Prevalence and clinical correlates of QT prolongation in patients with hypertrophic cardiomyopathy

Abstract

Aims: Congenital or acquired QT prolongation is a risk factor for life-threatening arrhythmias. In patients with hypertrophic cardiomyopathy (HCM), the QT interval may be intrinsically prolonged. However, the prevalence, cause, and significance of QT prolongation among patients with HCM are unknown.

Methods and results: After exclusion of patients on QT-prolonging drugs, a blinded, retrospective analysis of electrocardiograms, echocardiograms, and genotype status in 479 unrelated patients with HCM [201 females, age at diagnosis 41 ± 18 years, maximal left ventricular wall thickness (MLVWT) 22 ± 6 mm] from two independent centres was performed. The mean QTc was 440 ± 28 ms. The QTc exceeded 480 ms in 13% of patients. Age, gender, family history of HCM or sudden cardiac arrest, and genotype status had no association with QTc. Patients with a QTc over 480 ms were more symptomatic at diagnosis (P < 0.001), had a higher MLVWT (P = 0.03), were more obstructive (P < 0.001), and were more likely to have undergone septal reduction therapy (P = 0.02). There was a weak but significant direct linear relationship between QTc and peak outflow gradient (r(2) = 0.05, P < 0.0001).

Conclusions: Compared with <1 in 200 otherwise healthy adults, QT prolongation (QTc > 480 ms) was present in 1 out of 8 patients with HCM. The QTc was partly reflective of the degree of cardiac hypertrophy and left ventricular outflow tract obstruction. Because of its pro-arrhythmic potential and its potential relevance to management and risk stratification, routine QTc assessment should be performed in patients with HCM, particularly when concomitant use of QT-prolonging medications is considered.

Figure 1

QTc-distribution in health and disease. Shown are the distributions of normal QTc in healthy males and females as well as the Mayo long QT syndrome cohort and the studied hypertrophic cardiomyopathy cohort. Five per cent of patients with hypertrophic cardiomyopathy had a QTc exceeding the pro-arrhythmic threshold of 500 ms.

Figure 2

Bar diagrams showing significant differences between the subset of patients with a QTc ≤ 480 ms and a QTc > 480 ms. Patients with a QTc over 480 ms were more likely to be symptomatic at diagnosis (A), had a greater maximum left ventricular wall thickness (B), were more likely to be obstructive (C), and were more likely to have undergone septal reduction therapy by either septal ablation or surgical myectomy (D).

Figure 3

QTc plotted against basal left ventricular outflow tract gradient (A) and the maximum left ventricular wall thickness (B). QTc showed a weak, but significant relationship with left ventricular outflow tract gradient and maximum left ventricular wall thickness.