Automatic sensitivity control in an implantable cardiac rhythm management system

• US 5,269,300 A
• Filed: 07/30/1992
• Issued: 12/14/1993
• Est. Priority Date: 07/30/1992
• Status: Expired due to Term

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Kelly, David W., Stadler, Carol G., Dreher, Robert
• Primary Examiner(s): Kamm, William E.
• Assistant Examiner(s): SCHAETZLE, KENNEDY
• Application Number:
  US07/921,661
• Time in Patent Office: 502 Days
• Field of Search: 128/419 PG, 128/419 D, 128/419 PT
• US Class Current: 607/4
• CPC Class Codes: A61N 1/3704 Circuits specially adapted therefor, e.g. for sensitivity control

Abstract

A method and apparatus for automatically adjusting the sensing threshold in an automatic implantable cardioverter/defibrillator with pacing capability. Fixed sensitivity is used for a specified interval following each pacing pulse and automatic sensitivity adjustment is used when spontaneous cardiac depolarization is detected. For spontaneous cardiac depolarization, the sensing threshold is automatically adjusted to a value proportional to the amplitude of the sensed cardiac signal. The sensing threshold continuously decreases between sensed cardiac depolarizations, ensuring that a lower level cardiac signal will be detected. When a pacing pulse is delivered, the sensing threshold is set to a fixed value and held at that value for a predetermined period of time such that the sensing threshold will not be affected by the cardiac response evoked by the pacing pulse. At the end of the predetermined period of time, the sensing threshold is decreased as it would following a spontaneous cardiac depolarization.

Claims

1. A method for automatically adjusting the sensing threshold in a cardioverter/defibrillator system with pacing capability, the method comprising the steps of:

detecting the occurrence and magnitude of R-waves;

adjusting a sensing threshold to a value proportional to a magnitude of a sensed R-wave;

decreasing the sensing threshold from the value continuously until a next detected R-wave;

delivering a pacing pulse to the heart;

adjusting the sensing threshold to a fixed value for a predetermined period of time after delivery of the pacing pulse; and

continuously decreasing the sensing threshold from the fixed value after the predetermined period of time until a next detected R-wave.

2. A method for automatically adjusting the sensing threshold in a cardioverter/defibrillator system with pacing capability, the method comprising the steps of adjusting the sensing threshold to a value proportional to a sensed cardiac signal for spontaneous cardiac depolarization and decreasing the sensing threshold continuously thereafter;

and adjusting the sensing threshold to a fixed value for a predetermined period of time when a pacing pulse is delivered and decreasing the sensing threshold continuously after the predetermined period of time.

3. A system for automatically adjusting the sensing threshold in a cardioverter/defibrillator system with pacing capability, the system comprising:

detecting means for detecting cardiac signals;

amplifying means for amplifying cardiac signals according to a variable gain to generate amplified cardiac signals; and

sensing threshold control means for controlling the gain of the amplifying means to set a sensing threshold, said sensing threshold control means responsive to spontaneous cardiac depolarizations to set the variable gain of the amplifying means to a level proportional to the magnitude of the spontaneous cardiac depolarizations and to continuously change the variable gain of the amplifying means so that the sensing threshold decreases continuously from a first maximum value until a next cardiac depolarization, said sensing threshold control means being further responsive to delivery of pacing pulses to the heart of the patient to set the variable gain of the amplifying means to a fixed sensing threshold for a predetermined period of time and to continuously change the variable gain of the amplifying means so that the sensing threshold decreases continuously from a second maximum value after the predetermined period of time.

4. The system of claim 3, wherein the sensing threshold control means comprises:

gain control means for adjusting the variable gain of the amplifying means;

timer means connected to the gain control means and responsive to delivery of a pacing pulse for counting a predetermined time interval and delivering a fixed gain signal to the gain control means during said predetermined time interval;

comparing means connected to said gain control means for comparing the output of the amplifying means and issuing a detect signal in the event that the output of the amplifying means exceeds a first predetermined threshold, said detect signal indicative of the occurrence of depolarizations of the heart, and issuing a gain down signal in the event that the output of the amplifying means exceeds a second predetermined reference level which is greater than said first predetermined reference level.