Background
Long QT syndrome (LQTS) can present with sudden death during exertion.
Objective
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 had a treadmill exercise stress test. Blinded to both genotype and rendered diagnosis, the stress tests were scored for the presence of exercise-induced ventricular ectopy.
Results
The dismissal diagnosis was LQTS in only 177 (46%), catecholaminergic polymorphic ventricular tachycardia (CPVT, 16), miscellaneous cardiac disease (17), and normal (171). Exercise-induced ventricular ectopy was detected in 107 patients (28%). 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 either 5 (8%) with LQT2, or 3 (20%) with LQT3 (p < 0.0001). In contrast, exercise-induced ventricular ectopy beyond single PVCs was far more common among patients with CPVT (14/16, 88%, p < 0.0001) and included PVCs in bigeminy in 13 (81%), couplets in 7 (47%), and NSVT in 3 (20%). Of note, bi-directional 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 < 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 rather than LQTS.
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