Severely Impaired Cardiac Autonomic Nervous Activity After the Fontan Operation

Abstract

Background Elevated neurohumoral activity and an abnormal cardiopulmonary response to exercise are well-established characteristics in patients after the Fontan operation. However, there have been few studies addressing cardiac autonomic nervous activity (CANA) in these patients. Methods and Results We evaluated CANA in 63 post-Fontan patients and 44 controls. Cardiac parasympathetic nervous activity (PSNA) was estimated by heart rate (HR) changes after cholinergic blockade, HR variability, and arterial baroreflex sensitivity. Cardiac sympathetic nervous activity was estimated by the heart to mediastinum [ 123 I]metaiodobenzylguanidine activity ratio (H/M) and the HR increase (ΔHR) after isoproterenol infusion (β). ΔHR and peak oxygen uptake (V̇ o 2 ) were measured by exercise test. There was no difference in β between the Fontan group and controls. PSNA and H/M were markedly lower than in controls ( P <0.001). PSNA and β were related to ΔHR ( P <0.05); however, peak V̇ o 2 was not correlated with ΔHR. Neither PSNA nor H/M was associated with clinical features, including hemodynamics, type of repair, number of surgical procedures, age at Fontan operation, or follow-up period, and administration of an angiotensin-converting enzyme inhibitor did not improve the impaired CANA in these patients. Conclusions After the Fontan procedure, postsynaptic β-sensitivity is maintained and is important in ΔHR during exercise as is PSNA, although ΔHR does not determine exercise capacity. The lack of a relationship between CANA and clinical features implies that, in addition to surgical damage, the Fontan circulation per se may impair CANA. Angiotensin-converting enzyme inhibitor administration does not change this abnormality.