Short accessory pathway (AP) refractory period (RP), atrial fibrillation (AF), were reported as risk factors of sudden death in Wolff-Parkinson White syndrome (WPW). A short AP RP is defined as 240ms in control state (CS) and 200ms after isoproterenol (iso). The purpose of study was to evaluate the reproducibility of the measurement of AP RP during a same electrophysiological study (EPS).

76 patients (pts) aged from 8 to 68 years (mean 30 ± 16.5) were studied prospectively for a preexcitation syndrome. EPS consisted of programmed atrial stimulation in CS at a basic cycle length of 400ms with the introduction of one extrastimulus and the decrease of coupling until the effective AP RP or atrial RP. The measurement was repeated twice. Then, iso (0.02 to 1 μg.min⁻¹) was infused to increase the sinus rate to at least 130 beats/min and the programmed atrial stimulation was repeated twice in 56 pts.

We noted important variations of AP RPs with generally a shortening at the second measurement. Mean variations were 34 ± 51ms in CS and 32 ± 24 after iso. The mean values in CS were 280 ± 50ms and then 253.5 ± 59ms (p<0.003). The mean values after iso were 239 ± 45ms and then 209 ± 39ms (p<0.0001). In CS 55 pts had initially an AP RP > 240ms (mean 304 ± 36); at other study, mean values were 278 ± 44; 14 of them had an AP RP < 240ms at the other measurement. Most of changes (n = 9) occurred in pts with AP RP <280ms. 21 pts had a short AP RP (<250ms) (mean 220 ± 18). All of them had still a short AP RP at other measurement (mean 204 ± 24). After iso 49 pts had an AP RP longer than 190ms (mean 248 ± 41). At the other study mean value was 215 ± 35ms; 15 pts had an AP RP < 200ms at the other study; all of them had an initial value < 250ms. Among 7 pts with initial AP RP < 200ms all of them but one had an AP RP<200ms.

There are important variations of AP refractory periods during electrophysiological study except in patients with very short AP refractory periods. Therefore the values of AP RP’s should be interpreted carefully in association with the other data of electrophysiological study as the induction of tachycardias.