This study was supported by an operating grant from the Canadian Institutes of Health Research (CIHR) to Q.F. (grant #MOP-119600).

Breeding pairs of C57BL/6 and CD-1 IG-S mice were purchased from Charles River. Animals used in this study were handled in accordance with the guidelines of the Canadian Council on Animal Care, and study protocols were approved by the Animal Use Subcommittee at Western University, London, Canada.
1. Animal Care
<ol>
	<li>After birthing is complete and pups have been initially breast-fed by their mother for a few hr, place them in a different cage with a CD-1 foster mother. CD-1 mothers displ...

<ol>
	<li>Rosamond, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Heart+disease+and+stroke+statistics--2008+update:+a+report+from+the+American+Heart+Association+Statistics+Committee+and+Stroke+Statistics+Subcommittee.">Heart disease and stroke statistics--2008 update: a report from the American Heart Association Statistics Committee and Stroke Statistics Subcommittee.</a> Circulation. 117 (4), 25-146 (2008).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Meta-analysis+Global+Group+in+Chronic+Heart+Failure.+The+survival+of+patients+with+heart+failure+with+preserved+or+reduced+left+ventricular+ejection+fraction:+an+individual+patient+data+meta-analysis.">Meta-analysis Global Group in Chronic Heart Failure. The survival of patients with heart failure with preserved or reduced left ventricular ejection fraction: an individual patient data meta-analysis.</a> Eur Heart J. 33 (14), 1750-1757 (2012).</li><li>Soonpaa, M. H., Field, L. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessment+of+cardiomyocyte+DNA+synthesis+in+normal+and+injured+adult+mouse+hearts.">Assessment of cardiomyocyte DNA synthesis in normal and injured adult mouse hearts.</a> Am J Physiol. 272, 220-226 (1997).</li><li>D'Uva, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=ERBB2+triggers+mammalian+heart+regeneration+by+promoting+cardiomyocyte+dedifferentiation+and+proliferation.">ERBB2 triggers mammalian heart regeneration by promoting cardiomyocyte dedifferentiation and proliferation.</a> Nat Cell Biol. 17 (5), 627-638 (2015).</li><li>Oberpriller, J. O., Oberpriller, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Response+of+the+adult+newt+ventricle+to+injury.">Response of the adult newt ventricle to injury.</a> J Exp Zool. 187 (2), 249-253 (1974).</li><li>Poss, K. D., Wilson, L. G., Keating, M. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Heart+regeneration+in+zebrafish.">Heart regeneration in zebrafish.</a> Science. 298 (5601), 2188-2190 (2002).</li><li>Jopling, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Zebrafish+heart+regeneration+occurs+by+cardiomyocyte+dedifferentiation+and+proliferation.">Zebrafish heart regeneration occurs by cardiomyocyte dedifferentiation and proliferation.</a> Nature. 464 (7288), 606-609 (2010).</li><li>Porrello, E. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transient+regenerative+potential+of+the+neonatal+mouse+heart.">Transient regenerative potential of the neonatal mouse heart.</a> Science. 331 (6020), 1078-1080 (2011).</li><li>Haubner, B. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Complete+cardiac+regeneration+in+a+mouse+model+of+myocardial+infarction.">Complete cardiac regeneration in a mouse model of myocardial infarction.</a> Aging. 4 (12), 966-977 (2012).</li><li>Soonpaa, M. H., Kim, K. K., Pajak, L., Franklin, M., Field, L. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cardiomyocyte+DNA+synthesis+and+binucleation+during+murine+development.">Cardiomyocyte DNA synthesis and binucleation during murine development.</a> Am J Physiol. 271, 2183-2189 (1996).</li><li>Li, F., Wang, X., Capasso, J. M., Gerdes, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+transition+of+cardiac+myocytes+from+hyperplasia+to+hypertrophy+during+postnatal+development.">Rapid transition of cardiac myocytes from hyperplasia to hypertrophy during postnatal development.</a> J Mol Cell Cardiol. 28 (8), 1737-1746 (1996).</li><li>Feng, Q., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Elevation+of+an+endogenous+inhibitor+of+nitric+oxide+synthesis+in+experimental+congestive+heart+failure.">Elevation of an endogenous inhibitor of nitric oxide synthesis in experimental congestive heart failure.</a> Cardiovasc Res. 37 (3), 667-675 (1998).</li><li>Xiang, F. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cardiomyocyte-specific+overexpression+of+human+stem+cell+factor+improves+cardiac+function+and+survival+after+myocardial+infarction+in+mice.">Cardiomyocyte-specific overexpression of human stem cell factor improves cardiac function and survival after myocardial infarction in mice.</a> Circulation. 120 (12), 1065-1074 (2009).</li><li>van Kats, J. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Angiotensin-converting+enzyme+inhibition+and+angiotensin+II+type+1+receptor+blockade+prevent+cardiac+remodeling+in+pigs+after+myocardial+infarction:+role+of+tissue+angiotensin+II.">Angiotensin-converting enzyme inhibition and angiotensin II type 1 receptor blockade prevent cardiac remodeling in pigs after myocardial infarction: role of tissue angiotensin II.</a> Circulation. 102 (13), 1556-1563 (2000).</li><li>Mahmoud, A. I., Porrello, E. R., Kimura, W., Olson, E. N., Sadek, H. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surgical+models+for+cardiac+regeneration+in+neonatal+mice.">Surgical models for cardiac regeneration in neonatal mice.</a> Nat Protoc. 9 (2), 305-311 (2014).</li><li>Ahn, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Induction+of+myocardial+infarcts+of+a+predictable+size+and+location+by+branch+pattern+probability-assisted+coronary+ligation+in+C57BL/6+mice.">Induction of myocardial infarcts of a predictable size and location by branch pattern probability-assisted coronary ligation in C57BL/6 mice.</a> Am J Physiol Heart Circ Physiol. 286 (3), 1201-1207 (2004).</li><li>Kao, W. W., Xia, Y., Liu, C. Y., Saika, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Signaling+pathways+in+morphogenesis+of+cornea+and+eyelid.">Signaling pathways in morphogenesis of cornea and eyelid.</a> Ocul Surf. 6 (1), 9-23 (2008).</li><li>Redfors, B., Shao, Y. Z., Omerovic, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Myocardial+infarct+size+and+area+at+risk+assessment+in+mice.">Myocardial infarct size and area at risk assessment in mice.</a> Experimental &amp; Clinical Cardiology. 17 (4), 268-272 (2012).</li><li>Phifer, C. B., Terry, L. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Use+of+hypothermia+for+general+anesthesia+in+preweanling+rodents.">Use of hypothermia for general anesthesia in preweanling rodents.</a> Physiol Behav. 38 (6), 887-890 (1986).</li><li>Jesty, S. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=c-kit++precursors+support+postinfarction+myogenesis+in+the+neonatal,+but+not+adult,+heart.">c-kit+ precursors support postinfarction myogenesis in the neonatal, but not adult, heart.</a> Proc Natl Acad Sci U S A. 109 (33), 13380-13385 (2012).</li><li>Mahmoud, A. I., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Meis1+regulates+postnatal+cardiomyocyte+cell+cycle+arrest.">Meis1 regulates postnatal cardiomyocyte cell cycle arrest.</a> Nature. 497 (7448), 249-253 (2013).</li></ol>

The surgical LAD ligation demonstrated herein is a reliable method to produce MI in neonatal mice. This model provides researchers with a reproducible model with which to study mammalian heart regeneration. Visualization of the coronary vasculature is a key component of this method, ensuring correct suture placement and thus guaranteeing reproducibility. While adult mice do not possess poikilothermic capabilities, the body temperature and metabolic rate of neonatal mice is closely associated with ambient temperature. Fur...

Myocardial infarction (MI) is a leading cause of death worldwide, and remains responsible for about one third of heart failure cases1. While the advent of percutaneous intervention and continuous optimization of the use of thrombolytics has increased reperfusion following MI, cardiomyocyte death and loss of contractile myocardium nevertheless occurs. There also remain large numbers of &#34;no-option&#34; patients who are not candidates for or do not see benefit from these interventions. These patients continue to experience disabling ischemia leading to scar formation and deleterious ventricular remodeling as a mechanism of infarct healing. This process ultimately results in heart failure, for which prognosis remains poor despite optimal pharmacologic management with angiotensin-converting enzyme (ACE) inhibitors and beta blockers. Unfortunately, the one-year mortality rate for patients with severely impaired left ventricular function still remains as high as 26%2. Heart transplant is the final treatment option for patients with heart failure. However, the limited donor pool for heart transplantation does not make this a viable option for most patients. Thus, the discovery of novel therapeutic agents to restore the damaged myocardium remains paramount to solving the cardiac disease problem. Reliable animal models of cardiac injury are therefore required as a critical component of this process.
Traditional dogma has dictated that adult cardiomyocytes are post-mitotic, terminally differentiated cells, incapable of dividing or de-differentiating to replace the damaged myocardium3. As such, an adult mammalian heart could never completely recover from injury, and lost cardiomyocytes would be replaced with fibrous tissue. Thus, research has focused primarily on therapeutic agents to minimize infarct expansion and reduce scar formation. More recently however, a paradigm shift has occurred in the thinking surrounding cardiac healing and many research efforts have been redirected to focus on the potential for cardiac regeneration4.
Until recently, in vivo study of cardiac regeneration was restricted to non-vertebrate models, such as those in urodele amphibians and teleost fish5-7. However, the discovery of the capacity for cardiac regeneration in the neonatal mouse has led to the development of two surgical models of mammalian cardiac regeneration: resection of the cardiac apex and coronary artery occlusion to induce myocardial infarction8,9. In 2011, a mouse apex resection model was used to demonstrate that complete cardiac regeneration is possible at postnatal day 1 (P1). However, this capacity declines rapidly after the initial neonatal period. The mammalian heart loses its regenerative potential shortly after birth at P7 as progenitor cell numbers decline, and cardiomyocytes become binucleated, lose their proliferative competency, and permanently exit the cell cycle10,11. Understanding the fundamental differences between the neonatal and adult mammalian heart may lead to novel insights into cardiac regeneration.
While apex resection indeed offers insight into re-growth of contractile tissue, the model does not simulate typical human cardiac injury, and thus does not lend itself as well to the development of therapeutics. The coronary artery occlusion model, however, more directly simulates the pathophysiologic aspects of MI pathology, and thus may provide more useful insights into mechanisms that may be applicable to therapeutic advancement for human use.
Surgical coronary ligation has been used as a useful experimental technique in many animal models12-14. In the adult coronary artery ligation model, animals are anesthetized and intubated to allow opening of the chest cavity while maintaining respiration. The heart continues to beat regularly, permitting visualization of the coronary vasculature and allowing for accurate suture placement. Furthermore, the heart remains pink as perfusion continues, and after ligation the ischemic myocardium appears pale, indicating successful coronary artery ligation. The protocol described for neonatal mice, however, is less reliable as the coronary artery is not visualized and the surgeon must estimate where to place the suture15. Although the general anatomy of the coronary vasculature is the same, individual animal variability in the direction and branching of the LAD exists16. Thus, when &#34;going in blind,&#34; the artery could be easily missed. Other techniques such as echocardiography are then required to confirm successful induction of MI, and to ensure all surgeries result in a similar infarct size. Described here is an improvement on a recently published method15, where the position of the LAD can be established and thus LAD may be ligated to reproducibly induce MI.
This technique does not require endotracheal intubation or mechanical ventilation, as thoracotomy in a hypothermic state in the neonatal mouse does not result in lung collapse. However, in the previously described method, severe hypothermia must be induced to the point of both complete apnea and cessation of the cardiac rhythm15. The major limitation of this approach is that the coronary artery is no longer perfused and the heart appears pale even before LAD ligation. In the approach described herein, coronary artery visualization is possible at a point of torpor before deep hypothermia and cardiac rhythm cessation, with full recovery of the neonatal mouse after the surgery. This method offers a major advantage of 100% reproducibility.

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			<td height="21" style="height:21px;width:261px;">8-0 Nylon Suture</td>
			<td style="width:244px;">Microsurgery Instruments</td>
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			<td height="37" style="height:38px;width:261px;">11-0 Nylon Suture</td>
			<td style="width:244px;">Shanghai Pudong Medical Products Co Ltd</td>
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			<td height="21" style="height:21px;width:261px;">Fine Scissors</td>
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			<td height="21" style="height:21px;width:261px;">Small forceps</td>
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			<td height="21" style="height:21px;width:261px;">Zeiss Opmi 6s/S3 Microscope</td>
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			<td></td>
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			<td height="21" style="height:21px;width:261px;">Isoflurane Chamber</td>
			<td style="width:244px;">Made in Feng laboratory</td>
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			<td height="21" style="height:21px;width:261px;">Bead Sterilizer</td>
			<td style="width:244px;">Fine Science Tools</td>
			<td style="width:119px;">18000-45</td>
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			<td height="42" style="height:42px;width:261px;">2,3,5-Triphenyltetraolium chloride (TTC)</td>
			<td style="width:244px;">Sigma</td>
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			<td height="22" style="height:23px;width:261px;">Stereomicroscope SteREO Discovery. V8</td>
			<td style="width:244px;">Zeiss</td>
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			<td height="21" style="height:21px;width:261px;">AxioVision 8.0</td>
			<td style="width:244px;">Zeiss</td>
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			<td height="21" style="height:21px;width:261px;">Axiocam Icc5</td>
			<td style="width:244px;">Zeiss</td>
			<td style="width:119px;">426554</td>
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			<td height="21" style="height:21px;width:261px;">Heat pad</td>
			<td style="width:244px;">Sunbeam&#160;</td>
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			<td height="21" style="height:21px;width:261px;">Sterile Gloves</td>
			<td style="width:244px;">VWR</td>
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			<td height="21" style="height:21px;width:261px;">Gauze Sponges</td>
			<td style="width:244px;">Ducare</td>
			<td style="width:119px;">90212</td>
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			<td height="21" style="height:21px;width:261px;">Ice</td>
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myocardial infarction in neonatal mice, a model of cardiac regeneration

Myocardial infarction induced by coronary artery ligation has been used in many animal models as a tool to study the mechanisms of cardiac repair and regeneration, and to define new targets for therapeutics. For decades, models of complete heart regeneration existed in amphibians and fish, but a mammalian counterpart was not available. The recent discovery of a postnatal window during which mice possess regenerative capabilities has led to the establishment of a mammalian model of cardiac regeneration. A surgical model of mammalian cardiac regeneration in the neonatal mouse is presented herein. Briefly, postnatal day 1 (P1) mice are anesthetized by isoflurane and placed on an ice pad to induce hypothermia. After the chest is opened, and the left anterior descending coronary artery (LAD) is visualized, a suture is placed around the LAD to inflict myocardial ischemia in the left ventricle. The surgical procedure takes 10-15 min. Visualizing the coronary artery is crucial for accurate suture placement and reproducibility. Myocardial infarction and cardiac dysfunction are confirmed by triphenyl-tetrazolium chloride (TTC) staining and echocardiography, respectively. Complete regeneration 21 days post myocardial infarction is verified by histology. This protocol can be used to as a tool to elucidate mechanisms of mammalian cardiac regeneration after myocardial infarction.

The myocardial infarction procedure at P1 can be completed in 10 - 15 min and has a mortality rate of 7.8% (5 out of 64 pups). After surgery, mice recover from hypothermic anesthesia within the next 5 - 20 min (time of recovery depends on body temperature reached during anesthesia and speed of surgeon). When using P7 pups (for comparison with a non-regenerative myocardium), a longer period of cooling is required to reach torpor. P7 pups are much larger and have more difficulty recovering ...

Watch this Scientific Journal Video about Myocardial Infarction in Neonatal Mice, A Model of Cardiac Regeneration at JoVE.com

Myocardial Infarction in Neonatal Mice, A Model of Cardiac Regeneration

This protocol describes a highly reproducible model of cardiac regeneration by surgical induction of myocardial infarction in the left ventricle of postnatal day 1 mice. The method involves induction of hypothermic anesthesia and ligation of the left anterior descending coronary artery.

Myocardial infarction induced by coronary artery ligation has been used in many animal models as a tool to study the mechanisms of cardiac repair and ...

The overall goal of this surgical procedure is to reproducibly induce myocardial infarction in neonatal mice. This method can help answer key questions in cardiac regeneration such as what mechanisms support regeneration in neonates and how can adult heart regeneration be promoted after myocardial infarction. The main advantage of this technique is that the left anterior descending coronary artery, or LAD, can be visualized to ensure highly reproducible LAD ligation in the neonatal mouse heart.The changes in cardiac function after LAD ligation can be assessed by echocardiography. Before beginning the procedure place an anesthetized pup in the right lateral decubitus position on ice under the operating microscope and confirm the appropriate level of sedation by a lack of response to toe and tail pinch. Then gently disinfect the chest with povidone iodine followed by an ethanol swab.Next use a pair of forceps to carefully lift the skin between the xiphoid and left axilla and make an incision a few millimeters below the left fore leg. Using scissors cut through the underlying pectoral muscle layer, then open a pair of forceps along the muscles and ribs in the fourth intercostal space to perform a gentle thoracotamy. Visualize the left anterior descending coronary artery emerging from the left auricle behind the pulmonary vein and descending beyond the great cardiac vein.Location of the coronary artery is critical for the reproducibility of the technique. To ensure visualization of the artery maintain the mouse body temperature between eight and 15 degrees Celsius during the procedure. Then use a 007 mL diameter needle to pass an 11-0 nylon suture under the artery through the mid ventricle below the left auricle and ligate the artery.The ischemia is confirmed by the blanching of the myocardium below the suture site. Next use 0.15 mL diameter needles to place two 8-0 nylon rib sutures without tying to ensure both sutures are placed without injury to internal organs such as the lungs. Then tie the rib sutures to close the thoracic incision and move the mouse onto a sterile surgical towel over a 37 degrees Celsius heating pad.Close the muscle and skin with more 8-0 nylon sutures. Then use an ethanol swab to gently remove the povidone iodine and blood. When the animal has fully recovered from the anesthesia wipe it with bedding from the foster mother's cage to reduce the chance of maternal rejection and cannibalization and return the pup to the foster mother.Observe the behavior of the foster mother toward the pup every 10 to 15 minutes for two to three hours to confirm the acceptance of the pup. To measure the myocardial infarct size after four to six hours with the foster mother, the pup is euthanized by isofluorane overdose followed by decapitation. Next, grasp the lower rib cage and cut through the ribs and musculature longitudinally along the left mid axillary line from the diaphragm to the axilla.Holding the scissors at a transverse angle carefully cut through the diaphragm from the left to the right side. Then grasp the rib cage and cut the right side of the ribs and musculature along the right mid axillary line. Use the scissors to remove all of the vascular connections to the heart.Then grasp the base of the heart and remove it from the chest cavity. Using a surgical carbon steel razor blade section the heart along the short axis at the midpoint between the suture and the cardiac apex followed by a second cut at the suture. Then place the sections in 1%TTC at room temperature for 10 to 15 minutes, carefully watching the specimens to avoid overstaining.24 to 48 hours after LAD surgery cardiac function is assessed by echocardiography. Secure the pup in the supine position on a heated dock with its nose in an anesthesia cone and apply pre warmed echo gel to the left thoracic area. Next obtain a peristernal long axis view of the left ventricle below the suture with a 40 Mhz ultrasound probe.Then turn the probe 90 degrees and acquire a parasternal short axis view recording the end mode echocardiographic images. The end diastolic and end systolic left ventricular internal diameters can the be measured from the short axis end mode images. Upon histological examination at three days post myocardial infarction the typical evidence of an infarction including the infiltration of inflammatory cells is observed.At day seven the left ventricular tissue appears normal and by 21 the cardiac tissue has completely regenerated. In a total of 13 left anterior descending coronary artery ligation surgeries, 100%of the hearts were infarcted with an average infarct size of 36%To further confirm the infarct induction echocardiography can be performed 24 and 48 hours after the procedure. In this representative experiment at 24 hours post myocardial infarction the ejection fraction and the fractional shortening were significantly reduced.By 48 hours the ejection fraction and the fractional shortening were further reduced compared to the control animals which demonstrated no reduction at all. Once mastered this technique can be completed in 10 to 15 minutes if it is performed properly. While implementing the myocardial infarction it is important to remember to operate quickly and accurately to ensure the procedure is completed within the time window during which the LAD is visible.Following this procedure other methods like histological analysis can be performed to answer additional questions about how different treatments affect cardiac regeneration. The development of this technique paves the way for researchers in the field of cardiac biology to explore cardiac regeneration in mice. After watching this video you should have a good understanding of how to reproducibly induce myocardial infarction in neonatal mice by visualizing and ligating the LAD.

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18.0K ビュー.  Western University. The overall goal of this surgical procedure is to reproducibly induce myocardial infarction in neonatal mice. This method can help answer key questions in cardiac regeneration such as what mechanisms support regeneration in neonates and how can adult heart regeneration be promoted after myocardial infarction. The main advantage of this technique is that the left anterior descending coronary artery, or LAD, can be visualized to ensure highly reproducible LAD ligation in the neonatal mouse hear...

ビデオ: Myocardial Infarction in Neonatal Mice, A Model of Cardiac Regeneration

Acute Myocardial Infarction in Rats

With heart failure leading the cause of death in the USA (Hunt), biomedical research is fundamental to advance medical treatments for cardiovascular diseases. Animal models that mimic human cardiac disease, such as myocardial infarction (MI) and ischemia-reperfusion (IR) that induces heart failure as well as pressure-overload (transverse aortic constriction) that induces cardiac hypertrophy and heart failure (Goldman and Tarnavski), are useful models to study cardiovascular disease. In particular, myocardial ischemia (MI) is a leading cause for cardiovascular morbidity and mortality despite controlling certain risk factors such as arteriosclerosis and treatments via surgical intervention (Thygesen). Furthermore, an acute loss of the myocardium following myocardial ischemia (MI) results in increased loading conditions that induces ventricular remodeling of the infarcted border zone and the remote non-infarcted myocardium. Myocyte apoptosis, necrosis and the resultant increased hemodynamic load activate multiple biochemical intracellular signaling that initiates LV dilatation, hypertrophy, ventricular shape distortion, and collagen scar formation. This pathological remodeling and failure to normalize the increased wall stresses results in progressive dilatation, recruitment of the border zone myocardium into the scar, and eventually deterioration in myocardial contractile function (i.e. heart failure). The progression of LV dysfunction and heart failure in rats is similar to that observed in patients who sustain a large myocardial infarction, survive and subsequently develops heart failure (Goldman). The acute myocardial infarction (AMI) model in rats has been used to mimic human cardiovascular disease; specifically used to study cardiac signaling mechanisms associated with heart failure as well as to assess the contribution of therapeutic strategies for the treatment of heart failure. The method described in this report is the rat model of acute myocardial infarction (AMI). This model is also referred to as an acute ischemic cardiomyopathy or ischemia followed by reperfusion (IR); which is induced by an acute 30-minute period of ischemia by ligation of the left anterior descending artery (LAD) followed by reperfusion of the tissue by releasing the LAD ligation (Vasilyev and McConnell). This protocol will focus on assessment of the infarct size and the area-at-risk (AAR) by Evan's blue dye and triphenyl tetrazolium chloride (TTC) following 4-hours of reperfusion; additional comments toward the evaluation of cardiac function and remodeling by modifying the duration of reperfusion, is also presented. Overall, this AMI rat animal model is useful for studying the consequence of a myocardial infarction on cardiac pathophysiological and physiological function.

The rat model of acute myocardial infarction (AMI) is useful to study the consequence of a MI on cardiac pathophysiological and physiological function.

With heart failure leading the cause of death in the USA (Hunt), biomedical research is fundamental to advance medical treatments for cardiovascular ...

MRI and PET in Mouse Models of Myocardial Infarction

Myocardial infarction is one of the leading causes of death in the Western world. The similarity of the mouse heart to the human heart has made it an ideal model for testing novel therapeutic strategies.
In vivo magnetic resonance imaging (MRI) gives excellent views of the heart noninvasively with clear anatomical detail, which can be used for accurate functional assessment. Contrast agents can provide basic measures of tissue viability but these are nonspecific. Positron emission tomography (PET) is a complementary technique that is highly specific for molecular imaging, but lacks the anatomical detail of MRI. Used together, these techniques offer a sensitive, specific and quantitative tool for the assessment of the heart in disease and recovery following treatment.
In this paper we explain how these methods are carried out in mouse models of acute myocardial infarction. The procedures described here were designed for the assessment of putative protective drug treatments. We used MRI to measure systolic function and infarct size with late gadolinium enhancement, and PET with fluorodeoxyglucose (FDG) to assess metabolic function in the infarcted region. The paper focuses on practical aspects such as slice planning, accurate gating, drug delivery, segmentation of images, and multimodal coregistration. The methods presented here achieve good repeatability and accuracy maintaining a high throughput.

We describe how to perform MRI and PET imaging of the mouse heart. The protocol is tailored to assess treatment efficacy in models of myocardial infarction and heart failure.

Myocardial infarction is one of the leading causes of death in the Western world. The similarity of the mouse heart to the human heart has made it an ...

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 ...

Minimal Invasive Surgical Procedure of Inducing Myocardial Infarction in Mice

Myocardial infarction still remains the main cause of death in western countries, despite considerable progress in the stent development area in the last decades. For clarification of the underlying mechanisms and the development of new therapeutic strategies, the availability of valid animal models are mandatory. Since we need new insights into pathomechanisms of cardiovascular diseases under in vivo conditions to combat myocardial infarction, the validity of the animal model is a crucial aspect. However, protection of animals are highly relevant in this context. Therefore, we establish a minimally invasive and simple model of myocardial infarction in mice, which assures a high reproducibility and survival rate of animals. Thus, this models fulfils the requirements of the 3R principle (Replacement, Refinement and Reduction) for animal experiments and assure the scientific information needed for further developing of therapeutical strategies for cardiovascular diseases.

A highly reproducible model for myocardial infarction in mice with minimal invasive manipulations is described. The model can be easily performed, resulting in a high reproducibility and survival rate. Thus, the described model will reduce the number of required animals as requested by the 3R principle (Replacement, Refinement and Reduction).

Myocardial infarction still remains the main cause of death in western countries, despite considerable progress in the stent development area in the last ...

Permanent Ligation of the Left Anterior Descending Coronary Artery in Mice: A Model of Post-myocardial Infarction Remodelling and Heart Failure

Heart failure is a syndrome in which the heart fails to pump blood at a rate commensurate with cellular oxygen requirements at rest or during stress. It is characterized by fluid retention, shortness of breath, and fatigue, in particular on exertion. Heart failure is a growing public health problem, the leading cause of hospitalization, and a major cause of mortality. Ischemic heart disease is the main cause of heart failure.
Ventricular remodelling refers to changes in structure, size, and shape of the left ventricle. This architectural remodelling of the left ventricle is induced by injury (e.g., myocardial infarction), by pressure overload (e.g., systemic arterial hypertension or aortic stenosis), or by volume overload. Since ventricular remodelling affects wall stress, it has a profound impact on cardiac function and on the development of heart failure. A model of permanent ligation of the left anterior descending coronary artery in mice is used to investigate ventricular remodelling and cardiac function post-myocardial infarction. This model is fundamentally different in terms of objectives and pathophysiological relevance compared to the model of transient ligation of the left anterior descending coronary artery. In this latter model of ischemia/reperfusion injury, the initial extent of the infarct may be modulated by factors that affect myocardial salvage following reperfusion. In contrast, the infarct area at 24 hr after permanent ligation of the left anterior descending coronary artery is fixed. Cardiac function in this model will be affected by 1) the process of infarct expansion, infarct healing, and scar formation; and 2) the concomitant development of left ventricular dilatation, cardiac hypertrophy, and ventricular remodelling.
Besides the model of permanent ligation of the left anterior descending coronary artery, the technique of invasive hemodynamic measurements in mice is presented in detail.

Heart failure is the leading cause of hospitalization and a major cause of mortality. A model of permanent ligation of the left anterior descending coronary artery in mice is applied to investigate ventricular remodelling and cardiac dysfunction post-myocardial infarction. The technique of invasive hemodynamic measurements in mice is presented.

Heart failure is a syndrome in which the heart fails to pump blood at a rate commensurate with cellular oxygen requirements at rest or during stress. It ...

Primary Outcome Assessment in a Pig Model of Acute Myocardial Infarction

Mortality after acute myocardial infarction remains substantial and is associated with significant morbidity, like heart failure. Novel therapeutics are therefore required to confine cardiac damage, promote survival and reduce the disease burden of heart failure. Large animal experiments are an essential part in the translational process from experimental to clinical therapies. To optimize clinical translation, robust and representative outcome measures are mandatory. The present manuscript aims to address this need by describing the assessment of three clinically relevant outcome modalities in a pig acute myocardial infarction (AMI) model: infarct size in relation to area at risk (IS/AAR) staining, 3-dimensional transesophageal echocardiography (TEE) and admittance-based pressure-volume (PV) loops. Infarct size is the main determinant driving the transition from AMI to heart failure and can be quantified by IS/AAR staining. Echocardiography is a reliable and robust tool in the assessment of global and regional cardiac function in clinical cardiology. Here, a method for three-dimensional transesophageal echocardiography (3D-TEE) in pigs is provided. Extensive insight into cardiac performance can be obtained by admittance-based pressure-volume (PV) loops, including intrinsic parameters of myocardial function that are pre- and afterload independent. Combined with a clinically feasible experimental study protocol, these outcome measures provide researchers with essential information to determine whether novel therapeutic strategies could yield promising targets for future testing in clinical studies.

Reliable and accurate outcome assessment is the key for translation of preclinical therapies into clinical treatment. The current paper describes how to assess three clinically relevant primary outcome parameters of cardiac performance and damage in a pig acute myocardial infarction model.

Mortality after acute myocardial infarction remains substantial and is associated with significant morbidity, like heart failure. Novel therapeutics are ...

Real-time Pressure-volume Analysis of Acute Myocardial Infarction in Mice

Acute myocardial infarction can lead to acute heart failure and cardiogenic shock. The evaluation of hemodynamics is critical for the evaluation of any potential therapeutic approach directed against acute left ventricular (LV) dysfunction. Current imaging modalities (e.g., echocardiography and magnetic resonance imaging) have several limitations since data on LV pressure cannot directly be measured. LV catheterization in mice undergoing coronary artery occlusion could serve as a novel method for a real-time evaluation of LV function.
At the beginning of the procedure, mice were anesthetized followed by endotracheal intubation. For LV catheterization, the right carotid artery was exposed via middle-neck incision. The catheter was introduced and placed into the LV cavity. Left thoracotomy was conducted and the left main coronary artery (LCA) was ligated. To induce reperfusion, the suture was released after 45 min. Pressure-volume data was recorded at all times.
Ligation of the LCA caused a decrease in LV systolic function as evidenced by a 30% reduction in stroke volume, LV ejection fraction (EF), and cardiac output. Maximum dP/dt as a parameter for LV contractility was also significantly reduced and diastolic function was severely impaired (minimum dP/dt -40%). Reperfusion over a period of 20 min did not lead to a complete recovery of LV function.
Real-time pressure-volume analysis served as a valid procedure for monitoring cardiac function during acute myocardial infarction in mice. Maintaining stable anesthesia and a standardized surgical approach was crucial to ensure valid results. As the early phase of acute myocardial infarction is critical for morbidity and mortality, the delineated method could be beneficial for preclinical evaluation of new strategies for cardioprotection.

