Cardioversion/defibrillation lead impedance measurement system

• US 5,755,742 A
• Filed: 11/05/1996
• Issued: 05/26/1998
• Est. Priority Date: 11/05/1996
• Status: Expired due to Term

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Schmid, Barbara J., Gering, Jonathan R., Schuelke, Robert J.
• Primary Examiner(s): Jastrzab, Jeffrey R.
• Application Number:
  US08/741,757
• Time in Patent Office: 567 Days
• Field of Search: 607/4, 607/5, 607/8, 607/9, 607/27, 607/28, 128/734
• US Class Current: 607/27
• CPC Class Codes: A61N 1/3706 Pacemaker parameters stimulation threshold A61N1/371
• CPC Class Codes: A61N 1/3937 Monitoring output parameters

Abstract

A lead integrity measurement system for a cardiac pacemaker/cardioverter/defibrillator (PCD) of the type comprising an implantable pulse generator (IPG) and a lead system including one or more pacing leads each having a proximal end coupled to a pacing terminal of the IPG and a distal end with at least one pace/sense electrode in contact with a patient'"'"'s heart and a pair of defibrillation leads coupled to defibrillation terminals of the IPG and defibrillation electrodes implanted in relation to the patient'"'"'s heart. In a lead impedance test mode, the terminal of a selected defibrillation lead under test is coupled to system ground, and an excitation voltage is applied in an excitation path from a force lead terminal selected from the pacing leads. A measure lead is selected from among the other of the pacing leads and defibrillation leads, and the voltage induced in the lead under test is measured through the measure lead and the electrode/tissue interface of the measure lead and the defibrillation lead under test. The applied current in the excitation path is also measured, and an impedance value is derived from the measured current and voltage values. The test is continued with other selections of excitation and measure paths. Comparisons of the measured impedances with maximum and minimum impedance values are used to determine lead integrity failures. The lead impedance between two defibrillation leads is determined as a function of the sum of the derived defibrillation lead impedances.

Claims

1. In a tissue stimulation system having a pulse generator coupled through at least three terminals to at least three leads each having an electrode in contact with body tissue at an electrode/tissue interface, a method of testing current and voltage lead integrity of at least one of the leads comprising the steps of:

(a) selecting one of said at least three leads as a lead under test, a force lead and a measure lead;

(b) coupling the terminal of the lead under test to a fixed potential;

(c) driving an excitation voltage pulse in an excitation path including the terminal of the selected force lead, the force lead electrode/tissue interface, the lead under test electrode/tissue interface and the lead under test;

(d) measuring the excitation current value of the excitation voltage pulse delivered in the excitation path through the lead under test; and

(e) measuring an induced voltage in a measure path including the terminal of the selected measure lead, the measure lead electrode/tissue interface, the lead under test electrode/tissue interface and the lead under test to determine lead integrity of the lead under test.

2. The method of claim 1 further comprising the step of:

(f) determining the lead impedance of the lead under test from the measured excitation current value and the induced voltage value.

3. The method of claim 2 further comprising the step of:

(g) repeating step (a) and changing the selection of the lead under test, the force lead and the measure lead; and

(h) repeating steps (b)-(f) using the selection made in step (g).

4. The method of claim 3 further comprising the step of:

(i) repeating steps (g) and (h) until all leads of the tissue stimulation system are tested.

5. The method of claim 4 further comprising the steps of:

(j) comparing the lead impedances derived in step (f) with threshold impedance values; and

(k) determining lead integrity from the results of the comparisons made in step (j).

6. The method of claim 1 further comprising the step of:

(f) repeating step (a) and changing the selection of the lead under test, the force lead and the measure lead; and

(g) repeating steps (b)-(e) using the selection made in step (f).

7. The method of claim 6 further comprising the step of:

(h) repeating steps (f) and (g) until all leads of the tissue stimulation system are tested.

8. In a tissue stimulation system having a pulse generator coupled through at least three terminals to at least three leads each having an electrode adapted to be in contact with body tissue at an electrode/tissue interface, a system for testing current and voltage lead integrity of at least one of said leads comprising:

means for selecting one of said at least three leads as a lead under test, a force lead and a measure lead;

means for coupling the terminal of the lead under test to a fixed potential;

means for driving an excitation voltage pulse in an excitation path including the terminal of the selected force lead, the force lead electrode/tissue interface, the lead under test electrode/tissue interface and the lead under test;

means for measuring the excitation current value of the excitation voltage pulse delivered in the excitation path through the lead under test; and

means for measuring an induced voltage in a measure path including the terminal of the selected measure lead, the measure lead electrode/tissue interface, the lead under test electrode/tissue interface and the lead under test.

9. The system of claim 8 further comprising:

means for determining the lead impedance of the lead under test from the measured excitation current value and the induced voltage value.

10. The system of claim 9 further comprising;

means for changing the selection of the lead under test, the force lead and the measure lead for measuring the impedance of two or more of the leads in the system.

11. In an implantable pacing and defibrillation system having a pacing and defibrillation pulse generator coupled through a pacing lead terminal to at least one pacing lead having a pacing electrode implanted at a pacing electrode/tissue interface in relation to the patient'"'"'s heart, coupled through a defibrillation lead terminal to a defibrillation lead having a defibrillation electrode implanted at a defibrillation electrode/tissue interface in relation to a patient'"'"'s heart, and coupled through a further lead terminal to a further lead having an electrode implanted at a further electrode/tissue interface in relation to the patient'"'"'s heart, a method of testing lead integrity of at least one of said pacing lead, defibrillation lead, or further lead comprising the steps of:

selecting one of said pacing lead, said defibrillation lead and said further lead as a lead under test, a force lead and a measure lead;

coupling the terminal of the lead under test to a ground potential;

driving an excitation voltage pulse in an excitation path including the terminal of the selected force lead, the force lead electrode/tissue interface, the lead under test electrode/tissue interface and the lead under test;

measuring the electrical current value of the excitation voltage pulse delivered in the excitation path through the lead under test;

measuring an induced voltage in a measure path including the terminal of the selected measure lead, the measure lead electrode/tissue interface, the lead under test electrode/tissue interface and the lead under test; and

determining lead integrity of the lead under test from the measured electrical current value and the measured electrical voltage value.

