Impaired cardiac sympathetic activity can be evaluated by 123I-metaiodobenzylguanidine (MIBG) imaging.
Methods: We studied the significance of MIBG imaging for 24 patients (age 58+/-12 y) with dilated cardiomyopathy (DCM). We compared 12 patients (group A) treated with metoprolol (dose from 30-60 mg/d) with 12 patients treated with angiotensin-converting enzyme (ACE) inhibitors. Patients were studied before treatment, after 5 mo of treatment (only in group A) and after 1 y of treatment. Cardiac MIBG uptake was assessed as the heart-to-mediastinum activity ratio (H/M) and total defect score (TDS) from anterior planar and SPECT MIBG images, which were acquired in 4 h after tracer injection. New York Heart Association (NYHA) class and left ventricular ejection fraction (LVEF) calculated by echocardiography were also assessed.
Results: TDS decreased in both groups (in group A, from 30+/-7 through 23+/-9 to 18+/-10; P < 0.01, in group B, from 30+/-6 to 24+/-8; P < 0.01) and H/M was increased in both groups (in group A, from 1.87+/-0.31 through 2.03+/-0.28 to 2.14+/-0.29; P < 0.01, in group B, from 1.82+/-0.28 to 1.94+/-0.26; P < 0.05). But TDS and H/M were more improved in group A than in group B (P < 0.05). LVEF was significantly increased in only group A (from 38+/-6 through 43+/-8 to 49%+/-9%; P < 0.01). NYHA improved in both groups (in group A, from mean 2.5 through 2.1 to 1.8; P < 0.01, in group B, from mean 2.6 to 2.1; P < 0.05) but was more improved in group A than in group B (P < 0.05).
Conclusion: Cardiac function, symptom and cardiac sympathetic activity evaluated by MIBG images improved after the beta-blocker therapy more than with the treatment that used ACE inhibitors.