined further as inducing the aborting atrial impulse (A₃)_x at a time within the (A₃)_x aborting zone determined from the last determined average atrial cycle length and at a time relatively close in time to the start time of the (A₃)_x aborting zone.

34. The system of claim 31 wherein the step of inducing the aborting atrial impulse (A₃)_x is defined further as delivering an aborting electrical stimulus S(_A.sbsb.3)_x to the atrial cardiac muscle at a time within the (A₃)_x aborting zone to produce the aborting atrial impulse (A₃)_x, the aborting atrial impulse (A₃)_x being an atrial impulse arriving at the first or second pathways before the arrival of the inciting ventricular impulse (V₂)_x returning toward the atrium through the initially conducting first or second pathway and at a time during which the conducting cells of the first or second pathway other than the initially conducting first or second pathway still are refractory to excitation (unreceptive), thereby resulting in:

(1) the blocking of the aborting atrial impulse (A₃)_x in the first or second pathway other than the initially conducting first or second pathway; and

(2) the collison in the initially conducting first or second pathway of the aborting atrial impulse (A₃)_x being conducted towards the ventricles and the inciting ventricular impulse (V₂)_x being conducted back toward the atria, extinguishing both impulses (A₃)_x and (V₂)_x and aborting of the dual pathway tachycardia.

35. The system of claim 34 wherein the (A₃)_x aborting zone is defined further as having a start time and a stop time, the start time of the (A₃)_x aborting zone being a time before which a delivered electrical stimulus S(_A.sbsb.3)_x will not induce an aborting atrial impulse (A₃)_x because either:

(1) the atrial cardiac cells still are refractory to excitation (not yet reconditioned) following the received inciting atrial impulse (A₂)_x and the electrical stimulus S(_A.sbsb.3)_x will not result in an atrial impulse;

or (2) the resulting atrial impulse penetrates and blocks in both pathways and the conduction time of the inciting ventricular impulse (V₂)_x returning toward the atria through the initially conducting first or second pathway is sufficiently long to allow the cells of both the first and second pathways to recover excitability (become reconditioned) following the penetration of the first and second pathways by the atrial impulse (A₃)_x induced by the electrical stimulus S(_A.sbsb.3)_x , then the returning inciting ventricular impulse (V₂)_x can be conducted toward the ventricles through the initially conducting first or second pathway and reenter the first or second pathway other than the initially conducting first or second pathway and be conducted back through that pathway toward the ventricles initiating the dual pathway tachycardia; and

the stop time of the (A₃)_x aborting zone being a time after a sensed inciting atrial impulse (A₂)_x after which an electrical stimulus S(_A.sbsb.3)_x delivered to the atrial cardiac muscle will not result in an aborting atrial impulse (A₃)_x because the resulting atrial impulse will either;

(1) arrive at the junction of the first and second pathways near the atria at a time after the inciting ventricular impulse (V₂)_x returning towards the atria through the initially conducting first or second pathway has reentered the first or second pathway other than the initially conducting first or second pathway and is being conducted through the first or second pathway other than the initially conducting first or second pathway toward the ventricles;

or (2) arrive at the junction of the first and second pathways near the atria at a time after the conducting cells of the first or second pathway other than the initially conducting first or second pathway have become reconditioned to accept and conduct the arial impulse toward the ventricles.

36. The system of claim 1 wherein the dual pathway tachycardia is defined further as being due to either one or both atrioventricular nodal reentry and atrioventricular reentry using an anomalous atrioventricular connection for retrograde and an inciting ventricular impulse (V₂)_x originating in the ventricles and resulting in an inciting atrial impulse (A₂)_x and wherein the heart includes a first pathway adapted for conducting an electrical impulse generally between the atria and the ventricles and a second pathway adapted for conducting an electrical impulse generally between the atria and the ventricles;

and wherein the step of determining the echo zone is defined further as determining the A₂ echo zone following a sensed atrial impulse A₁ within which an inciting atrial impulse A₂ may occur resulting in dual pathway tachycardia and determining an (A₂)_x echo zone following a sensed atrial impulse A₁ within which an inciting atrial impulse (A₂)_x may occur resulting in dual pathway tachycardia; and

wherein the step of determining the aborting zone is defined further as determining the A₃ aborting zone following an inciting atrial impulse A₂ within which an aborting atrial impulse A₃ may be induced in the atrial cardiac muscle for aborting the dual pathway tachycardia which otherwise would have occurred as a result of the inciting atrial impulse A₂ and determining the (A₃)_x aborting zone following an inciting atrial impulse (A₂)_x within which an aborting atrial impulse (A₃)_x may be induced in the atrial cardiac muscle for aborting the dual pathway tachycardia which otherwise would have occured as a result of the inciting ventricular impulse (V₂)_x and its resultant inciting atrial impulse (A₂)_x ; and

wherein the step of sensing cardiac impulses is defined further as sensing atrial impulses A₁ '"'"'s in a heart; and

wherein the step of inducing an aborting cardiac impulse is defined further as inducing an aborting atrial impulse A₃ at a time within the A₃ aborting zone in response to sensing an inciting atrial impulse A₂ and inducing an aborting atrial impulse (A₃)_x at a time within the (A₃)_x aborting zone in response to sensing an inciting atrial impulse (A₂)_x.

