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The effect of graded coronary occlusion on myocardial shortening in different zones of the left ventricle is not clear. Therefore, in 15 dogs ultrasonic crystals were used to evaluate the effect of graded coronary occlusion on subendocardial and subepicardial contraction in both the left anterior descending coronary artery (LAD) and left circumflex coronary artery (Circ) distributions. Subepicardial shortening was evaluated along both the long and short axes. In the LAD zones, segment shortening decreased in parallel in the subendocardium and subepicardium. In the circumflex zone subendocardial and subepicardial long axis shortening fell off in parallel, while subepicardial short axis shortening fell off more rapidly. Thus there is a close relationship between endocardial and epicardial segment shortening following graded coronary occlusion. In the circumflex zone, however, fiber orientation may affect the measurement of segment motion.
Hattori et al. (Wed,) studied this question.