Histologic Analysis
The injured area was easily identified by the presence of vessel dilation and small periarterial hematoma. Diagonal branches and the distal LAD were tied; the proximal LAD was perfused through the ostium with 4.0 percent glutaraldehyde in phosphate-buffered saline (pH, 7.4) for 20 to 30 min at low pressure and flow. In preliminary experiments, we verified that perfusion at systemic pressure with the distal artery open was associated with high coronary flow and disruption of thrombi in some animals. The myocardial fragment containing the injured area and the 2.0-cm segments proximal and distal to it were immersion-fixed in glutaraldehyde, cut into 2-mm slices, and stained for light microscopy by the Verhoeff-van Gieson method, as well as with hematoxylin-eosin.
In 26 dogs, every third slice was prepared for scanning electron microscopy. These arterial slices were opened and cut into smaller fragments. Specimens were fixed with cyanoacrylate over appropriate supports and submitted to critical-point dehydration, followed by sputtering with gold. Histologic images were projected over paper with a microscopic slide projector (Carl Zeiss, Oberkochen, Germany). Mural thrombi were quantified with computer-assisted planimetry and expressed as percentage of lumen area for each section. Extent of mural thrombosis was given as the maximal arterial lumen encroachment for each dog. Histologic injury scores for balloon-induced injury have been described previously.