Circadian modulation on T-wave alternans activity in chronic heart failure patients

Average TWA activity has been shown to be an independent predictor of sudden cardiac death (SCD) in chronic heart failure (CHF) patients. However, the influence of circadian rhythms on TWA remains understudied. In this work, we assessed circadian TWA changes in a CHF population and evaluated whether the prognostic value of TWA indices is sensitive to the circadian pattern. Holter ECG recordings from 626 consecutive CHF patients (52 SCD) were analyzed. The index of average alternans (IAA), quantifying the average TWA level, was measured in 4 consecutive 6-hour intervals using a multilead fully-automated method. Survival analysis was performed considering SCD as an independent endpoint. IAA changed along the day, with statistically significant lower values during the night than during daytime. This pattern is similar to the one observed in the mean heart rate (HR). However, a low correlation (r=.18) was found between IAA and HR in windows of 128 beats. After dichotomization of patients based on the third quartile of IAA indices, IAA indices computed between hours 06-12 (IAA06-12) and 18-24 (IAA18-24) successfully predicted SCD (Hazard Ratio, HaR:2.34(1.33-4.13)per μV, andHaR:1.87(1.04-3.36) per μV, respectively). In conclusion, circadian variation should be considered for SCD risk prediction.