LONG-TERM SEQUENTIAL-CHANGES IN EXERCISE CAPACITY AND CHRONOTROPIC RESPONSIVENESS AFTER CARDIAC TRANSPLANTATION

Background Peak exercise capacity improves early after orthotopic card iac transplantation. However, the physiological response to exercise r emains abnormal, with a reduced rate of heart rate (HR) rise and reduc tions in peak exercise HR and the increment in HR from rest to peak ex ercise. 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 maxim al 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 c ardiopulmonary exercise tests performed in 57 clinically stable cardia c 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 te sts were also performed in 41 patients an average of 4.7 +/- 0.6 month s before transplantation. At 1 year after transplantation, peak oxygen consumption was 16.6 +/- 0.9 mL.kg(-1).min(-1), reflecting a 43% incr ease versus pretransplantation. Nevertheless, compared with control su bjects, maximal exercise capacity and the HR response to exercise were subnormal in transplant recipients. There were no further increases i n peak exercise capacity, peak exercise HR, or the peak increment in H R with exercise up to 5 years after transplantation. Conclusions One y ear after cardiac transplantation, peak exercise capacity and chronotr opic responsiveness are subnormal. There is no further improvement in peak exercise capacity or chronotropic responsiveness as late as 5 yea rs after transplantation. These data indicate that with regard to chro notropic responsiveness, functionally significant cardiac reinnervatio n does not occur between the first and fifth years after transplantati on.