EARLY AFTERDEPOLARIZATIONS IN THE FAMILIAL LONG QTU SYNDROME

Early Afterdepolarizations in Long QTU Syndrome. Torsade de pointes-induced syncopal episodes were almost invariably precipitated by emotional stress or menses in a 17-year-old female. U wave accentuation occurred during periods of heightened sympathetic tone. To document the role of early afterdepolarizations (EADs), monophasic action potentials were recorded during ventricular extrasystoles and torsade de pointes occurring spontaneously and induced by ventricular pacing in the control state and after intravenous lidocaine. The effects of verapamil, propranolol, and epinephrine were observed. Our data show that: (1) EADs may play a significant role in the genesis of familial long QTU syndrome and torsade de pointes; (2) a faster ventricular pacing rate for a longer duration is related to the emergence of subsequent pause-dependent EADs, U waves, and torsade de pointes; (3) atrial pacing with Wenckebach block can provoke large postpause U waves, thus eliciting dual ventricular tachycardia; (4) EADs are enhanced by epinephrine infusion in the absence of pause; and (5) EAD-triggered firing is inhibited by verapamil and propranolol but not by lidocaine.