Nonsustained polymorphic ventricular tachycardia induced by electrical stimulation in 3 week old canine myocardial infarction.

To study the electrophysiology of ventricular tachycardia 3 to 4 weeks after myocardial infarction in a canine model, an anteroapical transmural infarct was created in 40 dogs by ligation of the left anterior descending coronary artery. An average of 25 days after myocardial infarction 32 dogs that survived the infarction and 4 control dogs with a sham operation underwent open chest electrophysiologic study. No ventricular arrhythmias could be induced by any mode of ventricular stimulation in any of the four control animals. Twenty-seven of 32 dogs with myocardial infarction had reproducible ventricular arrhythmias in response to ventricular stimulation. In 17 animals sustained uniform ventricular tachycardia could be reproducibly initiated by programmed ventricular stimulation. In another 10 dogs with myocardial infarction, the same modes of ventricular stimulation reproducibly initiated ventricular fibrillation. Seven of these 10 dogs also manifested reproducible nonsustained polymorphic ventricular tachycardia, characterized by beat to beat variation in QRS complex configuration and cycle length, in response to programmed ventricular stimulation. Nonsustained polymorphic ventricular tachycardia and sustained uniform ventricular tachycardia were rarely observed in the same dog and appeared to have different underlying mechanisms.