QT dispersion in patients with chronic heart failure: beta blockers are associated with a reduction in QT dispersion.

OBJECTIVE—To compare QT dispersion in patients with impaired left ventricular systolic function and in matched control patients with normal left ventricular systolic function. DESIGN—A retrospective, case-control study with controls matched 4:1 for age, sex, previous myocardial infarction, and diuretic and β blocker treatment. SETTING—A regional cardiology centre and a university teaching hospital. PATIENTS—25 patients with impaired left ventricular systolic function and 100 patients with normal left ventricular systolic function. MAIN OUTCOME MEASURES—QT and QTc dispersion measured by three methods: the difference between maximum and minimum QT and QTc intervals, the standard deviation of QT and QTc intervals, and the "lead adjusted" QT and QTc dispersion. RESULTS—All measures of QT/QTc dispersion were closely interrelated (r values 0.86 to 0.99; all p < 0.001). All measures of QT and QTc dispersion were significantly increased in the patients with impaired left ventricular systolic function v controls (p < 0.001): 71.9 (6.5) (mean (SEM)) v 46.9 (1.7) ms for QT dispersion, and 83.6 (7.6) v 54.3 (2.1) ms−1−2 for QTc dispersion. All six dispersion parameters were reduced in patients taking β blockers (p < 0.05), regardless of whether left ventricular function was normal or impaired—by 9.4 (4.6) ms for QT dispersion (p < 0.05) and by 13.8 (6.5) ms−1−2 for QTc dispersion (p = 0.01). CONCLUSIONS—QT and QTc dispersion are increased in patients with systolic heart failure in comparison with matched controls, regardless of the method of measurement and independently of possible confounding factors. β Blockers are associated with a reduction in both QT and QTc dispersion, raising the possibility that a reduction in dispersion of ventricular repolarisation may be an important antiarrhythmic mechanism of β blockade. Keywords: QT dispersion; heart failure; β blockers; sudden death