Prolongation of the QT interval in heart failure occurs at low but not at high heart rates

Abnormal left ventricular structure and function as in, for example, left v entricular hypertrophy or chronic heart failure, is associated with sudden cardiac death and, when the ejection fraction is depressed, with prolongati on of the QT interval. The dependence on heart rate of QT interval prolonga tion in these conditions, and the relationship of any abnormalities either to deranged autonomic nervous system function or to an adverse prognosis, h as not been well studied. We therefore investigated (1) the dependence on h eart rate of the QT interval, and (2) the relationship between both QT inte rval and the QT/heart rate slope and markers of adverse prognosis in these two conditions. The QT interval was measured at rest and during exercise in 34 subjects with heart failure, 16 subjects with left ventricular hypertro phy and 16 age-matched controls with normal left ventricular structure and function. QTc (corrected QT) intervals at rest were significantly longer in heart failure patients (471 +/- 10 ms) than in controls (421 +/- 6 ms) or in subjects with hypertrophy (420+/-6 ms) (P < 0.05). At peak exercise, des pite the attainment of similar heart rates, the QT intervals no longer diff ered from each other, being 281+/-7 ms for controls, 296+/-11 ms in hypertr ophy and 303+/-10 ms in heart failure (no significant difference). The QT/h eart rate slope was significantly increased in heart failure [2.3 +/- 0.1 m s.(beats/min)(-1)] compared with controls [1.55 +/- 0.06 ms.(beats/min)(-1) ] and hypertrophy [1.66 +/- 0.1 ms.(beats/min)(-1)] (P < 0.001). In left ve ntricular hypertrophy, despite animal data suggesting that QT interval prol ongation should occur, no abnormalities were found in QT intervals at rest or during exercise. The QT/heart rate slope did not relate to any markers f or an adverse prognosis, except that of prolongation of QT interval. Long Q T intervals were associated principally with impairment of left ventricular systolic function. Our data emphasize the dynamic nature of the QT interva l abnormalities found in heart failure.