Myocardial Microinfarction after Coronary Microembolization in Swine: MR Imaging Characterization

Abstract

Purpose:To use first-pass perfusion and delayed-enhanced (DE) magnetic resonance (MR) imaging for the detection of the early effects of coronary microembolization on myocardial perfusion and viability. Materials and Methods:Approval was obtained from the institutional committee on animal research. A hybrid x-ray and MR imaging system was used to guide the endovascular catheter and quantify the left anterior descending coronary artery (LAD) perfusion territory before microembolization and ischemic myocardium and microinfarction after microembolization. The embolic agent was selectively delivered in the LAD in six pigs. First-pass perfusion MR imaging was performed 1 hour and 1 week after microembolization. Microinfarction was measured on DE MR images in beating and nonbeating hearts (high-spatial-resolution sequence) by using extracellular and blood pool MR contrast media and after death. The Wilcoxon signed rank test and correlation analysis were used. Results:The LAD perfusion territory was 35% of left ventricular (LV) mass Ϯ 2 (standard error of the mean). Microembolization caused perfusion deficit in 15.7% of LV mass Ϯ 2.6 compared with that of LAD territory (P ϭ .03). At 1 week, perfusion parameters improved and the extent of hypoperfused territory declined (4.6% of LV mass Ϯ 1.4, P ϭ .03). Microinfarction size expanded from 1.4% of LV mass Ϯ 0.2 at 1 hour to 7.5% of LV mass Ϯ 1.2 at 1 week. In nonbeating hearts and at triphenyltetrazolium chloride staining at 1 week, microinfarction size was 7.6% of LV mass Ϯ 1.4 and 7.2% of LV mass Ϯ 1.5, respectively. There was no correlation between the ejection fraction and the extents of microinfarction or hypoperfused territory. Histopathologic findings confirmed the presence of patchy microinfarction. Conclusion:Coronary microembolization caused persistent decline in myocardial perfusion at first-pass perfusion imaging. DE MR imaging has the potential to help reliably quantify subacute microinfarction. The magnitude of LV dysfunction is not related to the extents of microinfarction or hypoperfused territory. RSNA, 2009 See also Science to Practice in this issue. Note: This copy is for your personal, non-commercial use only. To order presentation-ready copies for distribution to your colleagues or clients, use the Radiology Reprints form at the end of this article. Coronary microemboli fragmented from atherosclerotic plaque in acute coronary syndrome and unstable angina (1,2) and after reperfusion at percutaneous coronary intervention (3-7) cause microinfarction and release of myocardial ischemic markers. It is difficult to separate the effects of reperfusion injury (8) from distal microinfarction after coronary intervention because they overlap in an uncontrolled fashion. Furthermore, invasive physiologic studies (9-12) have shown that the magnitude of left ventricular (LV) dysfunction is not closely related to the mass of microinfarction. Methodologic difficulties have hindered the use of noninvasive techniques in simultaneously measuring and linking microinfarct...

Heterogeneous Microinfarcts Caused by Coronary Microemboli: Evaluation with Multidetector CT and MR Imaging in a Swine Model

“…Eight adult healthy farm pigs (mean weight, 33 kg 6 1 [standard error of the mean ]) were anesthetized with a mixture of 2%-5% isofl urane and oxygen at a rate of 2-3 L/min, as described previously ( 8,9 ). Two animals died within 24 hours after delivery of the embolic materials.…”

“…Microinfarcts are defi ned as bright heterogeneous subregions seen on delayed contrast material-enhanced MR images and pale unstained necrotic subregions seen on histochemically stained specimens (8)(9)(10)(11). In several studies, researchers found heterogeneous microinfarcts in patients ( 2,5,12,13 ) and animals (8-11) on delayed contrastenhanced MR images.…”

“…The mean wall thickening of the microinfarcted segments was calculated and compared with that of the remote segments of the same short-axis section. First-pass perfusion images were used to quantify maximuim upslope, peak signal intensity, and time to peak in the LV blood pool, LAD coronary artery territory with microinfarct scar, and remote myocardium ( 9,25 ). The total extent of heterogeneous microinfarct scar was measured on delayed contrast-enhanced images by thresholding and selecting subregions with a signal intensity or attenuation three standard deviations above the signal intensity or attenuation of remote myocardium ( 9 (24)(25)(26).…”

Large Animal Models of Ischemic Cardiomyopathy: Are They Enough to Bridge the Translational Gap?

“…13 The most common animals used for large animal models are rabbits, dogs, sheep, and pigs. The most frequent procedures used to induce left ventricular dysfunction include coronary ligation and microembolization, 14,15 which create permanent macrovascular and microvascular injury, respectively, and coronary balloon catheter occlusion for various durations, which results in ischemia reperfusion injury. 16,17 The advantages and disadvantages of various large animal models in ischemic cardiomyopathy are detailed in Table 1.…”

“…18 Not surprisingly, the larger infarct sizes, however, resulted in a much higher mortality rate than observed in other models. [14][15][16][17]19 The question remains whether the benefit of larger infarct size outweighs the significant costs of over 50% mortality among instrumented animals.…”