急性心筋梗塞後の心原性ショックに対する補助循環の効果に関する研究 : 低流量群と高流量群の比較検討
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概要
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The effect of left heart bypass (left atrium-femoral artery) was evaluated in dogs with cardiogenic shock following acute myocardial infarction produced by multiple ligation of the coronary arteries. Aortic pressure, left ventricular pressure (LVP), left ventricular end-diastolic pressure (LVedp), cardiac output, and endocardial viability ratio (EVR) were monitored for a period of 2 hours after acute myocardial infarction. During the same monitoring period, electrocardiograms were also recorded, and lactate extraction in myocardium (LE%) was calculated. The infarct size was assessed from the area demarcated by nitroblue tetrazorium (NBT) staining and avascular area on postmortem coronary angiograms. Left heart bypass was initiated for those dogs with cardiogenic shock due to AMI. Subsequent increase in aortic systolic pressure and cardiac output was observed in low flow bypass group (bypass flow between 30% and 50% of total systemic blood flow), as the bypass time went on. No remarkable changes in hemodynamics were seen during high flow bypass (bypass flow above 50% of total systemic blood flow), except for LVedp which showed low value during high flow bypass as in case of low flow bypass in comparison with control group with coronary ligation alone. EVR was calculated DPTI/TTI which has been thought to be closely corelated with oxygen supply/demand ratio in the subendocardium. When the value of EVR decreases below 0.5, existence of the subendocardial ischemia is strongly suggested. On the other hand, lactate production in the ischemic myocardium indicates anaerobic metabolism. From the reasons mentioned above, EVR and lactate extraction (LE%) was used to evaluate hemodynamics and metabolism of the ischemic myocardium. Satisfactory results were obtained in EVR and LE(%) during low flow bypass. None of the dogs with low flow bypass revealed the value of EVR below 0.6. On the other hand, no improvement in EVR and LE(%) was obtained by high flow bypass, and 33% of dogs showed EVR below 0.6. These findings suggested that very severe myocardial damage was present in high flow bypass group in which mean aortic pressure was hardly maintained at 70〜80 mmHg only with bypass flow above 50% of total systemic blood flow. From these findings, following conclusions were obtained. (1) Left heart bypass was effective to improve hemodynamics and metabolism of the ischemic myocardium when low flow bypass could sustain the mean aortic pressure above 80 mmHg. (2) In high flow bypass group in which the mean aortic pressure was maintained at 70〜80 mmHg only with bypass flow as large as 50% or more of total systemic blood flow, left heart bypass was not effective in improving the hemodynamics and myocardial metabolism probably because of too severe myocardial damage.
- 神戸大学の論文