Prolonged QT dispersion which has been proposed as a marker of repolarisation inhomogeneity, may predispose to ventricular arrhythmias in a variety of cardiac disorders. The aim of this study was to compare some indices of QT dispersion in patients with heart failure compared to normal subjects. We have also tested the hypothesis that QT dispersion is a useful method for identifying the patients at high risk for ventricular arrhythmias.
Methods: There were 84 patients, divided into two groups. In the first group there were 62 patients with heart failure, in the sinus rhythm, while in second group there were 22 sex- and age-matched healthy subjects. Simultaneous 12-channel ECGs were recorded at a paper speed 50 mm/sec. Ventricular arrhythmias were quantified by 24-h Holter ECG and classified according to the Lown classification system. Only those patients with a class IVa, IVb, and V arrhythmia were considered to have complex ventricular premature contractions (PVCs). Measurements of QT, JT, and RR intervals were performed manually. Heart rate corrected QT and JT intervals (QTc and JTc) were calculated by Bazett's formula.
Results: RR intervals were similar in both groups (862 +/- 120 vs 840 +/- 86; ns). QT dispersion and rate corrected QT dispersion were significantly greater in heart failure patients than in controls (76 +/- 13 ms vs 37 +/- 11 ms and 89 +/- 21 ms vs 40 +/- 17 ms; p < 0.05). When, on the basis of the existing complex PVCs, heart failure patients were divided into two subgroups, QT dispersion and rate corrected QT dispersion were significantly greater in the subgroup with complex PVCs compared to patients without complex PVCs (84 +/- 14 ms vs 61 +/- 18 ms and 98 +/- 26 ms vs 66 +/- 21 ms; p < 0.05).
Conclusion: All indices of QT dispersion were significantly higher in heart failure patients. QT dispersion is useful, noninvasive method for identifying heart failure patients at high risk for ventricular arrhythmia.