Relationship of MRI delayed contrast enhancement to irreversible injury, infarct age, and contractile function

Background - Contrast MRI enhancement patterns in several pathophysiologies resulting from ischemic myocardial injury are controversial or have not been investigated. We compared contrast enhancement in acute infarction (AI), after severe but reversible ischemic injury (RII), and in chronic infarction. Methods and Results -In dogs, a large coronary artery was occluded to study AI and/or chronic infarction (n = 18), and a second coronary artery was chronically instrumented with a reversible hydraulic occluder and Doppler flow meter to study RII (n=8). At 3 days after surgery, cine MRI revealed reduced wall thickening in AI (5 ± 6% versus 33 ± 6% in normal, P<0.001). In RII, wall thickening before, during, and after inflation of the occluder for 15 minutes was 35 ± 5%, 1 ± 8%, and 21 ± 10% and Doppler flow was 19.8 ± 5.3, 0.2 ± 0.5, and 56.3 ± 17.7 (peak hyperemia) cm/s, respectively, confirming occlusion, transient ischemia, and reperfusion. Gd-DTPA-enhanced MR images acquired 30 minutes after contrast revealed hyperenhancement of AI (294 ± 96% of normal, P<0.001) but not of RII (98 ± 6% of normal, P=NS). Eight weeks later, the chronically infarcted region again hyperenhanced (253 ± 54% of normal, n=8. P<0.001). High- resolution (0.5 x 0.5 x 0.5 mm) ex vivo MRI demonstrated that the spatial extent of hyperenhancement was the same as the spatial extent of myocyte necrosis with and without reperfusion at 1 day (R=0.99, P<0.001) and 3 days (R=0.99, P<0.001) and collagenous scar at 8 weeks (R=0.97, P<0.001). Conclusions - In the pathophysiologies investigated, contrast MRI distinguishes between reversible and irreversible ischemic injury independent of wall motion and infarct age.