We thank Christiane Pahrmann for her technical assistance. D.W. was supported by the Max Kade Foundation. T.D. received grants from the Else Kro&#776;ner Fondation (2012_EKES.04) and the Deutsche Forschungsgemeinschaft (DE2133/2-1_. S. S. received research grants from the Deutsche Forschungsgemeinschaft (DFG; SCHR992/3- 1, SCHR992/4-1).

Animals received humane care in compliance with the Guide for the Principles of Laboratory Animals, prepared by the Institute of Laboratory Animal Resources, and published by the National Institutes of Health. All animal protocols were approved by the responsible local authority (the University of California San Francisco (UCSF) Institutional Animal Care and Use Committee).
1. Animal care
<ol>
	<li>Obtain mice at the age of 14 weeks weighing approximately 27 g (e.g., from the Institute of La...

<ol>
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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=A+murine+closed-chest+model+of+myocardial+ischemia+and+reperfusion.">A murine closed-chest model of myocardial ischemia and reperfusion.</a> Journal of Visualized Experiments : JoVE. (65), e3896 (2012).</li><li>Antonio, E. 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=Left+ventricle+radio-frequency+ablation+in+the+rat:+a+new+model+of+heart+failure+due+to+myocardial+infarction+homogeneous+in+size+and+low+in+mortality.">Left ventricle radio-frequency ablation in the rat: a new model of heart failure due to myocardial infarction homogeneous in size and low in mortality.</a> J Card Fail. 15 (6), 540-548 (2009).</li><li>Ovsepyan, A. 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This article describes a mouse cryoinjury model to investigate ACS and related pharmacological and therapeutic options.
The most crucial step is the application of the cryoprobe on the cardiac tissue. Contact duration must be tightly controlled in order to obtain the optimal infarct size and to guarantee reproducible results. Prolonged cooling of the myocardium will lead to oversized infarcts or ventricular perforation. In contrast, shortened cooling time generates limited epicardial lesions a...

Acute coronary syndrome (ACS) is the leading causes of death in the Western world1,2. Acute occlusion of the coronary arteries leads to activation of ischemic cascade and necrosis of the affected cardiac tissue3. Damaged myocardium is gradually replaced by non-contractile scar tissue, which manifestz clinically as a heart failure4,5. Despite recent advances in the treatment of ACS, the prevalence of ACS and ACS-related heart failure is rising, and therapeutic options are limited6,7. Therefore, developing animal models to study ACS and its complications are of immense interest.
To date, the most widely used animal model to study ACS and ACS-induced myocardial remodeling is the ligation of the left descending coronary artery (LAD). Ligation of the LAD leads to acute ischemia of the myocardium, similar to human myocardial tissue during ACS.&#160; However, inconsistent infarct sizes remain the Achilles&#39;&#160;heel of LAD ligation. Surgical variation and anatomical variability of the LAD lead to inconsistent infarct sizes and hinder the reproducibility and replicability of this procedure8,9,10. In addition, LAD ligation has a high intra- and postsurgical mortality. Despite recent endeavors to improve reproducibility and reduce mortality11,12, large numbers of animals are still needed to properly evaluate anti-remodeling therapies.
Alternative models of ACS have been proposed and studied over the recent years, including radio-frequency13, thermal14 or cryogenic injuries15,16,17,18. Current cryoinjury methods apply a metal rod pre-cooled in liquid nitrogen to damage the subject&#39;s cardiac tissue15,16. However, this procedure needs to be repeated several times to generate a sufficient infarct size. Due to the high conductivity and low heat capacity of the rod compared to the tissue, the probe warms quickly, and the tissue is cooled (and thus infarcted) heterogeneously. To overcome these limitations, we describe herein a cryoinfarction model utilizing a hand-held liquid nitrogen delivery system. This model is reproducible, easy to perform and can be established fast and reliably. A reproducible transmural infarct lesion independent of coronary anatomy is generated, which eventually leads to cardiac failure. This method is especially suitable to study the remodeling process for the evaluation of novel therapeutic pharmacological and tissue engineering-based strategies.

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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.

The cryoinjury infarct model is suitable to study ACS and its complications. Low mortality rates and efficient postsurgical recovery is seen in this model. Cryoinjury induced myocardial damage leads to reduced cardiac function, electrical uncoupling, and transmural remodeling.
Echocardiography can be used to monitor cardiac function noninvasively in vivo. In cryo-injured hearts, echocardiography demonstrates significantly reduced ejection fraction and fractional area change (<strong class="xfi...

