Ont Health Technol Assess Ser. 2007;7(3):1-56. Epub 2007 May 1.
This evidence-based health technology assessment systematically reviewed the published literature on multidetector computed tomography (MDCT) angiography (with contrast) as a diagnostic tool for coronary artery disease (CAD), and applied the results of the assessment to health care practices in Ontario.
Coronary artery disease is the leading cause of death in the western world. Occlusion of coronary arteries reduces coronary blood flow and oxygen delivery to the myocardium (heart muscle). The rupture of an unstable atherosclerotic plaque may result in myocardial infarction. If left untreated, CAD can result in heart failure and, subsequently, death. According to the Heart and Stroke Foundation of Canada, 54% of all cardiovascular deaths are due to CAD. Patient characteristics (e.g., age, sex, and genetics), underlying clinical conditions that predispose to cardiac conditions (e.g., diabetes, hypertension, and elevated cholesterol), lifestyle characteristics, (e.g., obesity, smoking, and physical inactivity), and, more recently, determinants of health (e.g., socioeconomic status) may predict the risk of getting CAD. In 2004/2005, The Ontario government funded approximately 15,400 percutaneous (through the skin) coronary interventions and 7,840 coronary bypass procedures for the treatment of CAD. These numbers are expected to reach 22,355 for percutaneous coronary interventions and 12,323 for coronary bypass procedures in 2006/2007. It was noted that more than one-half of all first coronary events occur in people without symptoms of CAD. In Ontario in 2000/2001, $457.9 million (Cdn) was spent on invasive ($237.4 million) and noninvasive ($220.5 million) cardiac services. The use of noninvasive cardiac tests, in particular, is rising rapidly.
Computed tomography (CT) is a medical imaging method employing tomography where digital geometry processing is used to generate a 3-dimensional image of the internals of an object from a large series of 2-dimensional X-ray images taken around a single axis of rotation. Multidetector computed tomography is performed for noninvasive imaging of the coronary arteries. Computer software quantifies the amount of calcium within the coronary arteries and calculates a coronary artery calcium score. Compared with conventional CT scanning, MDCT can provide smaller pieces of information and cover a larger area faster. Advanced MDCT technology (that is, 8-, 16-, 32-, and 64-slice systems) can produce more images in less time. For general CT scanning, this faster capability can reduce the length of time people are required to be still during the procedure and thereby reduce potential movement artifact. However, the additional clinical utility of images obtained from faster scanners compared with the images obtained from conventional CT scanners for current CT indications (i.e., nonmoving body parts) is unknown.
The Medical Advisory Secretariat completed a computer-aided search limited to English-language studies in humans from 1998 to 2007 in multiple medical literature databases, including MEDLINE, EMBASE, The Cochrane Library, and INAHTA/CRD. Case reports, letters, editorials, nonsystematic reviews, and comments were excluded. Additional studies that met the inclusion and exclusion criteria were obtained from reference lists of included studies. Inclusion and exclusion criteria were applied to the results according to the criteria listed below. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) system was used to evaluate the overall quality of the body of evidence (defined as 1 or more studies) supporting the research questions explored in this systematic review.
Screening the asymptomatic population for CAD using MDCT does not meet World Health Organization criteria for screening; hence, it is not justifiable. Coronary artery calcification measured by MDCT is a good predictor of future cardiovascular events. However, MDCT exhibits only moderately high sensitivity and specificity for detection of CAD in an asymptomatic population. If population-based screening were implemented, a high rate of false positives would result in increased downstream costs and interventions. Additionally, some cases of CAD would be missed, as they may not be developed, or not yet have progressed to detectable levels. There is no evidence for the impact of screening on patient management. Cardiovascular risk factors are positively associated with the presence of coronary artery calcification and cardiovascular events; however, risk factor stratification to identify high-risk asymptomatic individuals is unclear given the current evidence-base. Safety of MDCT screening is also an issue because of the introduction of increased radiation doses for the initial screening scan and possible follow-up interventions. No large randomized controlled trials of MDCT screening have been published, which indicates an important area of future research. Lastly, the policy implications for MDCT screening for CAD in the asymptomatic population are significant. There is no evidence on the long-term implications of screening, and the potential impact on the resources of the health care system is considerable.
