Reentrant ventricular arrhythmias in the late myocardial infarction period. 6. Effect of the autonomic system.

The effect of the autonomic system on conduction disorders in the infarction zone (IZ) and related reentrant ventricular arrhythmias (RVA) in the late myocardial infarction period in the dog was studied utilizing averaged recordings of the reentrant pathways from the epicardial surface of the IZ. Vagal (V) stimulation was found to have no significant direct electrophysiologic effect while sympathetic (S) stimulation resulted in a direct slight improvement of conduction in the IZ. However, because of the marked rate-dependency of conduction in the IZ, the effects of both V and S stimulation were modified through changes in the heart rate. The bradycardia produced by V stimulation resulted in improvement of conduction in the IZ and disappearance of RVA, while the tachycardia induced by S stimulation resulted in worsening of conduction in the IZ and the occurrence of RVA. Thus, in spite of its slight enhancing effect on conduction in the IZ, the propensity of S stimulation to induce RVA was primarily due to its tachycardiac effect.