Relationship between myocardial infarct size and occluded bed size in the dog: difference between left anterior descending and circumflex coronary artery occlusions.

Abstract

SUMMARY We compared myocardial infarct size produced by permanent occlusion of the middle left anterior descending (LAD) or circumflex (LCx) coronary artery in the anesthetized dog. The dogs were killed 3-10 days later, and the occluded coronary bed was visualized by postmortem arteriography. The outlines of the infarct and occluded bed were marked on tracings of weighed left ventricular (LV) rings and the size of the infarct and occluded bed was calculated by planimetry. For both arteries, infarct size and occluded bed size were linearly related to each other, but LAD infarcts were larger relative to occluded bed size (52.0% vs 32.3%, p < 0.05). A smaller occluded bed was necessary for the appearance of an infarct after LAD occlusion than after LCx occlusion (8.3% vs 18.5% of the left ventricle, p < 0.005). Reconstructed LV ring maps indicated a significantly wider margin of noninfarcted myocardium at the lateral edge of the occluded bed for LCx infarcts than for LAD infarcts. For dogs with similar occluded bed sizes in the range of 20-35% of the left ventricle, infarct size was considerably larger for LAD occlusion (15.9% vs 6.1% of the left ventricle, p < 0.001). In this subgroup, blood pressure and heart rate 10-20 minutes after occlusion were not significantly different for the two arteries, but collateral flow, measured with 9-,u radioactive microspheres, was approximately 50% lower after LAD occlusion. The relationship between the amount of myocardium with reduced blood flow and developed infarct size was similar for the two arteries. We conclude that occlusions of the middle LAD and LCx are not equivalent. For a given occluded bed size, LAD occlusions produce larger areas of infarction, apparently related to lower levels of collateral flow delivered to the occluded region.ONE of the most popular animal models for the study of regional ischemia and infarction is the dog in which one of the major coronary arteries has been temporarily or permanently occluded. The anterior descending (LAD) and circumflex (LCx) branches of the left coronary artery are both used for this purpose and are considered more or less interchangeable. Which branch is used in a given laboratory appears to depend more on custom than on any scientific considerations.Although more proximal occlusion of a coronary artery tends to result in a larger ischemic region and a larger completed infarct, a wide variation is found in infarct size, even with occlusion at a constant anatomic site.".2 This fact stems from the variability in coronary artery anatomy and pertains to both branches of the left coronary artery. The observed variability in infarct size, at least for LCx occlusions, can be accounted for in large measure by the size of the occluded coronary bed and the severity of ischemia within the occluded region. 2 No systematic comparison of LAD and LCx distribution infarcts has been undertaken. We therefore determined the intensity of ischemia and the size of developed infarct for dogs with permanent occlusion of one of these two coronar...

Magnitude and Time Course of Microvascular Obstruction and Tissue Injury After Acute Myocardial Infarction

“…8,[15][16][17] This technique has been validated in our laboratory against staining methods such as monastral blue dye injection. 18 In brief, myocardial pieces with MBF Ͻ50% of the MBF in the equivalent remote-region piece during coronary occlusion constituted the risk region.…”

Does the Extent of the Zone at Risk after Coronary Artery Occlusion Influence the Percentage of the Zone that Evolves to Infarction?

“…To minimize the influences of this variability and assess the effect of interven tions on myocardial infarct size accurately, several techniques have been developed for measuring the area at risk that could eventu ally evolve to necrosis [2][3][4][5], Even after cor rection for the area at risk, however, the per centage of the zone at risk that evolves to infarction varies among individual animals. Several other factors, including the amount of collateral blood flow [5][6][7][8][9], the duration of ischemia [6], the myocardial oxygen con sumption [8][9][10] and the coronary artery that is occluded [11], have been reported to influence the amount of necrosis within the risk zone under experimental conditions. Whether the extent of the zone at risk per se influences the percentage of the zone that develops infarction, however, remains a con troversial issue [5,9,12,13].…”

Severity of Exercise-induced Ischemia With Chest Pain and Recovery From Ischemia After the Disappearance of Chest Pain

“…Although the extension of ischemia in the direction of the long-axis of the left ventricle varies greatly depending on the size and the stenotic coronary artery, the extensive ischemia extends to all levels toward long axis of left ventricle. 10) Therefore, the extension of ischemia toward long-axis of left ventricle indicates the severe ischemia or poor prognosis. 11) We found that the presence of exercise-induced chest pain was more closely related to the extension of ischemic burden toward the long-axis of the left ventricle than the total extent and depth of ischemic burden, although the extension of ischemic burden toward the long-axis of the left ventricle was closely related to the total extent and depth of ischemic burden.…”