Modeling Principle

The Pig Aortic Coarctation Model is a SCI gold-standard large-animal pathological model of pressure overload-induced myocardial hypertrophy and heart failure, which is established by controllable surgical ligation constriction on the descending thoracic aorta via thoracotomy. It accurately recapitulates the complete pathological cascade triggered by congenital aortic coarctation and long-term elevated pressure load of hypertension in clinical practice, including persistently elevated left ventricular afterload, compensatory myocardial hypertrophy, hypertrophy and apoptosis of cardiomyocytes, massive deposition of myocardial interstitial collagen, pathological remodeling of ventricular configuration, myocardial fibrosis, impaired diastolic function, and progressive decompensated heart failure in the advanced stage. This model remedies the experimental deficiencies of rodent animals, which have obvious discrepancies with humans in cardiovascular size, ventricular anatomical structure, systemic hemodynamics, myocardial remodeling cycle and coronary microcirculation distribution.

The cardiac atrioventricular anatomical configuration, cardiomyocyte phenotype, myocardial collagen metabolic pathway, activation law of renin-angiotensin-aldosterone system (RAAS), coronary blood supply distribution and systemic pressure response mechanism of juvenile Bama minipigs are highly homologous to the human cardiovascular system. The descending thoracic aorta is exposed via surgical thoracotomy, and fixed-caliber cannula ligation is adopted to create aortic stenosis with a fixed stenosis degree, leading to obstructed blood outflow at the proximal aorta (left cardiac side) and persistently pathological elevation of left ventricular ejection afterload. In the early stage, the ventricle produces compensatory hypertrophy through cardiomyocyte hypertrophy and myofibril thickening to overcome blood flow resistance and stabilize cardiac output. Long-term sustained high pressure load activates RAAS, NF-κB inflammatory pathway and TGF-β1/Smad fibrotic signal axis, inducing myocardial inflammatory infiltration, cardiomyocyte apoptosis and abnormal accumulation of extracellular matrix in myocardial interstitium. The stiffness of left ventricular wall increases accompanied by pathological geometric remodeling of ventricle, and ventricular diastolic dysfunction gradually appears. With the extension of modeling cycle, it progresses to decompensated heart failure phenotypes such as decreased systolic function and systemic circulatory congestion. This model fully recapitulates the classic pathogenic cascade of human pressure overload cardiomyopathy: mechanical aortic stenosis-increased left ventricular afterload-compensatory myocardial hypertrophy-chronic myocardial inflammatory fibrosis-ventricular remodeling-heart failure.

Minipigs possess sufficient large blood vessel and cardiac dimensions, the caliber of aortic coarctation can be accurately quantified and regulated, the process of myocardial remodeling is mild with low individual dispersion, and there is no spontaneous cardiomyopathy. Three-stage pathological phenotypes can be clearly distinguished: early stage of compensatory myocardial hypertrophy, middle stage of ventricular fibrotic remodeling, and terminal stage of decompensated heart failure. It serves as a standardized large-animal gold-standard model for translational researches on the pathogenesis of pressure overload heart failure, cardioprotective drugs, anti-myocardial fibrosis preparations, interventional device therapy for heart failure and targeted intervention of cardiac remodeling.

Modeling Success Criteria

Macroscopic Cardiac Morphology and In-vivo Cardiac Functional Phenotype

Minipigs in the sham control group had normal activity and stable respiration; the general cardiac morphology was regular with normal left ventricular wall thickness, uniform ventricular cavity size and soft ruddy myocardium. At Week 8 terminal point, animals in model group showed decreased exercise tolerance and dyspnea after activity. Gross anatomical observation showed significant thickening of left ventricular wall, narrowed ventricular cavity, increased overall cardiac volume and remarkably elevated heart weight index (heart weight / body weight). The macroscopic phenotype of pressure overload myocardial hypertrophy was obvious with extremely significant statistical difference between groups, which could preliminarily confirm the successful construction of aortic coarctation model.

Quantitative Biochemical Gold-Standard Serum Indexes

Serum myocardial injury markers cTnI and CK-MB in the model group were extremely significantly higher than those in the sham group; the activities of RAAS components including Ang Ⅱ, ALD and renin were abnormally elevated; massive release of serum pro-inflammatory factors TNF-α and IL-6 was observed; the contents of TGF-β1 and type Ⅰ/Ⅲ collagen in serum and myocardial tissues were markedly increased, which fully conform to the biochemical diagnostic characteristics of clinical pressure overload cardiomyopathy: myocardial injury, excessive activation of RAAS, chronic low-grade inflammation and abnormal accumulation of myocardial collagen.

