A minimally invasive method for induction of myocardial infarction in an animal model using tungsten spirals

A novel experimental thrombotic myocardial infarction and primary angioplasty model in swine

AIMS

We sought to develop a reproducible animal model for acute myocardial infarction (AMI) in adult atherosclerosis-prone pigs.

METHODS AND RESULTS

A coil was placed in the right coronary artery or the left anterior descending artery in 26 downsized spontaneously hypercholesterolaemic pigs and left untreated until thrombotic occlusion. Then, we crossed the thrombotic occlusion with a guidewire, followed by predilatation, thrombus visualisation with optical coherence tomography (OCT) imaging and, finally, deployment of a stent and repeated OCT. After revascularisation, we calculated the index of microcirculatory resistance (IMR). After a feasibility phase (six animals), acute thrombotic occlusion was achieved in all 20 pigs. Eighteen animals were successfully revascularised and survived until sacrifice. Thrombus formation was confirmed by OCT, measurement of thrombin-antithrombin complexes and pathology examination. Myocardial necrosis was confirmed by troponin T elevation, myocardial staining and pathology examination. Distal thrombotic embolisation and microvascular obstruction were supported by increased IMR and pathology examination.

CONCLUSIONS

A porcine model of thrombotic occlusion AMI in miniaturised adult spontaneously atherosclerosis-prone pigs is feasible by percutaneous intracoronary placement of a coil. The reperfusion by angioplasty completed this model which mirrors human pathological conditions with myocardial infarction, necrosis and distal embolisation.

Ischemia/reperfusion injury in male guinea pigs: An efficient model to investigate myocardial damage in cardiovascular complications

Myocardial ischemia/reperfusion (I/R) injury is the major problem that aggravates cardiac damage. Several established animal models fail to explain the similarity in disease mechanism and progression as seen in humans; whereas guinea pig shows high similarity in cardiovascular parameters. Hence, current study is aimed to develop an animal model using guinea pigs that may best correlate with disease mechanism of human myocardial I/R injury. Male guinea pigs were randomized into three groups: normal diet (ND), high fat diet (HFD) and sham; fed with respective diets for 90 days. Myocardial infarction (MI) was induced by ligating left anterior descending artery (LAD) for 30 min followed by 24 h and 7 days of reperfusion in ND and HFD groups. Electrocardiogram (ECG) showed the alterations in electrical conduction during myocardial I/R injury. Elevated levels of lactate dehydrogenase (LDH) and creatine kinase-MB ((CK-MB)) were higher in HFD compared to ND. Inflammatory markers such as tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) were up-regulated in I/R injury animals compared to sham. Fold change of these protein expression levels were higher in HFD compared to ND. Elevated lipid profile and increased aortic wall thickness in HFD animals depicts the risk of developing cardiovascular complications. ECG analysis strongly confirmed MI through changes in sinus rhythm that are reflected in infarcted tissue as verified through TTC staining. Thus the combination of HFD followed by I/R injury proved to be an efficient model to study pathophysiology of myocardial I/R injury with minimal tissue damage and surgical mortality.

Preclinical modeling and multimodality imaging of chronic myocardial infarction in minipigs induced by novel interventional embolization technique

BACKGROUND

This study was designed to establish a chronic myocardial infarction (MI) model in minipigs with a novel coronary sequential balloons-sponge embolism technique.

METHODS

Eighteen healthy minipigs (25-30 kg) were randomly divided into three groups for left anterior descending artery (LAD) occlusion: conventional balloon occlusion group (BO group, temporary balloon occlusion for 60 mins), half-balloon embolism group (HB group), and sequential balloon-balloon-sponge embolism group (BBS group, two half-balloons with one sponge as the embolism clot). The incidence of ventricular fibrillation (VF), total mortality, operating time, and vascular recanalization 3 months post-MI was recorded and compared. Echocardiography, multimodality nuclear medical imaging, and histology staining were applied for the evaluation of infarction.

RESULTS

Thirteen out of 18 minipigs survived after the operation, while 5 animals died with VF (3 in the BO group, 1 in the HB group, and 1 in the BBS group), with an 83.3 % (5/6 minipigs) acute procedural survival rate in embolism groups. The operating duration was 60.0 ± 0.5 mins, 21.4 ± 5.2 mins, and 31.2 ± 4.7 mins in the three groups, respectively. LAD recanalization was found in three animals of the HB group but none in the BBS group by angiography follow-up. The infarct sizes were more stable and larger in the HB group and BBS group than that in the BO group (P < 0.05, n = 13).

