Quantitative Assessment of Myocardial Viability After Infarction by Dobutamine Magnetic Resonance Tagging

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Abstract
Background —The assessment of return of function within dysfunctional myocardium after acute myocardial infarction (MI) using contractile reserve has been primarily qualitative. Magnetic resonance (MR) myocardial tagging is a novel noninvasive method that measures intramyocardial function. We hypothesized that MR tagging could be used to quantify the intramyocardial response to low-dose dobutamine and relate this response to return of function in patients after first MI. Methods and Results —Twenty patients with a first reperfused MI (age, 53±12 years; 16 male; 11 inferior MIs) were studied. Patients underwent breath-hold MR-tagged short-axis imaging on day 4±2 after MI at baseline and during dobutamine infusion at 5 and 10 μg · kg −1 · min −1 . At 8±1 weeks after MI, patients returned for a follow-up MR tagging study without dobutamine. Quantification of percent intramyocardial circumferential segment shortening (%S) was performed. Low-dose dobutamine MRI was well tolerated. Overall, mean %S was 15±11% at baseline (n=227 segments), increased to 16±10% at 5 μg · kg −1 · min −1 dobutamine ( P =NS), 21±10% at peak ( P −1 · min −1 ), and 18±10% at 8 weeks ( P P P P Conclusions —The response of intramyocardial function to low-dose dobutamine after reperfused MI can be quantified with MR tagging. Dysfunctional tissue after MI demonstrates a larger contractile response to dobutamine than normal myocardium. A normal increase in shortening elicited by dobutamine within dysfunctional midwall and subepicardium predicts greater functional recovery at 8 weeks after MI, but the response within the subendocardium is not predictive.

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