Electrophysiologic characteristics at initiation of ventricular tachycardia and ventricular fibrillation in a canine infarct model

Local ventricular activation time and the conduction time during sinus rhythm at the induction of ventricular tachycardia (VT) and ventricular fibrillation (VF) were investigated using a canine model of chronic myocardial infarction. Of 26 dogs studied, 15 had inducible VT, 10 had inducible VF, and 1 had no inducible arrhythmias. Bipolar local ventricular electrograms were recorded during sinus rhythm from 136 sites in 10 dogs with VT and 164 sites in 11 dogs with VF. Mean activation time in dogs with inducible VT was significantly longer than in dogs with inducible VF. Furthermore, simultaneous local ventricular electrograms were recorded during the induction of VT (74 episodes) or VF (38 episodes) from the infarct border zone at the endocardium (B‐EN), the epicardium (B‐EP), and normal sites (N‐EN, N‐EP). During VT induction, the activation time at N‐EN and N‐EP was significantly longer than during VF induction (N‐EN: 94 ± 21, 70 ± 19 ms; N‐EP: 83 ± 21, 64 ± 10 ms; p < 0.05). Conduction time was measured at the initiation of VT or VF induced by orthodromic or antidromic pacing. The conduction times of the last paced beat between N‐EN and B‐EP (35 ± 11, 62 ± 24 ms), N‐EN and N‐EP (35 ± 12, 14 ± 13 ms), B‐EN and B‐EP (16 ± 10, 38 ± 25 ms), and B‐EP and N‐EP (77 ± 27, 44 ± 12 ms) were significantly different in dogs with inducible VT (p < 0.05), but not in dogs with VF. Dispersion of effective refractory period was also observed in dogs with VT. Percent infarct in inducible VT was larger than in inducible VF (VT: 16 ± 5%; VF: 10 ± 2%; p < 0.001). These studies suggest that dogs with inducible VT have prolonged ventricular activation time and significantly different bidirectional conduction time during VT induction. This may serve as a substrate for reentry.