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Impairment of Heart Rate Recovery After Peak Exercise Predicts Poor Outcome After Pediatric Heart Transplantation
Study Questions:
What is the natural history of heart rate recovery (HRR) after pediatric heart transplantation, and what is its significance?
Methods:
A retrospective review was performed at a single center. Exercise tests were performed on a yearly basis after cardiac transplantation. HRR was calculated using data collected in the first minute of recovery from exercise. Age-based Z-scores were assigned to the HRR slope based on normal data obtained from exercise tests of 160 healthy children.
Results:
A total of 360 maximal exercise tests were performed in 128 children following heart transplantation. The mean age at exercise testing was 14 ± 3 years with mean age of heart transplant 8.5 ± 5.1 years. HRR was impaired initially after heart transplant (average in the first 2 years post-transplant -1.9 ± 3.5), but normalized in most patients by 6 years after heart transplant (average, 0.6 ± 1.8). There was then a progressive decline after 6 years post-transplant (rate of Z = -0.11/year). After 27 ± 15 months from the most recent exercise test, 19 patients died or underwent repeat heart transplantation. For patients followed >6 years, HRR Z-score was the only predictor of death or re-transplantation (p = 0.003).
Conclusions:
The authors concluded that HRR is initially impaired after heart transplantation, normalizes by approximately 6 years post-transplant, but then progressively declines. The late decline in HRR Z score is associated with worse outcome.
Perspective:
Late graft failure can be insidious, sometimes resulting in sudden death. This study of longitudinal exercise testing after pediatric heart transplantation showed an early blunting of HRR, likely due to cardiac denervation. The normalization of HRR over the first 6 years may be related to progressive cardiac reinnervation, while the mechanism of the late decline in HRR seen in this study remains unclear. The relationship between HRR and development of late transplant complications, including coronary allograft vasculopathy, deserves further study.
Keywords: Exercise Tolerance, Denervation, Heart Defects, Congenital, Heart Failure, Heart Rate, Death, Sudden, Cardiac, Heart Transplantation, Exercise Test
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