Functional remodelling and left ventricular dysfunction after repeated ischaemic episodes - A chronic experimental porcine model

This experimental study was set up to investigate left ventricular function and remodelling after repeated ischaemic episodes using magnetic resonance imaging (MRI). A significant reduction in mortality due to coronary heart disease (CHD) has been explained by both a decline in the incidence of acute myocardial infarction (AMI) and an improved post-AMI survival rate, suggesting a change in the natural history of CHD. Experimental intracoronary microembolization can induce different ischaemic patterns and the functional impact of repeated ischaemic episodes different from occlusion of central epicardial arteries can be studied. In this study repeated intracoronary microembolizations were performed in 20 domestic pigs. After 129 d, MRI was performed for assessment of left ventricular volume, mass and wall stress. Six pigs underwent serial MRI at baseline, immediately after embolization and at the end of the observation period. Microembolizations induced acute myocardial infarct expansion and increased left ventricular wall stress preceding chronic remodelling. End systolic and end diastolic volumes increased from 15.1 ± 2.7 cm³ to 41.3 ± 11.5 cm³ (p < 0.002), and from 52.0 ± 6.7 cm³ to 81.1 ± 9.2 cm³ (p < 0.0007), respectively. End systolic wall stress increased from and 17.5 ± 2.7 to 29.7 ± 6.2 N/m² (p < 0.001). Left ventricular filling pressures and cardiac index were unchanged. Histological examination revealed a diffuse pattern of perivascular fibrosis covering 12 ± 3% of the left ventricular wail. This study demonstrates that repeated ischaemic episodes different from confined regional myocardial infarctions induce acute infarct expansion and chronic left ventricular remodelling in pigs. Serial assessment of absolute left ventricular volumes and mass is important during acute/chronic remodelling.