Preservation of regional myocardial ultrasonic backscatter and systolic function during brief periods of ischemia by synchronized coronary venous retroperfusion

Abstract

This study examines the effects of brief periods of ischemia on average and cardiac cycle-dependent variation of regional ultrasonic backscatter paralleled with changes in regional myocardial contraction, and to what extent these changes could be reversed by synchronized coronary venous retroperfusion. In five closed-chest dogs, the left anterior descending coronary artery was occluded on four occasions for a 2-minute period and retroperfusion was applled randomly to two of the coronary occlusions. Complete functional recovery was allowed between the occlusions. Two-dimensional echocardiographic images were obtained before and at the peak of the 2-minute occlusion period. Regional myocardial contraction as measured by fractional area change and systolic wall thickening during untreated occlusions decreased from 33.9 ± 14.0% to −0.15 ± 6.2%, and from 22.0 ± 1.8% to −17.9 ± 2.2%, whereas during retroperfusion-treated occlusions it changed from 37.4 ± 8.5% to only 23.4 ± 11.2% ( p < 0.005 versus baseline), and from 24.1 ± 2.8% to only 12.7 ± 2.0% ( p < 0.005 versus baseline), corresponding to a preservation of 62% and 52% of baseline regional contraction, respectively. Average regional gray level (arbitrary units) during untreated coronary occlusions exhibited a significant increase in the ischemic regions, from 5.6 ± 2.7 at baseline to 11.5 ± 4.4 during occlusion ( p < 0.005); during retroperfusion-treated occlusions, average gray level increased from 4.7 ± 3.6 to only 6.3 ± 3.6 (NS). Untreated coronary artery occlusions resulted in a systolic increase in gray level in the ischemic region, followed by a diastolic decrease. In contrast, retroperfusion-treated occlusions prevented the systolic increase in gray levels and the pattern of cyclic variation in backscatter remained similar to that observed at baseline. In conclusion, synchronized coronary venous retroperfusion partially preserves ischemic zone contractile function and almost fully prevents ischemic changes in ultrasonic backscattering properties of myocardium, as measured by regional gray-level distribution during brief periods of coronary artery occlusion.