Establishing New Porcine Ischemic Cardiomyopathy Model by Transcatheter Ischemia-Reperfusion of the Entire Left Coronary Artery System for Preclinical Experimental Studies

Heart failure associated with ischemic cardiomyopathy (ICM) as a result of myocardial infarction (MI) is an increasing health concern (1). Although a variety of new potential therapies have been reported to have the potential of fundamental therapeutic effects in preclinical animal experimental studies, it is difficult to prove its therapeutic effectiveness in the clinical trials. One of the reasons is that these therapies were not tested in appropriate heart failure models suitable for clinical situations. Thus, preclinical experimental studies using proper animal models are essential prior to clinical application for reassuring feasibility, safety, and therapeutic efficacy of the treatments. However, experimental model with large sized MI introducing global left ventricular (LV) dysfunction (i.e., ICM) has been difficult to develop, because sudden cardiac death frequently occurred in pigs due to fatal arrhythmias and an intolerance of ischemia. Our colleague reported that the model with a coronary ameroid constrictor insufficiently showed the typical physiologic and pathologic characters of ICM, such as global fibrosis in the entire myocardium and progressive dilatation of the LV cavity and deterioration of systolic ventricular function, seen in the clinical scenario where coronary artery was suddenly and repeatedly occluded and then, recanalized spontaneously or by interventional procedures (2). In addition, surgical thoracotomy, which needs to be performed to implant the ameroid ring or occlude coronary arteries externally, will exacerbate procedure-related mortality. Therefore, we hypothesized that ischemia-reperfusion stimuli in the entire left coronary artery system by trans-subcutaneous catheter approach might produce a clinically relevant ICM model appropriately used for preclinical studies with minimal procedure-related mortality. Sixteen female porcine (mini-pigs, 8–10 months old; Japan Farm Co Ltd, Kagoshima, Japan) were used in these experiments. Humane animal care was used in compliance with the “Principles of Laboratory Animal Care” formulated by the National Society for Medical Research and the “Guide for the Care and Use of Laboratory Animals” prepared by the Institute of Animal Resources and published by the National Institutes of Health (Publication No 85-23, revised 1996). Mini-pigs were anesthetized with intravenous administration of ketamine (6 mg/kg) and sodium pentobarbital (10 mg/kg), and maintained with inhaled isoflurane (1.5%) under mechanical ventilation. In a total of eight female pigs, we have developed porcine ICM model by inflating the balloon at the left anterior descending coronary artery (LAD) and the left circumflex artery for 90 min, followed by reperfusion, respectively, using the intracoronary catheter (group A). Under fluoroscopic guidance, a 6-Fr AL 0.75 guide catheter engaged the left main artery though a 10-Fr femoral venous sheath. Using a nonhydrophilic 0.36-mm guidewire, we advanced an over-the-wire 2.75×8 mm balloon into LAD and left circumflex artery, respectively. In another eight pigs, MI was induced by ligating the distal portion of the LAD, followed by placing an ameroid constrictor around the LAD (group B) (2). Procedure-related death occurred in two pigs in group A and two pigs in group B, respectively. Follow-up echocardiography and histologic findings were reported as mean (standard deviation) with analysis by repeated measures analysis of variance (version 16.0, SPSS Inc.). A P value <0.05 was considered statistically significant. Echocardiography showed that LV ejection fraction decreased in group A at 4, 8, and 12 weeks after the procedure, which tended to be lower than that in group B. In addition, LV volumes increased in group A at 4, 8, and 12 weeks after the procedure, which was significantly larger than those in group B. Cavity of LV was enlarged, and myocardial structures were more severely distracted in group A compared with group B, as determined by hematoxylin-eosin staining. The wall thickness of LV was globally thinned in group A, while the presence of LV wall thinning was localized in the anterior wall, which was assigned predominantly to territories of the LAD, and hypertrophy was detected in the posterior wall in group B. Collagen was densely accumulated in the infarct area and globally distributed in the remote area in group A, as assessed by Masson's trichrome staining. Size of infarct area, quantitatively assessed by computer-based planimetry of Masson's trichrome staining, was significantly higher in group A than that in group B at 12 weeks after the procedure (group A vs. B, 33.2%±3.4% vs. 19.4%± 2.8%; P=0.0003) (Fig. 1).FIGURE 1.: Echocardiographic analysis results in group A (blue line) and B (red line). LVEDV (A) and LVESV (B) were enlarged at 4, 8, and 12 weeks after the procedure in group A, which were significantly larger than those in group B. LVEF (C) was decreased at 4, 8, and 12 weeks after the procedure in group A, which tended to be larger in group B. Histologic findings of extirpated hearts (D and E). Macroscopic (×40) views of the heart: hematoxylin-eosin staining (D) and Masson's trichrome staining (E). LVEDV, left ventricular end-diastolic volume; LVESV, left ventricular end-systolic volume; LVEF, left ventricular ejection fraction. n=6 in each group. *P<0.05.The porcine ICM model generated here showed more severe LV remodeling characterized by progressive LV dilatation, associated functional deterioration, and accumulation of extracellular collagen in the entire myocardium, compared with that by ameroid constrictor ring implantation. Importantly, this procedure did not require surgical thoracotomy or produce substantial mortality. This new porcine ICM model would be more appropriate for preclinical studies than the previous models. ACKNOWLEDGMENT The authors thank Mr. Shigeru Matsumi for his excellent technical assistance. Yasuhiro Shudo1 Shigeru Miyagawa1 Satsuki Fukushima1 Atsuhiro Saito1 Naomasa Kawaguchi2 Nariaki Matsuura2 Yoshiki Sawa1 1Department of Cardiovascular Surgery Osaka University Graduate School of Medicine Suita, Osaka, Japan 2Department of Pathology Osaka University Graduate School of Medicine Suita, Osaka, Japan