Recovery of the cardiac adrenergic nervous system after long-term beta-blocker therapy in idiopathic dilated cardiomyopathy: Assessment by increase in myocardial I-123-metaiodobenzylguanidine uptake

In chronic heart failure, elevated plasma norepinephrine (NE) levels and a disparity between the neuronal release and the effective reuptake of NE lea d to an increased concentration of NE in the presynaptic cleft, causing a d ownregulation of the myocardial beta -adrenoceptors. The clinical and progn ostic effectiveness of beta -blocker therapy has been shown in patients wit h 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 car diac adrenergic nervous system as assessed by the myocardial uptake of I-12 3-metaiodobenzylguanidine (MIBG), an analog of NE, in idiopathic dilated ca rdiomyopathy (IDC). Methods: in 10 patients with [DC and stable chronic hea rt 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; bi soprolol, n = 1; and carvedilol, n = 4) in addition to standard medication. In parallel with the changes in MIBG uptake, the New York Heart Associatio n 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 I-123-MIBG uptake (P = 0.005) in par allel 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 fun ctional class under the beta -blocker therapy (P = 0.139) was also found. C onclusion: Assessment of the myocardial I-123-MIBG uptake is a useful nonin vasive tool for evaluating changes in cardiac sympathetic nerve activity un der medical therapy. Long-term treatment with beta -blockers in IDC causes a recovery of the cardiac adrenergic nervous system concomitantly with a cl inical and hemodynamic improvement.