Prevalence and Clinical Correlates of QT Prolongation in Patients With Hypertrophic Cardiomyopathy
What is the significance of QT prolongation in patients with hypertrophic cardiomyopathy (HCM)?
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.
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.
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.
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.
Keywords: Follow-Up Studies, Cardiomyopathy, Hypertrophic, Heart Conduction System, Electrocardiography, Genotype, Hypertrophy
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