Prolonged QT interval in hypertrophic and dilated cardiomyopathy in children.

When the QT interval is prolonged in a patient with structural heart disease, there is a question of whether the QT interval prolongation is the result of coexistent long QT interval syndrome or ventricular hypertrophy. The purpose of this study was to assess whether QT interval prolongation can be attributed to ventricular hypertrophy/dilation alone. Electrocardiograms (ECGs) of 25 children in each of six echocardiographically proven groups (right ventricular hypertrophy, left ventricular hypertrophy, biventricular hypertrophy, hypertrophic cardiomyopathy, dilated cardiomyopathy, and normals) were analyzed. All patients had QRS interval durations < 100 msec, and patients with ventriculotomies were excluded. No patients in the normal group had a QTc interval > or = 0.45 sec. Eight (32%) of 25 patients with dilated cardiomyopathy had a QTc interval > or = 0.45 sec (p = 0.007 vs normal), 6 (24%) of 25 patients with hypertrophic cardiomyopathy had a QTc interval > or = 0.45 sec (p = 0.03 vs normal), and 2 of 25 patients each with right ventricular hypertrophy, left ventricular hypertrophy, and biventricular hypertrophy had a QTc interval > or = 0.45 sec (p = NS vs normal). There was no relation of the QTc interval to age, QRS duration, T-wave axis, or heart rate in any group. In the dilated cardiomyopathy group, there was no relationship of QTc interval to age, shortening fraction, or left ventricular end diastolic dimension. In conclusion, (1) a significant number of patients (24% to 32%) with dilated or hypertrophic cardiomyopathy may have a long QTc interval on the surface ECG, and (2) ventricular hypertrophy/dilation may be additional rare causes of acquired prolongation of the QT interval.