O1006: Indication for Pediatric Heart Transplantation Affects Chronotropy on Post-operative Cardiopulmonary Exercise Testing

Background: Two common indications for pediatric heart transplantation (HTx) are congenital heart disease (CHD) and cardiomyopathy (CM). Cardiopulmonary exercise testing (CPET) can monitor functional capacity following HTx, with better performance correlating to reduced risk of major adverse cardiac events. A recent study of 35 patients found reduced heart rate response in CHD patients following HTx compared to patients who received HTx for CM. We aimed to validate these findings and to determine whether the number of pre-transplant sternotomies was associated with chronotropic incompetence.

Methods: A retrospective analysis of our institutional CPET data between 2004 – 2022 was performed. All HT patients between age 6 – 21 years with a maximal effort (respiratory exchange ratio > 1.10) CPET were included. The electronic health record was reviewed to obtain CPET results, demographic data, clinical data, and echocardiogram and cardiac catheterization results within 6 months of the CPET. Patients without catheterization or echocardiographic data available in our electronic medical record were excluded. Patients were stratified based on indication for transplantation into a CM group if they had either a congenital or acquired CM and CHD group which included all other forms of congenital cardiac anatomic abnormalities. Clinical and CPET data of patients within these two groups were compared using independent samples t-tests.

Results: Ninety-three patients met inclusion criteria. Patients with HTx due to CHD (n=40) differed from patients with HTx due to CM (n=53) by sex (70% male versus 45.3% male, p=0.017) and mean number of sternotomies prior to transplant (2.4 versus 0.5, p< 0.001). There were no significant differences in echocardiographic function or catheterization metrics. In CPET performance, the CHD group had a significantly higher resting heart rate (HR, 91.8 vs 86.4bpm, p=0.019), lower maximal HR (160.3 vs 170.8bpm, p=0.015), lower percentage of age-predicted maximal HR achieved (78.3% vs 83.2%, p=0.032) and lower HR reserve (68.6 vs 84.4bpm, p=0.001) despite a similar age and average time from HTx. There was no difference between groups in peak oxygen uptake.

Conclusion: Our data show increased chronotropic incompetence in patients who underwent HTx due to CHD compared to CM without a significant change in exercise capacity. These findings corroborate a prior study while using a significantly larger data set. The patient groups differ significantly by number of sternotomies, potentially supporting the hypothesis that prior surgical disruption in cardiac innervation may be related to post-HTx chronotropic response to exercise. Further studies are needed to evaluate CPET findings over time in these two groups and to determine if differences in CPET findings are associated with differences in long-term clinical outcomes.