Electrophysiological characteristics of accessory pathways with prolonged retrograde conduction.

Electrophysiological characteristics of an accessory pathway (AP) with a long ventriculoatrial (VA) interval (arbitrarily defined as > or = 50 ms and absence of continuous electrical activity) and no retrograde decremental property are described in this study. Fifteen patients (group 1) were compared with 171 patients with normal VA conduction (group 2). Mean VA conduction time was 77 +/- 24 versus 34 +/- 12 ms in group 1 versus group 2, respectively. Group 1 patients were older (55 +/- 14 vs 40 +/- 14 years), the male to female ratio was higher (2.8 vs 1.6), and APs were more prevalent on the right (60%) but manifest APs were lower (20% vs 54%) compared to group 2 patients (P < 0.05 in all cases). QRS morphology during induced atrioventricular reciprocating tachycardia was identical in both groups but the tachycardia cycle length was longer in group 1 (373 +/- 29 vs 344 +/- 50 ms, P < 0.05). Retrograde AP block cycle length and effective refractory period were greater in group 1 (362 +/- 59 vs 293 +/- 57 ms; 330 +/- 58 vs 273 +/- 55 ms, both P < 0.05). Adenosine (up to 18 mg) and verapamil (5-10 mg) failed to block the VA conduction via AP during ventricular pacing. In group 1 the number of radiofrequency lesions for a successful ablation were significantly less (3 +/- 2 vs 6 +/- 5, P < 0.05). In conclusion, APs with a long VA interval and no decremental retrograde conduction have electrophysiological characteristics that are different from those with a short VA interval. Role of aging deserves further exploration. Effect of Pacing Site and Lead Tip to Ring Distance