Myocardial infarction (MI) animal models that emulate the natural process of the disease in humans are crucial to understanding pathophysiological mechanisms and testing the safety and efficacy of new emergent therapies. Here, we describe an MI swine model created by deploying a percutaneous embolization coil.
Myocardial infarction (MI) is the leading cause of mortality worldwide. Despite the use of evidence-based treatments, including coronary revascularization and cardiovascular drugs, a significant proportion of patients develop pathological left-ventricular remodeling and progressive heart failure following MI. Therefore, new therapeutic options, such as cellular and gene therapies, among others, have been developed to repair and regenerate injured myocardium. In this context, animal models of MI are crucial in exploring the safety and efficacy of these experimental therapies before clinical translation. Large animal models such as swine are preferred over smaller ones due to the high similarity of swine and human hearts in terms of coronary artery anatomy, cardiac kinetics, and the post-MI healing process. Here, we aimed to describe an MI model in pig by permanent coil deployment. Briefly, it comprises a percutaneous selective coronary artery cannulation through retrograde femoral access. Following coronary angiography, the coil is deployed at the target branch under fluoroscopic guidance. Finally, complete occlusion is confirmed by repeated coronary angiography. This approach is feasible, highly reproducible, and emulates the pathogenesis of human non-revascularized MI, avoiding the traditional open-chest surgery and the subsequent postoperative inflammation. Depending on the time of follow-up, the technique is suitable for acute, sub-acute, or chronic MI models.
Myocardial infarction (MI) is the most prevalent cause of mortality, morbidity, and disability worldwide1. Despite current therapeutic advances, a significant proportion of patients develop adverse ventricular remodeling and progressive heart failure following MI, resulting in poor prognosis due to ventricular dysfunction and sudden death2,3,4. New therapeutic options to repair and/or regenerate injured myocardium are thus under scrutiny, and translational MI animal models are crucial in testing their safety and efficacy. Although several models have been used for cardiovascular research, including rats5,6, mice7,8, dogs9, and sheep10, pigs are one of the best choices for modeling cardiac ischemia studies because of their high similarity to humans in terms of heart size, coronary artery anatomy, cardiac kinetics, physiology, metabolism, and the post-MI healing process11,12,13,14,15.
In this context, many different open-surgical and percutaneous approaches are available to develop MI swine models. The open-chest approach involves a left lateral thoracotomy procedure and is useful in performing surgical coronary artery ligation16,17, myocardial cryo-injury, cauterization12, and coronary artery placement of a hydraulic occlude18 or an ameroid constrictor19, among others. Surgical coronary occlusion has been extensively used to test new therapeutic options such as cardiac tissue engineering and cell therapy, as it allows wide access and visual assessment of the heart; however, in contrast to human MI, it can result in surgical adhesions, adjacent scarring, and postoperative inflammation17. Myocardial cryo-injury and cauterization are easily reproducible techniques but do not reproduce the pathophysiological MI progression observed in humans12. On the other hand, several percutaneous techniques have been developed to produce temporary or permanent coronary blocking. These comprise transcoronary or intracoronary ethanol ablation20,21, occlusion by balloon angioplasty22, or delivery of thrombogenic materials such as agarose gel beads23, fibrinogen mixtures9, or coil embolization17,24. While balloon angioplasty is better suited for ischemia/reperfusion studies, coronary coil deployment is one of the best choices for modeling non-revascularized MI. This percutaneous approach is feasible, consistently reproducible, and avoids open-chest surgery. It allows precise control of the infarct location and results in pathophysiology similar to that of a human non-reperfused MI. Moreover, coil embolization is suitable for modeling acute, sub-acute, or chronic MI; chronic congestive heart failure; or valvular disease17.
The present protocol aims to describe how to develop an MI swine model by permanent coil deployment. Briefly, it comprises a percutaneous selective coronary artery cannulation through retrograde femoral access. Following coronary angiography, a coil is deployed at the target branch artery under fluoroscopic guidance. Finally, complete occlusion is confirmed by repeated coronary angiography.
This study was approved by the Animal Experimentation Unit Ethical Committee of the Germans Trias i Pujol Health Research Institute (IGTP) and Government Authorities (Generalitat de Catalunya; Code: 10558 and 11208), and complies with all guidelines concerning the use of animals in research and teaching as defined by the Guide for the Care and Use of Laboratory Animals25.
