ACE-INHIBITION REDUCES CARDIAC IODINE-123-MIBG RELEASE IN HEART-FAILURE

Radioiodinated metaiodobenzylguanidine (I-123-MIBG), an analog of nore pinephrine, has been used to assess cardiac sympathetic nerve activity . Decreased myocardial accumulation and enhanced washout of I-123-MIBG have been reported in patients with congestive heart failure (CHF), T he purpose of this study was to determine whether angiotensin converti ng enzyme (ACE) inhibition reduced I-123-MIBG release and improved car diac I-123-MIBG accumulation in patients with CHF. Methods: Twenty-nin e patients receiving conventional treatment for CHF, New York Heart As sociation (NYHA) functional class 23, were studied. Nineteen patients received additional treatment with enalapril, an ACE inhibitor, and 10 patients who were treated with conventional therapy alone were define d as a control group. Iodine-123-MIBG imaging and echocardiography wer e performed on all patients before treatment and repeated after 9.1 +/ - 3.0 mo of treatment. Images were obtained 30 min and 4 hr after inje ction of I-123-MIBG, and a heart to mediastinum (H/M) ratio was define d to quantify cardiac I-123-MIBG uptake as a fraction of the mean coun ts per pixel in the heart divided by those in the mediastinum. The was hout rate of I-123-MIBG from the heart was calculated as follows: (ear ly counts - delayed counts)/early counts x 100 (%). Results: In patien ts with enalapril group, the H/M ratio of I-123-MIBG was increased aft er treatment (early image: 1.60 +/- 0.22 vs. 1.73 +/- 0.28, p < 0.05, delayed image: 1.63 +/- 0.28 vs. 1.82 +/- 0.33, p < 0.01). The washout rate of I-123-MIBG was reduced from 38% +/- 11% to 30% +/- 12% after treatment (p < 0.01). However in the conventional therapy group, the H /M ratios in the early and delayed images (early image: 1.58 +/- 0.31 vs. 1.52 +/- 0.23, delayed image: 1.49 +/- 0.27 vs. 1.49 +/- 0.25) and the washout rate (34% +/- 8% vs. 33% +/- 7%) remained unchanged after treatment. In patients with an increased H/M ratio of enalapril group (n = 13), a left ventricular ejection fraction increased from 48% +/- 12% to 55% +/- 9% (p < 0.01) after treatment. Conclusion: ACE inhibit ion reduces cardiac I-123-MIBG release and thus lowers cardiac sympath etic nerve activity. Iodine-123-MIBG may be helpful in evaluating the therapeutic effects of ACE inhibition on the cardiac sympathetic nervo us system in patients with CHF.