Relation of the endocardial and epicardial ventricular fibrillation thresholds of the right and left ventricles

Ventricular fibrillation thresholds were measured on the endocardium and epicardium of the right or left ventricle, or both, in 13 dogs. The electrodes, introduced through a right or left atriotomy to avoid injury to the ventricles, were aligned opposite and parallel to each other on the endocardium and epicardium. The ventricular fibrillation threshold was measured during atrial pacing by delivering a train of impulses to the ventricle during the vulnerable period after every 12th paced complex in 1 milliampere (mA) increments of current until fibrillation ensued. The mean (± standard deviation) right ventricular epicardial and endocardial fibrillation thresholds were 18.3 ± 5.3 and 17.6 ± 5.3 mA, respectively, (values not significantly different). However, the fibrillation threshold of 36.1 ± 9.5 mA in the left ventricular epicardium was significantly higher than the value of 20.7 ± 9.4 mA on the left ventricular endocardium. These data suggest that the proximity of the fibrillating electrodes and Purkinje network may be a factor in the measurement of ventricular vulnerability.