Acute myocardial infarction in mice induces acute but incompletely characterized changes in left ventricular (LV) function. LV catheterization in mice undergoing coronary artery occlusion serves as a novel method for a real-time evaluation of LV function.

Acute myocardial infarction can lead to acute heart failure and cardiogenic shock. The evaluation of hemodynamics is critical for the evaluation of any ...

A Cryoinjury Model to Study Myocardial Infarction in the Mouse

The use of animal models is essential for developing new therapeutic strategies for acute coronary syndrome and its complications. In this article, we demonstrate a murine cryoinjury infarct model that generates precise infarct sizes with high reproducibility and replicability. In brief, after intubation and sternotomy of the animal, the heart is lifted from the thorax. The probe of a handheld liquid nitrogen delivery system is applied onto the myocardial wall to induce cryoinjury. Impaired ventricular function and electrical conduction can be monitored with echocardiography or optical mapping. Transmural myocardial remodeling of the infarcted area is characterized by collagen deposition and loss of cardiomyocytes. Compared to other models (e.g., LAD-ligation), this model utilizes a handheld liquid nitrogen delivery system to generate more uniform infarct sizes.

This article demonstrates a model to study cardiac remodeling after myocardial cryoinjury in mice.

The use of animal models is essential for developing new therapeutic strategies for acute coronary syndrome and its complications. In this article, we ...

Establishing a Swine Model of Post-myocardial Infarction Heart Failure for Stem Cell Treatment

Although advances have been achieved in the treatment of heart failure (HF) following myocardial infarction (MI), HF following MI remains one of the major causes of mortality and morbidity around the world. Cell-based therapies for cardiac repair and improvement of left ventricular function after MI have attracted considerable attention. Accordingly, the safety and efficacy of these cell transplantations should be tested in a preclinical large animal model of HF prior to clinical use. Pigs are widely used for cardiovascular disease research due to their similarity to humans in terms of heart size and coronary anatomy. Therefore, we sought to present an effective protocol for the establishment of a porcine chronic HF model using closed-chest coronary balloon occlusion of the left circumflex artery (LCX), followed by rapid ventricular pacing induced with pacemaker implantation. Eight weeks later, the stem cells were administered by intramyocardial injection in the peri-infarct area. Then the infarct size, cell survival, and left ventricular function (including echocardiography, hemodynamic parameters, and electrophysiology) were evaluated. This study helps establish a stable preclinical large animal HF model for stem cell treatment.

We sought to establish a swine model of heart failure induced by left circumflex artery blockage and rapid pacing to test the effect and safety of intramyocardial administration of stem cells for cell-based therapies.

Although advances have been achieved in the treatment of heart failure (HF) following myocardial infarction (MI), HF following MI remains one of the major ...

Intramyocardial Transplantation of MSC-Loading Injectable Hydrogels after Myocardial Infarction in a Murine Model

One of the major issues facing current cardiac stem cell therapies for preventing postinfarct heart failure is the low retention and survival rates of transplanted cells within the injured myocardium, limiting their therapeutic efficacy. Recently, the use of scaffolding biomaterials has gained attention for improving and maximizing stem cell therapy. The objective of this protocol is to introduce a simple and straightforward technique to transplant bone marrow-derived mesenchymal stem cells (MSCs) using injectable hydroxyphenyl propionic acid (GH) hydrogels; the hydrogels are favorable as a cell delivery platform for cardiac tissue engineering applications due to their ability to be cross-linked in situ and high biocompatibility. We present a simple method to fabricate MSC-loading GH hydrogels (MSC/hydrogels) and evaluate their survival and proliferation in three-dimensional (3D) in vitro culture. In addition, we demonstrate a technique for intramyocardial transplantation of MSC/hydrogels in mice, describing a surgical procedure to induce myocardial infarction (MI) via left anterior descending (LAD) coronary artery ligation and subsequent MSC/hydrogels transplantation.

Stem cell-based therapy has emerged as an efficient strategy to repair injured cardiac tissues after myocardial infarction. We provide an optimal in vivo application for stem cell transplantation using gelatin hydrogels that are able to be enzymatically cross-linked.

One of the major issues facing current cardiac stem cell therapies for preventing postinfarct heart failure is the low retention and survival rates of ...