Bigeminy Pacing: A New Protocol to Unmask Atrial Vulnerability

Abstract

One of the most exciting developments in our understanding of atrial fibrillation (AF) mechanisms has been the recognition that "AF begets AF" in a process termed atrial remodeling. Little information is available about the events that mediate short-term remodeling. In a bigeminy atrial pacing protocol that produces a continuous extrasystole-postextrasystole cycle length, we sought to evaluate the electrophysiologic consequences of irregular atrial pacing. This study included 22 consecutive patients with documented paroxysmal AF and 10 control subjects. After evaluating the effective refractory period (ERP) and functional refractory period (FRP), bigeminy atrial pacing was performed for 5 minutes. The S1-S2 coupling interval during bigeminy pacing was programmed to a mean value of 275 +/- 45 msec, i.e., 45 msec longer than the basic ERP measured at 100 beats/min. During bigeminy pacing, AF that lasted longer than 1 minute occurred in 12 AF patients and in none of the control subjects (group I). Short salvos of AF occurred in 5 patients and 3 controls (group II). No arrhythmia occurred in 5 patients and 7 controls (group III). Sensitivity, specificity, and negative and positive predictive values of sustained AF induced by bigeminy pacing were 54%, 100%, 50%, and 100%, respectively. No differences were observed between different pacing rates during bigeminy, the premature coupling interval S1-S2, or the conduction parameters S2-A2 and A2. Group I had the shortest basic ERP (222 +/- 38 msec) and group III the longest ERP (242 +/- 21 msec, P < 0.05); group II was intermediate. Atrial ERPs and FRPs measured immediately after termination of 5 minutes of bigeminy pacing were shorter than during baseline. The degree of shortening was similar in AF patients and in controls. The locoregional conduction delay A2 did not change after the bigeminy protocol. This study demonstrates that atrial bigeminy pacing highly increases atrial vulnerability. This protocol appears interesting because its sensitivity and specificity are higher than those of the conventional extrastimulation test. This makes it attractive for routine diagnosis of undocumented paroxysmal AF. Because it may induce atrial arrhythmias independently of the classic mechanisms of wavelength shortening, this study emphasizes the need for new modalities in the prevention of atrial arrhythmias.