1. Preprocedural preparation of animals
2. Sedation, anesthesia, and analgesia
3. Hemodynamic monitoring and preparation of the surgical area
4. Vascular access
5. Coronary angiography
6. Coil implantation
7. End of procedure
8. Postoperative procedure and animal recovery
9. Postoperative pain assessment and monitoring
10. Euthanasia method
MI survival rates and location
Fifty-seven pigs underwent coronary coil implantation in the LCX marginal branch (n = 25; 12 females and 13 males) or in the LAD between the first and the second diagonal branches (n = 32; 16 females and 16 males) of the coronary artery and were followed up for 30 days. The survival rate of animals submitted to an MI at the LCX marginal branch was 80% (n = 20). Three pigs died as a result of fatal complications related to atrioventricular (AV) block and asystole before coil deployment, and 2 pigs died after ventricular fibrillation (VF) related to transmural MI after coil placement. The survival rate of animals submitted to MI at LAD was 72% (n = 23): 1 pig died due to an AV block and asystole after coil deployment and 8 animals after VF (5 after coil deployment, 2 at 12-48 h post-MI, and one 26 days post-MI). The survival rates differed between the LCX marginal branch (2-2.5 mm in diameter) and middle LAD (2.5-3 mm in diameter) MI, probably due to the larger infarct extension in the LAD model.
Magnetic resonance imaging (MRI) analysis was performed in all animals 30 days post-MI. Figure 2 illustrates late gadolinium-enhanced MRI images of the LCX marginal branch (Figure 2A,C) and distal LAD (Figure 2B,D) infarct models. As depicted, coil deployment in the LCX marginal coronary artery affects the LV lateral wall, while the interventricular septum is the most affected area in distal LAD placement. These results were also confirmed after heart sectioning (Figure 2E,F).
Figure 1: Coronary angiography, anteroposterior projection. Representative images of pre- (A,B) and post-coil (white arrows) deployment (C,D) in the LCX marginal branch and distal LAD coronary artery. Please click here to view a larger version of this figure.
Figure 2: Magnetic resonance imaging and cardiac tissue sections. Representative T1 3-chamber (A,B) and short-axis (C,D) delayed enhancement images for LCX marginal and distal LAD infarction. Images reveal healthy (black) and infarcted (white) myocardium. Photographs of heart sections after LCX marginal (E) and distal LAD MI (F). Arrows indicate the location and extension of the infarcted area. Scale bar = 1 cm Please click here to view a larger version of this figure.
A coil deployed in a coronary artery provides a reproducible and consistent pre-clinical non-reperfused MI model in swine that can be used to develop and test new cardiovascular therapeutic strategies.
In our hands, mortality at follow-up was 19% related to complications of MI, mostly within the first 24 h of the procedure. All these deaths are related to the natural history of the non-reperfused MI and were the primary outcomes of the study. One of the most critical steps in this protocol relies on the entry of the microcatheter into the coronary arteries. In some cases, microcatheter advancement caused a vagal reaction leading to severe hypotension, AV block, and finally asystole. Nevertheless, this can be avoided by administering an IV bolus of adrenaline (0.001 mg/kg) before advancing the microcatheter. Another complication is the occurrence of malignant arrhythmias that can lead to VF. These episodes usually occur 30 min after MI instauration. We recommend using a lidocaine continuous infusion rate (50-100 µg/kg/min) for at least 1h to reduce the risk of ventricular arrhythmias. As an alternative, a continuous infusion of amiodarone (50-80 µg/kg/min) can be administered. However, if ventricular arrhythmic events occur, we recommend delivering a bolus of lidocaine (1.5–3.5 mg/kg). In case of severe bradycardia, we recommend the administration of atropine bolus (0.01 mg/kg), noradrenaline perfusion (0.05-3 µg/kg/min) for mild or moderate hypotension, and adrenaline (0.03 mg/kg) for severe hypotension, electromechanical dissociation, AV block, or asystole. However, when a VF occurs, a 320J ventricular defibrillation has to be applied with a monophasic cardiac defibrillator and repeated until the animal recovers its cardiac rhythm. When several ventricular defibrillations are needed or asystole occurs, perform manual chest compressions (80-90 compressions/min), depressing the ribcage 4 inches, and connect the animal to the mechanical ventilator under 100% O2.
If the interventional procedure is extended for more than one hour, it is useful to monitor the anticoagulation level with the activated clotting time test to ensure that it is greater than 300 seconds. If it is shorter, an extra dose of heparin should be administered.
