Subclinical Cardiomyopathy and Long QT Syndrome: An Echocardiographic Observation

Abstract

Long QT syndrome (LQTS) is a cardiac channelopathy predisposing to syncope and sudden death secondary to LQT-triggered ventricular arrhythmias. Long QT syndrome has been regarded as a purely electrical disease. Recent reports have shown by echocardiography that LQTS patients have contraction abnormalities that are associated with cardiac arrhythmias. The purpose of this study was to determine the spectrum and prevalence of echocardiographic anomalies in a large cohort of patients diagnosed genetically and/or clinically with LQTS. Two-dimensional and Doppler echocardiographic studies performed during medical evaluation in Mayo's LQTS Clinic were reviewed for 216 LQTS patients. Echocardiograms were evaluated for morphologic abnormalities and atrial and ventricular size and function. Left atrial volume was indexed by body mass. Arrhythmic events were defined as a history of aborted cardiac arrest, documented ventricular tachycardia or fibrillation, and syncope. While 75% of patients had normal standard echocardiograms, 54 patients (25%) had at least one abnormal echocardiographic finding. Most common were subclinical cardiomyopathic changes, including increased left atrial volume index (n = 25), left or right ventricular enlargement (n = 7), and grade I-II diastolic dysfunction (n = 7). Left atrial volume index was higher in LQTS patients with arrhythmic events compared with those without (24.4 ± 5.5 mL/m(2) vs. 22.3 ± 6.1 mL/m(2) , P =.02). Corrected QT intervals and left atrial volume index correlated significantly albeit weakly (r(2) = 0.04, P <.01). Concomitant congenital heart disease was found in two patients. Subclinical cardiomyopathic changes were found in nearly 20% of LQTS patients. Left atrial enlargement was the most common finding and was associated with prolonged corrected QT and arrhythmic events. These changes may stem from underlying contraction abnormalities caused by ion channel dysfunction.