Pre-excited RR intervals during atrial fibrillation in the Wolff-Parkinson-White syndrome: Influence of the atrioventricular node refractory period

AbstractThe ventricular rate and percent of pre-excited QRS complexes during atrial fibrillation were compared in two groups of patients with the Wolff-Parkinson-White syndrome. Group A consisted of 22 patients whose anterograde effective refractory period of the accessory pathway was longer than that of the atrioventricular (AV) node. Group B consisted of 23 patients in whom this relation was reversed. No patient had organic heart disease.Both groups had a similar effective refractory period of the accessory pathway (288 ± 37 vs. 280 ± 26 ms), whereas that of the AV node was shorter in group A than group B (242 ± 25 vs. 285 ± 27 ms, p = 0.0001). Patients in group A had a lower percent of pre-excited QRS complexes during atrial fibrillation (39 ± 43% vs. 93 ± 20%, p = 0.0001). In the 21 patients whose refractory period was measured, the difference was plotted against the percent of pre-excited QRS complexes; there was a significant correlation between the two (r = −0.83, p < 0.001).In patients in whom pre-excited RR intervals were present, the pre-excited RR intervals were compared between the two groups. Both groups had similar effective refractory periods of the accessory pathway (265 ± 22 vs. 280 ± 27 ms) and ventricle (200 ± 17 vs. 211 ± 26 ms). The effective refractory period of the AV node was shorter in group A (248 ± 22 vs. 285 ± 28 ms, p = 0.0005). The shortest pre-excited RR interval did not show any difference (244 ± 37 vs. 265 ± 41 ms). However, both the average (328 ± 39 vs. 397 ± 56 ms, p = 0.001) and longest (495 ± 109 vs. 666 ± 205 ms, p = 0.02) pre-excited RR intervals were shorter in group A.These data suggest that interaction between the refractory periods of the AV node and accessory pathway contributes to the percent of pre-excited QRS complexes. The effective refractory period of the AV node also indirectly contributes to the duration of pre-excited RR intervals. This contribution is greatest when RR intervals are long