Noise mode response at peak exercise in a DDD pacemaker.

The noise sampling period has been recognized as a cause of apparent sensing malfunction in demand pacemakers. Physiologic signals as well as external electromagnetic interference can cause certain demand pacemakers to remain refractory and escape asynchronously at a specified rate. In this case, noise mode reversion pacing at the programmed lower rate limit of a Cordis 415A DDD pacemaker was observed during exercise when P-waves fell within the noise sampling period.