The effect of cycle length on the atrial refractory period.

Abstract

The effect of cycle length upon refractory period of the atria was measured in 34 patients. The effect of abrupt change in paced cycle length on atrial refractory period was measured by introducing after every eighth paced cycle (CLP) a test cycle (CLT) at an interval which was either 100 ms longer (CLT = CLP + 100 ms) or shorter (CLT = CLP - 100 ms) than the paced cycle. These findings confirm that: (1) atrial refractory periods shorten with decreasing cycle length during steady state pacing; (2) an abrupt change in paced cycle length results in a change in refractory period. This change is similar in direction but smaller in magnitude than the change which occurs in response to steady state pacing; and (3) there is no correlation between intraatrial conduction time and refractoriness.