Lack of correlation between anatomic infarct size and ventriculographic variables following coronary occlusion in closed-chest dogs

1. Although the effects of therapeutic interventions upon infarct size are frequently assessed on the basis of left ventricular ejection fraction and segmental contraction, the correlation of these variables with infarct size has not been thoroughly evaluated. To explore such relationship, we occluded the left antior descending coronary artery of 22 closed-chest dogs and performed contrast ventriculography one week later. Regional myocardial functionwas evaluated by a computer in 60 radial segments. 2. Infarct size, measured by triphenyl-tetrazolium chloride staining, ranged 1.4 to 43.6% of the left ventricle. Infarcted dogs were arbitrarily divided into 3 groups by percentage of necrotic area: Group 1 (< ou = 15%, N = 5), Group 2 (15 to 30%, N = 10) and Group 3 (> ou = 30%, N = 7). 3. Although the ejection fraction was significantly reduced in infarcted animals as compared to preselected normal controls (38.9 ñ 11.6 [SD] vs 74.1 ñ 7.5%, P < 0.001), it was similar within each infarct subgroup. 4. There was a linear inverse correlation between ejection fraction and percentage of abnormally contractiong segments ( R = -0.63, - = 0.0017). However, neither ejection fraction nor abnormally contracting segments were correlated with infarct size (R = 0.17 and R = 0.11, respectively). 5. A more detailed analysis revealed that infarcted or infarct-adjacent segments were less depressed in Group 1 than in Group 2 or 3 and extent of depression was similar between Groups 2 and 3. Conversely, the extent of shortening of non- infarcted inferior wall segments increased from Group 1 to Group 3. 6. Thus, regional myocardial contration is significantly affected by non-necrotic infarct-adjacent segments and the ejection fraction is significantly influenced by non-ischemic myocardium. For infarcted areas up to 40% of the left ventricle, a single post-infarction determination of ejection fraction or the percentual of abnormally contracting segments seems unreliable, on a population basis, to judge the effects of infarct-sparing interventions