Contrast agent distribution in microvascular damage of infarcted pig myocardium

Purpose: We determined whether reperfusion damage was sufficient to allow extravasation of a large molecular weight contrast agent into infarcted pig myocardium. Material and Methods: Five pig hearts were subjected to in situ occlusion of the left anterior descending coronary artery (2 h) followed by reperfusion (1 h). The hearts were excised and perfused in the Langendorff mode for ex 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 significantly ( 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 polylysine-Gd-DTPA was not significantly higher in infarcted regions of the myocardium compared to normal tissue. However, infarcted myocardium displayed an increased permeability to the small molecular weight Gd-DTPA. We conclude that microvascular damage may not be sufficient to allow the extravasation of polylysine-Gd-DTPA in infarcted myocardium.