Background Peak O2 consumption (Vo2max) of ≤14 ml/kg/min has been widely accepted as being indicative of poor cardiac function warranting consideration for transplantation (Circulation 2010; 122:173). We examined whether this variable is a good indicator of cardiac function in overweight heart failure (HF) patients.
Methods We compared the cardiopulmonary exercise performance and non-invasive haemodynamics of overweight (BMI >34 kg/m2) and non-overweight (BMI ≤30) male heart failure patients in NYHA Classes II and III, with those of healthy male volunteers with no known cardiovascular diseases (n=101, age 43.2±18.1(SD) years, BMI 26.0±3.1) as controls. Their physical and cardiac functional reserves were measured during treadmill exercise testing with standard respiratory gas analyses and rebreathing method of non-invasively measuring cardiac outputs during peak exercise.
Results Consecutive overweight HF were screened and 24 patients (age 49±8(SD) years, BMI 44.9±6.8, NYHA 2.50±0.50) managed to exercise to acceptable cardiopulmonary limits (peak RER=1.01±0.12), and achieved Vo2max of 16.8±4.6 mls/kg/min which was significantly lower than controls (37.0±10.7 mls/kg/min, p<10−6) and also lower than those of 30 non-overweight HF counterparts (20.0±3.7 mls/kg/min, p=0.0019, age 49±15 years, BMI 25.0±2.9, NYHA 2.48±0.51). As shown in Abstract 99 figure 1, the overweight HF patients had Vo2max values which distributed around the 14 mls/kg/min cut-off value, and 9 of whom were indeed below this cut-off value. However, the uncorrected Vo2max were higher than those of non-overweight counterparts (Overweight: 2575±748 vs 1594±325 mls/min, p<10−6), and its range of 1485–4210 mls/min overlapped with the range of 1244–5774 mls/min in controls. The peak cardiac power output (CPOmax, 4.5±1.6 W, minimum 2.7 W) of overweight HF patients were clearly above those of non-overweight (2.4±0.6 W, p<10−6, Abstract 99 figure 2) and all above the transplant cut-off value of 1.5 W.
Conclusion These results indicate that in principle Vo2max in ml/kg/min as an indirect indicator of cardiac function or for cardiac transplantation selection is unreliable when applied to overweight heart failure patients. Extending this concept to the entire spectrum of body weights, the practice of correcting Vo2max by body weight in cardiological practice would also require urgent reconsideration.
- Heart failure
- cardiac transplantation