Determinants of peak aerobic capacity after heart transplantation

Exercise therapy for cardiac transplant recipients

Heart transplantation (HT) is an attractive treatment for patients with terminal heart failure from a variety of causes. Survival at 1- and 5 years after HT averages 90% and 70%, respectively. The physiologic response to exercise is abnormal after HT presumably because the transplanted heart is surgically denervated, although a minority of patients demonstrate signs of partial cardiac reinnervation several months after surgery. The heart rate response to exercise is typically blunted, and exercise capacity is below average for most HT recipients. Multiple studies have demonstrated the benefits of exercise training (ET) after HT. Peak exercise oxygen uptake improves by an average of 24% after 2 to 3 months of ET. Resistance training results in increased skeletal muscle mass and strength. Early mobilization and low-level ET may begin in the hospital after extubation. Outpatient ET, ideally in a supervised environment for at least several weeks, should begin immediately after hospital dismissal. Exercise prescription for HT patients is similar to that for other patients who have undergone cardiothoracic surgery, with the exception of a target heart rate. Ratings of perceived exertion are useful for prescribing exercise intensity. Exercise training does not affect the frequency or severity of episodes of acute rejection. There are no data regarding the effect of ET on survival after HT.

Exercise performance increases coincident to body weight over the first two years following cardiac transplantation

BACKGROUND

To determine whether exercise performance changed over time once patients stabilized after heart transplantation, metabolic stress testing was performed in patients one and two yr post-heart transplantation.

METHODS

The patient cohort includes those transplanted in our program who survived at least two yr and were able to perform metabolic stress tests during their one- and two-yr annual evaluations. Standard stress test parameters were assessed, including weight, body surface area, rest and exercise heart rate (HR) and blood pressure (BP), exercise time, anaerobic threshold (AT), and maximum VO2 (MVO2). Ejection fraction by echo was also collected. Each patient served as their own control and data were compared using paired t-testing.

RESULTS

Fifty patients were included in the cohort, 48 of whom were able to exercise to at least AT. Patient weight increased from year 1 to year 2 (82.4 ± 15.1 vs. 85.0 ± 17.0 kg, p = 0.035). Systolic BP increased approximately 40 mmHg with exercise with no change in diastolic BP, and there was no difference between years 1 and 2. HR increased approximately 25 bpm with exercise. There was no difference in resting HR but exercise HR increased significantly between yrs (148 ± 15 bpm vs. 154 ± 18 bpm, p = 0.017). Both VO2 at AT and MVO2 increased significantly from year 1 to year 2 (1116 ± 347 mL/min vs. 1192 ± 313 mL/min, p = 0.049 and 1523 ± 337 mL/min vs. 1599 ± 356 mL/min, p = 0.012, respectively) but when corrected for body weight, there were no differences (VO2-AT 13.6 ± 4.0 mL/kg/min vs. 14.0 ± 4.0 mL/kg/min; MVO2 18.7 ± 4.2 mL/kg/min vs. 18.8 ± 4.1 mL/kg/min). All other measured parameters were not different. There was a weak but statistically significant correlation between change in peak HR and change in VO2 at AT between one and two yr post-transplantation (r = 0.30, p = 0.04).

CONCLUSIONS

We conclude that exercise performance as measured by VO2 can increase over time post-heart transplantation and in our cohort appears to be related to both an increase in body weight and an increase in HR from years 1 and 2.