In case an occlusive thrombus does not form after coronary artery coil deployment, we recommend the placement of another coil. Another option could be to administrate protamine (1mg/100IU of UFH) to facilitate clot formation, although there is a risk of thrombus formation in the guiding catheter and subsequent embolization during control injection.
Many other occlusion models have been described to simulate MI based on cessation of coronary flow by arterial ligation, an ameroid constrictor, or balloon inflation. However, a deployed coil sets off the coagulation cascade with thrombus formation that occludes the coronary artery. This mechanism simulates as closely as possible the pathophysiology of human MI, compared with other non-invasive techniques like balloon occlusion. Despite the fact that non-reperfused MI results in more extensive scarring, less viable myocardium, and a greater reduction in terms of cardiac function than ischemia-reperfusion models27, it is more suitable for screening anti-inflammatory therapies, reverse cardiac remodeling, and gene or stem cell therapy for the treatment of cardiovascular disease28.
The authors have nothing to disclose.
We express our gratitude to the Center of Comparative Medicine and Bioimaging of Catalonia (CMCiB) and staff for their contribution to the animal model execution. This work was supported by the Instituto de Salud Carlos III (PI18/01227, PI18/00256, INT20/00052), the Sociedad Española de Cardiología, and the Generalitat de Catalunya [2017-SGR-483]. This work was also funded by the Red de Terapia Celular – TerCel [RD16/0011/0006] and CIBER Cardiovascular [CB16/11/00403] projects, as part of the Plan Nacional de I+D+I, and cofunded by the ISCIII-Subdirección General de Evaluación y el Fondo Europeo de Desarrollo Regional (FEDER). Dr. Fadeuilhe was supported by a grant from the Spanish Society of Cardiology (Madrid, Spain).
6-F JR4 0-71"guiding catheter | Medtronic | LA6JR40 | 6F JR4 90 cm Guiding catheter |
Adrenaline 1 mg/mL | B.Braun | National Code (NC). 602486 | Adrenaline |
Atropine 1 mg/mL | B.Braun | NC. 635649 | Atropine |
Betadine | Mylan | NC. 694109-1 | Povidone iodine solution |
Bupaq 0.3 mg/mL | Richter Pharma AG | NC. 578816.6 | Buprenorphine |
Dexdomitor 0.5 mg/mL | Orion Pharma | NC. 576303.3 | Dexmedetomidine |
Draxxin | Zoetis | NC. 576313.2 | Tulathromycin |
EMERALD Guidewire | Cordis | 502-585 | 0.035-inch J-tipped wire |
External defibrillator | DigiCare | CS81XVET | Manual external defibrillator |
Fendivia 100 µg/h | Takeda | NC. 658524.5 | Fentanyl transdermal patch |
Guidewire Introducer Needle 18 G x 7 cm | Argon | GWI1802 | Introducer needle |
Heparine 1% | ROVI | NC. 641647.1 | Heparin |
Hi-Torque VersaTurn F | Abbott | 1013317J | 0.014-inch 200 cm Guidewire |
IsoFlo | Zoetis | 50019100 | Isoflurane |
Ketamidor | Richter Pharma AG, | NC. 580393.7 | Ketamine |
Lidocaine 50 mg/mL | B.Braun | NC. 645572.2 | Lidocaine |
MD8000vet | Meditech Equipment | MD8000vet | Multi-parameter monitor |
Midazolam | Laboratorios Normon | NC. 624437.1 | Midazolam |
Prelude.6F.11 cm (4.3").0.035" (0.89 mm).50 cm (19.7").Double Ended.Stainless Steel.6F.16 | Merit | PSI-6F-11-035 | 6F Vascular sheath |
Propovet Multidosis 10 mg/mL | Zoetis | NC. 579742.7 | Propofol |
RENEGADE STC-18 150/20/STRAIGHT/1RO | Boston Scientific | M001181370 | 150 cm length with 0.017-inch inner diameter Microcatheter |
Ruschelit | Teleflex | 112482 | Endotracheal tube with balloon (#6.5) |
SPUR II | Ambu | 325 012 000 | Airway mask bag unit-ventilation (AMBU) |
Vasofix 20 G | B.Braun | 4269098 | 20 G Cannula |
Visipaque 320 mg/mL USB 10 x 200 mL | General Electrics | 1177612 | Iodinated contrast medium |
VortX-18 Diamond 3 mm/3.3 mm | Boston Scientific | M0013822030 | Coil |
WATO EX-35 | Mindray | WATO EX-35Vet | Anesthesia machine |