虚血左室における虚血部心筋収縮性低下の機序に関する心筋代謝からの検討

Left ventricular regional function and myocardial metabolic changes during ischemia

　虚血左室において虚血に陥った心筋（以下虚血部）が虚血早期から収縮低下をきたすことは良く知られた事実である^1,2）。しかし心筋収縮性の評価そのものが未だ確立されておらず，さらには局所心筋機能異常の原因に関しても明確な結論が得られていないのが現状である。

　我々は超音波クリスタル^3）を用いて部分長（segmentlength）及び壁厚（wall thickness）の動態から心筋収縮性の評価を試み，さらにその収縮異常の原因をdrill bio—psyの手法^4）を用いて心筋代謝変化の面から検討を加え，虚血部局所心筋機能の変化機序について考察した。

The mechanisms for the abnormality of regional myocardial function during acute coronary artery occlusion still remain in dispute. We studied them from the viewpoint of myocardial metabolic changes.

In left ventricle of 28 open-chest, anesthetized dogs, four pairs of ultrasonic dimension gauges were implanted in ischemic and non-ischemic regions, and segment length (SL), wall thickness (WT) and their first time derivatives were measured. Left ventricular pressure (LVP), aortic pressure (AoP), pH in myocardium, and lactate concentration in ascending aorta and coronary sinus blood were also measured. ATP and lactate concentration in myo-cardium were measured for drill-biopsied specimen.

In ischemic region, left anterior descending coro-nary artery (LAD) occlusion resulted in increase of end-diastolic SL and decrease of end-diastolic WT, % systolic shortening, maximum velocity of systolic shortening (max dL/dt), % systolic thicken-ing, and maximum velocity of systolic thickening (max dW/dt). In non-ischemic region, however, increase of % systolic shortening, max dL/dt, systolic thickening, and max dW/dt were observed after LAD occlusion. LVP and AoP as indices of total LV function did not change. Increased lactate concentration in myocardium may be a main cause of decrease in pH in ischemic myocardium. ATP concentration in ischemic myocardium and lactate concentration in ascending aorta and coronary si-nus blood did not change in early stage of ischemia.

After LAD occlusion, ischemic myocardium be-came hypokinetic, while there was a hyperkinesis in non-ischemic myocardium. We suppose that the hypokinesis of ischemic myocardium results from de-crease in pH, and not from decrease of ATP con-centration, as far as early stage of ischemia is con-cerned.