Abstract
To study the effects of nitroprusside infusion on the regional contractile performance of the left ventricle after coronary occlusion, local tension and segment length of the ischemic, border and nonischemic zones were studied using Walton-Brodie strain gauge arches and mercury-in-Silastic tubing segment length gauges in open chest dogs. The effect of this intervention on the time period for functional reversibility of the affected areas after revascularization was also examined. Fifteen minutes after occlusion of the left anterior descending coronary artery, nitroprusside (4 to 11 μg/kg per min) was infused to keep systolic pressure 20 to 25 percent below control levels for 2 hours after occlusion and then 1 hour after reperfusion. The ischemic zone showed no change in either tension or length although there was a gradual continuing decrease in tension. However, in the border zone, total tension, which had decreased to 81.4 ± 9.6 (standard error of the mean) percent of control level 15 minutes after coronary occlusion, increased to 87.5 ± 11.3 percent immediately after nitroprusside infusion and continued at that level for 2 hours. Preejection tension, rate of tension rise and ejection tension demonstrated parallel increases. Segment length, which had increased to 144.1 ± 4.5 percent of control level after coronary occlusion, declined to 115 ± 10.7 percent ( P < 0.02) immediately after the onset of infusion. The nonischemic zone showed a sustained increase in all tension variables ( P < 0.01) and a decrease in segment length during the period of nitroprusside infusion with a return to control value after discontinuation of the infusion. The immediate deterioration in tension in the ischemic zone caused by reperfusion after 2 hours of occlusion was prevented by nitroprusside. The border zone continued to maintain improved tension after reperfusion but exhibited an immediate decrease from 84.1 ± 7.8 percent to 69.1 ± 11.7 percent ( P < 0.05) after discontinuation of nitroprusside. In summary, nitroprusside infusion provides a sustained increase in tension and decrease in length of the border and the nonischemic zones after acute coronary occlusion whereas the ischemic zone remains unaffected. Although administration of nitroprusside fails to prolong the time period for functional reversibility of the affected zones with reperfusion, it appears to prevent further deterioration.
Published Version
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