Implantable cardiac stimulator with polarity detection for detecting ectopic beats

DETAILED DESCRIPTION Accordingly, there is herein provided an implantable medical device such as a pacemaker for electrically stimulating the heart to beat.
The implantable medical device includes an atrial sense circuit for detecting and monitoring electrical activity in the atria of the heart, commonly known as the atrial electrogram.
The atrial sense circuit includes a sense amplifier, band pass filter, and a threshold detector and provides detect signals to a logic and control unit upon detecting electrical activity in the atria.
Additionally, the threshold detector includes threshold logic to distinguish electrical activity originating at the heart's natural pacemaker (SA node) from electrical activity originating at ectopic sites, such as PVCs.
In a preferred embodiment, a plurality of latches in the threshold detector are activated by output pulses from a pair of comparators.
A positive comparator produces an output pulse upon detection of cardiac electrical activity exceeding a positive threshold voltage, and a negative comparator produces an output pulse upon detection of cardiac electrical activity more negative than a negative threshold.
The threshold logic produces output signals indicative of which comparator first produced an output pulse.
The logic and control unit monitors the output signals from the threshold logic and thus determines whether the associated cardiac electrical activity represented a normal heart beat or resulted from an ectopic beat so that pacing may be appropriately controlled.