Background-The predictive value of heart rate variability (HRV) in chronic heart failure (CHF) has never been tested in a comprehensive multivariate model using short-term laboratory recordings designed to avoid the confounding effects of respiration and behavioral factors. Methods and Results-A multivariate survival model for the identification of sudden (presumably arrhythmic) death was developed with data from 202 consecutive patients referred between 1991 and 1995 with moderate to severe CHF (age 52Ϯ9 years, left ventricular ejection fraction 24Ϯ7%, New York Heart Association class 2.3Ϯ0.7; the derivation sample). Time-and frequency-domain HRV parameters obtained from an 8Ј recording of ECG at baseline and during controlled breathing (12 to 15 breaths/min) were challenged against clinical and functional parameters. This model was then validated in 242 consecutive patients referred between 1996 and 2001 (validation sample). In the derivation sample, sudden death was independently predicted by a model that included low-frequency power (LFP) of HRV during controlled breathing Յ13 ms 2 and left ventricular end-diastolic diameter Ն77 mm (relative risk [RR] 3.7, 95% CI 1.5 to 9.3, and RR 2.6, 95% CI 1.0 to 6.3, respectively). The derivation model was also a significant predictor in the validation sample (Pϭ0.04). In the validation sample, LFP Յ11 ms 2 during controlled breathing and Ն83 ventricular premature contractions per hour on Holter monitoring were both independent predictors of sudden death (RR 3.0, 95% CI 1.2 to 7.6, and RR 3.7, 95% CI 1.5 to 9.0, respectively). Conclusions-Reduced short-term LFP during controlled breathing is a powerful predictor of sudden death in patients withCHF that is independent of many other variables. These results refine the identification of patients who may benefit from prophylactic implantation of a cardiac defibrillator. (Circulation. 2003;107:565-570.)

In moderate-to-severe chronic heart failure patients, the 6-min walk test is not related to cardiac function and only moderately related to exercise capacity. Walking performance does not provide prognostic information which can complement or substitute for that provided by peak VO2 or NYHA class. Hence the test is of limited usefulness as a decisional indicator in clinical practice.

A contraindication to exercise testing should be considered a priority for listing patients for heart transplantation. Only in less symptomatic male patients does a peak VO2 < or = 10 ml/kg per min identify short-, medium- and long-term high risk groups. A peak VO2 >18 ml/kg per min implies good prognosis with medical therapy.