Impairment of Heart Rate Recovery After Peak Exercise Predicts Poor Outcome After Pediatric Heart Transplantation

Abstract

A blunted heart rate recovery (HRR) from peak exercise is associated with adverse outcome in adults with ischemic heart disease. We assessed HRR after pediatric heart transplantation (HTx) and its prognostic use. Between 2004 and 2010 we performed 360 maximal exercise tests (median, 2 tests/patient; range, 1-7) in 128 children (66 men; age at test, 14 ± 3 years) who received HTx (age, 8.5 ± 5.1 years) because of cardiomyopathy (66%) or congenital heart defects (34%). The change in heart rate from peak exercise to 1 minute of recovery was measured as HRR and was expressed as Z score calculated from reference data obtained in 160 healthy children. HRR was impaired soon after HTx (average in first 2 years Z=-1.9 ± 3.5) but improved afterward (Z=+0.52/y), such that HRR Z score normalized in most patients by 6 years after HTx (average, 0.6 ± 1.8). A subsequent decline in HRR Z score was noted from 6 years after HTx (rate of Z=-0.11/y). After 27 ± 15 months from the most recent exercise test, 19 patients died or were re-heart transplantation. For the follow-up after 6 years, HRR Z score was the only predictor of death/re-heart transplantation (P=0.003). Patients in the lowest quartile of HRR Z score had a much higher 5-year event rate (event-free rate, 29% versus 84%; hazard ratio, 7.0; P=0.0013). HRR is blunted soon after HTx but normalizes at ≈ 6 years, potentially as a result of parasympathetic reinnervation of the graft, but then declines. This late decline in HRR Z score is associated with worse outcome.