This 63-year-old man presented with a history of paroxysmal atrial fibrillation (AF) and complete right bundle branch block on the electrocardiogram (ECG). He suffered 3 episodes of syncope without prodrome. An electrophysiologic study revealed an 82-ms HV interval, prompting the implantation of an Adapta® dual chamber pacemaker. Both pacing leads were properly positioned and associated with normal impedance, and satisfactory sensing and capture thresholds. The pacemaker was interrogated 3 days after the implant and recordings were obtained during the programming of various pacing modes. This first tracing was recorded in ODO mode.
On this and the following tracings, the first channel is lead I, upon which the event markers are superimposed, the second shows the interatrial, interventricular and atrioventricular (AV) intervals, the third is lead III and the fourth channel is lead II.
In ODO mode, pacing is not possible; consequently, it should never be programmed in pacemaker-dependent patients; however, since sensing takes place in the chambers explored, this mode allows an analysis of the spontaneous rhythm along with a concomitant visualization of the ECG and the event markers. The blanking periods are shortened in order to favor the effective sensing periods. Therefore, the ODO mode can be used to test the sensitivity. It can be programmed temporarily in non-dependent recipients of MRI-compatible pacemakers who need to undergo MR examination. Programming of the ODO mode prevents the reversion to VVI. One must, of course, not forget to re-interrogate and reprogram the pacemaker after using any temporary pacing mode.
