本研究的目的在於評估以血管內超音波(IVUS)來輔助確認左主冠狀動脈(LMCA)疾病，某些以X光做血管攝影所獲得的影像，是很難以判定其嚴重程度，並接受進一步的治療；若是輔以血管內超音波檢查，即可確定是否需要進一步的治療。先找81位曾經做過血管攝影的病人（其左主冠狀動脈是正常沒有病灶的），並測量他們左主冠狀動脈的管徑大小取得最小管徑面積(MLA)，取得一正常平均值(±2SD)來做對照組，再以24位做血管攝影而其結果是難以判定的病人，以IVUS輔助測其管徑大小，與對照組比較之。對照組的MLA低限值是6.5平方公厘。而實驗組24位中MLA<6.5平方公厘的有9位(37.5%)，WLA≧6.5平方公厘的有15位(62.5%)，MLA<6.5平方公厘的9位中有7位(77.7%)接受血管重建治療，MLA≧6.5平方公厘的15位中有13位(86.6%)不需要做治療。長期追蹤（1.3年±2.0）可觀察出MLA<6.5平方公厘有做治療的7位與MLA≧6.5平方公厘的13位在於MACE上並無顯著之差異（MACE：包含血管再發狹窄、心肌梗塞及死亡）。而影響結果最主要的危險因子是年齡、抽煙及非LMCA Vessels disease的數量。血管內超音波是評估不確定的左主冠狀動脈病灶最準確之方法之一，因此我們發現最小管徑面積≧6.5平方公厘是可以不到，故進一步治療，也就是說是安全的低限值。

The aim of the study was to estimate the effeotiveness of an intravascular ultrasound (IVUS)-guided manipulation for patients with angiographically indeterminate left main coronary artery (LMCA) disease. The evaluation of LMCA lesions using coronary angiography is after challenging; P/US supply efficient information for assessment of left main coronary artery disease. IVUS was performed on 46 patients with angographically normal minimum lumen area (MLA), defined as the mean -2SD. We conducted IVUS studies on 24 patients with angiographically indeterminate left main coronary artery lesions, and deferral of revascularization was recommended when the MLA was larger than this predetermined valve. The lower range of normal LMCA MLA was 6.5mm^2 Of the patients with angiographically indeterminate LMCA 9 (37.5%) had an MLA<6.5mm^2, and 15 (62.5%) an MLA≧6.5mm^2. LMCA revascularization was performed in 77.7% (7 of 9) of patients with an WLA<65mm^2, and deferred in 86.6% (13 of 15) of patients with an MLA≧6.5mm^2 Long-term follow-up (1.3±2.0 years) showed no significant difference major adverse cardiac events (target vessel revascularization, acute myocardial infarction, and death) between patients with an MLA<6.5mm^2 who underwent revascularization and those with an MLA≧6.5mm^2 deferred for revascularization. Based on outcome the best cut-off MLA by receiver operating characteristic was 8.4mm^2. Major risk factors of cardiac events were age, smoking, and number of non-LMCA vessels disease. IVUS is an accurate method to assess angiographically indeterminate lesions of the LMCA. Furthermore, deferring revascularization for patients with a minimum lumen area≧6.5mm^2 appears to be safe