[Evaluation of cardiac autonomic nerves by iodine-123 metaiodobenzylguanidine scintigraphy and ambulatory electrocardiography in patients after arterial switch operations].

The autonomic cardiac nerves reach the heart after passing through the vicinity of the aortic root and the pulmonary trunk. The arterial switch operation (ASO) completely transects the ascending aorta and the pulmonary trunk. Therefore, this surgical procedure virtually denerves the heart. Cardiac sympathetic denervation and reinnervation were evaluated in patients after ASO using iodine-123 metaiodobenzylguanidine (MIBG) myocardial scintigraphy and parasympathetic denervation and reinnervation using ambulatory electrocardiography [Holter electrocardiogram (ECG)]. MIBG scintigraphy was performed in 14 patients who underwent ASO (ASO group) and 3 patients who underwent other open heart surgery (control group). All patients in the ASO group underwent the operation in the neonatal or infantile period. Planar and single photon emission computed tomography (SPECT) images of the myocardium were obtained. Defect score was determined by the SPECT images as a semi-quantitative index. The mean interval between ASO and MIBG scintigraphy was 25.6 +/- 14.6 months. Holter ECG was also performed in 14 patients in the ASO group and 19 age-matched normal children. The Holter ECGs were plotted on a Lorenz plot. The H index, which is related to vagal tone for the cardiovascular system, was calculated from the R-R intervals. The mean interval between the ASO and Holter ECG was 8.3 +/- 9.7 months. MIBG scintigraphy in the control group demonstrated an almost normal homogeneous tracer uptake, but showed extremely reduced tracer uptake and significantly higher defect score in the ASO group. The extent and degree of the reduction of MIBG uptake improved with time after the ASO. The heart-to-mediastinum MIBG count ratio tended to increase with time. The H index of the ASO group was lower than that of normal children (< 12 months: Control group 0.0280 +/- 0.0068 vs ASO group 0.0219 +/- 0.0083), and gradually increased with time (1-3 years: 0.0470 +/- 0.0157 vs 0.0314 +/- 0.0124). These results indicate that MIBG scintigraphy reflects the presence of sympathetic denervation and the possibility of reinnervation after ASO, and that H index reflects the presence of parasympathetic denervation and the possibility of reinnervation after ASO. These are simple and useful methods for assessing the extent and degree of autonomic denervation and reinnervation.