Intramural funding was provided for this project by the Division of Intramural Research, National Heart, Lung and Blood Institute at the National Institutes of Health. We would like to acknowledge Dr. James Hawkins, Dr. Robert Hoyt, The NIH Division of Veterinary Resources and the staff of the Cardiothoracic Surgery Research program at the NIH.

The procedures described here were approved by the National Heart, Lung, and Blood Institute Animal Care and Use Committee at the National Institutes of Health and conform to the policies outlined in The Public Health Service Policy on Humane Care and Use of Laboratory Animals, The Animal Welfare Act, and the Guide for the Care and Use of Laboratory Animals.
NOTE: The purpose of this surgical procedure is to produce an animal model of chronic myocardial ischemia that can be used to develop treatments that are clinically relevant for patients with severe CAD. This cannot be accomplished using an in vitro model.
1. Animals
<ol>
	<li>Use male Yorkshire swine weighing between 12 and 15 kg.</li>
</ol>
2. Pre-surgical Procedures
<ol>
	<li>For a prophylactic antibiotic, use amoxicillin and clavulanate potassium (15 mg/kg) orally twice a day beginning 24 h prior to surgery. 
	NOTE: This oral antibiotic is started before surgery to make sure that the pig will swallow it and to also make sure that they will not have an allergic reaction to the medication post-operatively.</li>
	<li>Withhold food and water from the pig 12 h prior to surgery.</li>
	<li>On the day of surgery, anesthetize the pig with a cocktail of ketamine (33 mg/kg), midazolam (0.5 - 0.75 mg/kg), and glycopyrrolate (0.01 mg/kg) given intramuscular (IM).</li>
	<li>Place a 20 G intravenous (IV) catheter in an ear vein and intubate the animal with a 7.0 Fr endotracheal tube. 
	NOTE: Adjust the size of the IV catheter and the endotracheal tube as appropriate for the size of the pig.</li>
	<li>Remove the hair (shave) on the left side of the pig from the shoulder to the umbilicus and from the abdominal midline to the vertebral column.</li>
	<li>Administer the prophylactic antibiotics (piperacillin and tazobactam: 100 mg/kg IV) and pain medication (buprenorphine sustained release: 0.2 mg/kg subcutaneous (SC) or a fentanyl transdermal patch 25-50 &#181;g/h). 
	NOTE: The IV antibiotic is given because the animals are fasted for 12 h prior to surgery and do not receive the previously mentioned oral antibiotic during this time.</li>
	<li>Transport the pig to the operating room and connect the endotracheal tube to the anesthesia machine equipped with a sidestream sensor to monitor the airway gases. Mechanically ventilate the pig using a tidal volume of 10 mL/kg as a starting point and do not exceed an airway pressure of 30 cm H2O. Set the respiratory rate between 10-20 breaths per min (bpm) and adjust as needed to keep the end-tidal CO2 (PetCO2) levels between 28 and 35 mm Hg. Maintain the anesthesia with either isoflurane (1-3%) or sevoflurane (2-5%).</li>
	<li>Position the pig right-side down on the operating table. Attach all necessary probes to monitor body temperature (BT), electrocardiogram (ECG), pulse oximetry (SpO2), etc.</li>
	<li>Prepare the surgical site via three alternating scrubs with 2% chlorohexidine and 70% alcohol (apply in a circular motion beginning with center and moving outward).</li>
	<li>Drape the surgical site using aseptic technique21.</li>
</ol>
3. Surgical Procedure
<ol>
	<li>Expose the heart through a left thoracotomy.
	<ol>
		<li>Make a skin incision parallel to the 4th and 5th intercostal space about 8 - 9 cm in length using a no. 10 scalpel blade.</li>
		<li>Cut through the latissimus dorsi and serratus ventralis muscles using a pair of curved Metzenbaum scissors and Brown Adson forceps. Use electrocautery to maintain hemostasis as necessary.</li>
		<li>Enter the pleural cavity through the intercostal muscles between the 4th and 5th ribs with the Metzenbaum scissors cutting along the anterior aspect of the 4th rib. To reduce the chance of accidentally damaging the lung, turn the ventilator off on the exhale just prior to entering the pleural cavity. Once the pleural cavity has been breached, turn the ventilator back on.</li>
		<li>Use a small Finochietto retractor to spread the ribs apart, exposing the heart.</li>
	</ol>
	</li>
	<li>Use Debakey forceps to grasp and lift the pericardium. Use Potts scissors to make a small hole in the pericardium, allowing air to enter the pericardial space. Continue the incision with the Potts scissors over the junction of the LAD and LCX arteries.</li>
	<li>Use Babcock forceps to retract the left atrial appendage. Using Debakey and small right angle forceps, dissect the LCX artery from the surrounding tissue prior to or proximal to the 1st&#160;obtuse marginal branch.</li>
	<li>Place two vessel loops under the dissected LCX artery, one at each end. Hold a size 3.0 mm ameroid constrictor with the small right angle forceps and lift the vessel loops to gently guide the LCX artery through the opening of the constrictor. Gently rotate the constrictor so the opening is facing up. Remove the vessel loops. See Figure 1. 
	NOTE: Adequate dissection of the artery is essential to prevent kinking. Select the appropriate sized constrictor for the individual animal. The appropriate sized constrictor will closely encircle the vessel without initially constricting the vessel. Domestic pigs weighing between 12 and 15 kg require ameroid constrictors sized 2.5 - 3.5 mm. The location of the ameroid constrictor on the vessel depends on the desired size of the ischemic area.</li>
	<li>Re-approximate the pericardium and close with 4-0 polypropylene sutures.</li>
	<li>Reestablish the negative thoracic pressure by inserting a 12 Fr chest tube or equivalent in the pleural space with the end exiting out between the layers of closure, generally two intercostal spaces posterior to thoracotomy site. 
	NOTE: Observe the lung for atelectasis before closing the ribs. If any signs of underinflation are observed, re-inflate the lungs manually up to a pressure of 30 mm Hg.</li>
	<li>Close the chest using 1 polypropylene sutures for the intercostal layer, 0 polypropylene sutures for the serratus and fascial layer, 2-0 polypropylene sutures for the subcutaneous layer, and 3-0 polypropylene sutures for the subcuticular layer. Staple or suture the skin.</li>
	<li>Attach a three-way stop cock to the end of the chest tube and evacuate the air in the chest with a 40-60 cc syringe until a negative seal is achieved. Roll the animal onto its sternum or opposite side to facilitate removing all the air. Once the chest maintains negative pressure, remove the chest tube and suture the exit site. If animals are housed singly post-operatively, the incision can be bandaged for several days.</li>
</ol>
4. Post-operative
<ol>
	<li>Following closure, infiltrate the incision along both sides of the thoracotomy site with 0.25% bupivacaine.</li>
	<li>Wean the animal off the ventilator and turn off the anesthesia. Remove the endotracheal tube once the animal is breathing on its own and swallowing.</li>
	<li>Monitor the animal until it is fully recovered (awake and sternal). There should be no abnormalities or arrhythmias on the ECG, the BT should be 38.7 - 39.8 &#176;C, the SpO2 should be 95 - 100%, and the respiratory rate should be 32 - 58 bpm.</li>
	<li>Administer amiodarone (100 mg, orally twice a day) and clopidogrel bisulfate (75 mg, orally once a day) to prevent thrombosis and arrhythmias. Continue with amoxicillin and clavulanate potassium (15 mg/kg) orally twice a day for 10 days post-operation. Post-operative pain is controlled with buprenorphine SR &#160;(sustained release) 0.2 mg/kg. SQ every three days. &#160;The buprenorphine SR may be supplemented with carprofen (4.4 mg/kg) once and &#160;then (2.2 mg/kg) PO or IM BID.</li>
	<li>Keep all bedding and foraging material out of the animal&#39;s housing area until the incision is fully healed.</li>
</ol>

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The authors have no conflict of interest to disclose.

Ameroid constrictors have been used extensively to create animal models of chronic myocardial ischemia, chronic myocardial infarction, and heart failure5,6,7,9,10,11,12,13,15,16,17,18,19,22. Although these models can be created through the use of stents, hydraulic occluders, or fixed stenosis occluders, the prevalence of ameroid use in scientific literature allows researchers to more accurately compare the results of their work with previously published studies5,6,7,9,10,11,12,13,15,16,17,18,19,22. Another advantage of using the ameroid constrictor is that the procedure is relatively straightforward and can be performed successfully by anyone with reasonable surgical skills, and requires no specialized instruments. The other aforementioned methods require greater technical skills and, in the case of the hydraulic occluder, requires intense post-operative monitoring due to the externalized device6,13.
The main limitation of using the ameroid constrictor is the variability in the rate of occlusion9,13. In general, most studies using the ameroid constrictor have found the rate of stenosis to be highest in the first two weeks and then gradually taper off until complete occlusion occurs23,24. Ex vivo studies directly measuring the closure rate of the ameroid lumen have confirmed that the greatest reduction in lumen diameter occurs in the first two weeks and slows thereafter25,26. However, these same studies have also showed that surrounding glucose and protein concentrations can affect the rate and completeness of the ameroid closure, thereby suggesting that in vivo conditions are most likely responsible for the variability in ameroid occlusion rates25,26. Other investigators have suggested that mechanical trauma, inflammation, fibrosis, and thrombus formation caused by the ameroid placement procedure itself may contribute to this variability5,6,25. The latter scenario is most likely the reason for the premature deaths and heart failures observed in this study. It cannot be stressed enough the importance of doing delicate, yet adequate, artery dissection on either side of the ameroid to prevent kinking of the vessel.
Proper placement of the ameroid constrictor is critical to develop an ischemic area of the heart that is large enough to treat but not so large that it results in death. Placing the ameroid constrictor on the LCX before the first obtuse marginal branch appears to work best in Yorkshire pigs. As reported elsewhere, this resulted in an ischemic area of around 25-30% of the left ventricle6. Placing the ameroid any lower resulted in an ischemic area that was inadequate for the specific treatment that was being investigated in this study.
Arrhythmias occurring during the surgical procedure are rare. Administering oral amiodarone post-operation through the end of the study, may prevent arrhythmias during the 2 to 3 weeks post-operation, when the ameroid is closing off. Additionally, caretaking and medical staff should be especially vigilant in noting any coughing during this time, which could be an early sign of pulmonary edema/heart failure.
Over the years, the design of the ameroid constrictor has been improved upon. Ameroids are currently available in numerous sizes allowing the surgeon to select an ameroid that matches the diameter of the vessel to be occluded. The outer ring of the ameroid is available in stainless steel, titanium, or plastic. This is especially important when evaluating the affected hearts using MRI. All metal will cause an artifact on the MRI images. Titanium ameroids cause less of an artifact than stainless steel, while plastic leaves none at all. MRI images showing the difference between a titanium ameroid and a plastic ameroid are shown in Figure 2 and Figure 3, respectively. The artifact on the right side of the heart in Figure 2 is caused by the titanium ring encasing the ameroid. Until recently, the containment ring on the plastic ameroid was too bulky to place around a coronary artery without kinking the vessel. The ameroid constrictor used in this study (see Table of Materials) is a much more streamlined version, which has the same outer diameter as the metal ameroids.

Coronary artery disease (CAD), which leads to myocardial ischemia, is the leading cause of disability, death, and health care costs around the world4 and attributable for approximately 1 out of every 3 deaths in the U.S.1,2,3,4,5,6. Although there have been many advances in both percutaneous and surgical treatments, as many as one third of patients suffering from CAD are ineligible for these treatments due to age, poor health, or suboptimal anatomy4,5,6,7. In order to evaluate new methods of diagnostic imaging or treatment, the development of an appropriate animal model is critical.
When developing an animal model for a disease, the induced disorder should closely emulate the anatomical and physiological characteristics of the disorder in humans8,9. One of the most widely used large animals for cardiovascular studies is the pig. The pig heart is most closely analogous to the human heart in terms of size, anatomy, and physiology3,6. Similar to the human heart, the myocardium of the pig&#39;s heart does not possess an extensive collateral circulation6. Because of this, the pig heart does not tolerate acute coronary occlusion well, but it can tolerate a gradual coronary occlusion. If a coronary artery is slowly occluded, it can be used as a model for chronic myocardial ischemia, chronic myocardial infarction, and heart failure5,6,9,10,11,12,13. Chronic myocardial ischemia can be induced through stent implantation or the placement of a hydraulic occluder, a fixed stenosis occluder, or an ameroid constrictor. There are advantages and disadvantages for all these methods which are outlined in detail in various publications6,9,13 but the most commonly used method is the ameroid placement5,6,10,11.
The ameroid constrictor consists of casein material encased within a stainless steel, plastic, or titanium ring. Once placed around an artery (usually the left anterior descending coronary artery (LAD) or the left circumflex coronary artery (LCX)), the casein material absorbs the surrounding fluid causing the inner lumen to narrow gradually, mimicking the slow stenosis of an artery and resulting finally in full occlusion9,13,14. This procedure used by itself or in conjunction with other methods results in a region of chronic myocardial ischemia and/or infarction of the left ventricle of the heart that has been useful for developing and evaluating new imaging techniques8,10,15, therapeutic treatments7,16,17,18 and surgical procedures19,20.

<table><tbody><tr><td>Anesthesia: ketamine</td><td>Putney, INC</td><td></td><td>Dose: 25mg/kg, IM</td></tr><tr><td>Anesthesia: midazolam</td><td>App Pharmaceuticals</td><td></td><td>Dose: 0.75mg/kg, IM</td></tr><tr><td>Anesthesia: isoflurane</td><td>Baxter</td><td></td><td>Dose: 1-3%, INH</td></tr><tr><td>Antibiotics: amoxicillin and clavulanate potassium</td><td>WG Critical Care</td><td></td><td>Dose: 15mg/kg, IV</td></tr><tr><td>Antibiotics: piperacillin and tazobactam</td><td>Fresenius Kabl</td><td></td><td>Dose: 100mg/kg, PO</td></tr><tr><td>Analgesia: buprenorphine (sustained release)</td><td>Zoo Pharm</td><td></td><td>10mg/ml bottle, Dose: 0.2mg/kg SC</td></tr><tr><td>Analgesia: fentanyl patch</td><td>Mylan</td><td></td><td>Dose: 25-50mcg/hr, TD</td></tr><tr><td>Analgesia: bupivicaine 0.25%</td><td>Hospira</td><td></td><td>Give SC at incision site for analgesia</td></tr><tr><td>Alcohol 70%</td><td>Humco</td><td>NDC 0395-4202-28</td><td>for scrubbing surgical site</td></tr><tr><td>Chlorhexidine scrub 2%</td><td>Vet One</td><td>510083</td><td>for scrubbing surgical site</td></tr><tr><td>Datex-Ohmeda Aestiva /5 anesthesia machine</td><td>GE Healthcare Madison WI.</td><td></td><td></td></tr><tr><td>Pediatric anesthesia circuit</td><td>Westmed</td><td>7-8901</td><td>www.westmedinc.com</td></tr><tr><td>Water blanket</td><td>Cincinnati Sub Zero</td><td>Blanketrol 2</td><td></td></tr><tr><td>EKG</td><td>Medtronics- Physiocontrol</td><td>LifePak 20</td><td></td></tr><tr><td>Oxygen saturation monitor</td><td>GE Healthcare Madison WI.</td><td></td><td></td></tr><tr><td>Temperature probe</td><td>GE Healthcare Madison WI.</td><td></td><td></td></tr><tr><td>Electrical cautery unit</td><td>Valley Labs</td><td>Force 2</td><td>Cut-30 Coag-40</td></tr><tr><td>Endotracheal tube</td><td>Hudson RCI</td><td>HUD510312</td><td>Hudson brand - appropriate size for animal</td></tr><tr><td>Intravenous catheter, size 20 gauge</td><td>Santa Cruz Biotechnology, Inc</td><td>SC-360097</td><td>Fluid and drug administration</td></tr><tr><td>Lactated Ringers Solution</td><td>Hospira</td><td>NDC 0409-7953-03</td><td></td></tr><tr><td>Macro IV drip set 15 drops/ml</td><td>Hospira</td><td>12672-28</td><td></td></tr><tr><td>Surgical gowns</td><td>Kimberly Clark</td><td>90142</td><td></td></tr><tr><td>Utility drapes</td><td>Kimberly Clark</td><td>89731</td><td></td></tr><tr><td>Adult laparotomy drape</td><td>Medline</td><td>DYNJP3004</td><td></td></tr><tr><td>Sterile surgical gloves</td><td>Cardinal Health (Allegiance)</td><td>22537-570</td><td>Size 7 - use appropriate size for surgeon</td></tr><tr><td>Needle mat - sterile</td><td>Medline</td><td>NC30MBR</td><td></td></tr><tr><td>Cautery pencil</td><td>Medline</td><td>ESPB 2000</td><td></td></tr><tr><td>Suction tubing</td><td>Medline</td><td>DYND50251</td><td></td></tr><tr><td>Suction tip; Yankauer</td><td>Medline</td><td>DYND50130</td><td></td></tr><tr><td>Suction cannister</td><td>Cardinal Health (Allegiance)</td><td>65651-220</td><td></td></tr><tr><td>Ameroid constrictors sizes 2.5mm -3.5mm</td><td>Research Instruments SW, Inc.</td><td>760-764-9411</td><td>Types: Stainless steel, titanium, or plastic</td></tr><tr><td>3-way stopcock</td><td>Cardinal Health (Allegiance)</td><td>455991</td><td>For chest tube</td></tr><tr><td>Stomach tube - 18 Fr</td><td>Cardinal Health (Allegiance)</td><td>DC4418</td><td>For chest tube</td></tr><tr><td>60cc syringe</td><td>Cardinal Health (Allegiance)</td><td>SY35060LL</td><td>For chest tube</td></tr><tr><td>3cc syringe</td><td>Cardinal Health (Allegiance)</td><td>SY35003LL</td><td>For post-op analgesia injection</td></tr><tr><td>Skin stapler - 35W</td><td>Ethicon&amp;nbsp; Endo-Surgery</td><td>PMW 35</td><td>skin closure</td></tr><tr><td>Scalpel blade - size #10</td><td>Cardinal Health (Allegiance)</td><td>32295-010</td><td></td></tr><tr><td>Mini silicone vessel loops 1 Pak</td><td>Aspen Surgical</td><td>011001PBX</td><td>for elevating circumflex artery to apply ameroid</td></tr><tr><td>1 (polypropylene) taper</td><td>Ethicon</td><td>BB #8425H</td><td>close ribs</td></tr><tr><td>2-0 (polypropylene) taper</td><td>Ethicon</td><td>SH #8523</td><td>close muscle layers</td></tr><tr><td>4-0 (polypropylene) taper</td><td>Ethicon</td><td>BB #8581H</td><td>close pericardium</td></tr><tr><td>20 gauge needle</td><td>Cardinal Health (Allegiance)</td><td>81-200219</td><td>post-op analgesia injection</td></tr><tr><td>antimicrobial drape</td><td>3M</td><td>6640EZ</td><td></td></tr><tr><td>Finochietto rib retractor - infant size</td><td>Codman</td><td>50-8057</td><td></td></tr><tr><td>Potts-Smith scissors</td><td>Roboz</td><td>RS-6043</td><td></td></tr><tr><td>Babcock forceps</td><td>Roboz</td><td>RS-8022</td><td></td></tr><tr><td>Pean hemostatic forceps curved</td><td>Codman</td><td>30-4565</td><td></td></tr><tr><td>scalpel handle #7</td><td>Codman</td><td>11-5534</td><td></td></tr><tr><td>Brown Adson forceps</td><td>Roboz</td><td>RS-5231</td><td></td></tr><tr><td>Debakey forceps</td><td>Roboz</td><td>RS-7562</td><td></td></tr><tr><td>Mayo scissors</td><td>Roboz</td><td>RS-6870SC</td><td></td></tr><tr><td>Metzenbaum dissecting scissors</td><td>Codman</td><td>36-5011</td><td></td></tr><tr><td>Metzenbaum dissecting scissors</td><td>Codman</td><td>36-5016</td><td></td></tr><tr><td>Mayo-Hegar needle holder</td><td>Codman</td><td>36-2017</td><td></td></tr><tr><td>Ryder needle holder</td><td>Codman</td><td>36-3012</td><td></td></tr><tr><td>Kelly hemostatic forceps</td><td>Roboz</td><td>RS-7130</td><td></td></tr><tr><td>Reynolds hemostatic forcep</td><td>Roboz</td><td>RS-7211</td><td></td></tr><tr><td>Weitlander retractor</td><td>Roboz</td><td>RS-8612</td><td></td></tr><tr><td>Yorkshire domestic pigs</td><td></td><td></td><td></td></tr></tbody></table>

a chronic cardiac ischemia model in swine using an ameroid constrictor

Cardiovascular disease remains the number one cause of mortality in the United States. There are numerous approaches to treating these diseases, but regardless of the approach, an in vivo model is needed to test each treatment. The pig is one of the most used large animal models for cardiovascular disease. Its heart is very similar in anatomy and function to that of a human. The ameroid placement technique creates an ischemic area of the heart, which has many useful applications in studying myocardial infarction. This model has been used for surgical research, pharmaceutical studies, imaging techniques, and cell therapies.
There are several ways of inducing an ischemic area in the heart. Each has its advantages and disadvantages, but the placement of an ameroid constrictor remains the most widely used technique. The main advantages to using the ameroid are its prevalence in existing research, its availability in various sizes to accommodate the anatomy and size of the vessel to be constricted, the surgery is a relatively simple procedure, and the post-operative monitoring is minimal, since there are no external devices to maintain. This paper provides a detailed overview of the proper technique for the placement of the ameroid constrictor.

After analyzing the data obtained from ameroid placement surgeries performed in our facility over a two-year period, we found the survival rate to be 80%. The procedure was performed on 25 Yorkshire pigs weighing between 12 - 15 kg. Of the 25 pigs, 20 survived to the follow-up procedure, 2 fibrillated and died shortly after closing, 2 were euthanized for severe heart failure and pulmonary edema, and 1 had an anesthetic death during a follow-up radiograph. Necropsy revealed an infarcted area of the left ventricle in the animals that died within 24 hours of the procedure. It is suspected but could not be confirmed that the artery kinked due to the presence of the ameroid since the lumen of the ameroid was still open. The ameroids obtained from the animals that were euthanized due to heart failure were examined. There was total closure of the lumen at 18 days.
The surviving animals were imaged by Magnetic Resonance Imaging (MRI) at 28 days post-ameroid placement to measure the heart function and size of the ischemic area. Figure 2 and Figure 3 show the MRI images obtained from a pig with a titanium encased ameroid and a pig with a plastic encased ameroid, respectively. After imaging, a second thoracotomy was performed for either a cell injection or sham procedure. Animals were followed out as long as 16 weeks post-ameroid placement.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56190/56190fig1.jpg" /> 
Figure 1: Images of the pig heart during the ameroid placement procedure. (A) Image of the pig heart showing the LAD, LCX, and obtuse marginal artery (OM). (B) Image of the dissected LCX artery before the ameroid placement. (C) Image of the proper placement of the ameroid around the LCX with the opening of the ameroid facing up or away from the heart. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56190/56190fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56190/56190fig2.jpg" /> 
Figure 2: MRI image of pig heart with a titanium encased ameroid. MRI image of a pig heart taken four weeks after the placement of a titanium encased ameroid constrictor on the LCX artery. The arrow points to the artifact created by the titanium. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56190/56190fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56190/56190fig3.jpg" /> 
Figure 3: MRI image of a pig heart with a plastic encased ameroid. MRI image of a pig heart taken four weeks after the placement of a plastic encased ameroid constrictor on the LCX artery. The arrow points to the ameroid constrictor. No artifact is observed. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56190/56190fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about A Chronic Cardiac Ischemia Model in Swine Using an Ameroid Constrictor at JoVE.com

A Chronic Cardiac Ischemia Model in Swine Using an Ameroid Constrictor

The purpose of this protocol is to demonstrate the placement of a delayed constricting device (an ameroid constrictor) around a coronary artery in a swine model. This device creates an ischemic area of the heart that is useful for studying new diagnostic imaging techniques and new methods of treatment.

Cardiovascular disease remains the number one cause of mortality in the United States. There are numerous approaches to treating these diseases, but ...

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Nanyang Technological University

Research

JoVE Journal

Medicine

10.5K Views.  National Institutes of Health. Het doel van dit protocol is om aan te tonen van de plaatsing van een vertraagde beklemmende apparaat (een ameroid constrictor) rond een hartkransslagader in een varkens-model. Dit apparaat maakt een ischemische ruimte van het hart dat is handig voor het bestuderen van nieuwe diagnostische imaging technieken en nieuwe methodes van behandeling.

Video: A Chronic Cardiac Ischemia Model in Swine Using an Ameroid Constrictor

Myocardial Infarction and Functional Outcome Assessment in Pigs

Introduction of newly discovered cardiovascular therapeutics into first-in-man trials depends on a strictly regulated ethical and legal roadmap. One important prerequisite is a good understanding of all safety and efficacy aspects obtained in a large animal model that validly reflect the human scenario of myocardial infarction (MI). Pigs are widely used in this regard since their cardiac size, hemodynamics, and coronary anatomy are close to that of humans. Here, we present an effective protocol for using the porcine MI model using a closed-chest coronary balloon occlusion of the left anterior descending artery (LAD), followed by reperfusion. This approach is based on 90 min of myocardial ischemia, inducing large left ventricle infarction of the anterior, septal and inferoseptal walls. Furthermore, we present protocols for various measures of outcome that provide a wide range of information on the heart, such as cardiac systolic and diastolic function, hemodynamics, coronary flow velocity, microvascular resistance, and infarct size. This protocol can be easily tailored to meet study specific requirements for the validation of novel cardioregenerative biologics at different stages (i.e. directly after the acute ischemic insult, in the subacute setting or even in the chronic MI once scar formation has been completed). This model therefore provides a useful translational tool to study MI, subsequent adverse remodeling, and the potential of novel cardioregenerative agents.

This protocol describes the porcine myocardial infarction (MI) model using a 90 min closed-chest coronary balloon occlusion of the left anterior descending artery (LAD), followed by reperfusion. Furthermore, the protocol for several outcome parameters, such as cardiac function, hemodynamics, microvascular resistance, and infarct size, are also presented.

Introduction of newly discovered cardiovascular therapeutics into first-in-man trials depends on a strictly regulated ethical and legal roadmap. One ...

Surgical Placement of Catheters for Long-term Cardiovascular Exercise Testing in Swine

This protocol describes the surgical procedure to chronically instrument swine and the procedure to exercise swine on a motor-driven treadmill. Early cardiopulmonary dysfunction is difficult to diagnose, particularly in animal models, as cardiopulmonary function is often measured invasively, requiring anesthesia. As many anesthetic agents are cardiodepressive, subtle changes in cardiovascular function may be masked. In contrast, chronic instrumentation allows for measurement of cardiopulmonary function in the awake state, so that measurements can be obtained under quiet resting conditions, without the effects of anesthesia and acute surgical trauma. Furthermore, when animals are properly trained, measurements can also be obtained during graded treadmill exercise.
Flow probes are placed around the aorta or pulmonary artery for measurement of cardiac output and around the left anterior descending coronary artery for measurement of coronary blood flow. Fluid-filled catheters are implanted in the aorta, pulmonary artery, left atrium, left ventricle and right ventricle for pressure measurement and blood sampling. In addition, a 20 G&#160;catheter is positioned in the anterior interventricular vein to allow coronary venous blood sampling.
After a week of recovery, swine are placed on a motor-driven treadmill, the catheters are connected to pressure and flow meters, and swine are subjected to a five-stage progressive exercise protocol, with each stage lasting 3 min. Hemodynamic signals are continuously recorded and blood samples are taken during the last 30 sec of each exercise stage.
The major advantage of studying chronically instrumented animals is that it allows serial assessment of cardiopulmonary function, not only at rest but also during physical stress such as exercise. Moreover, cardiopulmonary function can be assessed repeatedly during disease development and during chronic treatment, thereby increasing statistical power and hence limiting the number of animals required for a study.

Here we present a protocol to assess cardiopulmonary function in awake swine, at rest and during graded treadmill exercise. Chronic instrumentation allows for repeated hemodynamic measurements uninfluenced by cardiodepressive anesthetic agents.

This protocol describes the surgical procedure to chronically instrument swine and the procedure to exercise swine on a motor-driven treadmill. Early ...

Surgical Swine Model of Chronic Cardiac Ischemia Treated by Off-Pump Coronary Artery Bypass Graft Surgery

Chronic cardiac ischemia that impairs cardiac function, but does not result in infarct, is termed hibernating myocardium (HM). A large clinical subset of coronary artery disease (CAD) patients have HM, which in addition to causing impaired function, puts them at higher risk for arrhythmia and future cardiac events. The standard treatment for this condition is revascularization, but this has been shown to be an imperfect therapy. The majority of pre-clinical cardiac research focuses on infarct models of cardiac ischemia, leaving this subset of chronic ischemia patients largely underserved. To address this gap in research, we have developed a well-characterized and highly reproducible model of hibernating myocardium in swine, as swine are ideal translational models for human heart disease. In addition to creating this unique disease model, we have optimized a clinically relevant treatment model of coronary artery bypass surgery in swine. This allows us to accurately study the effects of bypass surgery on heart disease, as well as investigate additional or alternate therapies. This model surgically induces single vessel stenosis by implanting a constrictor on the left anterior descending (LAD) artery in a young pig. As the pig grows, the constrictor creates a gradual stenosis, resulting in chronic ischemia with impaired regional function, but preserving tissue viability. Following the establishment of the hibernating myocardium phenotype, we perform off-pump coronary artery bypass graft surgery to revascularize the ischemic region, mimicking the gold-standard treatment for patients in the clinic.

This protocol presents a surgical large animal model of chronic, single vessel ischemia that results in regional abnormalities but does not create infarct, known as hibernating myocardium. Following establishment of chronic ischemia, animals are treated with off-pump LIMA-LAD coronary artery bypass graft surgery to revascularize the ischemic tissue.

Chronic cardiac ischemia that impairs cardiac function, but does not result in infarct, is termed hibernating myocardium (HM). A large clinical subset of ...

Standardized Model of Ventricular Fibrillation and Advanced Cardiac Life Support in Swine

Cardiopulmonary resuscitation after cardiac arrest, independent of its origin, is a regularly encountered medical emergency in hospitals as well as preclinical settings. Prospective randomized trials in human subjects are difficult to design and ethically ambiguous, which results in a lack of evidence-based therapies. The model presented in this report represents one of the most common causes of cardiac arrests, ventricular fibrillation, in a standardized setting in a large animal model. This allows for reproducible observations and various therapeutic interventions under clinically accurate conditions, hence facilitating the generation of better evidence and eventually the potential for improved medical treatment.

Cardiopulmonary resuscitation and defibrillation are the only effective therapeutic options during cardiac arrest caused by ventricular fibrillation. This model presents a standardized regimen to induce, assess, and treat this physiological state in a porcine model, thus providing a clinical approach with various opportunities for data collection and analysis.

Cardiopulmonary resuscitation after cardiac arrest, independent of its origin, is a regularly encountered medical emergency in hospitals as well as ...

Novel Percutaneous Approach for Deployment of 3D Printed Coronary Stenosis Implants in Swine Models of Ischemic Heart Disease

Minimally invasive methods for creating models of focal coronary narrowing in large animals are challenging. Rapid prototyping using three-dimensionally (3D) printed coronary implants can be employed to percutaneously create a focal coronary stenosis. However, reliable delivery of the implants can be difficult without the use of ancillary equipment. We describe the use of a mother-and-child coronary guide catheter for stabilization of the implant and for effective delivery of the 3D printed implant to any desired location along the length of the coronary vessel. The focal coronary narrowing was confirmed under coronary cineangiography and the functional significance of the coronary stenosis was assessed using gadolinium-enhanced first-pass cardiac perfusion MRI. We showed that reliable delivery of 3D printed coronary implants in swine models (n = 11) of ischemic heart disease can be achieved through repurposing mother-and-child coronary guide catheters. Our technique simplifies the percutaneous delivery of coronary implants to create closed-chest swine models of focal coronary artery stenosis and can be performed expeditiously, with a low procedural failure rate.

We describe a novel, cost-effective, and efficient technique for percutaneous delivery of three-dimensionally printed coronary implants to create closed-chest swine models of ischemic heart disease. The implants were fixed in place using a mother-and-child extension catheter with high success rate.

Minimally invasive methods for creating models of focal coronary narrowing in large animals are challenging. Rapid prototyping using three-dimensionally ...

An Intact Pericardium Ischemic Rodent Model

This protocol has shown that the pericardium and its contents play an essential anti-fibrotic role in the ischemic rodent model (coronary ligation to induce myocardial injury). The majority of pre-clinical myocardial infarction models require the disruption of pericardial integrity with loss of the homeostatic cellular milieu. However, recently a methodology has been developed by us to induce myocardial infarction, which minimizes pericardial damage and retains the heart&#39;s resident immune cell population. An improved cardiac functional recovery in mice with an intact pericardial space following coronary ligation has been observed. This method provides an opportunity to study inflammatory responses in the pericardial space following myocardial infarction. Further development of the labeling techniques can be combined with this model to understand the fate and function of pericardial immune cells in regulating the inflammatory mechanisms that drive remodeling in the heart, including fibrosis.

This protocol outlines the steps for inducing myocardial infarction in mice while preserving the pericardium and its contents.

This protocol has shown that the pericardium and its contents play an essential anti-fibrotic role in the ischemic rodent model (coronary ligation to ...

