SUDDEN CARDIAC DEATH AND POLYMORPHOUS VENTRICULAR-TACHYCARDIA IN PATIENTS WITH NORMAL QT INTERVALS AND NORMAL SYSTOLIC CARDIAC-FUNCTION

This study delineates the clinical spectrum of 15 patients with polymorphic ventricular tachycardia and normal QT intervals in the absence of apparent structural heart disease, adverse drug effects, or electrolyte disturbances. Patients presented with either palpitations in (n = 2), presyncope (n = 5), syncope (n = 4), no symptoms (n = 1), or aborted sudden death (n = 3). Mean age was 41 years (range 20 to 64), and mean follow-up 38 months (range 4 to 109). Left ventricular function was normal as determined by either echocardiogram (n = 9) or left ventriculography (n = 9). Episodes of polymorphic ventricular tachycardia (VT) were analyzed in terms of the preceding interval, and the relation of the initiating coupling interval to the QT interval (coupling interval/QT interval = polymorphic VT index). The mean QT for the group as a whole was 0.41 +/- 0.02 second. Patients could be separated into 3 distinct groups. Four patients had polymorphic VT reproducibly induced by exercise and initiated by late-coupled beats (mean polymorphic VT index 1.27 +/- 0.21). Isoproterenol induced polymorphic VT in 3 of 4 patients, and all 4 responded to chronic beta blockade. Two patients had polymorphic VT during episodes of coronary artery spasm, and both responded to calcium channel blockade. Polymorphic VT unrelated to exertion or coronary vasospasm occurred in 9 patients. Tachycardia onset was initiated by closely coupled beats (mean polymorphic VT index 0.95 +/- 0.16), and was preceded by a pause in 4 patients, and no pause in 5 patients. Sudden death occurred in 5 of 9 patients with the shortest polymorphic VT indexes. Drug therapy and chronic pacing were not reliable in preventing episodes of sudden death. Invasive electrophysiologic studies, including the use of monophasic action potential recordings, were not useful in the evaluation or management of these patients. Appropriate therapy for patients presenting with either exercise- or coronary vasospasm-induced polymorphic VT is usually associated with a good prognosis. Conversely, patients with spontaneous episodes of short-coupled polymorphic VI have a high incidence of sudden death, and should be considered for automatic implantable cardioverter defibrillator insertion.