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Effects of progressive reduction in coronary blood flow on regional and global left ventricular contraction and relaxation during normal and increased afterload: a roentgen videometric study.

The effects of step-wise reduction in left circumflex coronary blood flow on: 1) posteroinferior wall dynamics; 2) normally-perfused anterior wall dynamics; and 3) cavity function were assessed simultaneously by roentgen videometric analysis of left ventricular angiograms in open-chest dogs during normal and increased afterload. At control coronary flow with normal afterload, peak rates of systolic thickening and diastolic thinning of the posteroinferior and anterior walls were similar. Step-wise reduction in circumflex coronary flow resulted in a progressive fall in systolic and diastolic posteroinferior wall dynamics. Increased LV afterload resulted in a decrease in posteroinferior wall dynamics even at control coronary flow, and reduction in flow resulted in even greater deterioration than occurred with normal afterload. The decrease in posteroinferior wall dynamics with reduction in circumflex coronary flow was accompanied by an increase in peak rates of systolic thickening and diastolic thinning of the normally perfused anterior wall. The level of coronary blood flow at which this increase in anterior wall dynamics occurred, varied with LV loading conditions, occurring earlier when afterload was increased. There was no earlier or greater decrease in diastolic than systolic wall dynamics with progressive reduction in coronary flow with either normal or increased afterload. Left ventricular end-diastolic volume, end-diastolic pressure and ejection fraction changed little until coronary blood flow was reduced to 50% of control; by contrast, stroke-work was exquisitely sensitive to changes in coronary flow. There was no correlation between changes in regional and cavity systolic or diastolic function. The delay in onset of LV cavity dysfunction with ischemia may have been partly due to the "compensatory increase" in anterior wall dynamics, counterbalancing the impaired posteroinferior wall dynamics.