Muscular exercise capacity and body fat predict VO_2peak in heart transplant recipients

Heart transplant (HTx) recipients usually have reduced exercise capacity, with reported VO_2peak levels of 50–70% of predicted values. This study aimed to evaluate central and peripheral factors predictive of VO_2peak.

Fifty-one clinically stable HTx recipients >18 years old and 1–8 years after HTx, underwent maximal exercise testing on a treadmill. Clinical laboratory, haemodynamic and echocardiographic data, lung function, and isokinetic muscle strength and muscular exercise capacity were recorded. The mean ± SD age was 52 ± 16 years, 71% were male, and time from HTx was 4.1 ± 2.2 years. The patients were assigned to one of two groups: VO_2peak ≤or >27.3 ml/kg/min, which was the median value, corresponding to 80% of predicted value. The group with the higher VO_2peak had significantly lower body mass index, body fat, and triglycerides, and significantly higher body water, muscular exercise capacity, high-density lipoprotein (HDL) cholesterol, lung function, mitral annular velocity, peak ventilation, O₂ pulse, and VE/VCO₂ slope. Donor age, recipient age, sex, medication, ischaemic time, cardiac dimensions, systolic function, and chronotropic responses during exercise were similar. Multiple regression analysis showed that muscular exercise capacity and body fat were the strongest VO_2peak predictors.

Chronotropic incompetence is not a limiting factor for exercise capacity in a population of relatively fit HTx patients. The most significant predictors, representing only peripheral factors, are similar to those often determining VO_2peak in healthy, non-athletic individuals. Our findings emphasize the importance of a low percentage of body fat and high muscular exercise capacity in order to attain a sufficient VO_2peak level after HTx.