37. The system of claim 36 wherein the A₂ echo zone has a start time and a stop time and wherein the (A₂)_x echo zone has a start time and a stop time, and wherein the A₃ aborting zone has a start time and a stop time, and wherein the (A₃)_x aborting zone has a start time and a stop time and wherein the system is defined further to include:

determining the overlapping time period between the A₂ echo zone and the (A₂)_x echo zone, the overlapping time period being the combined A₂ -(A₂)_x echo zone;

determining the time period common to both the A₃ aborting zone and the (A₃)_x aborting zone, the common time period being the combined A₃ -(A₃)_x aborting zone; and

wherein the step of inducing an aborting cardiac impulse is defined further to include delivering an electrical stimulus S_A.sbsb.3 -S(_A.sbsb.3)_x to the atrial cardiac muscle to induce an aborting atrial impulse A₃ -(A₃)_x in response to sensing an inciting atrial impulse A₂ and in response to sensing an inciting atrial impulse (A₂)_x ; and

wherein the A₂ -(A₂)_x echo zone is defined further to have a start time and a stop time, the start time of the A₂ -(A₂)_x echo zone being the shorter of the start times of the A₂ echo zone and the (A₂)_x echo zone and the stop time of the A₂ -(A₂)_x echo zone being the longer of the stop times of the A₂ echo zone and the (A₂)_x echo zone; and

wherein the A₃ -(A₃)_x aborting zone has a start time and a stop time, the start time of the A₃ -(A₃)_x aborting zone being the longer of the start times of the A₃ aborting zone and the (A₃)_x aborting zone and the stop time of the A₃ -(A₃)_x aborting zone being the shorter of the stop times of the A₃ aborting zone and the (A₃)_x aborting zone.

38. The system of claim 37 wherein the heart'"'"'s cardiac impulses have cardiac cycle lengths (the time between maximum amplitudes of adjacent cardiac impulses, the cardiac cycles occurring in varying lengths which are referred to as ranges of cardiac cycle lengths);

and wherein the step of determining at least one echo zone is defined further to include determining a combined A₂ -(A₂)_x echo zone for each of a plurality of predetermined ranges of atrial cycle lengths; and

wherein the step of determining at least one aborting zone is defined further to include determining a combined A₃ -(A₃)_x aborting zone for each of a plurality of the predetermined ranges of atrial cycle lengths; and

wherein the step of sensing the atrial impulses A₁ '"'"'s is defined further as determining the period of time lapsed between the sensed atrial impulse A₁ and the last sensed atrial impulse A₁ ; and

wherein the system is defined further to include the steps of;

continuously determining the atrial cycle length;

continuously determining an average atrial cycle length for a predetermined time period or a predetermined number of sensed atrial impulses A₁ '"'"'s prior to the last sensed atrial impulse A₁ ;

determining the lapse of time between each sensed atrial impulse A₁ and the last sensed atrial impulse A₁ ;

determining, for each received atrial impulse A₁, the combined A₂ -(A₂)_x echo zone and the combined A₃ -(A₃)_x aborting zone corresponding to the last determined average atrial cycle length; and

comparing the determined lapse of time between each sensed atrial impulse A₁ and the last sensed atrial impulse A₁ with the combined A₂ -(A₂)_x echo zone determined from the last determined average atrial cycle length to determine if the received atrial impulse A₁ occurred at a time within such determined combined A₂ -(A₂)_x echo zone thereby determining if the received atrial impulse A₁ is an inciting atrial impulse A₂ -(A₂)_x.

39. The system of claim 36 defined further to include:

sensing ventricular impulses V₁ '"'"'s; and

wherein determining a sensed atrial impulse A₁ to be an inciting atrial impulse A₂ if such sensed atrial impulse A₁ occurred within the A₂ echo zone and only a single ventricular impulse V₁ was sensed between the last sensed atrial impulse A₁ and the sensed atrial impulse A₁, and determining an atrial impulse A₁ to be an atrial inciting impulse (A₂)_x if such sensed atrial impulse A₁ occurred within the (A₂)_x echo zone and only two ventricular impulses V₁ '"'"'s were sensed between the last sensed atrial impulse A₁ and the sensed atrial impulse A₁ and the second of the two sensed ventricular impulses V₁ '"'"'s occurs at a time following the first of the two sensed ventricular impulses V₁ '"'"'s determined to be within the (V₂)_x echo zone (for the last determined average atrial cycle length), an inciting ventricular impulse (V₂)_x being a ventricular impulse V₁ which occurs at a time within the (V₂)_x echo zone.

