EFFECTS OF ISOPROTERENOL ON ACCESSORY PATHWAY CONDUCTION IN INTERMITTENT OR CONCEALED WOLFF-PARKINSON-WHITE SYNDROME

The effects of isoproterenol on accessory pathway conduction were evaluated in 24 patients with intermittent and 60 patients with concealed pre-excitation, using ahial and ventricular incremental and extrastimulus testing techniques. The atrial paced cycle length that induced block in the accessory pathway could be compared in 11 of the 24 patients with intermittent preexcitation before and after isoproterenol; it decreased from 622 ± 212 ms to 408 ± 128 ms (mean ± standard deviation) after Isoproterenol (p <0.01). The anterograde effective refractory period of the accessory pathway could be compared in S patients before and after isoproterenol; it decreased from 460 ± 131 to 310 ± 48 ms after isoproterenol (p <0.01). None of the 60 patients with concealed preexcltation showed ventricular preexcitation with isoproterenol infusion. Eighty-one of the 84 patients had clinically documented supraventuicular tachycardia, suggesting the accessory pathway was capable of retrograde conduction. Retrograde study was performed in all 84 patients; 83 had retrograde conduction and the other had no retrograde conduction before and after isoproterenol. The vehicular paced cycle length that induced block do the accessory pathway could be compared in 38 patients before and after isoproterenol; it decreased from 342 ± 71 to 296 ± 39 ms after isoproterenol (p <0.001). The retrograde effective refractory period of the accessory pathway could be compared in S6 patients; it decreased from 283 ± 76 to 238 ± 36 ms after isoproterenol (p <0.001). in conclusion, isoproterenol facilitates anterograde and retrograde accessory pathway conduction, but the facilitation of anterograde conduction occurs only in those capable of spontaneous conduction. © 1990.