Multidetector Computed Tomography Imaging Before Aortic Valve Implantation
Angiography of the Aorta and the Iliofemoral Arteries Performed after a minimal delay (tube cooling) and taking advantage of the residual opacification of cardiac imaging, iliofemoral angiography requires a second injection of about 50 ml of contrast medium at a rate of 4 ml/s flushed by saline at a rate of 3.5 ml/s. The FOV is large and covers the abdominal–pelvic region from the diaphragmatic hiatus to at least 3 cm under the femoral tripod. Vascular reconstruction requires close attention since no blind segments can be accepted. The reconstruction is composed of luminal and short-axis views of the whole vessels. A 3D view (including anteroposterior, lateral, and oblique views) of the iliofemoral arteries allows the sinuosity, angulations, and global calcification of the vascular axis to be analyzed, as shown in Figure 4.
At our institution, when uni- or bilateral hip prosthesis is present we prefer a dual-energy CT examination, which consists of a dynamic switching acquisition between two different energy levels of X-rays (80 and 140 kVp). The dual-energy data are processed using Gemstone Spectral Imaging (GSI, GE Healthcare, Milwaukee, WI, US) to generate ‘quality-check’ images from high-kVp data (140 kVp) and monochromatic images with a metal artifact reduction algorithm. This technique allows better visualization and analysis of the iliofemoral artery adjacent to the metal implant. Wall vessel depiction and automatic vessel analysis are also improved compared with a conventional acquisition (see Figure 5). On short-axis views, the arterial puncture segment is analyzed in terms of caliber and calcification. Then, by simulating the passage of the prosthesis on the luminal view, we look for a critical caliber zone (based on the minimal and average diameter). This segment is optimally analyzed in its short axis. A critical caliber with a non-calcified vessel (or with a punctiform calcification) is less problematic than a vessel with stenosis and a circumferential or mirror calcification (see Figure 4).
The ideal patient for PHV implantation will have large-caliber iliofemoral arteries free of calcification. The radiologist’s role is ultimately to infer the arterial plasticity from CT data, including calibers, calcification, and tortuosity. Focal arterial dissection or aneurysms are not rare, and are considered contraindications to catheterization. The 23 mm PHV is compatible with a 22 Fr sheath, and the minimum diameter of the iliofemoral arteries is 7 mm. For the 26 mm PHV (24 Fr sheath), the minimal diameter of the iliofemoral arteries is 8 mm.4
Non-cardiovascular Findings
Screening MDCT examinations can often reveal incidental non-cardiovascular findings such as renal or lung cancer, liver and
1. Cribier A, Eltchaninoff H, Bash A, et al., Percutaneous transcatheter implantation of an aortic valve prosthesis for calcific aortic stenosis: first human case description, Circulation, 2002;106:3006–8.
2. Zajarias A, Cribier A, Outcomes and safety of percutaneous aortic valve replacement, J Am Coll Cardiol, 2009;53:1829–36.
3. Webb JG, Chandavimol M, Thompson CR, et al., Percutaneous aortic valve implantation retrograde from the femoral artery, Circulation, 2006;113:842–50.
4. Eltchaninoff H, Zajarias A, Tron C, et al., Transcatheter aortic valve implantation: technical aspects, results and indications, Arch Cardiovasc Dis, 2008;101:126–32.
gallbladder disease, inguinal hernia, or other disease. These findings should be reported and taken into consideration in the selection of patients for PHV implantation.
Evaluation Following Pulmonary Heart Valve Implantation
MDCT is of potential interest for evaluating the correct positioning and sizing of the Cribier-Edwards transcutaneous PHV.8
The accurate
positioning of the bioprosthesis and its relationship with the annulus, coronary ostia, interventricular septum, and mitral valve can be demonstrated by volume imaging, as can the position of the displaced native calcifications (see Figure 1). CT is used as a complement to echocardiography, which remains the reference technique to identify aortic regurgitation.9
Patients who have undergone valve replacement are imaged with a retrospectively gated cardiac CT protocol. similar to that used for pre-operative assessment.
The Role of Cardiac Magnetic Resonance Examination
Magnetic resonance (MR) is not recommended when planning vascular access analysis because of its limited spatial resolution. Furthermore, MR examination is difficult to perform in elderly patients who have difficulties supporting a prolonged decubitus and repeat multiple breath-holds. At our institution we perform MR examinations to define the anatomy (bicuspid versus tricuspid aortic valve) and maximal systolic opening in discordant cases. MR is often more efficient than CT for assessing systolic aortic valve area and bicuspid valvular anomalies because it is not disturbed by calcifications and has a better temporal resolution. Phase-contrast sequences are mostly used in this area. Another area where MR may be of interest is the identification of fibrosis from delayed-enhancement sequences.10
MR is not adapted for post-implantation evaluation
because the stent is a major source of artifacts. Nevertheless, the Edwards prosthesis is compatible with MR, and MR examination of other organs is not contraindicated.
Conclusion
PHV implantation has the potential to offer life-saving treatment to patients with inoperable and severe aortic stenoses. MDCT plays a key role in patient selection and evaluation. Not only radiologists but also general physicians, interventionalists, and surgeons should share and co-ordinate knowledge, skills, and clinical wisdom to ensure the successful future development of PHV implantation. n
5. Leipsic J, Wood D, Manders D, et al., The evolving role of MDCT in transcatheter aortic valve replacement: a radiologists’ perspective, AJR Am J Roentgenol, 2009;193:W214–W9.
6. Willmann JK, Weishaupt D, Lachat M, et al., Electrocardiographically gated multi-detector row CT for assessment of valvular morphology and calcification in aortic stenosis, Radiology, 2002;225:120–8.
7. Laissy JP, Messika-Zeitoun D, Serfaty JM, et al., Comprehensive evaluation of preoperative patients with aortic valve stenosis: usefulness of cardiac multidetector computed tomography, Heart, 2007;93:1121–5.
8. Webb JG, Wood DA, Ye J, et al., Transcatheter valve-in-valve implantation for failed bioprosthetic heart valves, Circulation, 2010;121:1848–57.
9. Tron C, Bertrand D, Dacher JN, et al., Sixty-four multislice computed tomography after transcutaneous implantation of a Cribier-Edwards bioprosthesis in the aortic position, Eur Heart J, 2008;29:2163.
10. Nigri M, Azevedo CF, Rochitte CE, et al., Contrast-enhanced magnetic resonance imaging identifies focal regions of intramyocardial fibrosis in patients with severe aortic valve disease: correlation with quantitative histopathology, Am Heart J, 2009;157:361–8.
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