Electrophysiologic effects on combined autonomic blockade in patients with sinus node disease

Thirty-two patients were studied before and after i.v. administration of 0.15-0.20 mg/kg of propranolol. Twenty-one of the 32 underwent combined autonomic blockade with the additional infusion of 0.04 mg of atropine. Twenty other patients with sinus node disease underwent electrophysiologic studies both before and after i.v. administration of 0.04 mg of atropine alone. Spontaneous cycle length, maximal corrected sinus node recovery time, sinoatrial conduction time, secondary pauses and intrinsic heart rate were measured. Secondary pauses were more common in those with abnormal intrinsic heart rates, and they did not correlate with changes in maximal corrected sinus node recovery time or sinoatrial conduction time. In patients with normal intrinsic heart rate, abnormal test measurements usually returned to normal after combined blockade (hypervagotonia); however, some patients showed a new abnormality after propranolol that was not reversible with atropine (catecholamine-dependent). Abnormal test responses in patients with abnormal intrinsic heart rate persisted or increased after combined blockade. We conclude that patients with sinus node disease may be categorized as (1) those with intrinsic sinus node disease; (2) those with normal intrinsic sinus node function but either relative hypervagotonia or catecholamine dependency; and (3) those with abnormal intrinsic sinus node function affected by vagal or catecholamine factors.