Contrast agent distribution in microvascular damage of infarcted pig myocardium

Purpose: We determined whether reperfusion damage was sufficient to allow e xtravasation of a large molecular weight contrast agent into infarcted pig myocardium. Material and Methods: Five pig hearts were subjected to in situ occlusion o f the left anterior descending coronary artery (2 h) followed by reperfusio n (1 h). The hearts were excised and perfused in the Langendorff mode for e x vivo MR imaging. Polylysine-Gd-DTPA (50,000 Da) and Gd-DTPA. (500-700 Da) were injected into the aorta (alternately) and followed by measurements of T1 relaxation and mean transit time (MTT). Results: In the normal myocardium, MTT of Gd-DTPA (56.8 +/- 23.2 s) was sig nificantly (p=0.02) longer than that of polylysine-Gd-DTPA (29.0 +/- 7 s). However, both normal and infarcted myocardium showed similar MTT (29.0 +/- 7.0 vs. 28.0 +/- 5.0 s, p>0.05) when using polylysine-Gd-DTPA. Conclusion: The results indicate that the permeability of capillaries to po lylysine-Gd-DTPA was not significantly higher in infarcted regions of the m yocardium compared to normal tissue. However, infarcted myocardium displaye d an increased permeability to the small molecular weight Gd-DTPA. We concl ude that microvascular damage may not be sufficient to allow the extravasat ion of polylysine-Gd-DTPA in infarcted myocardium.