Pacemaker noise rejection system
First Claim
1. An implantable cardiac medical device comprising means for sensing a cardiac signal, means for comparing the sensed cardiac signal with a variable threshold level, means for setting an initial threshold level responsive to the occurrence of a heartbeat, means for timing a re-triggerable relative refractory period, means responsive to said sensed cardiac signal exceeding said threshold level during said relative refractory period for re-triggering the relative refractory period timing and for increasing the threshold level, means responsive to a time-out of the relative refractory period without said sensed cardiac signal exceeding said threshold level for initiating a heartbeat sensing interval, means operative at the start of a heartbeat sensing interval for setting a threshold value equal to a predetermined value increased by a function of said threshold level at the end of the preceding relative refractory period, and means responsive to said sensed cardiac signal exceeding the threshold value during a heartbeat sensing interval for determining the occurrence of a heartbeat.
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Abstract
A noise rejection circuit for an implantable pacemaker. During re-triggerable relative refractory periods following a heartbeat, the peak noise level is sensed; the relative refractory period is re-started whenever the input signal exceeds the previous peak. Following a time-out of the relative refractory period, the peak value detected, representing the noise level, is added to the programmed threshold value; the sum is used as the threshold value during sensing.
194 Citations
16 Claims
- 1. An implantable cardiac medical device comprising means for sensing a cardiac signal, means for comparing the sensed cardiac signal with a variable threshold level, means for setting an initial threshold level responsive to the occurrence of a heartbeat, means for timing a re-triggerable relative refractory period, means responsive to said sensed cardiac signal exceeding said threshold level during said relative refractory period for re-triggering the relative refractory period timing and for increasing the threshold level, means responsive to a time-out of the relative refractory period without said sensed cardiac signal exceeding said threshold level for initiating a heartbeat sensing interval, means operative at the start of a heartbeat sensing interval for setting a threshold value equal to a predetermined value increased by a function of said threshold level at the end of the preceding relative refractory period, and means responsive to said sensed cardiac signal exceeding the threshold value during a heartbeat sensing interval for determining the occurrence of a heartbeat.
- 3. An implantable cardiac medical device comprising means for sensing a cardiac signal, means for comparing the sensed cardiac signal with a variable threshold level, means for setting an initial threshold level responsive to the occurrence of a heartbeat and for successively increasing the threshold level to a final value as the sensed cardiac signal increases until the final threshold level represents the noise level in said sensed cardiac signal, means responsive to said final threshold level representing the noise level in said sensed cardiac signal for initiating a heartbeat sensing interval, means operative at the start of a heartbeat sensing interval for setting a threshold value which is a function of said final threshold level, and means responsive to the sensed cardiac signal exceeding said threshold value during a heartbeat sensing interval for determining the occurrence of a heartbeat.
- 5. An implantable cardiac medical device comprising means for sensing a cardiac signal, means responsive to the determination of the occurrence of a heartbeat for deriving a signal representative of the noise level in said cardiac signal as a function of the cardiac signal only subsequent to such heartbeat, means responsive to derivation of said noise level representative signal for setting a threshold value which is a function thereof and for initiating a sensing interval, and means responsive to said cardiac signal exceeding said threshold value during said sensing interval for determining the occurrence of a heartbeat.
- 9. A method for determining the occurrence of a heartbeat comprising the steps of sensing a cardiac signal, comparing the sensed cardiac signal with a variable threshold level, setting an initial threshold level responsive to the occurrence of a heartbeat, timing a retriggerable relative refractory period, re-triggering the relative refractory period timing and increasing the threshold level responsive to said sensed cardiac signal exceeding said threshold level during said relative refractory period timing, initiating a heartbeat sensing interval responsive to a time-out of the relative refractory period without said sensed cardiac signal exceeding said threshold level, at the start of a heartbeat sensing interval setting a threshold value equal to a predetermined value increased by a function of said threshold level at the end of the preceding relative refractory period, and determining the occurrence of a heartbeat responsive to said sensed cardiac signal exceeding the threshold value during a heartbeat sensing interval.
- 11. A method for determining the occurrence of a heartbeat comprising the steps of sensing a cardiac signal, comparing the sensed cardiac signal with a variable threshold level, setting an initial threshold level responsive to the occurrence of a heartbeat and successively increasing the threshold level to a final value as the sensed cardiac signal increases until the final threshold level represents the noise level in said sensed cardiac signal, initiating a heartbeat sensing interval responsive to said final threshold level representing the noise level in said sensed cardiac signal, at the start of a heartbeat sensing interval setting a threshold value which is a function of said final threshold level, and determining the occurrence of a heartbeat responsive to the sensed cardiac signal exceeding said threshold value during a heartbeat sensing interval.
- 13. A method for determining the occurrence of a heartbeat comprising the steps of sensing a cardiac signal, responsive to the determination of the occurrence of a heartbeat deriving a signal representative of the noise level in said cardiac signal as a function of the cardiac signal only subsequent to such heartbeat, setting a threshold value which is a function of the derived representative signal and initiating a sensing interval, and determining the occurrence of a heartbeat responsive to said cardiac signal exceeding said threshold value during said sensing interval.
Specification