Prognostic significance of circadian variability of RR and QT intervals and QT dynamicity in patients with chronic heart failure.

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 Holter 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-curve fitting. 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.