The Repetitive Ventricular Response: Relationship to Ventricular Fibrillation Threshold in Dogs

The experiments investigated the hypothesis that the occurrence of repetitive ventricular responses elicited by the ventricular extrasystole (VES) technique are an indicator of ventricular vulnerability to fibrillation. A comparison was made between the incidence of repetitive responses elicited by the VES technique and the minimum electrical energy (VFT technique) necessary to elicit repetitive responses and ventricular fibrillation in normal dogs, dogs with acute infarction, and dogs with chronic infarction. The VES technique produced repetitive responses in 14 of 46 sites. Responses were of at least three types: (1) bundle branch re-entry; (2) activation at the pacing site, and (3) activation at the infarct zone. In contrast repetitive responses and the onset of fibrillation produced by the VFT technique appeared to be a single type with earliest activation at the pacing site. There were no differences in the ventricular fibrillation thresholds between dogs with and without repetitive responses produced by the VES technique. Thus the incidence of VES technique-induced repetitive responses is not a reasonable predictor of ventricular vulnerability to fibrillation. However, in 2 dogs with lower ventricular fibrillation thresholds, repetitive responses originating at the infarct zone were induced by the VES technique. Occurrence of these repetitive responses may be indicative of ventricular vulnerability to fibrillation.