トレッドミル運動負荷試験で陰性所見を示した直後に急性心筋梗塞を発症した1例

A Case of Acute Myocardial Infarction Immediately following Treadmill Stress Testing without Ischemic Change

　症例は56歳，男性．労作とは無関係で30分から1時間持続し，硝酸剤が無効な非典型的な胸痛が度々出現するため当院を受診した．トレッドミル運動負荷試験ではBruceプロトコール12分間の負荷中および回復期に胸痛はなく，心電図変化も陰性であった．検査終了5分後，胸痛と胸部誘導のST上昇が出現し急性心筋梗塞の診断で緊急入院となった．緊急冠動脈造影では前下行枝＃6に血栓像を伴う99％狭窄を認めたが硝酸イソソルビド2.5mgの冠注により50％まで改善した．前下行枝末梢に血栓が残存していたため，左冠動脈にチソキナーゼ（t-PA）640万国際単位の冠注を行った．しかし，＃6の血栓形成がかえって進行し，狭窄度は90％へと増悪した．このため＃6にPTCAを施行し25％まで開大した．慢性期の冠動脈造影ではPTCA部の再狭窄は認められなかったが，アセチルコリン負荷により冠攣縮が誘発された．本症例における急性心筋梗塞の発症機序として運動誘発性の血栓形成と冠攣縮の関与が考えられた．

A 56-year-old male presented himself complaining of frequent episodes of atypical chest pain lasting for from 30 to 60 minutes during periods of rest, and showing no improvement despite nitroglycerin administration. Subjected to treadmill stress testing, he completed Bruce stage 4 and a 9-minutes recovery phase with neither chest pain nor significant ST-T change in ECG. Five minutes after completion of the stress test, how-ever, he experienced chest pain, with ECG chest leads indicating ST segment elevation. He was promptly admitted with a diagnosis of acute myocardial infarc-tion (AMI). Coronary angiography performed 40 minutes after the onset of AMI revealed 99% eccentric stenosis (TIMI grade 1) with a thrombus in segment 6 of the left anterior descending coronary artery (LAD). Intracoronary administration of 2.5mg isosorbide dinitrate resulted in reduction of stenosis to 50%. The thrombus identified as being in the distal portion of LAD, 64,000 IU of tissue plasminogen activator (t-PA) was serially introduced by intracoronary administra-tion. Despite this, segment 6 stenosis increased to 90%. Percutaneous transluminal angioplasty (PTCA) was performed, and stenosis decreased to 25%. Coronary angiography 3 weeks later showed no stenosis in seg-ment 6, but acetylcholine induced coronary spasm in the distal portion of LAD. This case was considered impor-tant in that it bolsters the hypothesis that intracoronary thrombus formation, plaque rupture and coronary vasospasm, are related to the mechanisms of myocar-dial infarction induced by heavy exercise.