Effects of abrupt changes in cycle length on atrial refractory periods in man

Abstract

While the electrophysiologic effects of sudden changes in cycle length on the His-Purkinje System and ventricular myocardial refractoriness are better known, the behavior of atrial myocardium in this regard is poorly understood. The effects of an abrupt long to short cycle length change (11 patients: group A) and/or short to long cycle length alteration (18 patients: group B) on the atrial effective and functional refractory period were assessed during electrophysiologic studies. The values thus obtained were compared to those observed during the scanning of both constant long and constant short cycle lengths of the same duration. In group A the effective and functional refractory periods of the right atrium measured 250 ± 38 msec and 296 ± 31 msec during a constant long cycle length of 709 ± 80 msec, whereas the same parameters had values of 228 ± 30 msec and 260 ± 32 msec, respectively, at a constant short cycle length of 436 ± 81 msec. With an abrupt change in cycle length from long to short (a change of 273 ± 75 msec), the effective and functional atrial refractory periods were 225 ± 29 and 267 ± 29 msec in that order, and these values closely approximated those seen with a constant short cycle length. Similarly, the two atrial refractory period parameters in group B measured 218 ± 16 msec and 262 ± 19 msec during a constant short cycle length of 414 ± 68 msec and were 236 ± 17 msec and 284 ± 21 msec, respectively, at a constant long cycle length of 689 ± 92 msec. With a sudden short to long cycle length change of 275 ± 91 msec, the effective and functional atrial refractory periods measured 238 ± 15 and 284 ± 22 msec, respectively. The latter set of values are again quite similar to those obtained at a constant long cycle length. These data suggest that refractoriness of the human atrial myocardium adjusts abruptly and appropriately to the duration of the last cycle length. This behavior is indeed unique when compared to ventricular myocardium, which shows a cumulative effect of several preceding cycles, and His-Purkinje system, where the refractoriness overshoots in the direction of cycle length change.