BACKGROUND In patients with chronic heart failure (CHF), circadian variability of RR and QT intervals may be altered because of neurohumoral activation and functional and structural remodeling of the heart. OBJECTIVE The aim of this study was to evaluate the prognostic significance of circadian variability of the RR and QT intervals and QT dynamicity (QT/RR slope) in CHF patients.
METHODS We prospectively enrolled 121 patients with stable CHF in sinus rhythm (age 67 +/- 14 years, mean +/- SD;range 34 to 87 years). The RR, QT, and rate-corrected QT (QTc) intervals and the QT/RR slope measured from 24-hour Hotter electrocardiogram were fitted by cosine curves.
RESULTS During the follow-up period of 34 +/- 17 months, 40 (33%) patients died of cardiac causes, 10 of which were sudden. All patients showed significant circadian rhythms in the RR, QT, and QTc intervals and the QT/RR slope by cosine-curvefitting. In addition to the expected higher heart rate, Longer QT interval, and steeper QT/RR slope, we found that patient who died of cardiac causes had reduced circadian variability of QT interval (10 +/- 10 ms vs 21 +/- 13 ms) and a Later maximum RR interval (4.1 +/- 0.9 AM vs 2.3 +/- 2.1 AM) compared with survivors, among many other statistically significant circadian parameter differences. These 2 parameters were independent predictors of cardiac death in multivariate Cox proportional hazards regression analysis.
CONCLUSION Circadian variability analyses of Holter-derived RR and QT intervals may provide prognostic information beyond that provided by 24-hour averages of these parameters.