Abnormal QT interval variability in patients with hypertrophic cardiomyopathy: can syncope be predicted?

We sought to determine QT variability pattern in patients with hypertrophic cardiomyopathy (HCM) and its relationship with the risk of syncope. QT interval variability was assessed from 24-hour Holter monitoring in 10 HCM patients with history of syncope, 10 HCM patients without history of syncope, and 10 healthy subjects. QT variability was higher in patients with HCM, in particular in those with history of syncope, than in healthy controls. Time domain QT variability did not vary between waking and sleeping hours in HCM patients, whereas it was significantly shorter while asleep in the control group. Increased QT SDANN identified HCM patients with history of syncope with an accuracy of 75%. Our data show that QT variability is abnormal in HCM patients and indirectly support the concept that arrhythmia-related syncope in these patients may be, at least in part, related to an altered control of repolarization.