Prevalence and Clinical Correlates of QT Prolongation in Patients With Hypertrophic Cardiomyopathy

Mar 01, 2011
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Authors:
Johnson JN, Grifoni C, Bos JM, et al.
Citation:
Eur Heart J 2011;Feb. 22:[Epub ahead of print].
Summary By:
Fred Morady, MD, FACC

Study Questions:

What is the significance of QT prolongation in patients with hypertrophic cardiomyopathy (HCM)?

Methods:

This was a retrospective study of 479 patients (mean age 41 years) with HCM who were not taking a QT-prolonging drug and who underwent genotyping for HCM mutations. The corrected QT interval (QTc) was determined from electrocardiograms recorded at the time of HCM diagnosis.

Results:

The mean QTc was 440 ms, with 13% of patients having a QTc >480 ms and 5.2% having a QTc >500 ms. Compared to patients with QTc ≤480 ms, the patients with QTc >480 ms more often had left ventricular outflow tract (LVOT) obstruction (74% vs. 45%), had a higher mean LVOT gradient (52.6 vs. 38.9 mm Hg), and more often received an implantable cardioverter-defibrillator (29% vs. 17%). An HCM-associated mutation was found in 47% of patients, with no relationship between genotype and QTc. During a mean follow-up of 4.9 years, 12% of patients had an appropriate ICD discharge, with no significant relationship to QTc.

Conclusions:

The QTc is >480 ms in 13% of patients with HCM compared to <0.5% of otherwise healthy adults. The QTc routinely should be measured in patients with HCM because it may have clinical significance, particularly if treatment with a QT-prolonging medication is being considered.

Perspective:

The hypertrophy process results in abnormal repolarization, explaining the relationship between QTc and the severity of HCM in this study. The prognostic significance of a prolonged QTc is unclear, since QTc prolongation was not associated with a higher risk of ventricular tachycardia/ventricular fibrillation among the patients in this study, at least over 5 years of follow-up.

Clinical Topics: Arrhythmias and Clinical EP, Heart Failure and Cardiomyopathies, Implantable Devices

Keywords: Follow-Up Studies, Cardiomyopathy, Hypertrophic, Heart Conduction System, Electrocardiography, Genotype, Hypertrophy


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