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.
Tracing 3a: mode AAT programmed at 40 bpm;
Tracing 3b: programmed in AAT mode at 60 bpm;
Tracing 3c: programmed in VVT mode at 40 bpm;
Except for pacing triggered by sensed events, the triggered modes function like the corresponding inhibited modes and can be applied in 2 specific cases:
1) When sensing myopotentials or electromagnetic interference, the SST mode, instead of being inhibited, issues a paced event in response to each artifact sensed outside the refractory period, which prevents the occurrence of a pause in pacemaker-dependent patients. To prevent runaway pacing, one can, depending on the device model, either lengthen the refractory period or limit the upper pacing rate. This type of pacing mode was valuable in older pacemaker models, which were more sensitive to outside interferences because they functioned strictly in unipolar mode.
2) This mode allows a) an evaluation of sensing in the chamber concerned, b) a confirmation of the absence of crosstalk, and c) the proper sensing of extrasystoles. On this tracing, for example, the AAT mode enables the verification of a) accurate sensing of sinus activity, b) proper sensing of atrial extrasystoles, and c) absence of crosstalk.
It is noteworthy that on the 3c tracing (5) the QRS complex is not sensed at its onset. Sensing is, indeed, possible when the pacemaker has measured a greater ventricular signal amplitude than the programmed sensitivity value with a signal slope falling within the range of frequency between 20-30 and 80-125 Hz.
