Prevalence and characteristics of the catecholamine induced QT prolongation syndrome

Abstract Background We have recently described large families of idiopathic ventricular fibrillation characterised by catecholamine-induced QT interval prolongation (CIQTP). The patient presented with a normal QT duration at rest but an abnormal QT prolongation during a mental stress test (MST). Objective The aim of this study was to investigate the role of this new syndrome in inherited arrhythmic diseases. Methods Consecutive patients and their relatives, identified after unexplained familial sudden cardiac death or sudden cardiac arrest, were enrolled in the study in the presence of: - no other diagnosis after cardiac ultrasound, stress test, pharmacological test with adrenaline and ajmaline. - positive MST defined by a prolongation of the QT interval (>-11ms) during MST (as previously published). Results 134 families with unexplained SCD were examined. CIQTP was diagnosed in 15 families, representing a prevalence of 11.2%. Family screening of these 15 families identified a total of 43 individuals. Seven (16%) had symptoms prior to diagnosis, including sudden cardiac arrest in one. At baseline, the QTc interval was measured at 440+/-23 ms. MST increased the QTc interval by 49+/-33 ms. The identification of QT interval prolongation was less important in the exercise test (delta QTc 17+/-52 ms at 4 minutes after exercise) and the epinephrine test (delta QTc 19+/-36 at 1 minute according to the Krahn protocol). Treatment with beta-blockers was initiated in 19 patients (44%) on the basis of symptoms and major prolongation of the QT interval during the MST. After a mean follow-up of 7+/-2 years, only one patient developed ventricular fibrillation. This episode occurred during a short period when he was no observant for the treatment. Since then, there has been no recurrence of the arrhythmia on beta-blocker therapy. All other patients, including those who were previously symptomatic remained symptom-free on treatment. Conclusion CIQTP may explain a significant part of sudden cardiac arrest or syncope in young patients. Conventional screening using ECG, exercise test and epinephrine challenge may not be able to unmask CIQTP. Then MST may be systematically proposed for the screening of patient and their family. In CIQTP patients beta blocker therapy appears to be highly efficient to prevent symptoms.