Far-field sensing channel for implantable cardiac device

• US 20050288719A1
• Filed: 06/02/2004
• Published: 12/29/2005
• Est. Priority Date: 06/02/2004
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Gilkerson, James O., Zhang, Geng, Ni, Quan, Daum, Douglas R.
• Granted Patent: US 7,996,083 B2
• Time in Patent Office: Days
• US Class Current: 607/9
• CPC Class Codes: A61N 1/3621 for treating or preventing abnormally high heart rate
• CPC Class Codes: A61N 1/371 Capture, i.e. successful stimulation
• CPC Class Codes: A61N 1/3756 Casings with electrodes thereon, e.g. leadless stimulators

Abstract

An implantable pacemaker is provided with a far-field sensing channel which requires a reduced refractory period during the time when pacing pulses are delivered as compared with sensing channels using intra-cardiac electrodes. The far-field sensing channel may use the conductive housing of the implantable device or can and an indifferent electrode mounted on the device header as the electrodes for its differential inputs. Such a far-field sensing channel is able to sense activity occurring in either the atria or the ventricles for the purposes of arrhythmia detection and/or capture verification.

Claims

1. A device for delivering cardiac therapy, comprising:

an implantable housing which serves as a can electrode;

a header formed of insulating material mounted on the housing for receiving one or more sensing or pacing leads;

an indifferent electrode mounted on the header;

a pacing channel for delivering pacing pulses;

a controller for controlling the delivery of pacing pulses in accordance with a programmed mode,

a far-field sensing channel which includes a sense amplifier having the can electrode and the indifferent electrode as differential inputs for producing a far-field electrogram signal; and

,

circuitry for detecting ventricular senses when the amplitude of the far-field electrogram exceeds a specified threshold, measuring the intervals between senses, and detecting a ventricular arrhythmia when a specified rate criterion is met.

2. The device of claim 1 further comprising:

atrial and ventricular sensing channels which produce electrogram signals from intra-cardiac electrodes;

circuitry for detecting an atrial or ventricular sense when the electrogram signal in the atrial or ventricular sensing channel, respectively, exceeds a specified threshold; and

,

circuitry for verifying atrial or ventricular senses detected in the atrial or ventricular sensing channels by determining whether the electrogram signal amplitude in the far-field signal exceeds a specified threshold at the time of the sense being verified.

3. The device of claim 1 wherein the specified electrogram amplitude threshold for verifying senses in the far-field channel is different depending upon whether an atrial or a ventricular sense is being verified.

4. The device of claim 1 further comprising circuitry for verifying whether capture by a ventricular pacing pulse has occurred by determining whether the electrogram signal in the far-field sensing channel after a ventricular pace indicates an evoked response.

5. The device of claim 1 further comprising circuitry for verifying whether capture by an atrial pacing pulse has occurred by determining whether the electrogram signal in the far-field sensing channel after an atrial pace indicates an evoked response.

6. The device of claim 1 wherein the controller is programmed to utilize the far-field sensing channel for detecting arrhythmias by analyzing the morphology of the far-field electrogram signal generated by the far-field sensing channel.

7. The device of claim 1 further comprising:

a shock channel for delivering defibrillation shocks, wherein the shock channel is also used to produce electrogram signals for arrhythmia detection by morphology analysis; and

,

wherein the controller is programmed to utilize the far-field sensing channel to analyze the morphology of the far-field electrogram signal generated by the far-field sensing channel as a cross-check of the morphology analysis of the shock channel electrogram.

8. The device of claim 1 further comprising:

a switch matrix operated by the controller for switching the inputs of the sense amplifier to selected electrodes; and

,

wherein the controller is programmed to configure the far-field sensing channel with the indifferent electrode referenced to the can electrode.

9. The device of claim 8 further comprising:

a minute ventilation sensor which measures transthoracic impedance in order to generate a signal proportional to minute ventilation, the minute ventilation sensor including an exciter for supplying an oscillating excitation current between a pair of excitation current electrodes and a pair of voltage sense electrodes for generating an impedance signal;

wherein the controller is programmed to modulate the rate at which paces are delivered in accordance with the signal proportional to minute ventilation;

wherein the indifferent electrode is utilized by the minute ventilation sensor as an excitation current electrode or a voltage sense electrode; and

,

wherein the switch matrix is operated so that the far-field channel is active during periods when no excitation current is supplied.

10. The device of claim 1 wherein the far-field sensing channel is blanked for a period not exceeding 2 milliseconds following delivery of a pacing pulse.

12. The method of claim 1 further comprising:

producing electrogram signals from atrial and ventricular sensing channels which incorporate intra-cardiac electrodes;

detecting an atrial or ventricular sense when the electrogram signal in the atrial or ventricular sensing channel, respectively, exceeds a specified threshold; and

,

verifying atrial or ventricular senses detected in the atrial or ventricular sensing channels by determining whether the electrogram signal amplitude in the far-field signal exceeds a specified threshold at the time of the sense being verified.

13. The method of claim 1 wherein the specified electrogram amplitude threshold for verifying senses in the far-field channel is different depending upon whether an atrial or a ventricular sense is being verified.

14. The method of claim 1 further comprising verifying whether capture by a ventricular pacing pulse has occurred by determining whether the electrogram signal in the far-field sensing channel after a ventricular pace indicates an evoked response.

11. A method for operating a cardiac device, comprising:

delivering pacing pulses in accordance with a programmed mode,

producing a far-field electrogram signal in a far-field sensing channel which includes a sense amplifier having as its differential inputs an electrode formed by an implantable housing for the device and an indifferent electrode mounted on a header of the housing; and

,

detecting ventricular senses when the amplitude of the far-field electrogram exceeds a specified threshold, measuring the intervals between senses, and detecting a ventricular arrhythmia when a specified rate criterion is met.

15. The method of claim 11 further comprising verifying whether capture by an atrial pacing pulse has occurred by determining whether the electrogram signal in the far-field sensing channel after an atrial pace indicates an evoked response.

16. The method of claim 11 further comprising utilizing the far-field sensing channel for detecting arrhythmias by analyzing the morphology of the far-field electrogram signal generated by the far-field sensing channel.

17. The method of claim 11 further comprising:

delivering defibrillation shocks through a shock channel and also using the shock channel to produce electrogram signals for arrhythmia detection by morphology analysis; and

,

utilizing the far-field sensing channel to analyze the morphology of the far-field electrogram signal generated by the far-field sensing channel as a cross-check of the morphology analysis of the shock channel electrogram.

18. The method of claim 11 further comprising:

switching the inputs of sense amplifier to selected electrodes with a switch matrix; and

,

configuring the far-field sensing channel with the indifferent electrode referenced to the can electrode.

19. The method of claim 18 further comprising:

measuring transthoracic impedance with a minute ventilation sensor in order to generate a signal proportional to minute ventilation, the minute ventilation sensor including an exciter for supplying an oscillating excitation current between a pair of excitation current electrodes and a pair of voltage sense electrodes for generating an impedance signal;

modulating the rate at which paces are delivered in accordance with the signal proportional to minute ventilation;

utilizing the indifferent electrode as an excitation current electrode or a voltage sense electrode for the minute ventilation sensor; and

,

operating the switch matrix so that the far-field channel is active during periods when no excitation current is supplied.

20. The method of claim 11 wherein the far-field sensing channel is blanked for a period not exceeding 2 milliseconds following delivery of a pacing pulse.