12. The method of claim 11 wherein said determining step further comprises the steps of:

deriving the lead impedance of the lead under test from the measured excitation current value and the induced voltage value; and

comparing the lead impedance to a reference impedance value;

determining from the comparison if the derived lead impedance value falls within a normal or abnormal lead impedance range.

13. The method of claim 12 further comprising the step of:

changing the selection of the lead under test, the force lead and the measure lead; and

repeating the steps of the method using the changed selection.

14. The method of claim 13 wherein the selected lead under test is the defibrillator lead, the force lead is the pacing lead, and the measure lead is the further lead.

15. The method of claim 11 further comprising the step of:

changing the selection of the lead under test, the force lead and the measure lead; and

repeating the steps of the method using the changed selection.

16. In an implantable pacing and defibrillation system having a pacing and defibrillation pulse generator coupled trough pacing lead terminals to a pacing lead having a pacing electrode implanted at a pacing electrode/tissue interface, coupled through a first defibrillation terminal to a first defibrillation lead having a first defibrillation electrode implanted at a defibrillation electrode/tissue interface in contact with a heart chamber, and coupled through a second defibrillation terminal to a second defibrillation lead and electrode, a method of testing the lead integrity of said first defibrillation lead comprising the steps of:

selecting said pacing lead as a force lead;

selecting said second defibrillation lead as a measure lead;

selecting said first defibrillation lead as a lead under test;

coupling the first defibrillation lead terminal to a ground potential;

driving a first excitation voltage pulse in a first excitation path including the terminal of the selected force lead, the force lead electrode/tissue interface, the first defibrillation lead electrode/tissue interface and the first defibrillation lead;

measuring the electrical current value of the excitation voltage pulse delivered in the first excitation path through the first defibrillation lead;

measuring an induced voltage in a first measure path including the terminal of the selected measure lead, the measure lead electrode/tissue interface, the first defibrillation lead electrode/tissue interface and the first defibrillation lead;

deriving a first impedance value from the measured electrical current and voltage values;

selecting said first defibrillation electrode as a measure lead;

selecting said second defibrillation electrode as a lead under test;

coupling said second defibrillation lead terminal to a ground potential;

driving a second excitation voltage pulse in a second excitation path including the terminal of the selected force lead, the force lead electrode/tissue interface, the second defibrillation lead electrode/tissue interface and the second defibrillation lead;

measuring the electrical current value of the excitation voltage pulse delivered in the second excitation path through the second defibrillation lead;

measuring an induced voltage in a second measure path including the terminal of the selected measure lead, the measure lead electrode/tissue interface, the second defibrillation lead electrode/tissue interface and the second defibrillation lead;

deriving a second impedance value from the measured electrical current and voltage values; and

determining lead impedance between the first defibrillation lead and the second defibrillation lead from the sum of the first and second derived impedance values.

17. The method of claim 16 further comprising the steps of:

comparing the determined lead impedance with threshold impedance values; and

determining lead integrity from the results of the comparison.

18. A method implemented in a PCD IPG and operable in a lead impedance test mode for deriving defibrillation lead impedances in a defibrillation lead system having first and second defibrillation leads each having defibrillation electrodes positionable in relation to a patient'"'"'s heart for providing a defibrillation shock pathway through the patient'"'"'s heart and electrically connected to said PCD IPG and employing a pacing lead system having first and second pacing leads each having pace/sense electrodes positioned in relation to a patient'"'"'s heart for providing a pace/sense pathway through the patient'"'"'s heart and electrically connected to said PCD IPG, said method comprising the steps of:

driving a first lead impedance test pulse of known voltage having insufficient energy to capture the heart into a first force pathway including the first pacing lead, the patient'"'"'s body tissue and the first defibrillation lead;

measuring the current in the first force pathway during the first lead impedance test pulse;

measuring a first induced voltage, induced in response to said first lead impedance test pulse, across a first sense pathway including one of said second defibrillation lead or said second pacing lead, the patient'"'"'s body tissue, and said first defibrillation lead;

deriving a first defibrillation lead impedance value from said measured current and induced voltage;

driving a second lead impedance test pulse of known voltage having insufficient energy to capture the heart into a second force pathway including said second pacing lead, the patient'"'"'s body tissue and said second defibrillation lead;

measuring the current in said second force pathway during the second lead impedance test pulse;

measuring a second induced voltage, induced in response to said first lead impedance test pulse, across a second sense pathway including the other one of said second defibrillation lead or said second pacing lead, the patient'"'"'s body tissue, and said second defibrillation lead under test; and

deriving a second defibrillation lead impedance value from said measured current and induced voltage.

19. The method of claim 18 further comprising the steps of:

comparing the derived first and second defibrillation lead impedances with threshold impedance values; and

determining integrity of the first and second defibrillation lead impedances from the results of the comparison.

20. The method of claim 18 further comprising the step of:

summing the derived first and second defibrillation lead impedances to derive the impedance between the first and second defibrillation leads.