Figure 16 s

Tracings of a patient with a dual-chamber pacemaker who has underlying atrial fibrillation. Electrocardiograms and corresponding marker channels are shown for pacing modes DDD, DDI, and DVI, respectively. Note that during DDD the pacemaker rhythm is an irregularly irregular paced ventricular rhythm at, but not exceeding, the upper rate of the pacemaker. In the DDI mode, there is no tracking of the atrial fibrillation; therefore, it functions effectively as a VVI pacemaker so long as the patient is in atrial fibrillation. In the last tracing, the mode is DVI; therefore, there is no sensing of atrial electrograms, which accounts for the AV sequential pacing pattern. This mode is generally not used when the DDI mode is available. AR = sensed atrial electrogram in the pacemaker refractory period; AS = sensed atrial electrogram; VP = ventricular paced complex.

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