Background: Pre-excitation of the intra-atrial septum (IAS) by pacing at the ostium of the coronary sinus (CSO) can prevent atrial fibrillation (AF) in case of single atrial premature beats (APBs). We investigated whether pre-excitation of IAS, either by pacing at CSO or at the right ventricle in the presence of retrograde conduction (RV), can prevent atrial tachyarrhythmia triggered by single and multiple APBs. AF vulnerability was compared to pacing at the right atrium (RA) and sinus rhythm (SR).
Methods: Seventeen patients, age 52 +/- 21 years, who exhibited retrograde VA conduction and reproducible induction of atrial tachyarrhythmia during an electrophysiological procedure, were studied. Both during SR and pacing (S1-S1:600 ms) at RA, CSO, and right ventricle (RV), single (A1-S2:200 ms) and multiple premature stimuli (A1-S2-S3-S4:200-180-180 ms) were delivered at RA (4 x diastolic threshold).
Results: During pacing at RA, single and multiple APBs invariably induced runs of atrial tachyarrhythmia (mean duration 34 +/- 67 sec and 37 +/- 69 sec, range 1 sec to 20 min). During preventive pacing at CSO and RV, single APBs (A1-S2:200 ms) did not induce atrial arrhythmia (0 +/- 0 sec, 0 +/- 0 sec, P < 0.05 vs pacing at RA). In contrast, when multiple APBs were applied, pacing at CSO or RV failed to prevent initiation of AF (mean duration 36 +/- 63 sec, 38 +/- 65 sec, NS). Also during SR, single APBs did not induce AF (0 +/- 0 sec, P < 0.05 vs pacing at RA) whereas multiple APBs invariably induced AF (39 +/- 74 sec, NS).
Conclusions: Compared to pacing at RA, pre-excitation of IAS either by pacing at CSO or at RV with retrograde conduction can prevent initiation of paroxysms of atrial tachyarrhythmia triggered by single but not by multiple right APBs. These findings imply that the potential benefit of choosing an optimal pacing site in patients requiring atrial-based pacing is limited. Moreover, in the absence of bradycardia, no specific pacing site offers incremental benefit over the natural "protective" effect of sinus rhythm.