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Is cardiac computed tomography a reliable alternative to percutaneous coronary angiography for patients awaiting valve surgery
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     a Department of Interventional Radiology, Freeman Hospital, Newcastle, UK

    b Department of Cardiothoracic Surgery, James Cook University Hospital, Middlesbrough, UK

    Abstract

    A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was whether a CT angiogram could replace routine percutaneous coronary angiography for excluding coronary arterial disease for patients undergoing a non coronary cardiac procedure. Using the reported search 595 papers were identified. Eleven papers represented the best evidence on the subject and the author, journal, date and country of publication, patient group studied, study type, relevant outcomes, results and study comments and weaknesses were tabulated. We conclude that angiography with 64-slice multi-detector CT scanner provides reliable non-invasive imaging to exclude significant coronary artery stenoses prior to valve surgery. The negative predictive value of a normal CT scan is around 97%, thus providing a good alternative to conventional angiography in lower atherosclerotic risk patients. The ability of CT angiography to assess the reduction in luminal diameter is reduced in the presence of calcium deposits, and is also reduced in vessels under 1.5 mm. Further disadvantages include an inability to perform scans in patients with arrhythmias or atrial fibrillation, and a five times increased radiation dose compared to conventional angiography.

    Key Words: Thoracic surgery; Computed tomography; Angiography

    1. Introduction

    A best evidence topic was constructed according to a structured protocol. This protocol is fully described in the ICTVS [1].

    2. Clinical scenario

    You are seeing a 65-year-old patient who has been referred for aortic valve replacement due to aortic stenosis. He has no symptoms of angina but smoked for 25 years, finally quitting 10 years ago. His father also died of a heart attack when he was 60 years old. You tell him that you would like to get an angiogram to check his coronary arteries. He is not that keen on the idea and asks if there are any other scans that could do the same thing without the risks of angiography. You wonder whether a CT angiogram would be as sensitive a test for this patient.

    3. Three-part question

    In [patients who require exclusion of coronary artery disease] is [CT coronary angiography] comparable to [percutanous coronary angiography] for detecting/excluding clinically significant stenoses

    4. Search strategy

    Medline 2000–Oct 2006 using the OVID interface.

    [exp Tomography, X-Ray Computed/OR exp Tomography, Spiral Computed/OR computed tomography.mp] AND [64-slice.mp OR multislice.mp OR spiral.mp OR CVCT.mp or MSCT.mp or multidetector.mp] AND [coronary artery.mp or exp coronary vessels/] AND [exp coronary angiography/OR angiography.mp OR exp angiography/] LIMIT to Human.

    5. Search outcome

    Five hundred and ninety-five papers were found in MEDLINE. Eleven were deemed to be relevant. We included two systematic reviews and a guideline that considered papers of all generations of CT scanners and also documented all papers describing the results of 64-slice multidetector CT scanners. The papers are documented in Table 1.

    6. Comments

    The American Heart Association has published guidelines in this area in 2006 [2]. They documented studies up to 2006 and conclude that 64-slice multi-detector CT (MDCT) has a very high negative predictive value, thereby being able to rule out coronary artery disease in lower risk patients. They state that an MDCT to rule out coronary disease is a reasonable strategy compared to angiography (Class IIa, Level of Evidence B).

    Two meta-analyses have been performed. Schuijf et al. [3] summarised 24 studies with 1300 patients using 4–16-slice CT scanners compared to coronary angiography. They reported an overall per-segment sensitivity of 85% (1396/1650) and specificity of 95% (9064/9511) with an 87% rate of assessable coronary segments. The second meta-analysis was by Stein et al. [4], and they documented the per-patient sensitivity of 95% for 4–16-slice CT and specificity of 84% for 4–16-slice CT. They also documented that the number of evaluable segments increased from 78% for 4-slice scanners to 100% for the 64-slice study that they found. Both meta-analyses endorsed multislice CT scanning for exclusion of coronary disease in low risk patients.

    We identified eight studies documenting the effectiveness of 64-slice MDCT angiography [5–12]. These studies show a sensitivity of around 95% (range 73–100%) and a specificity of around 97% (range 93 to 100%) with a negative predictive value of 92–100%.

    88% to 97% of segments were evaluable and the radiation dose was around 10–15 mSv compared to a conventional angiography dose of around 2 mSv.

    Interestingly Plass et al. [12] studied 134 patients undergoing 64-slice MDCT and an angiogram, but asked two cardiac surgeons to report the scans. They obtained very good agreement between them and also an excellent sensitivity of 93% and specificity of 97% compared to routine angiography. Ninety-two percent segments were evaluable, with vessels <1.5 mm being excluded from analysis.

    Gilard et al. [13] performed a study specifically on 55 patients undergoing assessment prior to surgery for aortic stenosis. They used a 16-slice CT scanner, but successfully excluded coronary arterial disease in 35 patients with a negative predictive value of 100%. The weakness of the CT scan was again for patients with coronary arterial disease with calcium deposits, where quantification of stenotic lesions was difficult.

    Sixty-four-slice MDCT has an excellent negative predictive ability, and thus can accurately exclude the presence of coronary arterial disease. However, the presence of high levels of calcium reduce the sensitivity of the scan, as it remains difficult to assess the luminal narrowing in the presence of calcium. The number of segments that cannot be excluded are now markedly reduced, mainly only being vessels under 1.5 mm in diameter. The radiation dose is around five times that of an angiogram. A significant limitation is the inability to perform a scan on any patient who is not in sinus rhythm with a slow rate.

    7. Clinical bottom line

    Angiography with 64-slice multi-detector CT scanner may provide reliable non-invasive imaging to exclude significant coronary artery stenoses prior to valve surgery. The negative predictive value of a normal CT scan is around 97%, thus providing a good alternative to conventional angiography in lower atherosclerotic risk patients. The ability of CT angiography to assess the reduction in luminal diameter is reduced in the presence of calcium deposits, and is also reduced in vessels under 1.5 mm. Further disadvantages include an inability to perform scans in patients with arrhythmias or atrial fibrillation, and a five times increased radiation dose compared to conventional angiography.

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    Gilard M, Cornily JC, Pennec PY, Joret C, Le GG, Mansourati J, Blanc JJ, Boschat J. Accuracy of multislice computed tomography in the preoperative assessment of coronary disease in patients with aortic valve stenosis. [see comment]. J Am Coll Cardiol 2006; 47:2020–2024.(Vivek Shrivastavaa, Sriram Vundavallia, )