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 ventricul ar systolic function and in matched control patients with normal left ventr icular systolic function. Design-A retrospective, case-control study with controls matched 4:1 for ag e, sex, previous myocardial infarction, and diuretic and beta blocker treat ment. Setting-A regional cardiology centre and a university teaching hospital. Patients-25 patients with impaired left ventricular systolic function and 1 00 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 d eviation of QT and QTc intervals, and the ('lead adjusted') QT and QTc disp ersion. Results-All measures of QT/QTc dispersion were closely interrelated (r valu es 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 sys tolic 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 dispers ion. All six dispersion parameters were reduced in patients taking beta blo ckers (p < 0.05), regardless of whether left ventricular function was norma l 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 h eart failure in comparison with matched controls, regardless of the method of measurement and independently of possible confounding factors. beta Bloc kers are associated with a reduction in both QT and QTc dispersion, raising the possibility that a reduction in dispersion of ventricular repolarisati on may be an important antiarrhythmic mechanism of beta blockade.