Establishment and Characterization of an Experimental Model of Coronary Thrombotic Microembolism in Rats

Abstract

To establish a model of coronary thrombotic microembolism in rats, either automicrothrombotic particulates (CM group) or saline control (SHAM group) was injected into temporarily clamped aortas of male Sprague-Dawley rats. After automicrothrombotic particulate injection, serum c-troponin I and von Willebrand factor levels, the no-flow area as evaluated by Thioflavin S, myocardial leukocyte infiltration levels, myocardial expressions of tumor necrosis factor ␣ and interleukin-6, the percentage of arterioles obstructed by thrombosis, and myocardial fibrosis were all significantly increased whereas cardiac function as evaluated by echocardiography and hemodynamic measurements were significantly reduced compared with the sham group. Thus, aortic automicrothrombotic particulate injection could induce coronary microembolism in rats, and this model could be of value in improving the understanding of pathophysiology of coronary microembolism. Atherosclerotic plaque rupture is a key event in the pathogenesis of acute coronary syndrome and during coronary interventions.1 It does not always result in complete thrombotic occlusion of the epicardial coronary artery with subsequent impending myocardial infarction, but may in milder forms result in the embolization of atherosclerotic and thrombotic debris into the coronary microcirculation, which has recently been identified as a potential cause of no-reflow phenomenon, myocardium ischemia, and myocardial infarctlet. Atherosclerotic embolization in the microvasculature is associated with adverse prognosis. [1][2][3][4] Research results derived from suitable experimental models of coronary microembolism would help clinicians to understand the underlying pathological mechanisms and to develop effective therapies of coronary microembolism induced by atherosclerotic embolization in the microvasculature.5 Until now, plastic microspheres ranging from 20 to 900 m in diameter were injected into the coronary microcirculation to establish the coronary microembolism models in dog, swine and sheep.6 -11 Experimental models were also made by injecting adenosine-diphosphate or catecholamine to induce platelet aggregation in coronary microcirculation in pigs.12-13 However, injecting microspheres with unique sizing would only occlude respective vessels with comparable sizes, while thrombotic debris in patients might vary greatly in sizing and affect vessels with different diameters. Models using adenosine diphosphate or catecholamine could mimic the platelet aggregation process during coronary microthrombosis but could not reflect the influences of various embolism components of atherosclerotic plaques. Therefore, established coronary microembolism models could only partly mimic the in vivo situation of coronary microthrombosis. In the present study, we showed that coronary microembolism could be induced by intraaortic injection of automicrothrombotic particulates varying in sizing in rats. Increased myocardial inflammatory cells infiltration and fibrosis as well as reduced cardiac function w...

Effects of intravenous diltiazem in a rat model of experimental coronary thrombotic microembolism

“…In our previous study (9), thrombosis was observed at 1 h, peaked at 3 h and decreased at 12 h, while heart rate decreased significantly at 1 min and returned to baseline level at 5 min after the injection of automicrothrombotic particulates. Therefore, diltiazem was infused at doses of 10, 50, 100 or 200 μ g/min/kg (n=8 for each dose) through the tail vein for 175 min with an infuser at 5 min after the automicrothrombotic particulate injection.…”

“…Thirty-two rats were used for the dose-finding pilot study. Forty rats were subjected to an aortic saline injection (sham group, n=40) and 80 rats underwent procedures to induce CME, as described previously (9). Briefly, blood (0.5 ml) was obtained from the ventral tail artery of all rats 1 day prior to surgery (21).…”

“…Briefly, blood (0.5 ml) was obtained from the ventral tail artery of all rats 1 day prior to surgery (21). The blood was left to clot for 1 h and then dried overnight at 37°C (9,22). The dried blood was fragmented into thrombotic particulates with a Sabi Crush Easy Pill Smasher (SABI Co., Palo Alto, CA, USA) for 5 min.…”

“…Previous studies have demonstrated that calcium antagonists are capable of relieving microvascular spasm (17,18) and that the intravascular application of diltiazem may attenuate coronary artery spasms in patients with microvascular angina or acute myocardial infarction with ‘no-reflow’ phenomenon (19,20). In our previous experimental study, a rat CME model was established by the aortic injection of automicrothrombotic particulates (9). In the present study, we examined whether this model is suitable for testing and reflecting the therapeutic effects of drugs that may be capable of attenuating coronary microembolization.…”

Establishment of an experimental angiographic slow coronary flow model by microsphere embolism in swines

“…Clinical studies revealed that patients exhibiting no-reflow following reperfusion therapy for acute myocardial infarction (AMI) were associated with worse prognosis compared to patients without no-flow [1,2]. Currently, the mechanism of no-reflow has been exclusively studied in animal models of coronary artery ligation/ reperfusion [5] and coronary microembolization (CME) [3][4][5] in canine or pig models, as well as in the rat coronary autologous coronary thrombotic microembolism model [6]. However, ischemia/reperfusion model in pig and canine only partly reflects pathological changes of no-reflow, since clinical "no-reflow" phenomenon is largely induced by microemboli [1] but not induced by coronary artery occlusion.…”