Exercise hemodynamics and metabolisms in (very) sportive patients after orthotopic heart transplantation

Type of funding sources: None.

After orthotopic heart transplantation (HTX), patients benefit with improved survival and quality of life, but exercise physiology becomes complicated and exercise capacity usually remains limited at 60-70% of predicted values. However, there are also patients who return to demanding or competitive sports even after HTX. For these patients, optimal exercise hemodynamics and metabolisms are crucial. It was the aim of this study to investigate this question more closely in (very) sportive patients after HTX.

6 patients after orthotopic HTX (1 female, 54±16 yrs old, BMI 23.6±2.8, 11±7 yrs post-transplant) from different sports disciplines (Cycling [2x], Triathlon, Hockey, Table-Tennis, Scuba Diving) could be included (Table 1). We performed cardiopulmonary exercise test (CPET) on a bicycle ergometer using a ramp protocol (15 watts/minute) and consecutive inertgas rebreathing (IGR) on different exercise steps (rest, light, moderate, heavy) of each 4-5 minutes. The hemodynamic measurements and blood gas analysis were conducted at the last minute of each IGR step. The study was approved by the local ethics committee.

For CPET: one patient reached extraordinary exercise capacity with a peak load of 345 watts (182% of pred.) and a peak VO2 of 58.9 ml/kg/min (163% of pred.). Corresponding values at first ventilatory threshold (VT1) were 280 watts and 44.1 ml/kg/min. The results of the other patients showed a more homogenic profile: Mean peak load was 172±44 watts (104±14% of pred.) and peak VO2 was mean 25.6±4.5 ml/kg/min (91±14% of pred.). Values at VT1 were 108±27 watts and 18.0±2.5 ml/kg/min.

Selected IGR results for all patients are displayed in Table 2. The hemodynamic measurements revealed a steadily increase in cardiac output (CO), cardiac index (CI), arteriovenous oxygen difference (avDO2), heart rate and systolic blood pressure from rest to the different exercise steps. However, an increase in stroke volume (SV) beyond light to moderate exercise often remained limited (peak SV 101±14 ml/beat). Also, peak CO (13.9±1.8 l/min) remained slightly below predicted values (89% of pred.).

Hemodynamic measurements revealed satisfying exercise adaptions and adequate prerequisites for intensive physical activities in selected patients even after HTX. However, compared to healthy athletes, SV was clearly limited to normal values (<120 ml/beat). The deficit in CO occurs with moderate to heavy exercise levels could be partially compensated by increased avDO2 due to excellent peripheral function. Therefore, regular exercise training is crucial for this target group.