Ann Thorac Surg 2011;92:e47-e48. doi:10.1016/j.athoracsur.2011.03.126
© 2011 The Society of Thoracic Surgeons
Case Reports
Comprehensive Dynamic Aortic and Cardiac Analysis by 256-Slice Computed Tomography in Type A Dissection
Ricardo P.J. Budde, MD, PhDa,*,
Jolanda Kluin, MD, PhDb,
Lex A. van Herwerden, MD, PhDb,
Mathias Prokop, MD, PhDa
a Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands
b Department of Cardio-thoracic Surgery, University Medical Center Utrecht, Utrecht, The Netherlands
Accepted for publication March 25, 2011.
* Address correspondence to Dr Budde, Department of Radiology, University Medical Center Utrecht (HpN E01.132), Heidelberglaan 100, Utrecht 3584 CX, The Netherlands (Email: rbudde{at}umcutrecht.nl).
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Abstract
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The faster scanning speed of 256-slice computed tomographic scanners has enabled electrocardiographic-gated imaging of the entire thoraco-abdominal aorta in several seconds. Electrocardiographic-gated acquisition allows for image reconstruction in any desired phase of the cardiac cycle, as well as dynamic assessment by looping the different reconstruction phases. We describe the application of 256-slice computed tomography in a patient with Marfan syndrome and acute type A aortic dissection. A comprehensive static and dynamic aorto-cardiac analysis was performed from a single scan, including the aortic dissection, aortic valve prosthesis, and coronary arteries.
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Introduction
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Type A aortic dissection is an acute life-threatening entity that requires prompt diagnosis and surgical repair. Computed tomography (CT) is the gold imaging standard for diagnosing type A dissection. However, the fast and vigorous movements of the aortic root during the cardiac cycle can result in CT motion artifacts that mimic an intraluminal intimal flap making the diagnosis challenging [1]. Electrocardiographic (ECG)-gated CT image acquisition allows almost motion-free imaging during each desired phase of the cardiac cycle and has enabled dedicated cardiac CT imaging. Obtaining an ECG-gated acquisition may thus allow more confident diagnosis of a dissection due to the reduction or elimination of motion artefacts. Furthermore, this may allow assessment of the coronary arteries for stenosis, which are present in approximately one third of patients with acute type A aortic dissection [2]. However, dedicated retrospectively ECG-gated cardiac CT is usually performed at relatively high imaging settings (120 KV; 600 to 800 mAs). However, in suspected type A dissection, the entire aorta needs to be visualized to determine the extent of the false lumen. Integrating ECG gating for such long scan regions (entire aorta) at imaging settings used for dedicated cardiac imaging, results in extensive radiation exposure and the need for relatively long breatholds on slower 16-slice and 64-slice scanners, which are difficult for acute patients.
We present the application of a thoraco-abdominal ECG-gated CT scan protocol on a 256-slice scanner using a lower (250) mAs setting than for dedicated cardiac CT to illustrate its potential for comprehensive dynamic aorto-cardiac assessment in a patient with a type A aortic dissection.
A 32-year-old patient with Marfan syndrome presented to our hospital with acute chest pain. Previously, the patient had a limited aortic root replacement with an aortic root bioprosthesis (Medtronic Freestyle; Medtronic, Minneapolis, MN) and mitral valve repair. The coronary arteries had been reimplanted in the graft. An acute aortic dissection was suspected and the patient underwent emergent retrospectively ECG-gated thoraco-abdominal CT with intravascular contrast. The scan was performed on a 256-slice scanner (120 KV, 250 mAs, iCT [Philips, Best, The Netherlands]). Total scan length was 66 cm (from 6 cm above the aortic arch to 10 cm below the femoral head). Eight image data sets were reconstructed at each 12.5% of the ECG interval. A scan length of 66 cm requires 10.6 seconds scan time and is associated with a radiation dose of 18.9 mSv, which is higher than a standard non-ECG-gated scan (12 mSv), but less than a dedicated ECG-gated cardiac scan protocol (43 mSv) of the same scan length.
The CT demonstrated an acute type A aortic dissection with the entry site in the distal ascending aorta and proximal aortic arch (Fig 1
). The intimal flap extended to the aortic bifurcation. Proximally, the flap ended at the level in which the aortic root bioprosthesis and the native aorta had been anastomosed. By looping the CT reconstructions at each 12.5% of the ECG interval, the dynamics of the intimal flap and entry site, as well as the aortic root bioprosthesis, was clearly visualized as illustrated by the systolic and diastolic reconstructions presented in Figure 2
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Fig 1. Diastolic coronal computed tomographic image reconstruction of the aortic root and ascending aorta showing the entry site (arrowhead) of the aortic type A dissection. Note how the intimal flap extends upstream and ends at a circular ridge where the native aorta and graft were joined (black arrow). The leaflets of the aortic valve bioprosthesis are severely calcified (white arrow).
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Fig 2. Systolic (A) and diastolic (B) axial computed tomographic images of the type A dissection. Note the different position of the intimal flap in both reconstruction phases.
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Comment
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The ECG-gated reconstructions also allow static and dynamic imaging of the aortic valve and coronary arteries. The aortic valve bioprosthetic leaflets were shown to be thin and severely degenerated as evidenced by extensive calcification (Fig 3
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Fig 3. Systolic (A) and diastolic (B) in plane reconstruction of the aortic valve prosthesis. The valve leaflets are severely calcified. The valve opens nicely during systole and closes completely during diastole.
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The coronary arteries were all adequately visualized and showed no calcifications or stenosis. No dissections were seen in the coronary arteries, which was not expected because they had been reimplanted in the graft.
The patient underwent emergency reoperation under deep hypothermia with replacement of the aortic valve, root, arch, and part of the descending aorta with a mechanical valve prosthesis and vascular grafts. Surgery was technically challenging, but it was successfully completed. Postoperative recovery was complicated by pneumonia, transient muscle weakness, and impaired vision due to insufficient control of elevated cerebrospinal fluid pressure. The patient was discharged in good condition, but the impaired vision persisted.
Retrospectively ECG-gated, 256-slice thoraco-abdominal CT provides images at different time points in the cardiac cycle, which facilitates detection of an aortic dissection. The ECG-gated images also provide dynamic assessment of the intimal flap, as well as aortic valve function. Furthermore the coronary arteries can be adequately assessed. Therefore, we routinely use this imaging protocol in all patients with suspected type A dissection and other acute aortic pathology, because it can provide a comprehensive aorto-cardiac analysis from a single scan.
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References
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- Batra P, Bigoni B, Manning J, et al. Pitfalls in the diagnosis of thoracic aortic dissection at CT angiography Radiographics 2000;20:309-320.[Abstract/Free Full Text]
- Creswell LL, Kouchoukos NT, Cox JL, Rosenbloom M. Coronary artery disease in patients with type A aortic dissection Ann Thorac Surg 1995;59:585-590.[Abstract/Free Full Text]
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Abstract
Introduction
