Accurate cardiac event detection in an implantable cardiac stimulus device

A method of event detection in an implantable medical device having a plurality of electrodes adapted for implantation in a patient and operational circuitry coupled to the electrodes to receive cardiac signals from the electrodes, the method comprising:

• the operational circuitry detecting a first cardiac electrical event from a cardiac signal captured using the electrodes;
• the operational circuitry detecting a second cardiac electrical event from the cardiac signal captured using the electrodes;
• the operational circuitry preparing to detect a third cardiac electrical event by:
• comparing the first cardiac electrical event to the second cardiac electrical event;
• and either:
• setting a first threshold shape for detecting the third cardiac electrical event if the first and second cardiac electrical events are similar;
• or
• setting a second threshold shape different from the first threshold shape for detecting the third cardiac electrical event if the first and second cardiac electrical events are dissimilar;
• and
• the operational circuitry detecting the third cardiac electrical event using the set threshold shape.

An implantable medical device (IMD) comprising a plurality of electrodes and operational circuitry coupled to the plurality of electrodes to receive cardiac signals from the electrodes, the operational circuitry configured to detect cardiac cycles by detecting cardiac events by:

• detecting a first cardiac electrical event in the cardiac signals received from the electrodes;
• detecting a second cardiac electrical event in the cardiac signals received from the electrodes;
• preparing to detect a third cardiac electrical event by:
• comparing the first cardiac electrical event to the second cardiac electrical event;
• and either:
• setting a first threshold shape for detecting the third cardiac electrical event if the first and second cardiac electrical events are similar;
• or
• setting a second threshold shape different from the first threshold shape for detecting the third cardiac electrical event if the first and second cardiac electrical events are dissimilar;
• and
• detecting the third cardiac electrical event using the set threshold shape.

An implantable medical device (IMD) comprising a plurality of electrodes and operational circuitry coupled to the plurality of electrodes to receive cardiac signals from the electrodes, the operational circuitry configured to:

• determine a current cardiac rate estimate;
• compare the current cardiac rate estimate to a tachycardia threshold;
• and
• if the tachycardia threshold is not exceeded, perform a step for avoiding overdetection of cardiac events by assessing similarity of a previously detected cardiac event to stored data;
• or
• if the tachycardia threshold is exceeded, bypass the step for avoiding overdetection of cardiac events;
• and
• detect a new cardiac event.