Cardiac rhythm management system with respiration synchronous optimization of cardiac performance using atrial cycle length

• US 20040034391A1
• Filed: 08/16/2002
• Published: 02/19/2004
• Est. Priority Date: 08/16/2002
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Kadhiresan, Veerichetty A., Baumann, Lawrence S.
• Granted Patent: US 6,876,881 B2
• Time in Patent Office: Days
• US Class Current: 607/25
• CPC Class Codes: A61N 1/3627 for treating a mechanical deficiency of the heart, e.g. congestive heart failure or cardiomyopathy
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance
• CPC Class Codes: A61N 1/3682 with a variable atrioventricular delay
• CPC Class Codes: A61N 1/3684 for stimulating the heart at multiple sites of the ventricle or the atrium
• CPC Class Codes: A61N 1/36843 Bi-ventricular stimulation

Abstract

A cardiac rhythm management device includes a dual chamber pacemaker, especially designed for treating congestive heart failure. The device incorporates a program microcontroller which is operative to adjust the pacing site, AV delay and interventricular delay of the pacemaker so as to achieve optimum hemodynamic performance. Atrial cycle lengths measured during transient (immediate) time intervals following a change in the site, AV delay and interventricular delay are signal processed and a determination can then be made as to which particular configuration yields the optimum performance. Paced transient beats following periods of baseline beats are synchronized to the patient'"'"'s respiratory cycle to minimize effects of respiratory noise on atrial cycle length measurements.

Claims

1. A method of optimizing the site and intersite delay configuration of a dual chamber pacemaker of the type having means for sensing atrial depolarization events, means for sensing ventricular depolarization events and means for applying cardiac stimulating pulses selectively to the right, left or both ventricular chambers at predetermined intersite intervals following detection of atrial depolarization events, comprising the steps of:

(a) tracking a patient'"'"'s intrinsic atrial depolarization events;

(b) deriving from a transthoracic impedance signal a cyclic respiratory signal representative of a patient'"'"'s tidal volume;

(c) measuring the patient'"'"'s cycle length between successive depolarization events over a first predetermined number of heart beats, N₁, at a first intersite interval and storing the measured cycle lengths as an array in a memory to establish a baseline value;

(d) changing at least one of intersite delay interval and pacing site configuration by changing, for a second predetermined number of heart beats, N₂, less than the first predetermined number of heart beats,

(i) the intersite delay interval of the pacemaker from the baseline value to a different intersite delay interval less than the value at which intrinsic atrial depolarization is established, or

(ii) the site(s) of the ventricle(s) to which the stimulating pulses are applied;

(e) measuring the patient'"'"'s cycle length between successive atrial depolarization events over the second predetermined number of heart beats and storing the measured cycle lengths in the array in said memory;

(f) calculating and storing a cycle length feature value obtained from the patient'"'"'s cycle length measured in steps (c) and (e);

(g) repeating steps (a)-(f) in iterative cycles over a range of intersite delay intervals and ventricular chamber(s) selected for receiving the cardiac stimulating pulses where the second predetermined number of beats, N₂, for each iterative cycle begins at a corresponding phase of the said cyclic respiratory signal;

(h) after step (f) for each pacing site and intersite delay configuration, calculating the average of the cycle length features over all of the occurrences of the configuration;

(i) determining the optimal configuration from among the averages determined in step (g); and

(j) setting the intersite delay and pacing site configuration of the pacemaker to the optimal intersite delay and pacing site configuration established in step (i).

2. The method of claim 1 wherein the ACL feature value is calculated by the steps of:

(k) smoothing the array of cycle lengths;

(l) determining from the smoothed array of ACLs a maximum value and a minimum value in a first predetermined interval measured in beats for each intersite delay and pacing site configuration;

(m) determining from the smoothed array a mean value of cycle lengths in a second predetermined interval measured in beats for each intersite delay and pacing site configuration;

(n) computing an absolute value of the difference between said maximum value and said mean value and computing an absolute value of the difference between said minimum value and said mean value;

(o) comparing the absolute value of the difference between the maximum value and the mean value with the absolute value of the difference between the minimum value and the mean value to determine which is the larger; and

(p) setting the cycle length feature value to the difference between the maximum value and the mean value when the absolute value of that difference is greater than the absolute value of the difference between the minimum value and the mean value, and setting the cycle length feature value to the difference between the minimum value and the mean value when the absolute value of the difference between the maximum value and the mean value is less than or equal to the absolute value of the difference between the minimum value and the mean value.

