Measurement of functional capacity to discriminate of clinical from subclinical heart failure in Patients ≥65 years of age

In order to show that reduced functional capacity in subclinical heart failure portends a higher risk of clinically overt (stage C) heart failure, we obtained the Duke activity status index (DASI) and 6-minute walk distance (6MWD) in 814 patients (age 70 [interquartile range 67 to 74] years, 51% female) with nonischemic subclinical heart failure. Reduced functional capacity was defined as: (1) DASI-derived metabolic equivalents <7, (2) 6MWD <2 standard deviations below the age-based normative mean (excluding those with mobility impairment) and (3) reduced 6MWD with reclassification where DASI was discordant. Based on reduced functional capacity and left ventricular dysfunction (LVD), subjects were classified into; (1) Stage A heart failure (436 with neither LVD nor reduced functional capacity), (2) Stage A with reduced functional capacity (n = 80), (3) Stage B heart failure (182 with LVD but preserved functional capacity) and (4) early stage C heart failure (52 with LVD and reduced functional capacity). Outcome was assessed by Kaplan-Meier survival estimates and Cox proportional hazard ratios. After a median follow-up of 13 months [interquartile range 11 to 19]), 76 (9%) developed heart failure - 6% of Stage A, 10% of Stage A-reduced functional capacity, 9% of Stage B and 37% of early Stage C (p < 0.001). After adjustment (for heart failure risk score, atrial fibrillation, pulmonary disease and therapy), the hazard ratio for development of overt heart failure in early Stage C was 5.92 (95% confidence intervals 2.92 to 11.54, p < 0.001) compared with Stage A and 3.08 (95% confidence intervals 1.47 to 6.47, p = 0.003) compared with Stage B.