993-45 Atrial Fibrillation: Sotalol's Heart Rate Reductions are Selective for Circadian Hours Where Heart Rate is High

Abstract

We used 24-hour ambulatory ECG monitoring (AEM) to determine sotalol's circadian heart rate (HR) effects in chronic atrial fibrillation. Sixty subjects on a stable digoxin dosage had AEM after one week of single-blind placebo (PLC) and then again after 2 weeks of double-blind sotalol (80 or 160 mg qd) or continued PLC. Circadian HR patterns (average, high and low) for AEM's with = 18 paired hours (average = 23.2 hrs) were analyzed. Baseline and endpoint HR curves (open and closed symbols) are shown for sotalol and placebo groups. Circadian HR patterns on continued placebo were stable, but sotalol produced reductions in HR which were equal for the 80 and 160 mg doses. The largest HR reductions occurred between 11 am and 7 pm, where sympathetic tone is high - consistent with sotalol's beta blocking activity. Mean reductions in 24 hour high, average and low HR were 18 BPM, 11 bpm and 7 bpm, respectively, with the high and average HR reductions being significant (p < 0.05). Sotalol's HR lowering effects in atrial fibrillation are selective for circadian hours when HR is high, having lesser effects on low HR values. The threshold for beta blocking activity is 80 mg qd, with no further lowering seen at 160 mg qd 2 .