A nonthoracotomy myocardial infarction model in an ovine using autologous platelets

Abstract

Objective: There is a paucity of a biological large animal model of myocardial infarction (MI). We hypothesized that, using autologous-aggregated platelets, we could create an ovine model that was reproducible and more closely mimicked the pathophysiology of MI.

Methods: Mepacrine stained autologous platelets from male sheep (n = 7) were used to create a myocardial infarction via catheter injection into the mid-left anterior descending (LAD) coronary artery. Serial daily serum troponin measurements were taken and tissue harvested on post-embolization day three. Immunofluorescence microscopy was used to detect the mepacrine-stained platelet-induced thrombus, and histology performed to identify three distinct myocardial (infarct, peri-ischemic "border zone," and remote) zones.

Results: Serial serum troponin levels (μg/mL) measured 0.0 ± 0.0 at baseline and peaked at 297.4 ± 58.0 on post-embolization day 1, followed by 153.0 ± 38.8 on day 2 and 76.7 ± 19.8 on day 3. Staining confirmed distinct myocardial regions of inflammation and fibrosis as well as mepacrine-stained platelets as the cause of intravascular thrombosis.

Conclusion: We report a reproducible, unique model of a biological myocardial infarction in a large animal model. This technique can be used to study acute, regional myocardial changes following a thrombotic injury.

Figure 1

Electrocardiogram (ECG) readings during embolization. Myocardial infarction verification through electrocardiogram changes. Representative electrocardiogram (ECG) readings from Lead II during the embolization procedure in one animal showing (a) baseline, or preembolization ECG showing absence of ischemia, and (b) 3 minute-post embolization showing “tombstone” or significantly elevated ST segments consistent with a large anterior infarction.

Figure 2

Pre- and postembolization angiograms and infarct area at cardiectomy. Illustrative example of embolization and corresponding area of infarctionat cardiectomy. (a) Preembolization angiogram showing the relationship of the nativeovine coronary anatomy and selection of embolization target of the LAD. (b) Area of thrombus formation immediately postembolization (note that ∗ corresponds to the location of embolization injection). (c) Final pathology showing the corresponding area of infarction (note that ∗ once again shows area of embolization with arrows demarcating the area effected by infarction).

Figure 3

Histological analysis highlighting the three distinct zones of myocardium post-embolization. Representative regional myocardial histology (20x magnification). (a) Infarct tissue showing significant area of inflammation (H&E) and fibrosis (Masson's trichrome), (b) border zone myocardium showing the transition (delineated by blocked arrows) between normal myocytes (top) and ischemic tissue (bottom), and (c) remote zone showing normal myocardial cell structure and no fibrosis.

Figure 4

Intravascular thrombus confirmation with mepacrine-labeled platelets. Representative intravascular thrombus secondary to mepacrine-labeled platelet embolization (magnification 63x). (a) H&E showing inflammation and intravascular thrombus. (b) Masson's trichrome showing early fibrosis and organization of immature collagen deposition. (c) Immunohistochemistry showing intravascular presence of mepacrine labeled platelets.