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In patients with idiopathic dilated cardiomyopathy (IDC) the increased sympathetic activity owing to chronic congestive heart failure leads to an imbalance of cardiac autonomic tone, as reflected by decreased heart rate variability (HRV). Iodine-123-metaiodobenzylguanidine (123-I-MIBG), which has the same affinity for sympathetic nerve endings as norepinephrine, can be used to assess the integrity and function of the cardiac sympathetic nervous system. The aim of the present study was to measure cardiac sympathetic activity 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 MIBG 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 MIBG uptake and HRV in time domain, the linear regression between the M/C ratio, a new scintigraphic parameter, and the mean RR interval or the HRV triangular index, respectively, was determined. A significant correlation between the M/C ratio and mean RR interval (r = 0.52; p = 0.016) or M/C ratio and HRV triangular index (r = 0.76; p = 0.003), respectively, was found. Thus, the significant correlation between the M/C ratio and HRV indicate that they are both suitable noninvasive methods for evaluating cardiac sympathetic activity in patients with IDC and, furthermore, favor the view that there is evidence of a relation between HRV and the disorder of the cardiac presynaptic sympathetic nerve endings as demonstrated by a reduced M/C ratio. [ABSTRACT FROM AUTHOR]

Unlabelled: In chronic heart failure, elevated plasma norepinephrine (NE) levels and a disparity between the neuronal release and the effective reuptake of NE lead to an increased concentration of NE in the presynaptic cleft, causing a downregulation of the myocardial beta-adrenoceptors. The clinical and prognostic effectiveness of beta-blocker therapy has been shown in patients with chronic heart failure in several large trials. The purpose of this study was to investigate the effect of long-term beta-blocker therapy on the cardiac adrenergic nervous system as assessed by the myocardial uptake of 123I-metaiodobenzylguanidine (MIBG), an analog of NE, in idiopathic dilated cardiomyopathy (IDC)., Methods: In 10 patients with IDC and stable chronic heart failure the myocardial MIBG uptake was measured at baseline and at 1 y (median, 11.5 mo) after treatment with beta-blockers (metoprolol, n = 5; bisoprolol, n = 1; and carvedilol, n = 4) in addition to standard medication. In parallel with the changes in MIBG uptake, the New York Heart Association functional class, the left ventricular ejection fraction (LVEF), and the left ventricular end-diastolic diameter (LVEDD) were documented before and after 1 y of therapy with beta-blockers., Results: During the 1-y follow-up, a significant increase in myocardial 123I-MIBG uptake (P = 0.005) in parallel with an improved LVEF (P = 0.005) and a reduced LVEDD (P = 0.019) was found. A trend toward an improvement of the New York Heart Association functional class under the beta-blocker therapy (P = 0.139) was also found., Conclusion: Assessment of the myocardial 123I-MIBG uptake is a useful noninvasive tool for evaluating changes in cardiac sympathetic nerve activity under medical therapy. Long-term treatment with beta-blockers in IDC causes a recovery of the cardiac adrenergic nervous system concomitantly with a clinical and hemodynamic improvement.