Ventricular ectopy during treadmill exercise stress testing in the evaluation of long QT syndrome

BackgroundLong QT syndrome (LQTS) can present with sudden death during exertion.ObjectiveThe purpose of this study was to determine the diagnostic importance of exercise-induced ventricular ectopy in the evaluation of LQTS.MethodsFrom 1998 to 2006, 381 patients with a referral diagnosis of LQTS underwent a treadmill exercise stress test. An investigator blinded to both genotype and rendered diagnosis scored the stress tests for the presence of exercise-induced ventricular ectopy.ResultsThe dismissal diagnosis was LQTS in 177 (46%), catecholaminergic polymorphic ventricular tachycardia (CPVT) in 16, miscellaneous cardiac disease in 17, and normal in 171. Exercise-induced ventricular ectopy was detected in 107 (28%) patients. However, only 34 patients (9% overall) had exercise-induced ventricular ectopy greater than single premature ventricular contractions (PVCs). Among the 171 patients dismissed as normal, only 2% had ectopy greater than single PVCs. Among the genotype-positive LQTS patients, no significant ectopy was recorded in 80 with LQT1, compared to 5 (8%) patients with LQT2 and 3 (20%) patients with LQT3 (P <.0001). In contrast, exercise-induced ventricular ectopy beyond single PVCs was far more common among patients with CPVT (14/16 [88%]; P <.0001) and included PVCs in bigeminy in 13 (81%), couplets in 7 (47%), and nonsustained ventricular tachycardia in 3 (19%). Of note, bidirectional VT was not present in any of the 16 patients diagnosed with CPVT, including the 10 with genetically proven, RYR2-mediated CPVT.ConclusionExercise-induced ventricular ectopy exceeding single PVCs was observed in less than 10% of patients referred for LQTS evaluation, including 2% of patients ultimately dismissed as normal. Exercise-induced bigeminy is strongly associated with the presence of significant cardiovascular disease but is far more likely to indicate CPVT than LQTS.