Rapid Atrial Pacing in Man

The first ten cycles following cessation of atrial pacing were evaluated in 44 control subjects (mean age 52.9 ± 14.88 yr) and 39 patients (mean age 62.9 ± 15.41 yr) suspected of having sinus node dysfunction (SND). The maximal cycle length for each postpacing cycle following several pacing periods in each control subject was determined, and was normalized by dividing it by the subject's mean spontaneous control cycle length (9r). Using the control group, a normalized maximal post-pacing response pattern (mean and SD) was derived. For each SND patient, a composite SD for each post-pacing cycle was calculated by adding the patient's STL variance to the variance determined for each post-pacing cycle in the control group. Two compoSite SD above the mean value for each post-