Functional significance of cardiac reinnervation in heart transplant recipients

Background: There is accumulating evidence of structural sympathetic reinnervation after human cardiac transplantation. However, the functional significance of reinnervation in terms of exercise capacity has not been established as yet; we therefore investigated the influence of reinnervation on cardiopulmonary exercise testing. MethodsAfter orthotopic heart transplantation 35 patients (mean age, 49.1 ± 8.4 years) underwent positron emission tomography with scintigraphically measured uptake of C₁₁-hydroxyephedrine (HED), lung function testing, and cardiopulmonary exercise testing. Two groups were defined based on scintigraphic findings, indicating a denervated group (n = 15) with a HED uptake of 5.45%/min and a reinnervated group (n = 20) with a HED uptake of 10.59%/min.ResultsThe two study groups did not show significant differences with regard to anthropometric data, number of rejection episodes, preoperative hemodynamics, and postoperative lung function data. The reinnervated group had a significant longer time interval from transplantation (1625 ± 1069 versus 800 ± 1316 days, p < .05). In transplant recipients with reinnervation, heart rate at maximum exercise (137 ± 15 versus 120 ± 20 beats/min, p = .012), peak oxygen uptake (21.0 ± 4 versus 16.1 ± 5 mL/min/kg, p = .006), peak oxygen pulse (12.4 ± 2.9 versus 10.2 ± 2.7 mL/min/beat, p = .031), and anaerobic threshold (11.2 ± 1.8 versus 9.5 ± 2.1 mL/min, p = .046) were significantly increased in comparison to denervated transplant recipients. Additionally, a decreased functional dead space ventilation (0.24 ± 0.05 versus 0.30 ± 0.05, p = .004) was observed in the reinnervated group.ConclusionsOur study results support the hypothesis that partial sympathetic reinnervation after cardiac transplantation is of functional significance. Sympathetic reinnervation enables an increased peak oxygen uptake. This is most probably due to partial restoration of the chronotropic and inotropic competence of the heart as well as an improved oxygen delivery to the exercising muscles and a reduced ventilation-perfusion mismatching. Copyright (C) 1999 International Society for Heart and Lung Transplantation.