Catecholamine-induced T-wave lability in congenital long QT syndrome: A novel phenomenon associated with syncope and cardiac arrest

Objective: To determine the effects of phenylephrine and dobutamine on repolarization lability in patients with genotyped long QT syndrome (LQTS). Patients and Methods: Between December 1998 and August 2000,23 patients with genotyped LQTS (13 LQT1, 7 LQT2, and 3 LQT3) and 16 controls underwent electro-cardiographic stress testing at the Mayo Clinic in Rochester, Minn. Aperiodic repolarization lability was quantified from digitized electrocardiograms recorded during catecholamine stress testing with phenylephrine and dobutamine. T-wave lability was quantified as a root-mean-square of the differences between corresponding signal values of subsequent beats. The magnitude of aperiodic T-wave lability was quantified by using a newly derived T-wave lability index (TWLI). Results: The TWLI was significantly greater in patients with LQTS than in controls (0.0945+/-0.0517 vs 0.0445+/-0.0123; P<003). Marked T-wave lability (TWLI greater than or equal to.095) was detected in all 3 LQTS genotypes (10/23) but in no controls (P<003). There was no correlation between the TWLI and the baseline corrected QT interval. All high-risk patients having either a history of out-of-hospital cardiac arrest or syncope had a TWLI of 0.095 or greater. Conclusions: Beat-to-beat nonalternating T-wave lability occurs in LQT1, LQT2, and LQT3 patients during catecholamine provocation and is associated with a history of prior cardiac, events. The quantification of this novel phenomenon may assist in identifying LQTS patients with increased risk of sudden cardiac death.