MR imaging of contrast-enhanced porcine myocardial infarction. Assessment of reperfusion and tissue viability.

To assess the usefulness of Dy-DTPA-BMA-induced signal reduction, as an indicator of myocardial viability, myocardial infarction was induced in 17 domestic pigs by ligating a diagonal branch of the left anterior descending coronary artery (LAD). In 6 pigs, Dy-DTPA-BMA (1 mmol/kg b.w.) was administered 4 hours after induction of ischaemia. In 5 additional pigs, Gd-DTPA-BMA (0.3 mmol/kg b.w.) and Dy-DTPA-BMA (1 mmol/kg b.w.) were simultaneously injected after 4 hours of ischaemia to ascertain whether Dy-DTPA-BMA counteracted the signal enhancement effect of Gd-DTPA-BMA. A further 6 pigs with infarctions, not administered contrast medium, served as controls. All pigs were sacrificed after 6 hours of ischaemia, and the extirpated hearts were investigated with MR (ex vivo). The concentrations of Dy and Gd were determined in tissue samples from infarcted and non-ischaemic myocardium. The extracellular concentrations of both contrast media were monitored over time during 2 hours in the double-contrast group (in vivo), using a microdialysis technique and analysed by inductively coupled plasma atomic emission spectrometry (ICP-AES). The infarctions demonstrated a high SI in the proton density- and T2-weighted sequences, in both the Dy-DTPA-BMA and control groups, although the former group demonstrated a 3-fold greater concentration of Dy in infarcted compared with non-ischaemic myocardium. Dy-DTPA-BMA did not counteract the Gd-DTPA-BMA-induced enhancement of the infarcted tissue despite a 3-fold higher concentration. This lack of detectable susceptibility effects of Dy may be caused by a loss of cell membrane integrity in the infarcts, resulting in a homogeneous intra- and extracellular distribution of the contrast agent. This hypothesis of an expanded volume of distribution in infarcted tissue was further supported by the microdialysis data, demonstrating a similar extracellular concentration of contrast agents in infarcted and non-ischaemic myocardium, despite a proven 3-fold greater concentration in infarcted tissue samples. To investigate whether Gd-DTPA-BMA-enhanced MR imaging (ex vivo) permits differentiation between reperfused and non-reperfused myocardial infarction, and whether Dy-DTPA-BMA-enhanced MR imaging enables a differentiation between reversible and irreversible myocardial injury following reperfusion, myocardial infarction was induced in 24 domestic pigs (divided into 4 groups) by placing a patched ligature around a diagonal branch of the LAD. Four additional hearts were reperfused after 2 min of brief occlusion, not long enough to cause irreversible injury.(ABSTRACT TRUNCATED AT 250 WORDS)