Differential Effects of Vagal Activation on the Sinus and Atrioventricular Nodes: Report of 2 Cases.

Vagal activation usually affects both sinus and atrioventricular (AV) nodes, manifesting as sinus slowing accompanied by varying degrees of AV block. AV block accompanying sinus acceleration as during treadmill testing is usually considered pathologic. We report 2 cases of vagally mediated reflex AV block accompanied by sinus tachycardia and acceleration.