The spatial dispersion of atrial refractoriness and atrial fibrillation vulnerability

The local dispersion of conduction and refractoriness has been considered e ssential for induction of atrial arrhythmias. This study sought to determin e whether a difference of refractoriness and vulnerability for induction of atrial fibrillation between trabeculated and smooth as well as high and lo w right atrium may contribute to initiation of atrial fibrillation in dogs. In 14 healthy mongrel dogs weighing 22.4 +/- 1 kg, closed-chest endocardial programmed stimulation was performed from four distinct right atrial sites . Atrial refractory periods and vulnerability for induction of atrial fibri llation or premature atrial complexes were determined during a basic cycle length of 400 and 300 ms and an increasing pacing current strength. For a pacing cycle length of 300ms, atrial refractory periods were longer o n the smooth, as compared to the trabeculated right atrium (102 +/- 25 vs. 97 +/- 17ms, p < 0.05), whereas for a pacing cycle length of 400ms, there w as no significant difference. The duration of the vulnerability zone for in duction of atrial fibrillation was longer on the smooth right atrium, for a cycle length of both 400 ms (40 +/- 30 vs. 31 +/- 22 ms; p < 0.05) and 300 ms (33 +/- 25 vs. 23 +/- 21 ms; p < 0.01). When comparing high and low rig ht atrium, refractory periods were longer on the the low right atrium, for a cycle length of both 400 ms (111 +/- 23 vs. 94 +/- 24ms; p < 0.01) and 30 0 ms (104 +/- 20 vs. 96 +/- 23ms; p < 0.01). For a pacing cycle length of 3 00 ms, the duration of the atrial fibrillation vulnerability zone was longe r for the high, as compared to the low right atrium (34 +/- 22 vs. 22 +/- 2 2, p < 0.01). Seven dogs with easily inducible episodes of atrial fibrillat ion demonstrated significantly shorter refractory periods as compared to 7 non-vulnerable dogs, regardless of pacing site and current strength. In conclusion, significant differences in refractoriness and vulnerability for induction of atrial fibrillation can be observed in the area of the cri sta terminalis in healthy dogs. Thus, local anatomic factors may play a rol e in the initiation of atrial fibrillation.