Ventricular demand pacemaker tutorial

A single pacemaker spike (marked by red lines) is followed by a QRS complex which is wide and bizarre and resembles a ventricular beat. There are some normal intervening QRS complexes that suppress the pacemaker when they occur faster than the rate set for the pacemaker.

The normal P wave in sinus rhythm is slightly notched since activation of the right atrium precedes that of the left atrium. The P wave is upright in a positive direction in leads I and II. A P wave with a uniform morphology precedes each QRS complex. The rate is between 60 and 100 beats per minute and the cycle length is uniform between sequential P waves and QRS complexes. In addition, the P wave morphology and PR intervals are identical from beat to beat.