Partial normalization of the heart rate response to exercise after cardiac transplantation: Frequency and relationship to exercise capacity

Objective: To determine the frequency of partial normalization of the heart rate response to graded exercise and its relationship to exercise capacity in cardiac transplant recipients. Subjects and Methods: The study subjects were 95 adults (77 men, 18 women) who were available to perform a cardiopulmonary exercise test 1 year after orthotopic cardiac transplantation, which occurred between June 1988 and September 1998. All subjects received standard immunosuppressant medications. At the time of the exercise tests, the mean ± SD age of the subjects was 49±14 years. The mean ± SD resting left ventricular ejection fraction was 62%±8%. All subjects participated in a 6- to 8-week supervised exercise program, starting no later than 1 month after surgery. Subjects were given an exercise prescription for independent exercise training after finishing the supervised program. Self-reported weekly exercise training had a median value of 90 minutes (interquartile range, 0-210 minutes). Symptom-limited graded exercise was performed on a treadmill, with breath-by-breath analysis of expired air. Results: For the entire cohort, peak exercise oxygen uptake was 19.9±4.8 mL · kg^-1 · min^-1 (61%±15% of age and sex predicted). Thirty-two subjects (34%) had a partially normalized heart rate response to graded exercise. The frequency was similar for men (25/77 [33 %]) and for women (7/18 [39%]) and was independent of recipient or donor age. Peak exercise heart rate (147±18 vs 134±21 beats/min; P=.008) and heart rate reserve (46±15 vs 33±15 beats/min; P<.001) were greater for subjects with a partial normalization of heart rate response. Peak exercise oxygen uptake was similar for subjects with or without partial normalization of the heart rate response (20.9±5.8 vs 19.4±4.2 mL · kg^-1 · min^-1; P=.22). Submaximal exercise oxygen uptake during the first few minutes of exercise was also not affected by normalization of the heart rate response. Conclusion: At 1 year after cardiac transplantation, approximately one third of subjects had partial normalization of the heart rate response to graded exercise. However, a higher peak exercise heart rate and a larger heart rate reserve did not result in better aerobic exercise capacity.