40. The system of claim 1 wherein the dual pathway tachycardia is defined further as being induced by an inciting ventricular impulse (V₂)_x originating in the ventricles;

and wherein the heart includes a first pathway adapted for conducting an electrical impulse generally between the atria and the ventricles and a second pathway adapted for conducting an electrical impulse generally between the atria and the ventricles; and

wherein the step of determining the echo zone is defined further as determining the (V₂)_x echo zone within which an inciting ventricular impulse (V₂)_x may occur resulting in dual pathway tacardia; and

wherein the step of determining the aborting zone is defined further as determining the (A₃)_y aborting zone within which an aborting atrial impulse (A₃)_y may be induced in the atrial cardiac muscle for aborting the dual pathway tachycardia which otherwise would have occurred as a result of the inciting ventricular impulse (V₂)_x ; and

wherein the step of sensing cardiac impulses is defined further as sensing atrial impulses A₁ '"'"'s and sensing ventricular impulses V.sub. 1 '"'"'s in a heart; and

wherein the step of inducing an aborting cardiac impulse is defined further as inducing an aborting atrial impulse (A₃)_y at a time within the (A₃)_y aborting zone in response to sensing an inciting ventricular impulse (V₂)_x, the inciting ventricular impulse signal (V₂)_x being determined to be a sensed ventricular impulse V₁ occuring within the (V₂)_x echo zone without an intervening sensed atrial impulse A₁ between the received ventricular impulse V₁ and the last sensed atrial impulse signal A₁.

41. The system of claim 40 defined further to include delivering an electrical stimulus S.sub.(A.sbsb.3.sub.).sbsb.y to the atrial cardiac muscle to induce the aborting impulse (A₃)_y.

42. The system of claim 40 wherein the (A₃)_y aborting zone is defined further as having a start time and a stop time, the start time being timed from the sensed inciting ventricular impulse (V₂)_x to induce an aborting atrial impulse (A₃)_y arriving at the junction of the first and second pathways near the atria at a time:

(1) before the inciting ventricular impulse (V₂)_x traveling toward the atria through the intially conducting first or second pathway arrives at the junction of the first and second pathways near the atria; and

(2) while the conducting cells of the first or second pathway other than the initially conducting first or second pathway still are refractory to excitation and therefore unable to conduct the aborting atrial impulse (A₃)_y toward the ventricles through that pathway, thereby resulting in;

(1) block of the aborting atrial impulse (A₃)_y in the first or second pathway other than the initially conducting first or second pathway; and

(2) collision in the initially conducting first or second pathway of the aborting atrial (A₃)_y impulse traveling toward the ventricles and the inciting ventricular impulse (V₂)_x traveling toward the atria, resulting in the aborting of the initiation of the dual pathway tachycardia which might have occurred as a result of the inciting ventricular impulse (V₂)_x ; and

wherein there is a period of time following the sensed inciting ventricular impulse (V₂)_x before which an electrical stimulus delivered to the atrial cardiac cells will not result in an aborting atrial impulse (A₃)_y because either;

(1) the atrial cardiac cells still are refractory to excitation (not yet reconditioned) following the last received atrial impulse A₁ and therefore the electrical stimulus will not result in an atrial impulse;

or (2) the resulting atrial impulse penetrates and blocks in the atrial side of both the first and second pathways due to the arrival of the atrial impulse at the atrial side of the first and second pathways at a time while the conducting cells of both the first and second pathways still are refractory to excitation following the last received atrial impulse A₁, but the conduction time of the inciting ventricular impulse (V₂)_x traveling towards the atria through the initially conducting first or second pathway is sufficiently long to allow the cells of both the first and second pathways to recover excitability (become reconditioned) following the penetration of the first and second pathways by the atrial impulse induced by the electrical stimulus, then the inciting ventricular impulse (V₂)_x can be conducted towards the atria through the initially conducting first or second pathway and enter the first or second pathway other than the initially conducting first or second pathway and be conducted through the first or second pathway other than the initially conducting first or second pathway toward the ventricles initiating the dual pathway tachycardia;

the start time of the (A₃)_y aborting zone being a time before which an electrical stimulus delivered to the atrial cardiac cells will not induce an aborting atrial stimulus (A₃)_y and the stop time of the (A₃)_y aborting zone being a time following the sensed inciting ventricular impulse (V₂)_x, after which an electrical stimulus delivered to the atrial cardiac muscle will not result in an aborting atrial impulse (A₃)_y because the resulting atrial impulse will either;

(1) arrive at the atrial side of the first and second pathways at a time after the inciting ventricular impulse (V₂)_x traveling towards the atria through the initially conducting first or second pathway has entered the pathway other than the initially conducting first or second pathway and is being conducted through the pathway other than the initially conducting first or second pathway toward the ventricles;

or (2) arrive at the atrial side of the first and second pathways after the conducting cells of the first or second pathway other than the initially conducting first or second pathway have become reconditioned to accept and conduct the atrial impulse induced by electrical stimulus towards the ventricles.

