Is low [formula omitted]O2max/kg in obese heart failure patients indicative of cardiac dysfunction?

Abstract

PurposeLow peak O2 consumption (V˙O2max/kg) has been widely used as an indirect indicator of poor cardiac fitness, and often guides management of patients with severe heart failure (HF). We hypothesized that it should be as good an indicator of cardiac dysfunction in obese and non-obese HF patients. MethodsWe compared the cardiopulmonary exercise performance and non-invasive hemodynamics of 152 obese (BMI>34kg.m−2) and 173 non-obese (BMI≤32) male HF patients in NYHA classes II and III, with reference to 101 healthy male controls. Their physical and cardiac functional reserves were measured during treadmill exercise testing with standard respiratory gas analyses and CO2 rebreathing to measure cardiac output non-invasively during peak exercise. Data are given as mean±SD. ResultsObese HF patients with BMI 40.9±7.5kg·m−2 (age 56.1±14.0years, NYHA 2.5±0.5) exercised to acceptable cardiopulmonary limits (peak RER=1.07±0.12), and achieved a mean V˙O2max/kg of 18.6±5.2ml·kg−1·min−1, significantly lower than in non-obese HF counterparts (19.9±5.6ml·kg−1·min−1, P=0.02, age 55.8±10.6years, BMI 26.6±3.1, NYHA 2.4±0.5, peak RER=1.07±0.09), with both lower than controls (38.5±9.7ml·kg−1·min−1, P<10−6). In contrast, the uncorrected V˙O2max was higher in obese (2.31±0.69ml·min−1) than non-obese HF patients (1.61±0.49ml·min−1, P<10−6). When cardiac dysfunction was evaluated directly, peak cardiac power was significantly greater in obese than non-obese HF patients (4.11±1.21W vs 2.73±0.82W, P<10−6), with both lower than controls (5.42±1.04W, P<10−6). ConclusionThese results demonstrate that V˙O2max/kg is not a generally reliable indicator of cardiac fitness in all patients. Instead, we found that despite having lower V˙O2max/kg, obese HF patients had stronger hearts capable of generating greater cardiac power than non-obese HF patients of equivalent clinical HF status.