Arrhythmic risk and echocardiographic correlation of increased QTc interval in patients with hypertrophic cardiomyopathy

Background: Due to the underlying muscle disease, patients with hypertrophic cardiomyopathy (HCM) have a high risk for life-threatening arrhythmias and may have an increased QT interval. However, the independent contribution of the long QT interval to the arrhythmic risk in this population is not well known. Purpose: The purpose of this study was to investigate the role of increased long QT corrected (QTc) interval in the development of malignant arrhythmias in a population of patients with hypertrophic cardiomyopathy (HCM), and also the relationship between QTc and clinical and echocardiographic variables in these patients. Methods: We studied 312 patients with HCM (118 females, age at diagnosis 47±19, maximal left ventricular wall thickness (MLVWT) 19±6mm]. A clinical, an electrocardiographic and an echocardiographic evaluation were carried out in each of them. Results: In this group of patients, 31% (n=96) had prolonged QT interval in the electrocardiogram, defined as QTc value >460ms, being the mean value of the QTc in this population of 447ms±32ms. Of these patients, 244 (78%) underwent to 24-hours electrocardiogram monitoring, presenting 23% of them (n=56) at least one episode of non-sustained ventricular tachycardia (NSVT) on Holter. However, no significant differences in QTc interval between both groups were shown (446±34ms in patients with documented NSVT vs 445±30ms in idividuals with no evidence of NSVT on Holter; p = 0.6). There were no statistically significant differences between the presence/development of atrial fibrillation or syncope and prolongated QTc interval. Finally, there was a weak but significant direct linear relationship between QTc and maximal left ventricular wall thickness (MLVWT) (r2=0.07 p<0.0001). Conclusions: QT prolongation was present in 31% of the patients with HCM studied. This study corroborates the findings of previous publications that the QTc interval is related with the degree of cardiac hypertrophy, and adds that there is no significant relationship with the presence of NSVT on 24h Holter, atrial fibrillation or syncope.