63-year-old man with a history of paroxysmal atrial fibrillation; full right bundle branch block pattern on the electrocardiogram; 3 episodes of sudden syncope; electrophysiological study with HV interval measurement at 82 ms; implantation of an Adapta dual-chamber pacemaker; the 2 leads are well positioned with normal pacing impedance, proper sensing and satisfactory pacing thresholds; 3 days after implantation, pacemaker control; programming of various pacing modes and recording of tracings; for this first tracing, programming in ODO mode.
Programming in DOO mode 40 beats/minute;
Fixed-rate asynchronous modes were the only modes available on early pacemaker models. The DOO mode induces asynchronous atrioventricular sequential pacing, without inhibition by intrinsic events. As seen on this tracing, when the patient is not pacemaker-dependent, parasystole occurs with competition between spontaneous activity and paced activity. This mode enables verifying the effectiveness of the pacing and avoiding inhibition in case of exposure to external interference (electric scalpel in a pacemaker-dependent patient for example). Pacing is effective and captures the atrium or ventricle only when occurring outside the absolute physiological refractory period following a spontaneous atrial or ventricular activity.
This tracing shows the risk of this type of mode. Several ventricular stimuli occur at the peak of the T wave of an undetected spontaneous QRS. This is the vulnerable period with risk of induction of a ventricular rhythm disorder. The risk of ventricular fibrillation is limited although increases in the presence of myocardial ischemia or metabolic disorder. Similarly, asynchronous atrial pacing in the atrial vulnerable period can induce atrial fibrillation.
Asynchronous modes are now obsolete and are only used in 2 specific circumstances:
