Effect of Corwin (ICI 118587) on resting and exercise heart rate and exercise tolerance in digitalised patients with chronic atrial fibrillation.

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Abstract
The effect of Corwin, a new oral beta1 partial agonist, on the ventricular response to atrial fibrillation was studied in digitalized patients during 24 h ambulatory electrocardiography and during exercise on a treadmill in a double blind placebo controlled crossover trial. Corwin reduced the maximum heart rate during exercise from 162(16) beats/min to 120(9) beats/min and reduced the peak heart rate during ambulatory electrocardiography from 113(11) to 90(6) beats/min consistent with a .beta. adrenoreceptor antagonist action at higher levels of sympathetic nervous system activity. Minimum heart rate during ambulatory electrocardiography was increased from 62(5) to 70(5) beats/min indicating that at lower levels of sympathetic activity the drug acts as a .beta. agonist. The drug increased exercise tolerance significantly. Serum digoxin concentrations were not affected by the drug. Corwin appears to be effective in stabilizing heart rate during atrial fibrillation at rest and during exercise in digitalized patients.