REGIONAL MYOCARDIAL SYMPATHETIC DYSINNERVATION IN ARRHYTHMOGENIC RIGHT-VENTRICULAR CARDIOMYOPATHY - AN ANALYSIS USING I-123 METAIODOBENZYLGUANIDINE SCINTIGRAPHY

Background In patients with arrhythmogenic right ventricular cardiomyopathy (ARVC), the frequent provocation of ventricular tachycardia during exercise, the sensitivity toward catecholamines, and the response toward antiarrhythmic drug regimen with antiadrenergic properties suggest an involvement of the sympathetic nervous system in arrhythmogenesis. Methods and Results To analyze the presence, extent, and location of impaired myocardial sympathetic innervation in ARVC, I-123-meta-iodobenzylguanidine (I-123-MIBG) scintigraphy was performed in 48 patients with ARVC. For comparison, 9 patients with idiopathic ventricular tachycardia and a control group of 7 patients without heart disease were investigated. In patients with ARVC, the clinical sustained (n=25; 52%) or nonsustained (n=23; 48%) ventricular tachycardia originated in the right ventricular outflow tract in 38 patients (79%), whereas in the remaining 10 patients (21%), the site of origin was the apical (n=5) or inferior (n=5) right ventricle. In 33 patients (69%), nonsustained or sustained ventricular tachycardia was provocable by exercise (n=28 of 48; 58%) and/or by isoproterenol infusion (n=16 of 37; 43%), whereas programmed ventricular stimulation induced sustained or nonsustained ventricular tachycardia in 16 patients each (33% each). With I-123-MIBG scintigraphy, the right ventricle was not visible in any patient. No areas of intense I-123-MIBG uptake (''hot spots'') were observed. Ah patients of the control group and 7 of 9 patients (78%) with idiopathic ventricular tachycardia showed a uniform tracer uptake in the left ventricle. In contrast, only 8 of 48 ARVC patients (17%) showed a homogeneous distribution of I-123-MIBG uptake, whereas 40 patients (83%) demonstrated regional reductions or defects of tracer uptake. In 3 of 48 patients (6%), the defect area was <15%; in 21 patients (44%), it was 15% to 30%; and in 16 patients (33%), it was >30% of the polar map area of the left ventricle (mean, 23+/-15%; range, 0% to 57%). In 38 of 40 patients (95%) with an abnormal I-125-MIBG scan, reduced tracer uptake was located in the basal posteroseptal left ventricle, involving the adjacent lateral wall in 10, the anterior wall in 2, and the apex in 12 patients. Only 2 patients demonstrated isolated defects of the anterior or lateral wall; one involved the apex. Perfusion abnormalities in the areas of I-123-MIBG defects were excluded by stress/redistribution Tl-201 single-photon emission computed tomography scintigraphy and by normal coronary angiograms in all patients. Abnormalities in I-123-MIBG scintigraphy in patients with ARVC correlated with the site of origin of ventricular tachycardia, demonstrating a regionally reduced tracer uptake in 36 of 38 patients (95%) with right ventricular outflow tract tachycardia compared with only 4 of 10 patients (40%) with other right ventricular origins of tachycardia. There was no correlation between the results of I-123-MIBG scintigraphy and the extent of right ventricular contraction abnormalities, right ventricular ejection fraction, biopsy results, coronary anatomy, or left ventricular involvement in ARVC. Conclusions In patients with ARVC, regional abnormalities of sympathetic innervation are frequent and can be demonstrated by I-123-MIBG scintigraphy. Sympathetic denervation appears to be the underlying mechanism of reduced I-123-MIBG uptake and may be related to frequent provocation of ventricular arrhythmias by exercise or catecholamine exposure in ARVC. Therefore, in patients with ARVC, the noninvasive detection of localized sympathetic denervation by I-123-MIBG imaging may have implications for the early diagnosis and for the choice of antiarrhythmic drugs in the treatment of arrhythmias.