CONCLUSIONS

The method of sequential balloons-sponge embolization could induce myocardial infarction with consistent and sustained embolization and gain higher operation success rate and better repeatability in minipigs, which holds a promising method for preclinical MI study.

Comparison of two preclinical myocardial infarct models: coronary coil deployment versus surgical ligation

Background

Despite recent advances, myocardial infarction (MI) remains the leading cause of death worldwide. Pre-clinical animal models that closely mimic human MI are pivotal for a quick translation of research and swine have similarities in anatomy and physiology. Here, we compared coronary surgical ligation versus coil embolization MI models in swine.

Methods

Fifteen animals were randomly distributed to undergo surgical ligation (n = 7) or coil embolization (n = 8). We evaluated infarct size, scar fibrosis, inflammation, myocardial vascularization, and cardiac function by magnetic resonance imaging (MRI).

Results

Thirty-five days after MI, there were no differences between the models in infarct size (P = 0.53), left ventricular (LV) ejection fraction (P = 0.19), LV end systolic volume (P = 0.22), LV end diastolic volume (P = 0.84), and cardiac output (P = 0.89). Histologically, cardiac scars did not differ and the collagen content, collagen type I (I), collagen type III (III), and the I/III ratio were similar in both groups. Inflammation was assessed using specific anti-CD3 and anti-CD25 antibodies. There was similar activation of inflammation throughout the heart after coil embolization (P = 0.78); while, there were more activated lymphocytes in the infarcted myocardium in the surgical occlusion model (P = 0.02). Less myocardial vascularization in the infarction areas compared with the border and remote zones only in coil embolization animals was observed (P = 0.004 and P = 0.014, respectively).

Conclusions

Our results support that surgical occlusion and coil embolization MI models generate similar infarct size, cardiac function impairment, and myocardial fibrosis; although, inflammation and myocardial vascularization levels were closer to those found in humans when coil embolization was performed.

Evaluation of experimental myocardial infarction models via electromechanical mapping and magnetic resonance imaging

The diagnostic characteristics of electromechanical mapping (EMM) were evaluated in porcine myocardial infarction (MI) models with the parallel application of cardiac magnetic resonance imaging (cMRI) from the aspect of different pathophysiology and localization. Balloon occlusion in the left anterior descending coronary artery (LAD balloon group) or coil deployment in the LAD (LAD coil group) or circumflex artery (Cx coil group) was applied percutaneously in 16 domestic pigs. Regional left ventricular viability data were captured via cMRI and EMM. The unipolar voltage (UV) value was significantly decreased in segments containing transmural and subendocardial late enhancement compared with viable segments in the LAD balloon, LAD coil, and Cx coil groups. Receiver operating characteristic analysis revealed area under the curve values of 0.809 and 0.691 in the LAD infarct territory, and 0.864 and 0.855 in the Cx infarct territory for the UV compared with cMRI viability results as transmural late enhancement or viable tissue and subendocardial late enhancement or viable tissue, respectively. In conclusion, the UV value detected the presence of scar tissue with differential transmural extent and which represented proper diagnostic features both in the reperfused and nonreperfused models. This data could provide additional benefit in the clinical use of EMM for diagnostic purposes.

Overview of large animal myocardial infarction models (review)

There are several experimental models for the in vivo investigation of myocardial infarction (MI) in small (mouse, rat) and large animals (dog, pig, sheep and baboons). The application of large animal models raises ethical concerns, the design of experiments needs longer follow-up times, requiring proper breeding and housing conditions, therefore resulting in higher cost, than in vitro or small animal studies. On the other hand, the relevance of large animal models is very important, since they mostly resemble to human physiological and pathophysiological processes. The first main difference among MI models is the method of induction (open or closed chest, e.g. surgical or catheter based); the second main difference is the presence or absence of reperfusion. The former (i.e. reperfused MI) allows the investigation of reperfusion injury and new catheter based techniques during percutaneous coronary interventions, while the latter (i.e. nonreperfused MI) serves as a traditional coronary occlusion model, to test the effects of new pharmacological agents and biological therapies, as cell therapy. The reperfused and nonreperfused myocardial infarction has different outcomes, regarding left ventricular function, remodelling, subsequent heart failure, aneurysm formation and mortality. Our aim was to review the literature and report our findings regarding experimental MI models, regarding the differences among species, methods, reproducibility and interpretation.