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

Abstract

Background: Long QT syndrome (LQTS) can present with sudden death during exertion.

Objective: The purpose of this study was to determine the diagnostic importance of exercise-induced ventricular ectopy in the evaluation of LQTS.

Methods: From 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.

Results: The 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.

Conclusion: Exercise-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.

Figure 1. Spectrum and Frequency of Exercise-Induced Ventricular Ectopy

Shown is the spectrum and frequency of exercise-induced ventricular ectopy. “Other” ventricular ectopy included triplets, PVCs in trigeminy and quadgeminy. No TdP was recorded