Usefulness of Non-Invasive Measurement of Cardiac Output During Sub-Maximal Exercise to Predict Outcome in Patients With Chronic Heart Failure

Peak oxygen consumption (Vo₂) is a powerful prognostic predictor of survival in patients with chronic heart failure (CHF) because it provides an indirect assessment of a patient's ability to increase cardiac output (CO). However, many patients with CHF who undergo cardiopulmonary exercise testing are unable to perform maximal exercise. New metabolic carts coupled with the inert gas rebreathing technique provide a noninvasive measurement of CO. Whether the noninvasive measurement of CO at a fixed submaximal workload can predict outcome is unknown. This study's population comprised 259 patients (mean age 54 ± 14 years, mean left ventricular ejection fraction 27 ± 14%) with CHF who underwent symptom-limited incremental cardiopulmonary exercise testing. Vo₂ and CO were measured at rest, at 25 W, and at peak exercise. Submaximal exercise was defined as <80% peak Vo₂. Among 259 patients, 145 had Vo₂ at 25 W <80% of peak. Vo₂ at 25 W averaged 9.3 ± 1.8 ml/kg/min. This Vo₂ represented 62 ± 11% of peak Vo₂, which averaged 15.4 ± 4.4 ml/kg/min. Prospective follow-up averaged 521 ± 337 days. In this cohort, there were 15 outcome events (death, urgent heart transplantation, or implantation of a left ventricular assist device as a bridge to transplantation). On univariate Cox hazard analysis, CO at 25 W (hazard ratio 0.64, 95% confidence interval 0.48 to 0.84, p = 0.002) was found to be significant predictor of events of outcome. In conclusion, CO at 25 W measured noninvasively during submaximal exercise may have potential value as a predictor of outcomes in patients with CHF.