Changes in isovolumic segment shortening following acute coronary occlusion: disproportionate effects of anterior versus posterior ischemia

Abstract

We evaluated the changes in left ventricular pressure and isovolumic segment shortening in both the ischemic and nonischemic areas following acute coronary occlusion in 12 conscious dogs instrumented for the measurement of subendocardial segment lengths perfused by the left circumflex coronary artery and left anterior descending coronary artery, and left ventricular pressure. An externally inflatable pneumatic occluder was placed around the left circumflex coronary artery. In 6 dogs, another occluder was installed around the proximal left anterior descending coronary artery. Under the resting conditions, the isovolumic segment shortening in the areas supplied by the left anterior descending coronary artery and the left circumflex coronary artery were 2.1 ± 0.5% (SE) and −0.1 ± 0.5% ( P < 0.01; versus values in the area of the left anterior descending coronary artery), respectively. During a 1-min occlusion of the left circumflex coronary artery, the isovolumic shortening in the anterior segment increased to 3.8 ± 0.5% ( P < 0.001; versus values in the basal state), while the posterior segment produced isovolumic elongation (− 2.2 ± 0.5%, P < 0.001; versus values in the basal state). By contrast, during a 1-min occlusion of the left anterior descending coronary artery, the extent of isovolumic bulge in the anterior segment and the augmentation in the isovolumic shortening in the posterior segment was less prominent compared with the occlusion of the left circumflex coronary artery. It is concluded that there is a significant isovolumic ventricular asynchrony between different areas of the left ventricle and the effects of coronary occlusion on the isovolumic contractile characteristics of the ischemic and nonischemic segments are recognized in terms of inherent ventricular asynchrony and changes in tension development due to ischemia.