The cat as a model for myocardial infarction

Coronary artery occlusion results in both rhythm disturbances and the development of ischaemia leading to infarction. The usefulness of the cat as an experimental model for studying both arrhythmia and infarction was examined by performing slow ligation of the left anterior descending (LAD) coronary artery. The presence of ventricular rhythm disturbances occurring 12 to 24 h after LAD occlusion ie,late arrhythmia, was determined and correlated with the extent of infarction. Slow ligation of the LAD in 16 cats resulted in less severe arrhythmia immediately after occlusion with no ventricular fibrillation. In addition there was no sustained period of late ventricular arrhythmia unless LAD occlusion was produced in the presence of complete heart block. In 11 cats with complete heart block LAD occlusion produced a period of late multifocal ventricular arrhythmia that started at 20 to 24 h and persisted for up to 70 to 80 h after occlusion. Infarct size was determined by macroscopic dehydrogenase staining and confirmed by histological examination in cats with LAD occlusion only (n=9). The infarct involved 32.6±2.7% of the ventricular myocardium, 72.2±5.6% of which was interventricular septum. In cats with complete heart block and LAD occlusion (n=15) the infarct involved 32.2±2.2% of the ventricular myocardium, 63.2±4.4% of which was interventricular septum. There was a significant correlation between the extent of infarction and the number of ectopic ventricular beats at 24 h after LAD occlusion (P<0.05). A significant correlation also existed between infarct weight and heart weight (P<0.05).