The effects of reverse atrial electrical remodeling on atrial defibrillation thresholds

The implantable atrial defibrillator is a developing therapeutic option for paroxysmal atrial fibrillation, but shock related discomfort continues to be a limiting factor. To further characterize successful defibrillation, the relationship between reverse atrial electrical remodeling and internal atrial defibrillation thresholds in canines with chronic atrial fibrillation was examined. Testing was performed in 21 dogs. Chronic atrial fibrillation was induced in eight dogs by creating moderate mitral regurgitation and rapidly pacing the right atrium for > or = 6 weeks. The atrial fibrillation cycle length, atrial effective refractory period, refractory period dispersion, and internal atrial defibrillation thresholds were determined after establishment of chronic atrial fibrillation after 4 hours of sinus rhythm postcardioversion and 7 days of sinus rhythm postcardioversion. These measurements were then compared to a normal population of 13 dogs. The atrial defibrillation thresholds were 6.6 J (1.9-10.1 J) initially, 2.9 J (1.5-3.7 J) after 4 hours of sinus rhythm, and 0.9 J (0.4-1.3 J) after 7 days of sinus rhythm (P = 0.04). This decrease was associated inversely with the atrial effective refractory period (P < 0.03), and atrial fibrillation cycle length (P < 0.05), and with a decrease in atrial refractory period dispersion after 7 days of sinus rhythm (P = 0.04). These electrophysiological measurements reached normal population levels by 7 days. Atrial defibrillation thresholds decrease as atrial reverse electrical remodeling occurs and this reduction corresponds to increased atrial fibrillation cycle length, increased atrial refractoriness, and decreased refractory period dispersion.