The potential ability of electrophysiologic abnormalities to predict recurrence of atrial flutter was evaluated. Twenty-five patients with chronic atrial flutter resistant to combined digitalis and quinidine therapy were studied electrophysiologically after restoration of sinus rhythm by overdrive pacing or by eventual direct current cardioversion. Recurrence of atrial flutter was observed in 12 patients during a mean follow-up period of 17 months (range 3 to 50). Electrophysiologic testing included programmed high right atrial stimulation at a paced drive cycle length of 600 ms and incremental pacing up to 200-ms paced intervals. When coupling intervals of 90% of the drive cycle length were compared to coupling intervals of 48% of the drive cycle length, the increase in S1A1 interval, defined as the interval between the stimulus artifact and the atrial activation near the atrioventricular junction, was greater in patients with subsequent recurrence of atrial flutter (47 +/- 11 vs 21 +/- 18 ms). Stepwise logistic regression analysis identified the S1A1 increase to be the sole independent predictor of recurrence (p = 0.0082) while previous episodes of atrial flutter or the presence of organic heart disease were identified as dependent variables. Reclassification showed a 91% sensitivity and a 92% specificity. Correct classification was achieved in 92% of patients. The initiation of atrial dysrhythmia had no predictive value. The assessment of the S1A1 interval by programmed atrial stimulation appears helpful in delineating the patient risk of recurrent atrial flutter after termination by overdrive pacing.