43. The system of claim 1 wherein the dual pathway tachycardia is defined further as being due to any one of atrioventricular nodal reentry or atrioventricular reentry using an anomalous atrioventricular connection for retrograde conduction, induced by an inciting ventricular impulse (V₂)_x originating in the ventricles wherein the heart includes a first pathway adapted for conducting an electrical impulse generally between the atria and the ventricles and a second pathway for conducting an electrical impulse generally between the atria and the ventricles;

and wherein the step of determining the echo zone is defined further as determining the (V₂)_x echo zone within which an inciting ventricular impulse (V₂)_x may occur resulting in dual pathway tachycardia; and

wherein the step of determining the aborting zone is defined further as determining the (V₃)_z aborting zone within which an aborting ventricular impulse (V₃)_z may be induced in the ventricles for aborting dual pathway tachycardia which otherwise would have occurred as a result of the inciting ventricular impulse (V₂)_x ; and

wherein the step of sensing cardiac impulses is defined further as sensing ventricular cardiac impulses V₁ '"'"'s in a heart; and

wherein the step of inducing an aborting cardiac impulse is defined further as inducing an aborting ventricular impulse (V₃)_z at a time within the (V₃)_z aborting zone in response to sensing an inciting ventricular impulse (V₃)_z, the aborting ventricular impulse (V₃)_z which is conducted to the ventricular side of the first and second pathways at such a time;

(1) before the inciting ventricular impulse (V₂)_x returning toward the ventricles through the first or second pathway other than the initially conducting first or second pathway arrives at the junction of the first and second pathways near the ventricles; and

(2) while the conducting cells of the initially conducting first or second pathways still are refractory to excitation following the received inciting ventricular impulse (V₂)_x and are unable to conduct the aborting ventricular impulse (V₃)_z toward the atria through that initially conducting first or second pathway, thereby resulting in;

(1) block of the aborting ventricular impulse (V₃)_z in the initially conducting first or second pathway; and

(2) collision in the first or second pathway other than the initially conducting first or second pathway of the aborting ventricular impulse (V₃)_z traveling toward the atria and the inciting ventricular impulse (V₂)_x traveling back toward the ventricles with the result being the aborting of the initiation of the dual pathway tachycardia by the inciting ventricular impulse (V₂)_x.

44. The system of claim 43 wherein the (V₃)_z aborting zone is defined further as having a start time and a stop time, the start time of the (V₃)_z aborting zone being a time at the end of a period of time following the sensed ventricular impulse (V₂)_x before which an electrical stimulus delivered to the ventricular cardiac muscle will not result in an aborting ventricular impulse (V₃)_z because either:

(1) the ventricular cardiac muscle cells still are refractory to excitation [not yet reconditioned following the received inciting ventricular impulse (V₂)_x], and thus the electrical stimulus will not result in a ventricular impulse;

or (

     2) the resulting ventricular impulse penetrates and blocks in the ventricular side of both of the first and the second pathways due to the arrival of the ventricular impulse at the junction of the first and the second pathways near the ventricles at a time while the conducting cells of both the first and the second pathways still are refractory to excitation following the received inciting ventricular impulse (V.sub.

     2)_x and the conduction time of the inciting ventricular impulse (V₂)_x returning back towards the ventricles through the first or second pathway other than the initially conducting first or second pathway is sufficiently long in time to allow the conducting cells of both the first and second pathways to recover excitability (become reconditioned) following the penetration of the first and the second pathways by the ventricular impulse induced by the electrical stimulus, the inciting ventricular impulse (V₂)_x then can be conducted towards the ventricles through the first or second pathway other than the initially conducting first or second pathway and reenter the initially conducting first or second pathway and be conducted back toward the atria through the initially conducting first or second pathway initiating the dual pathway tachycardia; and

wherein the stop time of the (V₃)_z aborting zone is defined further as being a time following the sensed inciting ventricular impulse (V₂)_x after which an electrical stimulus delivered to the ventricular cardiac muscle cells will not result in an aborting ventricular impulse (V₃)_z because the resulting ventricular impulse will either;

(1) arrive at the junction of the first and the second pathways near the ventricular at a time when the inciting ventricle impulse (V₂)_x traveling back toward the ventricles through the first or second pathway other than the initially conducting first or second pathway has reentered the initially conducting first or second pathway and is being conducted through the initially conducting first or second pathway back toward the atria;

or (2) arrive at the junction of the first or second pathways near the ventricles at a time after the conducting cells of the initially conducting first or second pathway have become reconditioned to accept and conduct the ventricular impulse induced by the electrical stimulus towards the atria, the result being the failure to abort the dual pathway tachycardia.

