Electrophysiologic and anatomic characteristics of ventricular tachycardia induced at the right ventricular outflow tract but not at the apex.

The site of ventricular stimulation is an important variable in the initiation of ventricular tachycardia (VT) by programmed ventricular stimulation. Among 169 patients studied consecutively, 17 (10%) had ventricular tachycardia induced by programmed electrical stimulation from the right ventricular outflow tract but not from the apex. Fourteen of these 17 patients had had prior myocardial infarction (12 had inferior, and two had both inferior and anterior myocardial infarction), two had a dilated cardiomyopathy, and one had a localized cardiomyopathy. Fourteen patients had echocardiograms suitable for analysis. Of these, 12 had posterior/inferior ventricular wall motion abnormalities located at the base of the heart. The ventricular effective refractory periods from the right ventricular outflow tract and right ventricular apex were 237 +/- 4 and 244 +/- 5 msec, respectively (p less than 0.05, mean +/- SEM). Induced VT had a cycle length of 229 +/- 4 msec and had the morphology of right bundle branch block in 12 patients, of left bundle branch block in three patients, and had both morphologies in two patients. In 14 patients the axis was superior. VT was initiated with two extrastimuli in 15 patients and with burst right ventricular pacing in two patients. Similar pacing techniques with identical pacing intervals did not induce VT at the right ventricular apex in 14 of these 17 patients. Further, among the 15 patients whose VT was induced at the right ventricular outflow tract with two extrastimuli, neither burst pacing (n = 13) nor two extrastimuli introduced at faster paced rates (n = 12) induced VT at the right ventricular apex.(ABSTRACT TRUNCATED AT 250 WORDS)