Ventricular pacing with 100 percent capture

Every QRS complex is preceded by a pacemaker stimulus (marked by red lines). The QRS complex is abnormal, wide, and bizarre, resembling a ventricular beat. The QRS complexes usually have a left bundle branch block configuration since the ventricular lead is most commonly located in the right ventricle.

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.