The pacemaker is firing at a ventricular rate of 125/minute. There is a PVC approximately half-way across the rhythm strip with a compensatory pause which allows you to notice a P wave – and the ventricular pacer follows the atrial activity. This is a dual chamber pacer, which is more physiologic than a single lead ventricular pacemaker. The pacer allows the ventricle to follow the sinus rate during exercise or other situations of appropriate increased heart rate.

Rhythm strip – 4^th beat is PVC with following compensatory pause revealing P waves with following ventricular paced beats.

This elder man is febrile and dehydrated – both good reasons for sinus tachycardia at 125/minute. Appropriate treatment of this pacemaker-mediated tachycardia is fluid resuscitation and acetaminophen!