Effect of halothane on myocardial infarct size in rats

The effect of halothane on myocardial infarction caused by ligation of the left descending coronary artery was studied in rats. The extent of infarction was quantified 48 hours after ligation of the artery by planimetric measurement of left ventricular slices stained with nitrobluetetrazolium. Animals exposed to halothane one per cent for three hours after the coronary ligation were compared with a control group which received halothane for only 5-7 minutes during surgery. It was found that halothane caused a small increase in infarction size (31.3 +/- 1.5 per cent of the left ventricle compared to 25.7 +/- 2.3 per cent, p less than 0.05). This effect was accompanied by a decrease in systolic blood pressure (91 +/- 2 mmHg compared to 113 +/- 3 mmHg, p less than 0.001). Heart rate did not change significantly. Analysis of our results in comparison to previously reported data on the effect of halothane on myocardial ischaemia in different experimental conditions shows that halothane may produce beneficial as well as detrimental effect on ischaemic injury to the myocardium. The latter can result when the drug causes marked hypotension in the absence of a significant decrease in heart rate.