45. The system of claim 1 wherein the heart includes a first pathway adapted for conducting electrical impulses between the atria and the ventricles and a second pathway adapted for conducting an electrical impulse generally between the atria and the ventricles;

and wherein the step of sensing the cardiac impulses is defined further as sensing atrial impulses A₁ '"'"'s and sensing ventricular impulses V₁ '"'"'s in a heart; and

wherein the step of inducing an aborting cardiac impulse is defined further as inducing an aborting ventricular impulse V₃ for aborting dual pathway tachycardia; and

wherein the step of determining the echo zone is defined further as determining the A₂ echo zone and the V₂ echo zone; and

wherein the step of determining the aborting zone is defined further as determining the V₃ aborting zone; and

wherein the inciting ventricular impulse signal V₂ is defined further as being a ventricular impulse resulting from the conduction to the ventricles through the initially conducting first or second pathway of an inciting atrial impulse A₂ ; and

wherein the inciting ventricular impulse signal V₂ is further defined as being;

(1) the first ventricular impulse signal occuring after a sensed inciting atrial impulse A₂ (an atrial impulse occurring with the A₂ echo zone); and

(2) occuring within the V₂ echo zone; and

wherein the V₂ echo zone is further defined as having a start time and a stop time, the start time of the V₂ echo zone being defined as a time of occurrence of the first ventricular impulse after the sensed inciting atrial impulse initially conducting first or second pathway of the aborting ventricle impulse V₃ traveling toward the atria and the inciting atrial impulse traveling back toward the ventricles, thereby resulting in the aborting of the initiation of the dual pathway tachycardia which otherwise might have occurred as a result of the inciting atrial impulse A₂.

46. The system of claim 45 wherein the V₃ aborting zone is defined further as having a start time and a stop time, the start time of the V₃ aborting zone being a time after a period of time following the sensed inciting ventricular impulse V₂ before which an electrical stimulus delivered to the ventricular cardiac cells will not result in an aborting ventricular impulse V₃ because either:

(1) the ventricular cardiac cells still are refractory to excitation (not yet reconditioned) following the received inciting ventricular impulse V₂ and thus the electrical stimulus will not result in a ventricular impulse;

or (2) the resulting ventricular impulse penetrates and blocks in the ventricular side of the first and the second pathways due to the arrival of the induced ventricular impulse at the junction of the first and the second pathways near the ventricles at a time while the conducting cells of both the first and the second pathways still are refractory to excitation, and the conduction time of the inciting atrial impulse A₂ returning back towards the ventricles through the initially conducting first or second pathway is sufficiently long to allow the conducting cells in both the first and second pathways to recover excitability (become reconditioned) following the penetration of those pathways by the ventricular impulse induced by the electrical stimulus so the inciting atrial impulse A₂ can be conducted towards the ventricles through the initially conducting first or second pathway and reenter the first or second pathway other than the initially conducting first or second pathway and be conducted through the first or second pathway other than the initially conducting first or second pathway back towards the atria initiating dual pathway tachycardia; and

wherein the stop time of the V₃ aborting zone is defined further as being a time following the sensed inciting ventricular impulse V₂ after which an induced electrical stimulus delivered to the ventricular cardiac cells will not result in an aborting ventricular impulse V₃ because the resulting ventricular impulse will either;

(1) arrive at the junction of the first and the second pathways near the ventricles at a time after the inciting atrial impulse A₂ returning toward the ventricles through the initially conducting first or second pathway has reentered the first or second pathway other than the initially conducting first or second pathway and is being conducted through the first or second pathway other than the initially conducting first or second pathway toward the atria;

or (2) arrive at the junction of the first and second pathways near the ventricles at a time after the conducting cells of the first or second pathway other than the initially conducting first or second pathway have become reconditioned to accept and conduct the induced ventricular impulse toward the atria, thereby resulting in failure to abort dual pathway tachycardia.

47. The system of claim 1 wherein the step of sensing cardiac impulses is defined further as sensing atrial impulses A₁ '"'"'s and sensing ventricular impulses V₁ '"'"'s and wherein the heart includes a first pathway for conducting an electrical impulse generally between the atria and the ventricles and a second pathway for conducting an electrical impulse generally between the atria and the ventricles;

and wherein the step of inducing an aborting cardiac impulse is defined further to include the step of delivering an electrical stimulus S.sub.(V.sbsb.3.sub.).sbsb.R timed from a sensed inciting atrial impulse A₂ which would induce an aborting ventricular impulse (V₃)_R which is conducted to the junction of the first and the second pathways near the ventricles at a time;

(1) before the inciting atrial impulse A₂ traveling toward the ventricles through the initially conducting first or second pathway arrives at the junction of the first and the second pathways near the ventricles; and

(2) while the conducting cells of the first or the second pathway other than the initially conducting first or second pathway still are refractory to excitation and thus cannot conduct the aborting ventricle impulse (V₃)_R toward the atria through the first or second pathway other than the initially conducting first or second pathway, thereby resulting in;

(1) block of the aborting ventricle impulse (V₃)_R in the first or second pathway other than the initially conducting first or second pathway; and

(2) collision in the initially conducting first or second pathway of the aborting ventricle impulse (V₃)_R traveling toward the atria and the inciting atrial impulse A₂ traveling toward the ventricles, thereby resulting in the aborting of the initiation of dual pathway tachycardia by the inciting atrial impulse A₂ ; and

wherein the step of determining the echo zone is defined further as determining the A₂ echo zone within which an inciting atrial impulse signal A₂ may occur resulting in dual pathway tachycardia; and

wherein the step of determining the aborting zone is defined further as determining the (V₃)_R aborting zone within which an aborting ventricular impulse (V₃)_R may be induced in the ventricles for aborting the dual pathway tachycardia which otherwise might have occurred as a result of the inciting atrial impulse A₂.

