The hemodynamic impact of diffuse myocardial ischemic lesions: an animal experimental model based on intracoronary microembolization.

ABSTRACT

In ischemic heart disease, left ventricular function is affected by a diffuse and segmental loss of myocardium. The decline in the incidence of myocardial infarction and improved early revascularization in acute transmural ischemia predict a change in the natural history of ischemic heart disease. It is now believed that, minor ischemic episodes, which are known to induce multifocal myocardial degeneration, will predominate in the near future. The objective of the present study was to develop a clinically relevant experimental model for investigation of the pathophysiological significance of diffuse ischemic myocardial lesions. Cardiac performance was gradually depressed by selective intracoronary microembolization in 13 pigs. Left ventricular function was quantitated by ejection fraction (EF), pulmonary pressure, cardiac output, and derivatives of left ventricular pressure. Left ventricular volume was estimated by epicardial echocardiography, using a new, unbiased stereological volume estimator. A chronic substudy was performed in order to characterize the histological changes and to evaluate the feasibility of establishing a chronic preparation of the model. Embolization induced acute left ventricular dysfunction; left ventricular pressure change decreased from 966+/-274 to 637+/-146 mmHg/s, and early diastolic relaxation from 1403+/-515 to 824+/-344 mmHg/s, respectively. Ejection fraction decreased by 45%+/-5% and cardiac output by 29%+/-11%. End-diastolic volume increased significantly, from 66.1+/-13.2 to 77.0+/-19.4 cm3, and end-systolic volume increased from 35.9+/-13.9 to 52.3+/-7.6 cm3. No change in heart rate or left ventricular filling pressure was observed. Diffuse ischemic myocardial injury was identified after a mean follow-up of 40 days. Intracoronary microembolization induces acute left ventricular dysfunction due to microinfarcts. Increased left ventricular end-diastolic volume is the initial compensatory response to the acute impairment of cardiac performance in nontransmural myocardial ischemia. This model is suitable for the evaluation of the hemodynamic changes secondary to acute and chronic diffuse loss of functional myocardium.