專題討論11:冠狀動脈病診斷與治療新進展
New Advannces in Diagnosis and Treatment of CAD

程 序 表

S11-1
新MDCT診斷可替代冠狀動脈攝影嗎?
王宗道
臺大醫院內科部心臟內科

  Computed tomography (CT), particularly multirow detector CT (MDCT), is quickly evolving into a remarkably useful imaging tool for evaluating the burden of atherosclerosis and the severity and character of coronary artery disease (CAD). Numerous studies have demonstrated that the diagnostic performance of coronary CT angiography (CTA) is at least comparable if not superior to all competing imaging modalities. In general, segment-based positive and negative predictive values of MDCT in detecting stenosis ?50% are 85-90% and 95-99%, respectively. However, calcium can obscure the vessel lumen and make it difficult to determine the severity of coronary stenoses. Coronary CTA may not be done if calcium score is greater than 1000 units and diffuse.

  American guidelines for the use of coronary CTA have been published in 2010. The most widely agreed indication is the evaluation of patients with a low to intermediate probability of CAD who present with a chest pain syndrome but no electrocardiographic or biomarker evidence of acute ischemia. In these patients, a normal CTA can reliably exclude obstructive CAD given its excellent negative predictive value. In other words, CTA can indeed replace invasive coronary angiography in this scenario. It should be emphasized that assessment of coronary calcium score alone is not sufficient to exclude CAD.

  The second indication for coronary CTA is in patients who have equivocal results with conventional stress testing, including discordance between symptoms, ST segment analysis, and wall motion or perfusion. A normal coronary CTA can obviate the need for invasive angiography. One study showed that approximately two-thirds of patients with equivocal stress tests have no obstructive CAD by coronary CTA, thus avoiding further expenditure.

  The use of CT to assess in-stent restenosis is reliable only in selected patients, mainly those with proximal stents ?3.0 mm in diameter. Coronary CTA is very useful for evaluation of coronary bypass grafts and coronary artery anomalies. CT provides a complete three-dimensional visualization of coronary anomalies, including the course of each vessel and its anatomic relationship to the aorta and the pulmonary artery.

  According to the guidelines, it is inappropriate to perform CTA in patients presenting with chest pain who have a high pretest probability of CAD. Screening of asymptomatic patients with coronary CTA is still not recommended.

  Both measurements of calcium score and CTA expose patients to ionizing radiation. In the recent past, the effective dose of CTA was about 12 mSv.