48. The system of claim 47 wherein the (V₃)_R aborting zone is defined further as having a start time and a stop time, the start time of the (V₃)_R aborting zone occurring at a time following a period of time before which an electrical impulse delivered to the ventricular cardiac cells will not result in an aborting ventricular impulse (V₃)_R because either:

(1) the ventricular cardiac cells still are refractory to excitation (not yet reconditioned) following the last received ventricular impulse V₁ and thus the electrical stimulus will not result in a ventricular impulse or;

(2) the resulting ventricular impulse penetrates and blocks in the ventricular side of both the first and second pathways due to the arrival of the ventricular impulse at the junction of the first and second pathways near the ventricles at a time while the conducting cells of the first and second pathways still are refractory to excitation following the last sensed ventricular impulse V₁ and the conduction time of the inciting atrial impulse A₂ traveling toward the ventricles through the initially conducting first or second pathway is sufficiently long to allow the conducting cells in the first and the second pathways to recover excitability (become reconditioned) following the penetration of the first and the second pathways by the ventricular impulse induced by the electrical stimulus so the inciting atrial impulse A₂ can be conducted towards the ventricles through the initially conducting first or second pathway and enter the first or second pathway other than the initially conducting first or second pathway and be conducted through the first or second pathway other than the initially conducting first or second pathway toward the atria initiating dual pathway tachycardia; and

wherein the stop time of the (V₃)_R aborting zone is defined as a time following the sensed inciting atrial impulse A₂ after which an electrical stimulus delivered to the ventricular cardiac cells will not result in an aborting ventricular impulse (V₃)_R because the resulting ventricular impulse will either;

(1) arrive at the junction of the first and second pathways near the ventricles at a time after the inciting atrial impulse A₂ traveling toward the ventricles through the initially conducting first or second pathway has already entered the first or second pathway other than the initially conducting first or second pathway and is being conducted through the first or second pathway other than the initially conducting first or second pathway back toward the atria;

or (2) arrive at the junction of the first and second pathways near the ventricles at a time after the conducting cells in the first or second pathway other than the initially conducting first or second pathway have become reconditioned to accept and conduct the ventricular impulse induced by the electrical stimulus toward the atria, the result being in the failure to abort dual pathway tachycardia.

49. The system of claim 1 wherein the heart includes a first pathway adapted for conducting an electrical impulse generally between the atria and the ventricles and a second pathway adapted for conducting an electrical impulse generally between the atria and the ventricles;

and wherein the step of sensing cardiac impulses is defined further as sensing atrial impulses A₁ '"'"'s in a heart; and

wherein the system is defined further to include the steps of;

continuously determining the atrial cycle length (the time between maximum amplitudes of adjacent atrial impulses A₁ '"'"'s);

continuously determining an average atrial cycle length for a predetermined period or a predetermined number of sensed atrial impulses A₁ '"'"'s prior to the last sensed atrial impulse A₁ ;

determining the lapse of time between each sensed atrial impulse A₁ and the last sensed atrial impulse A₁ ;

determining, for each received atrial impulse A₁, one of an A₂ echo zone, an (A₂)_x echo zone and a combined A₂ -(A₂)_x echo zone or combinations thereof and determining one of an A₃ aborting zone, an (A₃)_x aborting zone or a combined A₃ -(A₃)_x aborting zone or combinations thereof corresponding to the last determined atrial cycle length; and

comparing the determined lapse of time between each sensed atrial impulse A₁ and the last sensed atrial impulse A₁ with one of the A₂ echo zone, the (A₂)_x echo zone or the combined A₂ -(A₂)_x echo zone or combinations thereof determined from the last determined atrial cycle length to determine if the received atrial impulse A₁ occurred at a time within such determined one of the A₂ echo zone, the (A₂)_x echo zone or the combined A₂ -(A₂)_x echo zone or combinations thereof thereby determining if the sensed atrial impulse A₁ is one of an inciting atrial impulse A₂ or an inciting atrial impulse (A₂)_x or combinations thereof; and

wherein the step of inducing an aborting cardiac impulse is defined further as delivering one of an aborting electrical stimulus S_A.sbsb.3 or an aborting electrical stimulus S.sub.(A.sbsb.3.sub.).sbsb.x or an aborting electrical stimulus S_A.sbsb.3 -S.sub.(A.sbsb.3.sub.).sbsb.x or combinations thereof at a time within the respective predetermined A₃ aborting zone, (A₃)_x aborting zone or combined A₃ -(A₃)_x aborting zone established for the last determined atrial cycle length to the atrial cardiac muscle thereby inducing one of the aborting atrial impulse A₃, the aborting atrial impulse (A₃)_x or the aborting atrial impulse A₃ -(A₃)_x.

