Twenty-one patients were studied to investigate whether cardiac acceleration above control values occurred after cessation of enhanced vagal tone (postvagal tachycardia), and to determine the effects of selective autonomic blockade on postvagal tachycardia. Patients had neither sinus arrhythmia nor sinus nodal dysfunction. Enhanced vagal tone was induced by neck suction using a lead neck collar connected to a vacuum source. For each patient intracollar negative pressures of 50 to 60 mm Hg were induced for 2 seconds on 10 occasions. For all patients, sinus cycle length increased from 821 ± 99 to 1,067 ± 241 ms (p < 0.001) during neck suction and decreased to 760 ± 96 ms after termination of neck suction, a value significantly (p < 0.001) less than control. Five of 16 patients had no postvagal tachycardia. Maximal shortening of sinus cycle length occurred 3 to 8 complexes after cessation of neck suction. Neck suction was induced in 7 patients before and during propranolol administration, 0.15 mg/kg intravenously, and the degree of postvagal tachycardia was unchanged. Atropine, 0.03 mg/kg intravenously, prevented neck suction-induced sinus slowing and acceleration in 3 of 3 patients. We conclude that postvagal tachycardia occurs and is not mediated through β-adrenergic activity, but is inhibited by muscarinic blockade.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine