Cardiac sympathetic activity as measured by myocardial 123-I-metaiodobenzylguanidine uptake and heart rate variability in idiopathic dilated cardiomyopathy

In patients with idiopathic dilated cardiomyopathy (IDC) the increased symp athetic activity owing to chronic congestive heart failure leads to an imba lance of cardiac autonomic tone, as reflected by decreased heart rate varia bility (HRV). Iodine-123-metaiodobenzylguanidine (123-I-MIBG), which has th e same affinity for sympathetic nerve endings as norepinephrine, can be use d to assess the integrity and function of the cardiac sympathetic nervous s ystem. The aim of the present study was to measure cardiac sympathetic acti vity by assessing 123-I-MIBG uptake compared with HRV in patients with IDC. In 12 patients with IDC and mild to moderate heart failure, myocardial MIB G uptake was calculated from the myocardial (M) to left ventricular cavity (C) voxel values density ratio and the 123-I activity in a blood sample as a reference (= M/C ratio) using a double radionuclide study with 123-I-MIBG and technetium-99m-MIBI. To investigate the relation between myocardial MI BG uptake and HRV in time domain, the linear regression between the M/C rat io, a new scintigraphic parameter, and the mean RR interval or the HRV tria ngular index, respectively, was determined. A significant correlation betwe en the M/C ratio and mean RR interval (r = 0.52; p = 0.016) or M/C ratio an d HRV triangular index (r 0.76; p = 0.003), respectively, was found. Thus, the significant correlation between the MIC ratio and HRV indicate that the y are both suitable noninvasive methods for evaluating cardiac sympathetic activity in patients with IDC and, furthermore, favor the view that there i s evidence of a relation between HRV and the disorder of the cardiac presyn aptic sympathetic nerve endings as demonstrated by a reduced MIC ratio. (C) 1999 by Excerpta Medica Inc.