Sinus Node Recovery Time Assessment Revisited: Role of Pharmacologic Blockade of the Autonomic Nervous System

Sinus node recovery time assessment is used to diagnose clinically significant sinus node dysfunction (SND) when Holter has failed to prove a relationship between sinus bradyarrhythmias and symptoms, but consensus has not been reached as to the value of including assessment after pharmacologic blockade of the autonomic nervous system. This issue was addressed in the present study performed on 52 patients with syncope or presyncope/dizziness (n = 48), sinus bradyarrhythmias (n = 45), or both (n = 41). Group 1 consisted of 13 patients with a proven relationship between symptoms and sinus bradyarrhythmias. Group 2 consisted of 39 patients with suspected SND. The protocol included three pacing periods at two pacing rates and was performed at baseline (n = 52), after single doses of atropine and propranolol (0.02 mg/kg and 0.1 mg/kg, respectively) (n = 41), and again after a second dose (n = 29). The sensitivity of prolonged recovery times was 77% in group 1. Among group 2 patients, 56% had prolonged recovery times at baseline (79% when including the results after the first dose of drugs). The second dose did not contribute diagnostic information, but it caused significant adverse reactions in 7 of 29 patients (P < 0.001). These 7 patients were all older than 60 years. Assessment of sinus node recovery time after pharmacologic blockade of the autonomic nervous system thus increases the sensitivity of the method in patients with suspected SND and normal baseline results. However, only 50% of the initially suggested doses of atropine and propranolol is sufficient and eliminates the risk for significant adverse reactions.