Yang A et al. (2006) Identification of “substrate fibrillators” and “trigger fibrillators” by pacemaker diagnostics. Heart Rhythm 3: 682–688

Patients requiring a pacemaker often have atrial fibrillation (AF), which increases the risk of thromboembolism and, consequently, the risk of morbidity and mortality. To maintain sinus rhythms, atrial pacing algorithms have been incorporated into pacemaker software. These algorithms target modification of atrial substrate and suppress AF triggers, including premature atrial contractions (PACs), believed to be a primary inducer of AF. Using data from dual-chamber pacemakers with advanced diagnostic functions, Yang et al. have identified various AF onset patterns in patients with paroxysmal AF and described those patients who might benefit most from PAC-suppressing pacing algorithms.

Patients with high PAC activity in the 5 min before AF onset had fewer recurrent AF episodes than those with moderate PAC activity, and a lower mean episode duration than those with low PAC activity, resulting in reduced AF burden. These patients with high PAC activity most likely have little alteration in atrial substrate, and their AF development is probably induced by high trigger activity. These patients (who the authors believe to be those at an early disease stage) are most likely to respond to PAC-suppressing pacing algorithms.

Patients with low PAC activity before AF onset, on the other hand, have a prolonged arrhythmia episode duration and high AF burden, probably caused by a high atrial substrate factor. In these patients, severe structural and electrophysiological changes in the atrial myocardium, induced by a few PACs or even occurring in the absence of PACs, are presumed to be key in initiating AF. Atrial substrate factor serves to sustain rather than trigger arrhythmia, and patients with low PAC activity are less likely to respond to the pacing algorithms.