Background: Peak exercise capacity improves early after orthotopic cardiac transplantation. However, the physiological response to exercise remains abnormal, with a reduced rate of heart rate (HR) rise and reductions in peak exercise HR and the increment in HR from rest to peak exercise. This chronotropic incompetence is due in large part to cardiac denervation. If reinnervation occurs after transplantation, it might result in an improvement in both chronotropic responsiveness and maximal exercise capacity. We therefore hypothesized that the chronotropic response to exercise and maximal exercise capacity would improve with time after transplantation.
Methods and results: Peak symptom-limited cardiopulmonary exercise tests performed in 57 clinically stable cardiac transplant recipients (mean age, 45 +/- 2 years) serially for up to 5 years after transplantation and in 33 control subjects without heart disease were analyzed retrospectively. Pretransplantation exercise tests were also performed in 41 patients an average of 4.7 +/- 0.6 months before transplantation. At 1 year after transplantation, peak oxygen consumption was 16.6 +/- 0.9 mL.kg-1.min-1, reflecting a 43% increase versus pretransplantation. Nevertheless, compared with control subjects, maximal exercise capacity and the HR response to exercise were subnormal in transplant recipients. There were no further increases in peak exercise capacity, peak exercise HR, or the peak increment in HR with exercise up to 5 years after transplantation.
Conclusions: One year after cardiac transplantation, peak exercise capacity and chronotropic responsiveness are subnormal. There is no further improvement in peak exercise capacity or chronotropic responsiveness as late as 5 years after transplantation. These data indicate that with regard to chronotropic responsiveness, functionally significant cardiac reinnervation does not occur between the first and fifth years after transplantation.