50. The system of claim 49 wherein the step of delivering the aborting electrical stimulus S_A.sbsb.3, the aborting electrical stimulus S.sub.(A.sbsb.3.sub.).sbsb.x or the aborting electrical stimulus S_A.sbsb.3 -S.sub.(A.sbsb.3.sub.).sbsb.x or combinations thereof is defined further as delivering the aborting electrical stimulus S_A.sbsb.3, the aborting electrical stimulus S.sub.(A.sbsb.3.sub.).sbsb.x or the aborting electrical stimulus S_A.sbsb.3 -S.sub.(A.sbsb.3.sub.).sbsb.x or combinations thereof at a time within the respective A₃ aborting zone, (A₃)_x aborting zone or the A₃ -(A₃)_x aborting zone or combinations thereof as near as possible to the start time of that respective aborting zone determined for the particular average atrial cycle length, each of the A₃ aborting zone, the (A₃)_x aborting zone and the combined A₃ -(A₃)_x aborting zone having a start time and a stop time, the start time being a time after which an aborting electrical stimulus delivered to the atrial cardiac muscle will induce an aborting atrial impulse which will result in the aborting of the initiation of dual pathway tachycardia and the stop time being the time after which the inducing of an atrial aborting impulse will not result in the aborting of the initiation of dual pathway tachycardia.

51. The system of claim 1 wherein the heart includes a first pathway adapted for conducting an electrical impulse generally between the atria and the ventricles and a second pathway adapted for conducting an electrical impulse generally between the atria and the ventricles;

and wherein the step of sensing cardiac impulses is defined further as sensing ventricular impulse signals in a heart; and

wherein the system is defined further to include the steps of;

continuously determining the ventricular cycle length (the time between maximum amplitudes of adjacent ventricular impulses V₁ '"'"'s);

determining an average ventricular cycle length for a predetermined period of time or a predetermined number of sensed ventricular impulses V₁ '"'"'s prior to the last sensed ventricular impulse V₁ ;

determining the lapse of time between each sensed ventricular impulse V₁ and the last sensed ventricular impulse V₁ ;

determining, for each received ventricular impulse, the (V₂)_x echo zone and the (V₃)_z aborting zone corresponding to the last determined average ventricular cycle length; and

comparing the determined lapse of time between each sensed ventricular impulse V₁ and the last sensed ventricular impulse V₁ with the (V₂)_x echo zone determined from the last determined average ventricular cycle length to determine if the received ventricular impulse V₁ occurred at a time within such determined (V₂)_x echo zone thereby determining if the sensed ventricular impulse V₁ is an inciting ventricular impulse (V₂)_x ; and

wherein the step of inducing an aborting cardiac impulse is defined further as delivering an electrical stimulus S.sub.(V.sbsb.3.sub.).sbsb.z to the ventricular cardiac muscle at a time within the (V₃)_z aborting zone for the last determined average ventricular cycle length to induce an aborting ventricular impulse (V₃)_z in the ventricular cardiac muscle.

52. The system of claim 1 wherein the heart includes a first pathway adapted for conducting an electrical impulse generally between the atria and the ventricles and a second pathway adapted for conducting an electrical impulse generally between the atria and the ventricles;

and wherein the step of sensing the cardiac impulses is defined further as sensing the atrial impulses A₁ '"'"'s and sensing the ventricular impulses V₁ '"'"'s; and

wherein the system is defined further to include the step of;

continuously determining the atrial cycle length (the time between maximum amplitudes of adjacent atrial impulses A₁ '"'"'s);

continuously determining an average atrial cycle length for a predetermined period or a predetermined number of sensed atrial impulses A₁ '"'"'s prior to the last sensed atrial impulse A₁ ;

determining the lapse of time between each sensed atrial impulse A₁ and the last sensed atrial impulse A₁ ;

continuously determining the ventricular cycle length (the time between maximum amplitudes of adjacent ventricular impulses V₁ '"'"'s);

continuously determining an average ventricular cycle length for a predetermined time period or a predetermined number of sensed ventricular impulses V₁ '"'"'s prior to the last sensed ventricular impulse V₁ ;

determining the lapse of time between each sensed ventricular impulse V₁ and the last sensed ventricular impulse V₁ ;

determining, for one of each received atrial impulse A₁ or ventricular impulse V₁ or combinations thereof, one of the A₂ echo zone, the (V₂)_x echo zone, the V₂ echo zone or the (A₂)_x echo zone and one of the A₃ aborting zone, the (A₃)_x aborting zone, the (A₃)_y aborting zone, the (V₃)_z aborting zone, the V₃ aborting zone or the (V₃)_R aborting zone or combinations thereof corresponding to the respective last determined average atrial cycle length or average ventricular cycle length or both.

53. The system of claim 52 defined further to include the step of:

comparing the determined lapse of time between each sensed atrial impulse A₁ and the last sensed atrial impulse A₁ with only a single intervening ventricular impulse V₁ with the A₂ echo zone determined from the last determined average atrial cycle length to determine if the sensed atrial impulse A₁ occurred at a time within such determined A₂ echo zone thereby determining if the sensed atrial impulse A₁ is an inciting atrial impulse A₂ ; and

wherein the step of inducing the aborting cardiac impulse is defined further as delivering an aborting electrical stimulus S_A.sbsb.3 to the atrial cardiac muscle at a time within the A₃ aborting zone determined from the last determined average atrial cycle length.

