増田 佳純, 浅沼 俊彦, 中谷 敏

Kasumi MASUDA, Toshihiko ASANUMA, Satoshi NAKATANI

大阪大学大学院医学系研究科保健学専攻機能診断科学講座

Division of Functional Diagnostics, Department of Health Sciences, Osaka University Graduate School of Medicine

キーワード : early systolic lengthening, echocardiography, ischemic memory, myocardial strain, post-systolic shortening

目的：Post-systolic shortening（PSS）は心筋虚血改善後もしばらく残存するため，虚血メモリー評価に有用と考えられる．心筋虚血時にはearly systolic lengthening（ESL）も生じるが，近年これをスペックルトラッキング心エコー法で同定できることが明らかになった．虚血再灌流後に生じたESLが虚血メモリーの指標となりうるか検討した．対象と方法：麻酔開胸犬16頭において，左冠動脈回旋枝を2分間閉塞後，再灌流した．閉塞前，閉塞時，再灌流10，30分後において，円周方向ストレインを解析した．虚血領域と非虚血領域の収縮期最大ストレイン（ε_S），post-systolic index（PSI），ESLのストレイン振幅（ε_ESL）および，ESLの持続時間（ESL時間）を計測した．結果：虚血領域において，ε_Sは一旦低下，ε_ESLは増加するものの再灌流後速やかに元の値に回復した．一方，PSI，ESL時間は閉塞時に高値を示し，再灌流10分後も閉塞前のレベルまで回復しなかった．ROC曲線による再灌流10分後の虚血メモリー診断精度は，ESL時間で感度63％，特異度81％，PSIでは感度94％，特異度94％であった．結語：ESL時間は虚血メモリーの指標となりうる可能性が示唆された．しかし，その診断精度においては，ESL指標に比べ，PSS指標の方が優れていた．

Purpose: Myocardial ischemic memory can be evaluated by post-systolic shortening (PSS) because it persists for a while after brief ischemia. Recently, early systolic lengthening (ESL) assessed by speckle tracking echocardiography has been reported to be a novel useful parameter for detecting myocardial ischemia. However, it is still unclear whether ESL persists after brief ischemia and can be used for evaluating ischemic memory. Subjects and Methods: The left circumflex coronary artery was occluded for 2 minutes followed by reperfusion in 16 dogs. Short-axis images were acquired at baseline, during occlusion, and 10 and 30 minutes after reperfusion. Circumferential strain was analyzed in the ischemic and non-ischemic areas. Peak systolic strain (ε_S), post-systolic index (PSI) as a parameter of PSS, the amplitude of ESL (ε_ESL), and time from the onset of QRS to the beginning of regional contraction over the initial length (ESL time) were measured. Diagnostic accuracy for evaluating ischemic memory after reperfusion was calculated by receiver operating characteristics (ROC) curve analysis. Results: In the risk area, ε_S decreased and ε_ESL increased during occlusion, which recovered to the baseline level after reperfusion. In contrast, PSI and ESL time significantly increased during occlusion, and the significant increase still persisted at 10 minutes after reperfusion (PSI: 0.02 ± 0.04 vs. 0.19 ± 0.10, p<0.05; ESL time: 88 ± 30 vs. 118 ± 38 ms, p<0.05). The sensitivity and specificity of ischemic memory at 10 minutes after reperfusion were 63% and 81% for ESL time, and 94% and 94% for PSI, respectively. Conclusion: ESL time derived from speckle tracking echocardiography seems to be able to detect ischemic memory. However, PSI was better than ESL time in terms of diagnostic accuracy of ischemic memory.