End-systolic pressure-thickness relationship in the ischemic canine ventricle

The relatively load-independent end-systolic pressure-thickness relationship (ESPTR) was used to describe the effect of acute regional ischemia on ischemic- and nonischemic-zone function in six open-chest dogs. During a 90-second coronary occlusion that rendered 20% of the left ventricle ischemic, the ischemic zone ESPTR shifted leftward due to a change in thickness-axis intercept, not slope. Despite a marked augmentation of nonischemic-zone wall thickening during acute ischemia, the nonischemic-zone ESPTR was unchanged from preocclusion, indicating no change in inotropic state. Nonischemic-zone hyperkinesis was due to a combination of augmented preload and reduced afterload and resulted mainly from increased ejection-phase thickening. These changes were the same before and after β-blockade. In conclusion, the ESPTR is an easily measured, reliable descriptor of regional function in the acutely ischemic ventricle which, unlike simple dimension-change measures of regional function, incorporates information about loading conditions into its expression. Using this index we showed that, in this model, acute regional ischemia produces hyperkinesis resulting from augmentation of ejection phase wall thickening in the nonischemic zone attributable solely to change in loading conditions, with no change in contractility.