Myocardial Histopathological Characteristics

Sequential pathological injury changes induced by aortic coarctation can be observed via combined staining of myocardial tissues with HE, Masson, WGA and TUNEL:

1. Compensatory hypertrophy stage at Week 4 after modeling: enlarged cardiomyocyte volume, regular arrangement of muscle fibers, scattered infiltration of a small number of inflammatory cells, and only a small amount of collagen deposition around blood vessels observed by Masson staining;
2. Remodeling middle stage at Week 6 after modeling: aggravated cardiomyocyte hypertrophy, disordered arrangement of muscle fibers, obvious proliferation of collagen fibers in myocardial interstitium and increased number of TUNEL-positive apoptotic cells;
3. Terminal heart failure stage at Week 8 after modeling: hypertrophic and deformed cardiomyocytes with massive apoptosis, extensive deposition of large-area blue-stained collagen fibers in myocardial interstitium, and myocardial fibers divided and destroyed by collagen tissue, which perfectly recapitulates the progressive pathological changes of myocardial hypertrophy-fibrosis-cardiac function decline caused by increased pressure load in human beings.

Gold-Standard Indexes of Fibrosis and RAAS Signaling Pathway

The RAAS axis in myocardial tissues of the model group was persistently and abnormally activated, and the downstream TGF-β1/Smad fibrotic pathway was overactivated to drive fibroblast transformation and massive collagen synthesis & secretion. The NF-κB-mediated inflammatory pathway remained continuously open, aggravating cardiomyocyte apoptosis and interstitial fibrosis. Sarcomeric proteins increased compensatorily, and the synthesis of myocardial contractile proteins was disordered under long-term load. It accurately matches the complete pathological mechanism induced by mechanical aortic constriction: blood flow obstruction-increased left ventricular afterload-RAAS activation-upregulation of inflammatory and fibrotic pathways-myocardial hypertrophy and remodeling-heart failure, serving as the core academic basis for judging successful model formation.

Model Advantages

This model is a well-recognized exclusive large-animal gold-standard model for pressure overload heart failure prepared by surgical constriction in the field of cardiovascular SCI. The 8-week standardized surgical modeling can stably recapitulate complete pathological phenotypes of heart failure highly homologous to humans, including left ventricular compensatory hypertrophy, myocardial fibrosis, ventricular remodeling and decreased cardiac function. The aortic diameter, ventricular mechanical response, RAAS activation pattern and kinetic process of myocardial remodeling of minipigs are highly consistent with human beings. The progression gradient of lesions is mild and uniform with low intra-group data dispersion, and the experimental repeatability is obviously superior to small animals such as rodents and rabbits. The modeling method adopts physical mechanical stenosis without non-specific myocardial injury interference caused by chemical drugs and hormone intervention, which highly simulates clinical pressure overload cardiomyopathy induced by congenital aortic coarctation and long-term hypertension. Non-invasive echocardiographic follow-up and blood collection can be carried out for many times on a single animal with abundant cardiac tissue samples, which is suitable for preclinical efficacy and safety evaluation of novel cardioprotective drugs, anti-fibrotic preparations, targeted heart failure drugs and ventricular remodeling interventional devices. The data obtained from this model are widely recognized by high-impact SCI journals of cardiovascular medicine, pharmacology and cardiology, which is applicable for National Natural Science Foundation projects, master & doctoral proposal writing, graduation theses of cardiovascular medicine and translational medical researches on regenerative repair of heart failure.

Research Applications

The Pig Aortic Coarctation Model is mainly applied to analyze the basic pathological mechanisms including elevated left ventricular afterload caused by mechanical obstruction, compensatory myocardial hypertrophy, abnormal activation of RAAS system, chronic myocardial inflammatory infiltration, TGF-β1-mediated collagen deposition, pathological ventricular remodeling and the initiation & progression of pressure overload heart failure. It is specially used for screening and verifying small-molecule targeted drugs, active components of traditional Chinese medicine, cardioprotective biological preparations and interventional treatment regimens for ventricular remodeling with functions of inhibiting excessive RAAS activation, alleviating myocardial inflammatory response, blocking the activation of myocardial fibroblasts, reducing abnormal collagen deposition, reversing ventricular remodeling, improving myocardial systolic and diastolic function and delaying the progression of heart failure. It is widely adopted for excavation of pathogenic molecular targets of pressure overload heart failure, elucidation of interactive regulatory network between myocardial hypertrophy and fibrosis, as well as preclinical in-vivo efficacy verification of anti-heart failure drugs and medical devices in large animals. It acts as an essential and scarce standardized large-animal gold-standard model in the fields of cardiovascular pharmacology, pathophysiology of heart failure and intervention of cardiac remodeling.

pig aortic coarctation model, surgical thoracic aortic constriction, pressure overload heart failure, myocardial hypertrophy, left ventricular remodeling, cardioprotective drug & ventricular remodeling intervention preclinical evaluation