Myocardial Contractile Response to Increasing Doses of Dobutamine in Patients with Reperfused Acute Myocardial Infarction by Cardiac Magnetic Resonance Imaging

Abstract

Background: Cardiac magnetic resonance imaging uses contractile response to dobutamine (DCMR) and delayed contrast enhancement (DE) to assess myocardial viability. However, early after acute myocardial infarction (AMI) the optimal dose of dobutamine is unclear. Methods: In patients early after reperfused AMI, DCMR at 5, 10 and 20 µg*kg^–1*min^–1 and measurement of DE was performed. On three short-axis slices 18 segments were graded as no DE, DE <50% and DE ≧50%. Thickening (systolic-diastolic wall thickness) and contractile reserve (max. thickening – rest) were determined. Segments were classified dysfunctional if thickening was >2 SD below normal or <2 mm. Results: Forty-nine patients participated. In segments with no DE, thickening increased continuously but contractile reserve was low (0.9 ± 3.2 mm) and dysfunctional segments were unchanged (rest: 13.1% vs. 20 µg: 14.8%). In segments with DE, contractile reserve was high (1.4 ± 3.0 mm and 1.5 ± 3.0 mm) and dysfunctional segments decreased from rest to 20 µg (50 vs. 24.8% and 79.9 vs. 43.2%). Between 5 and 10 µg no change of thickening and of dysfunctional segments occurred. Conclusion: Early after AMI, DCMR demonstrated no diagnostic benefit in segments with no DE. In segments with DE, higher dose of dobutamine can provide additional information on contractile reserve and dysfunctional segments.