Figure 16 r

Top. Sinus tachycardia in a patient with atrioventricular block and a DDD pacemaker with a programmed upper rate of 100 beats per minute, which is less than the intrinsic sinus rate. Note that the interval between the sensed P wave and the paced ventricular complex lengthens progressively, until there is a P wave (within the T wave) following the first, fourth, and seventh paced ventricular complexes without subsequent ventricular pacing, consistent with pacemaker Wenckebach. Bottom. The pacemaker is programmed in the DDDR mode with upper rate of 100 beats per minute. The presence of rate response, during activity, acts to smooth the upper rate, preventing the longer pauses during pacemaker Wenckebach.

Mitrani,R.D. and others,Cardiac Pacemakers,Hurst's The Heart,10th edition,Vol.1,pp.963-992