本循证卫生技术评估系统回顾了已发表的关于多排螺旋计算机断层扫描（MDCT）血管造影（使用造影剂）作为冠状动脉疾病（CAD）诊断工具的文献，并将评估结果应用于安大略省的医疗实践。
冠状动脉疾病是西方世界的主要死因。冠状动脉阻塞会减少冠状动脉血流以及向心肌（心脏肌肉）的氧气输送。不稳定动脉粥样硬化斑块的破裂可能导致心肌梗死。如果不进行治疗，CAD会导致心力衰竭，进而导致死亡。根据加拿大心脏与中风基金会的数据，所有心血管死亡中有54%归因于CAD。患者特征（如年龄、性别和遗传因素）、易患心脏疾病的潜在临床状况（如糖尿病、高血压和胆固醇升高）、生活方式特征（如肥胖、吸烟和缺乏身体活动），以及最近的健康决定因素（如社会经济地位）可能预测患CAD的风险。在2004/2005年，安大略省政府为治疗CAD资助了约15,400例经皮（通过皮肤）冠状动脉介入手术和7,840例冠状动脉搭桥手术。预计在2006/2007年，这些数字将分别达到经皮冠状动脉介入手术22,355例和冠状动脉搭桥手术12,323例。值得注意的是，所有首次冠状动脉事件中有超过一半发生在没有CAD症状的人群中。在2000/2001年的安大略省，花费了4.579亿加元用于侵入性（2.374亿加元）和非侵入性（2.205亿加元）心脏服务。特别是，非侵入性心脏检查的使用正在迅速增加。
计算机断层扫描（CT）是一种医学成像方法，采用断层扫描技术，通过数字几何处理从围绕单个旋转轴拍摄的大量二维X射线图像生成物体内部的三维图像。多排螺旋计算机断层扫描用于冠状动脉的非侵入性成像。计算机软件对冠状动脉内的钙含量进行量化，并计算冠状动脉钙化积分。与传统CT扫描相比，MDCT可以提供更详细的信息，并能更快地覆盖更大的区域。先进的MDCT技术（即8层、16层、32层和64层系统）可以在更短的时间内生成更多图像。对于一般的CT扫描，这种更快的能力可以减少患者在检查过程中需要保持静止的时间，从而减少潜在的运动伪影。然而，与从传统CT扫描仪获得的图像相比，更快的扫描仪获得的图像对于当前CT适应症（即非移动身体部位）的额外临床效用尚不清楚。
医学咨询秘书处完成了一项计算机辅助搜索，限于1998年至2007年在多个医学文献数据库（包括MEDLINE、EMBASE、Cochrane图书馆和INAHTA/CRD）中发表的英文人体研究。病例报告、信件、社论、非系统综述和评论被排除。从纳入研究的参考文献列表中获取了符合纳入和排除标准的其他研究。根据以下列出的标准将纳入和排除标准应用于结果。采用推荐分级评估、制定与评价（GRADE）系统来评估支持本系统综述中探索的研究问题的证据总体质量（定义为一项或多项研究）。
使用MDCT对无症状人群进行CAD筛查不符合世界卫生组织的筛查标准；因此，这是不合理的。通过MDCT测量的冠状动脉钙化是未来心血管事件的良好预测指标。然而，MDCT在无症状人群中检测CAD的敏感性和特异性仅为中等高度。如果实施基于人群的筛查，高假阳性率将导致下游成本和干预增加。此外，一些CAD病例可能会被漏诊，因为它们可能尚未发展，或者尚未进展到可检测水平。没有证据表明筛查对患者管理有影响。心血管危险因素与冠状动脉钙化的存在和心血管事件呈正相关；然而，鉴于当前的证据基础，用于识别高危无症状个体的危险因素分层尚不清楚。由于初始筛查扫描引入了更高的辐射剂量以及可能的后续干预，MDCT筛查的安全性也是一个问题。尚未发表关于MDCT筛查的大型随机对照试验，这表明这是未来研究的一个重要领域。最后，对无症状人群进行MDCT筛查CAD的政策影响重大。没有关于筛查长期影响的证据，并且对医疗保健系统资源的潜在影响相当大。
