System and method for estimating defibrillation impedance based on low-voltage resistance measurements using an implantable medical device

• US 8,676,317 B1
• Filed: 07/20/2005
• Issued: 03/18/2014
• Est. Priority Date: 07/20/2005
• Status: Active Grant

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated), Rohm and Haas Company (Dow, Inc.)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Inventors: Kroll, Mark W., Mouchawar, Gabriel A., Moulder, J. Christopher
• Primary Examiner(s): Lavert, Nicole F
• Application Number:
  US11/186,741
• Time in Patent Office: 3,163 Days
• Field of Search: 607/4, 607 27- 28, 600/547, 324/600
• US Class Current: 607/27
• CPC Class Codes: A61B 2560/0276 Determining malfunction
• CPC Class Codes: A61B 5/0538 invasively, e.g. using a catheter
• CPC Class Codes: A61B 5/361 Detecting fibrillation
• CPC Class Codes: A61B 5/686 Permanently implanted devices, e.g. pacemakers, other stimulators, biochips A61B5/6861 takes precedence
• CPC Class Codes: A61B 5/6869 Heart
• CPC Class Codes: A61N 1/3706 Pacemaker parameters stimulation threshold A61N1/371
• CPC Class Codes: A61N 1/3937 Monitoring output parameters

Abstract

Techniques are provided for estimating defibrillation impedance of an implantable cardioverter/defibrillator (ICD). Briefly, at least two low-voltage resistance values are measured at different voltages using a pair of stimulation electrodes connected to the ICD. High-voltage defibrillation impedance is then estimated by the ICD based on a weighted combination of the measured resistance values. In one example, a set of weight coefficients, calculated during an initial calibration procedure, are applied to the measured resistance values to produce the estimate of the high-voltage defibrillation impedance. The weight coefficients are updated whenever a defibrillation shock is delivered, based on actual defibrillation impedance values measured during the shock.

Claims

1. A method for estimating the defibrillation impedance of a pair of implanted electrodes, said method comprising:

a) performing the following X times, where X is at least equal to N;

delivering a series of N different types of low-voltage pulses between the pair of electrodes;

for each type of low-voltage pulse delivered, measuring the resistance (R) between the pair of electrodes to obtain a resistance value;

delivering a high-voltage defibrillation shock between the electrodes; and

measuring the impedance between the electrodes resulting from the defibrillation shock to obtain an impedance value (Z);

b) determining a plurality of weight coefficients (K), each corresponding to one of the N different types of low-voltage pulses by processing the resistance values and the impedance values;

c) subsequently delivering the series of N different types of low-voltage pulse between the pair of electrodes and measuring corresponding resistances for each type of low-voltage pulse; and

d) processing the corresponding resistances and the weight coefficients to obtain the estimated defibrillation impedance for the pair of electrodes.

2. The method of claim 1 wherein the N different types of low-voltage pulses comprises at least one of a DC pulse and one of an AC pulse.

3. The method of claim 1 wherein the N different types of low-voltage pulses comprise a DC pulse at a first voltage and a DC pulse at a second voltage.

4. The method of claim 1 wherein determining a plurality of weight coefficients (K), each corresponding to one of the N different types of low-voltage pulses by processing the resistance values and the impedance values comprises:

solving the following matrix equation for K_{n=1 . . . N}

5. The method of claim 1 wherein the pair of electrodes comprises a right ventricular coil (RVC) electrode and a device housing electrode.

6. The method of claim 1 wherein the pair of electrodes comprises a right ventricular coil (RVC) electrode and a superior vena cava (SVC) electrode.

7. The method of claim 1 wherein the pair of electrodes comprises a superior vena cava (SVC) electrode and a device housing electrode.

8. The method of claim 1 wherein processing the corresponding resistances (R) and the weight coefficients (K) to obtain the estimated defibrillation impedance for the pair of electrodes comprise:

calculating;

Z=K₁R₁+K₂R₂+ . . . +K_NR_N.

9. The method of claim 1 further comprising periodically repeating a) and b) to obtain updated coefficient values.

10. The method of claim 1 further comprising repeating a) and b) to obtain updated coefficient whenever a defibrillation shock is delivered.

11. The method of claim 1 wherein:

delivering a defibrillation pulse comprises charging a capacitor; and

the series of N different types of low-voltage pulses are delivered prior to charging of the capacitor.

12. The method of claim 1 wherein:

delivering a defibrillation pulse comprises charging a capacitor; and

the series of N different types of low-voltage pulses are delivered after charging of the capacitor but prior to delivery of the defibrillation shock.

13. A system for estimating the defibrillation impedance of a pair of implanted electrodes, said system comprising:

a measurement system operative to performing the following X times, where X is at least equal to N;

deliver a series of N different types of low-voltage pulses between the pair of electrodes;

for each type of low-voltage pulse delivered, measure the resistance (R) between the pair of electrodes to obtain a resistance value;

deliver a high-voltage defibrillation shock between the electrodes; and

measure the impedance between the electrodes resulting from the defibrillation shock to obtain an impedance value (Z);

determine a plurality of weight coefficients (K), each corresponding to one of the N different types of low-voltage pulses by processing the resistance values and the impedance values;

a defibrillation impedance estimation system operative to;

subsequently deliver the series of N different types of low-voltage pulse between the pair of electrodes and measure corresponding resistances for each of the low-voltage pulses; and

process the corresponding resistances and the weight coefficients to obtain the estimated defibrillation impedance for the pair of electrodes.