Limitations of myocardial revascularization in restoration of regional contraction abnormalities produced by coronary occlusion

Abstract

The effect of reperfusion instituted from 30 minutes to 3 hours after coronary occlusion on the contractile characteristics of the ischemic zone, border zone and nonischemic myocardium was studied in 29 dogs using Walton-Brodle strain gauge arches and mercury-in-Silastic ® tubing segment length gauges. After 30 and 45 minutes of coronary occlusion, reperfusion resulted in an immediate reversal of abnormalities in segment length and tension of the ischemic zone to near normal. Preejection tension Increased from 32.3 ± 5.1 to 95.2 ± 4.7 percent of control level, ejection tension from zero to 71.7 ± 7.0 percent, total tension from 27.5 ± 2.5 to 87.1 ± 6.2 percent and dT dt from 42.1 ± 4.1 to 100.0 ± 4.5 percent. Phasic segment length decreased from 150.2 ± 5.1 percent to 100.0 ± 5.0 percent of control value. Aneurysmal bulging disappeared completely. However, after 1 hour of coronary occlusion, reperfusion resulted In a significant ( P < 0.01) further decrease in all contraction variables In the ischemic zone. Preejection tension decreased from 58.7 ± 7.9 to 31.2 ± 5.5 percent, ejection tension decreased initially but recovered to prereperfusion levels, total tension decreased from 48.5 ± 5.9 to 24.0 ± 4.0 percent and dT dt declined from 60.7 ± 7.2 to 30.9 ± 5.7 percent of control levels. Phasic segment length gradually decreased from 162.5 ± 6.0 to 137.5 ± 12.5 percent of control value. The border zone exhibited similar decreases in function In four studies, and improved in two. After 2 and 3 hours of coronary occlusion, reperfusion was uniformly followed by further decreases In function of both ischemic and border zones. In conclusion, contraction abnormalities produced by 45 minutes of coronary occlusion are reversible with reperfusion. However, when reperfusion is instituted after 1 hour of occlusion, the abnormalities are often accentuated and this becomes invariable after 2 hours of occlusion. Thus, the myocardial impairment appears to be functionally irreversible after this time period.