Normalization of the heart rate response to exercise 6 months after cardiac transplantation

Heart transplant recipients show an abnormal heart rate (HR) response to exercise due to complete cardiac denervation after surgery. They present elevated resting HR, minimal increase in HR during exercise, with maximal HR reached during the recovery period. The objective of this study was to study the frequency of normalization of the abnormal HR in the first 6 months after transplantation.

We prospectively studied 27 heart transplant recipients who underwent treadmill exercise tests at 2 and 6 months after heart transplantation (HT). HR responses to exercise were classified as normal or abnormal, depending on achieving all of the following criteria: (1) increased HR for each minute of exercise, (2) highest HR at the peak exercise intensity, and (3) decreased HR for each minute of the recovery period. The HR response at 2 months was compared with the results at 6 months post-HT.

At 2 months post-HT, 96.3% of the patients showed abnormal HR responses to exercise. Four months later, 11 patients (40.7%) had normalized HR responses (P<.001), which also involved a significant decrease in the time to achieve the highest HR after exercise (124.4±63.8 seconds in the first test and 55.6±44.6 seconds in the second). A significant improvement in exercise capacity and chronotropic competence was also shown in tests performed at 6 months after surgery.

We observed important improvements in HR responses to exercise at 6 months after HT, which may represent early functional cardiac reinnervation.