Role of concealed and supernormal conductions during atrial fibrillation in the preexcitation syndrome

Abstract

The hypothesis that retrograde concealed and anterograde supernormal conductions over the accessory pathway are determinants of anterograde accessory pathway conduction during atrial fibrillation (AF) was prospectively tested. For 17 patients during AF, 90 ± 13 (mean ± standard deviation) consecutive beats were analyzed for morphology and VV interval preceding each QRS complex. In 15 patients with both preexcited and normal QRS complexes, after normal complexes, the cycle length preceding the first preexcited QRS complex was 389 ± 69 ms, which was longer than the average cycle length of consecutive preexcited complexes (325 ± 55 ms; p = 0.001). The mean difference was 61 ± 53 ms. After preexcited QRS complexes, the cycle length preceding the first normal QRS complex averaged 423 ± 65 ms, which was significantly longer than the average cycle length of 345 ± 47 ms between consecutively conducted normal QRS complexes (p < 0.001). The mean difference was 86 ± 45 ms. These findings suggest retrograde concealed conduction of normally conducted QRS complexes to the accessory pathway can affect anterograde conduction over the accessory pathway, and vice versa. In 2 patients with multiple accessory pathways, 1 accessory pathway conducted only after short preceding cycle lengths (355 to 360 and 181 to 185 ms), which was consistent with supernormal conduction. In conclusion, retrograde concealed conduction to the accessory pathway and anterograde supernormal accessory pathway conduction are factors that, in part, determine accessory pathway conduction during AF.