Despite considerable advances in diagnosis and management over the last three decades, acute myocardial infarction (AMI) continues to be a major public health problem. In the United States nearly 1.5 million patients annually suffer from AMI. Although the acute mortality of AMI is decreasing in the U.S., the prevalence of ischemic cardiomyopathy is rapidly increasing due to an increased life expectancy, and the morbidity, mortality, and economic costs related to ischemic cardiomyopathy are steadily increasing.
Almost all myocardial infarctions result from acute transbotic occlusion of pre-existing arteriosclerotic plagues of coronary arteries, which has been mimicked by ligation of the left coronary artery in a variety of animal models, including rats and mice. Myocardial infarction induces global changes in the ventricular architecture, a process called ventricular remodeling. The infarcted heart progressively dilates and accelerates the deterioration of ventricular dysfunction that eventually results in heart failure. As seen in other models of cardiac dysfunction, fetal-type genes, such as ANP and b-MHC genes, are activated (Weber, 1997). At 4 weeks after MI, collagen types I and III and cytokine gene expression increases (Yue et al., 1998). These genes serve as positive control marker genes in systematically evaluating gene expression profiles associated with ventricular remodeling and heart failure after MI.
The experimental protocol for left coronary artery ligation has been previously described (Li et al., 1997; Harada et al., 1999) and is routinely performed in our laboratory. We first assess changes in left ventricular geometry and function using 2-dimensional and M-mode echocardiography to compare end-diastolic diameters, relative wall thickness, and % fractional shortening. We expect to see progressive left ventricular dilation and impaired cardiac function starting one week after the ligation. Mice are sacrificed 1 hour, 4 hours, 24 hours, and 48 hours after the procedure to analyze immediate early and early responses and then one week, two weeks, four weeks, and two months after the intervention. Hearts are excised and the infarct size calculated and expressed as a percentage of left ventricular surface area. Animals with less than 30% of infarct size after one week will be excluded from the studies, as they generally do not show typical left ventricular remodeling. Ventricles are isolated and snap-frozen in liquid nitrogen for gene-expression analyses. Part of the hearts is used for histopathological analysis.
After an adequate depth of anesthesia is attained the mouse is fixed in a supine position with tape. A 5-0 ligature is placed behind the front upper incisors and pulled taut so that the neck is slightly extended. The tongue is retracted and held with forceps, and a 20-G i/v catheter is inserted into the trachea. The catheter is then attached to the mouse ventilator (Model 687, Harvard Apparatus) via the Y-shaped connector. Ventilation is performed with a tidal volume of 200ul and a respiratory rate of 133/min. 100% oxygen is provided to the inflow of the ventilator. Prior to the incision the chest is disinfected with betadine solution and 70% ethyl alcohol. The chest cavity is opened by an incision of the left fourth intercostal space. Chest retractor is applied to facilitate the view. The heart is exposed, the pericardial sac is opened and pulled apart, and the left anterior descending (LAD) artery is visualized. Ligation is proceeded with a 7-0 silk suture passed with a tapered needle underneath the LAD artery about 1-2 mm lower than the tip of the left auricle. Occlusion is confirmed by pallor of the anterior wall of the left ventricle. A drop of 1% lidocaine is placed on the apex of the of the heart to prevent arrhythmia. Lungs are overinflated, and the chest cavity, muscles, and skin are closed layer by layer with 6-0 nylon and 6-0 absorbable (for muscles) sutures. The duration of the whole procedure amounts to about 10-15 min.
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Page last modified: 26-Jan-2004
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