Watch this Scientific Journal Video about A Cryoinjury Model to Study Myocardial Infarction in the Mouse at JoVE.com

A Cryoinjury Model to Study Myocardial Infarction in the Mouse

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 ...

This method is reliable to study the generation of myocardial infarction and an excellent platform to use for investigating cardiac recovery after, for example, stem cell transplantation. The main advantage of this procedure is that it can be used to generate uniform infarct sizes in a quick, easy, and reproducible manner. Novel experimental interventions, such as pharmacological, or the tissue engineered based strategies, can be tested in this model.And successfully test that options can be further confirmed in large animal models. After confirming a lack of response to pain reflex in an anesthetized 27 gram, 14 week old mouse, use a hair trimmer to remove the fur of the chest and neck of the animal and place the mouse in a supine position on a heated pad. Tape the hind and forelimbs in a spread eagle position and use sequential povidone-iodine and 80%ethanol scrubs to disinfect the exposed skin.Make a midline skin incision from the lower third of the sternum to the chin, and use curved forceps to carefully separate the muscles around the neck to expose the trachea. Use micro scissors to perform a tracheotomy between the second and third cartilage rings. And set the ventilator to a ventilation frequency of 110 per minute with a tidal volume of 0.5 milliliters.Then, insert a plastic, 20 gauge cannula connected to the ventilator into the trachea. Next, use cautery to detach the right pectoralis muscle from its sternal origin between the third and seventh ribs. And use side angled spring scissors to cut the fourth to six ribs as close as possible to the sternum.Dissect the underlying connective tissue to obtain a clear view into the chest cavity, cauterizing the mammary artery to stem bleeding as necessary. Insert a mini gold stain retractor to spread the ribs and keep the chest cavity open. And use blunt forceps to open the pericardium to expose the heart.Use a blunt rod to lift the heart from the thoracic cavity and decrease the tension of the retractor to reduce the chest opening and to keep the heart from falling back into the abdominal cavity. Pre-cool a three millimeter diameter cryoprobe for 10 seconds, and apply the cryoprobe on the interior left ventricle wall for 10 seconds to generate a left ventricular, cryoinjury infarct. Detach the cryoprobe from the left ventricular wall with room temperature saline irrigation and reenlarge the chest opening with the retractor.Use the rod to gently return the heart to the thoracic cavity and remove the retractor. Use a 6-0 suture to connect the sternotomy with a single knot. And use a running 6-0 suture to close the chest cavity.Use a 10 milliliter syringe to evacuate any remaining air from the chest before tying the knot and adapt the skin at the caudal edge before using a running 5-0 suture to close the tissue to the point of the tracheal opening. After reducing the isoflurane and the animal gains spontaneous breathing remove the tracheal catheter and close the tracheal incision with one 8-0 suture. Replace the ventral neck muscles back to their anatomical position over the trachea and complete the skin suture.Then, add metamizole to the drinking water for pain analgesia for three days with daily animal monitoring for eight weeks. In cryoinjured hearts echocardiography reveals a significantly reduced ejection fraction and fractional area change, with functional impairment observed from day seven post-surgery until the experimental endpoint at 56 days. As assessed by pressure-volume loop analysis, cryoinfraction leads to an impaired left ventricle function which is reflected as a decrease in stroke volume, stroke work, cardiac output, and pre-load adjusted maximal power.Ex-vivo optical mapping of fluorescent voltage-sensitive dyed hearts demonstrates a blockage of electrical conduction at the border of injury, indicating a local electrical uncoupling. Histological staining with Masson's trichrome reveals transmural fibrotic tissue formation at the site of injury. The infarct size can be calculated by measuring the infarct scar area or midline scar length.In addition, immunofluorescent staining against a cardiomyocyte marker and Collagen-I confirm the presence of fibrotic remodeling and the loss of cardiomyocytes at the site of injury. It's important to maintain the same contact duration of the cryoproblem each animal as different duration may lead to incongruent infarct sizes. Once mastered this technique can be performed in 20 minutes if it is performed properly.After watching this video you should have a good understanding how to perform the cryoinjury model. Good luck with your experiments.

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Research

JoVE Journal

Medicine

9.0K visualizações.  University Heart Center. Este método é confiável para estudar a geração de infarto do miocárdio e uma excelente plataforma para usar para investigar a recuperação cardíaca após, por exemplo, o transplante de células-tronco. A principal vantagem deste procedimento é que ele pode ser usado para gerar tamanhos de infarto uniformes de forma rápida, fácil e reprodutível. Novas intervenções experimentais, como a farmacológica, ou as estratégias baseadas em tecidos, podem ser testadas neste modelo....