Prolonged QT interval and reduced heart rate variability in patients with uncomplicated essential hypertension

A prolonged QT interval is a risk factor for ischemic heart disease in hypertensive subjects. Heart rate variability (HRV) is both an index of autonomic function and an important prognostic factor in several diseases. The aim of the present study was to evaluate the relation between a prolonged QT interval and autonomic nervous system function in patients with untreated uncomplicated essential hypertension. Two hundred and fifteen untreated patients with essential hypertension underwent a Holter ECG equipped with software dedicated to HRV and QT analyses. Nine percent of the patients showed a corrected QT (QTc) >or=440 ms. The HRV indexes in the time domain (SDNN, SDNN index, RMSSD, and pNN50) were significantly reduced in the patients with a prolonged QTc compared to those with a normal QTc (SDNN 24 h: 126.4+/-29.9 vs. 143.9+/-35.4 ms, p=0.02; SDNN index [nighttime]: 85.9+/-32.4 vs. 115.5+/-36.7 ms, p=0.0006; RMSSD 24 h: 22.2+/-7.7 vs. 31.2+/-13.0 ms, p=0.0007; pNN50 24 h: 4.4+/-4.9 vs. 9.7+/-8.4%, p=0.0006). The linear correlation analysis between QTc length and HRV parameters showed a significant negative correlation with all the time-domain indexes. Such a correlation was maintained for RMSSD 24 h, pNN50 24 h and SDNN index (nighttime) after correction for gender and age. The present study shows that, even prior to the development of cardiac hypertensive disease, a prolongation of the QTc and a reduced HRV, both markers of cardiovascular risk, coexist in a proportion of patients with untreated essential hypertension. Further studies are warranted to evaluate whether the combination of such markers can identify hypertensive patients at risk for life-threatening arrhythmias and sudden death.