Dual chamber atrial sensing pacemaker

There is a normal or intrinsic P wave which, after a preset PR interval, is followed by a pacemaker spike and a paced QRS complex that has a bizarre morphology resembling a left bundle branch block or a ventricular complex.

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.