Method and device for implantable cardiac stimulus device lead impedance measurement

• US 20080077189A1
• Filed: 09/22/2006
• Published: 03/27/2008
• Est. Priority Date: 09/22/2006
• Status: Active Grant

• Current Assignee: Cameron Health Inc (Boston Scientific Corporation)
• Original Assignee: Cameron Health Inc (Boston Scientific Corporation)
• Inventors: Ostroff, Alan H.
• Granted Patent: US 7,877,139 B2
• Time in Patent Office: Days
• US Class Current: 607/27
• CPC Class Codes: A61N 1/3706 Pacemaker parameters stimulation threshold A61N1/371
• CPC Class Codes: A61N 1/3956 Implantable devices for applying electric shocks to the heart, e.g. for cardioversion

Abstract

Methods and devices for testing lead impedance in an implantable cardiac stimulus device. A resistor is placed in series with the lead impedance, and a predetermined or known voltage is applied to the resistor and lead impedance. The voltage across the resistor is measured, and it is then determined whether the lead impedance falls within an acceptable range.

Claims

1. A method of testing lead impedance in an implantable cardiac stimulation device having at least a first electrode disposed on a lead and a second electrode, a power capacitor for storing stimulation energy, charging circuitry for charging the power capacitor, and control circuitry for controlling device operation, device operation including a stimulus operation including a step of charging the power capacitor to a stimulus voltage and discharging the power capacitor, the method comprising:

providing a testing resistor placed such that, when in a testing configuration, a testing current applied between the first and second electrodes passes through the testing resistor;

charging the power capacitor to a testing voltage, the testing voltage being less than the stimulus voltage;

applying a current from the power capacitor through the first and second electrodes such that at least some current passing between the first and second electrodes also passes through the testing resistor;

observing the voltage across the testing resistor during the discharging step; and

determining whether the lead impedance falls within an acceptable range using the observed voltage across the testing resistor.

2. The method of claim 1, further comprising providing a bypass switch configured to allow current to bypass the testing resistor when not in the testing configuration.

3. The method of claim 1, further comprising providing a testing capacitor in parallel with the testing resistor and a testing switch therebetween, wherein the step of observing the voltage across the testing resistor includes closing the testing switch during the step of applying the current, and thereafter opening the testing switch to at least temporarily hold a voltage corresponding to the voltage across the testing resistor during the step of at least partly discharging the testing voltage.

4. The method of claim 1, further comprising providing a sample and hold circuit in association with the testing resistor, wherein the step of observing the voltage across the testing resistor includes activating the sample and hold circuit to sample and hold the voltage across the testing resistor during the step of applying the current.

5. The method of claim 1, wherein:

the device comprises an H-bridge output circuit having a high side with first and second legs and a low side with first and second legs;

the testing resistor is positioned to receive current from the low side of the H-bridge; and

the step of applying a current includes passing current through the first high side leg, out the first electrode and to the second electrode through the patient, and through the second low side leg.

6. The method of claim 5, further comprising:

applying a current a second time by passing current through the second high side leg, out the second electrode and to the first electrode through the patient, and through the first low side leg;

observing the voltage across the testing resistor during the step of applying a current a second time; and

again finding lead impedance using the voltage observed across the testing resistor during the step of applying a current a second time.

7. An implantable cardiac stimulation device comprising:

at least a first electrode disposed on a lead and a second electrode;

a power capacitor for storing stimulation energy;

charging circuitry for charging the power capacitor;

control circuitry configured to direct a stimulus operation including charging the power capacitor to a stimulus voltage and discharging the power capacitor; and

a testing resistor placed such that, when in a testing configuration, a testing current applied between the first and second electrodes passes through the testing resistor;

wherein the control circuitry is further configured to direct a testing operation including charging the power capacitor to a testing level and applying current from the power capacitor through the first and second electrodes such that at least some current passing between the first and second electrodes also passes through the testing resistor, the testing level being less than the stimulus level.

8. The device of claim 7, further comprising a bypass device placed such that, during the stimulus operation, the bypass device is configured to allow stimulus current to bypass the testing resistor during cardiac stimulus.

9. The device of claim 7, wherein the bypass device is a switch, wherein the control circuitry is further configured such that, during the stimulus operation, the bypass switch allows stimulus current to bypass the testing resistor.

10. The device of claim 7, further comprising a sample and hold circuit coupled to the testing resistor to capture a voltage across the testing resistor.

11. The device of claim 10, wherein the sample and hold circuit comprises at least a sampling capacitor and a holding switch.

12. The device of claim 10, wherein the control circuitry is coupled to the sample and hold circuit such that the control circuitry captures a tested voltage sampled and held by the sample and hold circuit.

13. The device of claim 12, wherein the control circuitry is configured to use the tested voltage to find a lead impedance.

14. The device of claim 7, further comprising an H-bridge circuit having a high side and a low side, the high side coupling the power capacitor to the first and second electrodes and the low side coupling the first and second electrodes to the testing resistor.

15. The device of claim 14, wherein the H-bridge comprises a number of switches and is configured for a first shocking delivery configuration and a second shocking delivery configuration, wherein the control circuitry controls the delivery configurations, and the first and second shocking delivery configurations allow a stored voltage on the power capacitor to be applied in either of two polarities to the first and second electrodes.

16. The device of claim 15, wherein the testing operation includes a first portion for testing lead impedance of the first shocking delivery configuration and a second portion for testing lead impedance of the second shocking delivery configuration.

17. An implantable cardiac stimulation device comprising:

at least a first electrode disposed on a lead and a second electrode;

an H-bridge having a high side for delivering current to the first and second electrodes and a low side for receiving current from the first and second electrodes, the H-bridge enabling at least first and second configurations for current passage via the first and second electrodes;

first, second and third legs for receiving current from the low side, the first leg being a testing leg, the second leg being a pacing leg, and the third leg being a high energy pulse leg; and

control circuitry configured to operate the device in at least the following modes;

a controlled current pacing mode;

a high energy pulse mode; and

a low energy testing mode.

18. An implantable stimulation device comprising:

at least a first electrode and a second electrode;

circuitry for delivering a cardiac stimulus having a first energy level;

a testing resistor and a non-linear device positioned in parallel with one another and configured such that current passing between the first and second electrodes passes through at least one of the resistor and/or the non-linear device;

control circuitry for controlling device operation, wherein the control circuitry is configured to have a stimulus mode and a testing mode, wherein during the stimulus mode the control circuitry causes delivery of cardiac stimulus, and during the testing mode the control circuitry causes delivery of a testing pulse and observes the voltage across the testing resistor to find impedance relative to the first electrode and the second electrode, the testing pulse having an amplitude that is less than an amplitude of the cardiac stimulus.

19. The device of claim 18, wherein the non-linear device is a switch.

20. The device of claim 18, wherein the non-linear device is a diode.