Method and device for implantable cardiac stimulus device lead impedance measurement

• US 7,877,139 B2
• Filed: 09/22/2006
• Issued: 01/25/2011
• 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.
• Primary Examiner(s): Patel; Niketa I
• Assistant Examiner(s): Stoklosa; Joseph
• Application Number:
  US11/525,497
• Publication Number:
  US 20080077189A1
• Time in Patent Office: 1,586 Days
• Field of Search: 607 5- 8, 607 27- 28, 324/526, 324/610
• US Class Current: 607/8
• 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. An implantable cardiac stimulation device comprising:

a first electrode;

a second electrode;

a housing containing operational circuitry including;

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 predetermined stimulus voltage and discharging the power capacitor to deliver therapy using at least the first and second electrodes, the control circuitry including a delivery 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, the high and low sides each comprising first and second electric switches; 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 voltage and closing a high side switch and a low side switch of the H-bridge to apply 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 voltage being less than the stimulus voltage.

2. The device of claim 1, 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.

3. The device of claim 2, 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.

4. The device of claim 1, further comprising a sample and hold circuit coupled to the testing resistor to capture a voltage across the testing resistor.

5. The device of claim 4, wherein the sample and hold circuit comprises at least a sampling capacitor and a holding switch.

6. The device of claim 4, 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.

7. The device of claim 6, wherein the control circuitry is configured to use the tested voltage to find impedance between the first and second electrodes.

8. The device of claim 1, wherein delivery circuit takes the form of an H-bridge 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.

9. The device of claim 8, wherein the testing operation includes a first portion for testing impedance of the first shocking delivery configuration and a second portion for testing impedance of the second shocking delivery configuration.

10. The device of claim 1 further comprising a lead electrode assembly on which the first electrode is disposed, wherein the second electrode is disposed on the housing.

11. The device of claim 1 wherein each of the first and second electrodes are placed on the housing.