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16 Multislice CT in Coronary Heart Disease KCE Reports 82 implemented, a high rate of false positives would result in increased downstream costs and interventions. The radiation dose associated with MSCT represents one of the major reasons to preclude its use as a screening tool for asymptomatic patients. 43 Even in the year 2008, this advice remains: “For the time being, MSCT continues not to be recommended as a screening tool, and the low radiation dose of the step-and-shoot mode in selected patients should not be taken as a justification for using this indication.” 44 2.4.2.2 MSCT as an alternative for invasive coronary angiography As compared to CCA, MSCT has the advantage of avoiding some of the inconveniences and of the morbidity associated with CCA. Nevertheless, the exposure to ionising radiation and the need for contrast medium injection remains a matter of concern. On the other hand, if revascularisation is indicated, an invasive procedure with a second exposure to radiation remains necessary. MSCT seems especially useful when the result shows normal coronary arteries but then, one might question if the same conclusion could not have been obtained by other noninvasive techniques in a more efficient way. Moreover, false postive examinations will lead to further invasive tests and may annihilate the alleged advantages of the noninvasive angiography. 2.4.2.3 MSCT as an additional noninvasive test The diagnostic accuracy of MSCT has to be compared with that of other tests such as ECG stress testing, MPS and DSE. The latter tests however have the advantage that they provide information on myocardial perfusion, additional to the mere documentation of coronary stenoses. MSCT can only visualise coronary lesions without assessing the functional impact of them. It might be possible that future generation scanners will be able to assess the nature of coronary plaques and give information that thus far is not obtainable by any other noninvasive test. This is a matter of current research. 2.4.2.4 MSCT for the evaluation of coronary artery stents and bypass grafts Owing to the artifacts caused by metal, visualization of the coronary lumen within stents by MSCT is more challenging than evaluation of the native coronary arteries. Clinical studies published so far, show a consistently low sensitivity to identify in-stent restenosis. The limited spatial resolution of MSCT, the type of stent, and stent diameter 36, 45 all contribute to limited clinical results. Visualisation of bypass grafts with MSCT on the other hand, is generally less problematic because they are larger than native vessels and less subject to motion artifacts. The presence of metal clips on mammary artery grafts can be problematic due to blooming artifacts. Despite the high degree of accuracy to detect lesions within grafts, MSCT has limited value after CABG, because an assessment of the native coronary arteries is also required, which tend to be more challenging because native vessels often are heavily calcified in postoperative patients. 36 The role of MSCT in patients after CABG or PCI will not be further discussed in this report, that focuses on native coronary arteries.
KCE Reports 82 Multislice CT in Coronary Heart Disease 17 Key points • The feasibility of anatomic imaging of the continuously moving coronary arteries by CT became possible by the introduction of spiral scanning and multislice CT scanning, which provide smaller pieces of information and cover a larger area faster than conventional CT. • The main areas of concern for MSCT are (1) motion artifacts from rapid or irregular heart rhythm, (2) artifacts from coronary artery calcium, and (3) high radiation dose. • The radiation dose delivered by MSCT is higher than that of CCA although newer generation scanners and newer scanning protocols induce less radiation in selected patients. However, there is a tradeoff between dose reduction and the diagnostic efficacy of the images. 2.5 TREATMENT OPTIONS IN CHD Treatment of CAD aims at two different objectives: (1) to alleviate symptoms or (2) to improve prognosis by preventing MI and death. This can be achieved by medical treatment and by myocardial revascularisation, the latter referring to a restoration of the impaired blood flow surgically (coronary artery bypass grafting – CABG) or percutaneously (percutaneous coronary intervention – PCI). There is a large international variation in the proportion of patients that undergo revascularisation, both in acute and non-acute ischemic syndromes. 46 Apart from the management of ischemia, treatment is further supplemented with secondary preventive measures, including life style changes and drug treatment, in an attempt to prevent recurrent events and improve life expectancy. 2.5.1 Treatment of stable angina In patients with stable angina, symptomatic treatment can be implemented by medical treatment (nitrates, beta-blockers, calcium-blockers, antiplatelets), by lifestyle changes (smoking cessation, weight reduction, physical activities), or through myocardial revascularization. Except for patients with left main stem disease who are generally excluded from randomized trials, there is no robust evidence that revascularisation improves survival. 46, 47 Although guidelines advocate an initial approach with pharmacological treatment, PCI became common practice in the initial management strategy of patients with stable CAD. 4, 48 Very recently, the results of the COURAGE trial in 2287 patients comparing optimal medical therapy with or without PCI for stable CAD were published. 2 The primary outcome of the study was death from any cause and nonfatal MI during a median follow-up period of 4.6 years. Nearly 70% of patients had multi-vessel disease and in more than 30% the proximal left anterior descending artery (LAD) was involved. The 4.6-year cumulative primary-event rates were 19.0% in the PCI group and 18.5% in the medical therapy group (hazard ratio for the PCI group, 1.05; 95% CI 0.87-1.27). There were no significant differences between the PCI group and the medical therapy group in the composite of death, myocardial infarction and stroke. PCI resulted in a better symptomatic outcome of patients. Nearly 33% of patients crossed from medical therapy to revascularisation during the 4.6 year period, but since there was no increased risk of death or MI and no significant difference in hospitalization for ACS, the conclusion of the trialists that PCI can be safely deferred in patients with stable angina stood firm, provided optimal medical therapy is instituted and maintained. When these results were added to a previously published meta-analysis, calculations reinforced the absence of a difference between PCI and medical therapy in patients with stable coronary artery disease, with no difference in outcomes in terms of MI or death from any cause. 49 Another trial (MASS-II), also published in 2007, compared medical therapy, PCI and CABG in 611 patients with stable angina, multi-vessel disease and
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