Myocardial scintigraphy using iodine-123 15-(p-iodophenyl)-3-R, S-methylpentadecanoic acid predicts the response to beta-blocker therapy in patients with dilated cardiomyopathy but does not reflect therapeutic effect.

Myocardial fatty acid metabolism is disturbed in patients with idiopathic dilated cardiomyopathy. Myocardial scintigraphy using iodine-123 15-(p-iodophenyl)-3-R, S-methylpentadecanoic acid(BMIPP) was used to assess the response to beta-blocker therapy in 19 patients with dilated cardiomyopathy. BMIPP myocardial scintigraphy was performed before and 6 months after initiating beta-blocker therapy with metoprolol. Cardiac BMIPP uptake was assessed as the total defect score (TDS) and heart-to-mediastinum activity (H/M) ratio. Patients were classified retrospectively as responders with an improvement of at least one functional class (New York Heart Association) or an increase in ejection fraction of > or = 0.10 at 6 months, or as nonresponders meeting neither criterion. Responders had a significantly better pretreatment TDS (p < 0.005) and H/M ratio (p < 0.0001) than nonresponders. TDS exhibited no significant changes over 6 months in either group (responders: 13.2 +/- 3.7 vs 12.5 +/- 3.3; nonresponders: 20.8 +/- 6.5 vs 20.5 +/- 3.0). Responders showed no significant changes in H/M ratio (2.47 +/- 0.28 vs 2.43 +/- 0.42); paradoxically, nonresponders showed a significant increase from 1.82 +/- 0.11 to 2.10 +/- 0.19 (p < 0.05), suggesting that beta-blocker therapy protected the myocardial fatty acid metabolism even in the absence of clinical improvement. BMIPP myocardial scintigraphy provides a prediction of response to beta-blocker treatment, but does not reflect the therapeutic effect in responders at 6 months.