Nonclinical polymorphic ventricular tachycardia induced by programmed cardiac stimulation: incidence, mechanisms and clinical significance.

We analyzed the morphology and rate of ventricular tachycardia induced by programmed cardiac stimulation in 18 patients with recurrent sustained ventricular tachycardia who had only one type of ventricular tachycardia during spontaneous episodes. In nine of 18 patients, we induced only one type of ventricular tachycardia, with a morphology and rate similar to those noted during spontaneous ventricular tachycardia. In the other nine patients, the induced ventricular tachycardia was either different from spontaneous ventricular tachycardia (two patients) or was polymorphic (seven patients). The multiple morphologies were induced in addition to those similar to spontaneous ventricular tachycardia. Seven of these nine patients had ischemic heart disease. Only one patient had a left ventricular aneurysm. The morphology and rate of induced tachycardia could be changed by changing the basic cycle length (two patients), the method of initiation of tachycardia (one patient), and by introducing paced ventricular beats during tachycardia (four patients). Our data suggest that ventricular tachycardia induced by programmed cardiac stimulation is nonclinical in 50% of patients with recurrent ventricular tachycardia. The clinical course and prognosis of patients with polymorphic ventricular tachycardia compared with those without polymorphic tachycardia are not known.