Enhanced parasympathetic tone shortens atrial refractoriness in man.

The purpose of this study was to determine the effects of enhanced vagal tone on human right atrial refractoriness in 12 patients. A specially built neck collar connected to a vacuum source was placed around the patient's neck and enhanced vagal tone was produced during neck suction using intracollar negative pressures of 50 to 60 mm Hg. Refractory periods were determined with a catheter electrode positioned in the high right atrium near the sinus node. Induced neck suction increased the spontaneous sinus cycle length from 837 +/- 96 to 1.136 +/- 273 ms (p less than 0.001) and shortened the atrial effective refractory period from 241 +/- 24 to 230 +/- 20 ms (p less than 0.01) and the atrial functional refractory period from 272 +/- 32 to 262 +/- 29 ms (p less than 0.01). In 2 of 2 patients, collar-induced decreases in atrial refractoriness and increases in spontaneous cycle length were prevented after atropine (0.03 mg/kg) was given intravenously. It is concluded that enhanced vagal tone mediated through muscarinic receptors shortens atrial refractory periods in man.