3. A method for optimizing the intersite delay interval and pacing site configuration of a programmable dual chamber cardiac pacemaker of the type having means for sensing atrial and ventricular depolarization events, including a microprocessor-based controller for selectively stimulating the right, the left or both ventricular chambers with pacing pulses at predetermined intersite delay intervals following detection of atrial depolarization events, the microprocessor-based controller having means for determining atrial cycle lengths and a memory for storing data in an addressable array, comprising the steps of:

(a) deriving a cyclic respiratory signal corresponding to a patient'"'"'s tidal volume from a transthoracic impedance signal;

(b) storing in the memory a listing of pacing site and intersite delay configurations, each such configuration specifying ventricular chamber(s) to be stimulated and an intersite delay interval to be utilized;

(c) pacing the ventricular chamber(s) in accordance with a pacing site intersite delay configuration selected randomly from said listing for a first number of beats, N₁, following a second number of intrinsic beats, N₂, sufficient to establish a base line;

(d) repeating step (c) where the first number of beats, N₁, begin at a same phase in the cyclic respiratory signal, for each pacing site and intersite delay configuration contained in the listing;

(e) determining the ACL values between each of the N₁ and N₂ beats resulting from steps (b) and (c) and storing said ACL value in the addressable array in the memory;

(f) repeating steps (b) through (d) a predetermined number of instances, N₃;

(g) smoothing the array of ACLs;

(h) determining for all N₃ instances of each pacing site and intersite delay configuration the maximum value of the smoothed ACLs in a first interval beginning after a change to the first number of beats N₁ and ending after a change to the second number of beats, N₂, and a minimum value of the smoothed ACLs in a second interval beginning a predetermined number of beats prior to a change from the N₂ beats to the N₁ beats and ending with the beat associated with the maximum value;

(i) computing a smoothed ACL feature as the difference between the maximum value and the minimum value;

(j) calculating the mean value of the smoothed ACL features computed in step (h) over the N₃ instances for each pacing site and intersite delay configuration and determining the configuration yielding the largest mean value;

(k) determining among the N₃ instances associated with the configuration yielding the largest mean value a median value and a maximum value of smoothed ACL features; and

(l) programming the pacemaker to the configuration determined in step (j) when the difference between the ratio of maximum value and the median value is less than a predetermined value.

4. The method of claim 3 and when the ratio of maximum value and the median value of smoothed ACL features is greater than or equal to the predetermined threshold value, repeating steps (j) and (k) after recalculating the mean of the instances of the configuration associated with the largest mean value of smoothed ACL features after removing the instance having the maximum value of smoothed ACL features from the instances.

5. A method of optimizing the intersite delay and pacing site configuration of a dual chamber pacemaker of the type having means for sensing atrial depolarization events, means for sensing ventricular depolarization events and means for applying cardiac stimulating pulses selectively to the right, left or both ventricular chambers at predetermined intersite delay intervals following detection of atrial depolarization events, comprising the steps of:

(a) tracking a patient'"'"'s intrinsic ventricular depolarization events;

(b) deriving from a sensed transthoracic impedance signal a cyclic signal related to a patient'"'"'s tidal volume;

(c) measuring the patient'"'"'s ventricular cycle length (VCL) between successive ventricular depolarization events over a first predetermined number of heart beats, N₁, at a first intersite delay interval and storing the measured VCLs as an array in a memory to establish a baseline value;

(d) changing at least one of intersite delay interval and pacing site configuration by changing, for a second predetermined number of heart beats, N₂, less than the first predetermined number of heart beats,

(i) the intersite delay interval of the pacemaker from the baseline value to a different intersite delay interval less than the value at which intrinsic ventricular depolarization events is established;

(ii) the ventricular sites to which the stimulating pulses are applied;

(e) measuring the patient'"'"'s VCLs between successive ventricular depolarization events over the second predetermined number of heart beats and storing the measured VCLs in the array in said memory;

(f) calculating and storing a VCL feature value obtained from the patient'"'"'s ventricular cycle length measured in steps (b) and (d);

(g) repeating steps (a)-(f) in iterative cycles over a range of intersite delay intervals and ventricular sites selected for receiving the cardiac stimulating pulses where the second predetermined number of beats, N₂, for each iterative cycle begins at a corresponding phase of said cyclic signal;

(h) after step (g) for each pacing site and intersite delay configuration, calculating the average of the VCL features over all of the occurrences of the configuration;

(i) determining the optimal configuration from among the averages determined in step (h); and

(j) setting the intersite delay and pacing site configuration of the pacemaker to the optimal delay and pacing site configuration established in step (i).

6. The method of claim 5 wherein the VCL feature value is calculated by the steps of:

(k) smoothing the array of VCLs;

(l) determining from the smoothed array of VCLs a maximum value and a minimum value in a first predetermined interval measured in beats for each intersite delay and pacing site configuration;

(m) determining from the smoothed array a mean value of VCLs in a second predetermined interval measured in beats for each intersite delay and pacing site configuration;

(n) computing an absolute value of the difference between said maximum value and said mean value and computing an absolute value of the difference between said minimum value and said mean value;

(o) comparing the absolute value of the difference between the maximum value and the mean value with the absolute value of the difference between the minimum value and the mean value to determine which is the larger; and

(p) setting the VCL feature value to the difference between the maximum value and the mean value when the absolute value of that difference is greater than the absolute value of the difference between the minimum value and the mean value, and setting the VCL feature value to the difference between the minimum value and the mean value when the absolute value of the difference between the maximum value and the mean value is less than or equal to the absolute value of the difference between the minimum value and the mean value.

7. A method for optimizing the intersite delay interval and pacing site configuration of a programmable, dual-chamber, cardiac pacemaker of the type having means for sensing atrial and ventricular depolarization events, including a microprocessor-based controller for selectively stimulating the right, the left or both ventricular chambers with pacing pulses at predetermined intersite delay intervals following detection of atrial depolarization events, the microprocessor-based controller having means for determining ventricular cycle lengths (VCLs) and a memory for storing data in an addressable array, comprising the steps of:

(a) deriving a cyclic signal corresponding to a patient'"'"'s tidal volume;

(b) storing in the memory a listing of pacing site and intersite delay configurations, each such configuration specifying ventricular sites to be stimulated and an intersite delay interval to be utilized;

(c) pacing the ventricular sites in accordance with a pacing site and intersite delay configuration selected randomly from said listing for a first number of beats, N₁, following a second number of intrinsic beats, N₂, sufficient to establish a baseline;

(d) repeating step (c) for each pacing site and intersite delay configuration contained in the listing where the first number of beats, N₁, on successive iterations begins at the same phase in the cyclic signal;

(e) determining the VCL values between each of the N₁ and N₂ beats resulting from steps (c) and (d) and storing said VCL value in the addressable array in the memory;

(f) repeating steps (c) through (e) a predetermined number of instances, N₃;

(g) smoothing the array of VCLs;

(h) determining for all N₃ instances of each pacing site and intersite delay configuration the maximum value of the smoothed VCLs in a first interval beginning after a change to the first number of beats, N₁, and ending after a change to the second number of beats, N₂, and a minimum value of the smoothed VCLs in a second interval beginning a predetermined number of beats prior to a change from the N₂ beats to the N₁ beats and ending with the beat associated with the maximum value;

(i) computing a smoothed VCL feature as the difference between the maximum value and the minimum value;

(j) calculating the mean value of the smoothed VCL features computed in step (i) over the N₃ instances for each pacing site and intersite delay configuration and determining the configuration yielding the largest mean value;

(k) determining among the N₃ instances associated with the configuration yielding the largest mean value a median value and a maximum value of smoothed VCL feature; and

(l) programming the pacemaker to the configuration determined in step (j) when the difference between the ratio of maximum value and the minimum value is less than a predetermined value.

8. The method of claim 7 and when the ratio of maximum value and the median value of smoothed VCL features is greater than or equal to the predetermined threshold value, repeating steps (j) and (k) after recalculating the mean of the instances of the configuration associated with the largest mean value of smoothed VCL features after removing the instance having the maximum value of smoothed VCL features from the instances.

9. A method for optimizing the intersite delay interval and pacing site configuration of a cardiac pacemaker comprising the steps of:

(a) deriving a cyclic signal corresponding to a patient'"'"'s tidal volume,

(b) selecting a first of a plurality of predetermined pacing site and intersite delay interval configuration;

(c) establishing a baseline value of intrinsic intersite intervals over a predetermined number of intrinsic heart beats;

(d) initiating pacing of the patient'"'"'s heart with the first of the plurality of predetermined pacing site and intersite delay interval configurations for a predetermined number of paced beats;

(e) repeating step (c); and

(f) repeating step (d) with a second of the plurality of predetermined pacing site and intersite delay interval configurations where a first pacing pulse of the predetermined number of paced beats begins at a same phase of the cyclic signal as a first pacing pulse of the predetermined number of paced beats used in step (d).