The effect of left atrial-to-aortic assistance on infarct size.

Left atrial-to-aortic (La-A) assistance is effective in supporting the failing circulation. This study evaluated its effect in salvaging ischemic myocardium in both large and small infarct models. In a control group, good correlation was shown between measurements of infarct size by ST-segment mapping at 20 minutes, triphenyl tetrazolium chloride staining at 5 hours, and the distribution of radioactive microspheres (P less than 0.01). A servo controlled assist pump was used which controlled pump speed according to the left atrial pressure. This allowed greater degrees of bypass for prolonged periods with reduced risk of air embolism. La-A assistance reduced systolic left ventricular pressure, and reduced the pressure time index (P less than 0.05). La-A assistance did not reduce infarct size measured by ST-segment mapping in a large infarct model when instituted before occlusion or 20 minutes after occlusion. Triphenyl tetrazolium chloride staining, however, showed less severe and homogenous damage in the assisted group as compared to controls. Electron microscopy confirmed the patchy nature of the ischemia. In a small infarct model, La-A assistance reduced nST from 6.3 +/- 0.8 to 3.8 +/- 1.5 and ST from 4.9 +/- 0.6 to 2.7 +/- 0.9 (P less than 0.05). The endocardial to epicardial ratio in the ischemic area fell from 0.69 +/- 0.05 to 0.43 +/- 0.05 in the control group (P less than 0.05) and a similar fall occurred in the assisted groups. La-A assistance is thus effective in reducing myocardial ischemia in a small infarct model, but appears to be less effective in a large infarct model.