Effects of vagal stimulation on regional myocardial flows and ischemic injury in dogs.

The effects of vagal stimulation on regional myocardial blood flow (RMBF) and epicardial ST-segment were investigated in the normal and ischemic myocardium and anesthetized dogs. In non-ischemic myocardium, vagal stimulation increased calculated coronary resistance and decreased RMBF. In ischemic myocardium, vagal stimulation increased endocardial RMBF, endo/epi ratio and ischemic/nonischemic areas flow ratio, thus inducing a 'reverse coronary steal phenomenon'. Simultaneously, epicardial ST-segment elevation was reduced. All these effects were independent of the induced bradycardia since they persisted during atrial pacing, but resulted from muscarinic receptors activation since they were abolished by atropine.