Hematological Changes in an Ovine Model of Acute Myocardial Infarction

Today, acute myocardial infarction (MI) is the foremost cause of mortality in many countries around the world. When studying MI in large mammals, pigs or sheep are usually used. We chose sheep because, unlike pigs, whose cardiomyocytes have up to 32 nuclei, ovine cardiomyocytes have only 1–4 nuclei, thus being more similar to the human (Adler et al., 1996). In addition, pigs are more prone to develop irreversible ventricular fibrillation than sheep, this leading to higher mortality. A detailed guide with a practical, safe and reliable for induction of MI in ovine models by ligating the main diagonal branch of the left anterior descending (LAD) coronary artery has been reported previously (Kim et al., 2005; Rabbani et al., 2008).

Many studies have been published for hematologic and biochemical analysis in relation to acute MI in human (Friedman et al., 1974; Jan et al., 1975; Zalokar et al., 1981; Tahnk-Johnson and Sharkey, 1993; Kobayashi et al., 2001), however, few studies for the observation of alterations in these indices from acute MI has been accomplished (Dodds et al., 1980; Nikolaidis et al., 2003; Aronson et al., 2007). The present study was designed to explore the relationship between the extent of myocardial injury following coronary ligation and the degree of hemodynamic changes in sheep within 1 week after LAD ligation.

All procedures were approved by the Laboratory Animal Care and Use Committee of the University of Tehran, and performed in accordance with the Guide for Care and Use of Laboratory Animals, published by the US National Institutes of Health (NIH publication 85-23, revised 1996). Ten healthy, non-obese, adult, male sheep weighing 30-35 kg were randomly divided into two groups (n=5 each) including Group І (without MI or sham-operated control group) and Group ІІ (with MI) with age- and sex-matched ones. During the study, the animals had free access to water and were fed with a mixed diet of hay and sheep pellets.

All animals were housed for 1 week in the animal house so they would be adapted to the environment. They were examined by a veterinarian and a cardiologist, clinically, and some were excluded from the study if any serious morbidity was detected. Animals in group II were subjected to coronary artery ligation after lateral thoracotomy. Surgical procedures were performed under general anesthesia by intravenous injection of sodium pentobarbital (30 mg/kg) and electrocardiographic monitoring (Kim et al., 2005; Rabbani et al., 2008). Acute MI was inducted by ligating the second diagonal branch of the LAD, as described previously by Rabbani et al. (2008).

This method has been documented as a practical, reliable and safe ovine model of inducing MI in paraclinical investigations. After surgical preparation/drape, a 15- to 20-cm-long left lateral thoracotomy incision was carried out through the fourth intercostals space. After the pericardium was opened, the coronary anatomy was inspected. The second diagonal branch of LAD coronary artery was ligated using a curved round needle and 6-0 prolene suture at a point approximately 40% distant from its base. Occlusion of the coronary artery was confirmed by the cyanotic appearance of the ischemic area (Fig.1), and ventricular hypokinesia plus ST-segment changes on electrocardiography (ECG).

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(Author: Ezzatollah Fathi, Raheleh Farahzadi, Elaheh Pishgahzadeh

Published by Macrothink Institute)