Large Animal Model for Evaluating the Efficacy of the Gene Therapy in Ischemic Heart

Coronary artery disease is one of the significant causes of mortality and morbidity worldwide. Despite the progression of current therapeutics, a considerable proportion of coronary artery disease patients remain symptomatic. Gene therapy-mediated therapeutic angiogenesis offers a novel therapeutic method for improving myocardial perfusion and relieving symptoms. Gene therapy with different angiogenic factors has been studied in few clinical trials. Due to the novelty of the method, the progress of myocardial gene therapy is a continuous path from bench to bedside. Therefore, large animal models are needed for evaluating the safety and efficacy. The more the large animal model identifies the original disease and the endpoints used in clinics, the more predictable outcomes are from clinical trials. Here, we introduce a large animal model for evaluating the efficacy of the gene therapy in the ischemic porcine heart. We use clinically relevant imaging methods such as ultrasound imaging and 15H2O-PET. For targeting the gene transfers into the desired area, electroanatomical mapping is used. The aim of this method is: (1) to mimic chronic coronary artery disease, (2) to induce therapeutic angiogenesis at hypoxic areas of the heart, and (3) to evaluate the safety and efficacy of the gene therapy by using relevant endpoints.

Myocardial gene therapy for ischemic heart disease holds great promise for future therapeutics. Here, we introduce a large animal model for evaluating the efficacy of gene therapy in the ischemic heart.

Coronary artery disease is one of the significant causes of mortality and morbidity worldwide. Despite the progression of current therapeutics, a ...

Myocardial Infarction by Percutaneous Embolization Coil Deployment in a Swine Model

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) 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 ...

Swine Models of Aneurysmal Diseases for Training and Research

Large animal models, specifically swine, are widely used to research cardiovascular diseases and therapies, as well as for training purposes. This paper describes two different aneurysmal swine models that may help researchers to study new therapies for aneurysmal diseases. These aneurysmal models are created by surgically adding a pouch of tissue to carotid arteries in swine. When the model is used for research, the pouch must be autologous; for training purposes, a synthetic pouch suffices.
First, the right external jugular vein (EJV) and right common carotid artery (CCA) must be surgically exposed. The EJV is ligated and a vein pouch fashioned from a short segment. This pouch is then sutured to an elliptical arteriotomy performed in the CCA. Animals must be kept heparinized during model creation, and local vasodilators may be used to decrease vasospasms. Once the suture is completed, correct blood flow should be inspected, checking for bleeding from the suture line and vessel patency. Finally, the surgical incision is closed by layers and an angiography performed to image the aneurysmal model.
A simplification of this aneurysmal carotid model that decreases invasiveness and surgical time is the use of a synthetic, rather than venous, pouch. For this purpose, a pouch is tailored in advance with a segment of a polytetrafluoroethylene (PTFE) prosthesis, one end of which is sutured close using polypropylene vascular suture and sterilized prior to surgery. This "sac" is then attached to an arteriotomy performed in the CCA as described. 
Although these models do not reproduce many of the physiopathological events related to aneurysm formation, they are hemodynamically similar to the situation found in the clinical setting. Therefore, they can be used for research or training purposes, allowing physicians to learn and practice different endovascular techniques in animal models that are close to the human system.

Description of two different aneurysmal swine models for neuroradiology training courses and research studies. This study provides evidence of the feasibility of these aneurysm porcine model creations and the reproducible methods that are close to the clinical setting.

Large animal models, specifically swine, are widely used to research cardiovascular diseases and therapies, as well as for training purposes. This paper ...

Ascending Aortic Banding for Studying Pressure-Overload Induced Heart Failure

A Minimally Invasive Model of Aortic Stenosis in Swine

Large animal models of heart failure play an essential role in the development of new therapeutic interventions due to their size and physiological similarities to humans. Efforts have been dedicated to creating a model of pressure-overload induced heart failure, and ascending aortic banding while still supra-coronary and not a perfect mimic of aortic stenosis in humans, closely resembling the human condition.
The purpose of this study is to demonstrate a minimally invasive approach to induce left ventricular pressure overload by placing an aortic band, precisely calibrated with percutaneously introduced high-fidelity pressure sensors. This method represents a refinement of the surgical procedure (3Rs), resulting in homogenous trans-stenotic gradients and reduced intragroup variability. Additionally, it enables swift and uneventful animal recovery, leading to minimal mortality rates. Throughout the study, animals were followed for up to 2 months after surgery, employing transthoracic echocardiography and pressure-volume loop analysis. However, longer follow-up periods can be achieved if desired. This large animal model proves valuable for testing new drugs, particularly those targeting hypertrophy and the structural and functional alterations associated with left ventricular pressure overload.

Author Spotlight: Development of a Minimally Invasive Large-Animal Model for Reliable and Reproducible Cardiovascular Research 

This protocol describes a minimally invasive surgical procedure for ascending aortic banding in swine.

Large animal models of heart failure play an essential role in the development of new therapeutic interventions due to their size and physiological ...

A Chronic Cardiac Ischemia Model in Swine Using an Ameroid Constrictor

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