54. The system of claim 52 defined further to include the step of comparing the lapse of time between each sensed ventricular impulse A₁ and the last sensed ventricular impulse V₁ without an intervening atrial impulse A₁ with the (V₂)_x echo zone thereby determining if the sensed ventricular impulse V₁ is an inciting ventricular impulse (V₂)_x.

55. The system of claim 52 defined further to include the step of:

comparing the determined lapse of time between each sensed atrial impulse A₁ and the last sensed atrial impulse A₁ with only a single intervening ventricular impulse V₁ with the A₂ echo zone determined from the last determined average atrial cycle length to determine if the sensed atrial impulse A₁ occurred at a time within such determined A₂ echo zone thereby determining if the sensed atrial impulse A₁ is an inciting atrial impulse A₂ ; and

wherein the step of inducing an aborting cardiac impulse is defined further as delivering one or a combination thereof of;

(1) an aborting electrical stimulus S_A.sbsb.3 to the atrial cardiac cells timed from the inciting atrial impulse A₂ and during the A₃ echo zone determined for the last determined average atrial cycle length;

(2) delivering an aborting electrical stimulus S_V.sbsb.3 to the ventricular cardiac cells timed from the inciting ventricular impulse V₂ and during the V₃ aborting zone for the last determined average atrial cycle length; and

(3) delivering an aborting electrical stimulus S.sub.(V.sbsb.3.sub.).sbsb.R to the ventricular cardiac cells timed from the inciting atrial impulse A₂ and during the (V₃)_R aborting zone for the last determined average atrial cycle length.

56. The system of claim 52 defined further to include the step of:

comparing the lapse of time between each sensed ventricular impulse V₁ and the last sensed ventricular impulse V₁ without an intervening atrial impulse A₁ with the (V₂)_x echo zone determined from the last determined average ventricular cycle length to determine if the received ventricular impulse V₁ occurred at a time within such determined (V₂)_x echo zone thereby determining if the received ventricular impulse signal is an inciting ventricular impulse (V₂)_x ; and

wherein the step of inducing the aborting cardiac impulse is defined further as delivering one or a combination of;

(1) an aborting electrical stimulus S.sub.(A.sbsb.3.sub.).sbsb.x to the atrial cardiac cells timed from the inciting atrial impulse (A₂)_x and during the (A₃)_x aborting zone for the last average atrial cycle length;

(2) deliver an aborting electrical stimulus S.sub.(A.sbsb.3.sub.).sbsb.y to the atrial cardiac cells timed from the inciting ventricular impulse (V₂)_x and during the (A₃)_y aborting zone for the last average atrial cycle length; and

(3) delivering an aborting electrical stimulus S.sub.(V.sbsb.3.sub.).sbsb.z to the ventricular cardiac cell timed from the inciting ventricular impulse (V₂)_x and during the (V₃)_z aborting zone for the last determined average atrial cycle length.

57. The system of claim 1 wherein the step of sensing the cardiac impulses is defined further as sensing the cardiac impulses at a position on the atrial cardiac muscle as close as possible to the atrioventricular node;

and wherein the step of inducing the aborting cardiac impulse is defined further as inducing the aborting cardiac impulse at a position in the atrial cardiac muscle as close as possible to the atrioventricular node.

58. The system of claim 1 wherein the heart includes a first pathway adapted for conducting an electrical impulse generally between the atria and the ventricles and a second pathway adapted for conducting an electrical impulse generally between the atria and the ventricles;

and wherein the step of sensing the cardiac impulses is defined further as sensing the cardiac impulses at a position as close as possible to one of the first and the second pathways which conducts the inciting cardiac impulse.

59. The system of claim 1 wherein the heart includes a first pathway adapted for conducting an electrical impulse generally between the atria and the ventricles and a second pathway adapted for conducting an electrical impulse generally between the atria and the ventricles;

and wherein the dual pathway tachycardia is defined further as being due to atrioventricular nodal reentry; and

wherein the step of sensing the cardiac impulses is defined further as sensing the ventricular cardiac impulses V₁ '"'"'s at a position on the ventricular cardiac muscle as near as possible to the ventricular side of the atrioventricular node or HIS bundle.

60. The system of claim 1 wherein the heart includes a first pathway adapted for conducting an electrical impulse generally between the atria and the ventricles and a second pathway adapted for conducting an electrical impulse generally between the atria and the ventricles;

and wherein the dual pathway tachycardia is defined further as being due to atrioventricular reentry using an accessory atrioventricular pathway (or anomalous atrioventricular connection) for retrograde conduction; and

wherein the step of sensing the cardiac impulses is defined further as sensing the ventricular cardiac impulses V_1'"'"' s at a position on the ventricular cardiac muscle as near as possible to the ventricular side of the accessory atrioventricular pathway (anomalous atrioventricular connection).