Partial Normalization of the Heart Rate Response to Exercise After Cardiac Transplantation: Frequency and Relationship to Exercise Capacity

Abstract

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. 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. For the entire cohort, peak exercise oxygen uptake was 19.9+/-4.8 mL x kg(-1) x 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 x kg(-1) x 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. 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.