Mechanism of late gadolinium enhancement in patients with acute myocardial infarction.

PURPOSE To investigate the mechanism of late gadolinium enhancement in irreversibly damaged myocardium in patients with acute myocardial infarct by determining kinetics of Gd-DTPA over time. METHODS Twenty-nine patients (24 men; 64 +/- 9 years) with acute myocardial infarction were imaged with functional and gadolinium enhanced cardiovascular magnetic resonance (CMR) 18 minutes post 0.2 mmol/kg Gd-DTPA. T1 of blood, remote and enhanced myocardium, as well as microvascular obstruction (MVO) was determined before and 5-40 minutes post contrast injection (Look-Locker), and the partition coefficient (lambda) was calculated. RESULTS T1 and lambda were significantly different from 5-40 minutes post contrast in enhanced (lambda = 0.90 +/- 0.09, p < 0.001) compared to remote myocardium (lambda = 0.40 +/- 0.07). lambda achieved a steady state in remote but increased continuously in infarcted myocardium and to an even greater extent in MVO. T1 of enhanced myocardium was higher from 5-15 minutes, equal at 20 minutes and lower 25-40 minutes post contrast compared to blood, indicating a changing contrast between blood and late gadolinium enhancement over time. CONCLUSION Enhancement in patients with acute infarction is mainly due to an increased lambda, although reduced wash-in-wash-out adds to the effect. Differentiation between blood and enhanced myocardium may be difficult to achieve, if only little differences of T1 are available. Imaging at a later point will restore the contrast.