Acute Electrophysiologic Effects of Nadolol

: The acute effects of intravenous nadolol (0.01 and 0.02 mg/kg) on cardiac electrophysiologic parameters were assessed with His bundle recording and programmed atrial stimulation. The higher dose of nadolol reduced resting heart rate (71 vs. 65 beats/min, P < 0.02), and the degree of slowing was related to the initial heart rate (r = −0.68, P < 0.05). Atrioventricular conduction time as defined by the paced A—H interval, rose by 12 msec (P < 0.001) after nadolol (0.02 mg/kg) administration. Atrial refractoriness increased (by 10 msec, P < 0.02) only at the higher dose level with nadolol. At both dose levels, atrioventricular nodal effective and functional refractory periods were increased (P < 0.02) by a mean of 45 and 21 msec, respectively, suggesting greater sensitivity of atrioventricular nodal refractoriness to beta‐adrenergic blockade. Nadolol's effects were generally similar to those of previously reported studies with other beta‐adrenergic blockers. These data suggest that nadolol slows conduction through the atrioventricular node and increases atrial and atrioventricular nodal refractoriness.