Ascending–descending aortic bypass surgery in aortic arch coarctation: Four-dimensional magnetic resonance flow analysis
2006; Elsevier BV; Volume: 133; Issue: 1 Linguagem: Inglês
10.1016/j.jtcvs.2006.08.061
ISSN1097-685X
AutoresAlex Frydrychowicz, C Schlensak, Aurélien F. Stalder, Max Russe, Matthias Siepe, Friedhelm Beyersdorf, Mathias Langer, Jürgen Hennig, Michael Markl,
Tópico(s)Aortic Disease and Treatment Approaches
ResumoIn light of the current discussion about the effect of blood flow on arterial wall remodeling,1Richter Y. Edelman E.R. Cardiology is flow.Circulation. 2006; 113: 2679-2682Crossref PubMed Scopus (105) Google Scholar, 2Cheng C. Tempel D. van Haperen R. et al.Atherosclerotic lesion size and vulnerability are determined by patterns of fluid shear stress.Circulation. 2006; 113: 2744-2753Crossref PubMed Scopus (722) Google Scholar, 3Wentzel J.J. Corti R. Fayad Z.A. et al.Does shear stress modulate both plaque progression and regression in the thoracic aorta? Human study using serial magnetic resonance imaging.J Am Coll Cardiol. 2005; 45: 846-854Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar the investigation of vascular hemodynamics within the aorta is of great interest. It has the potential to greatly enhance the understanding of the pathogenesis and progression of vascular diseases and to aid in the decision of whether treatment is warranted. Noninvasive magnetic resonance imaging (MRI), with its intrinsic sensitivity to blood flow, offers the unique possibility to simultaneously acquire morphology and spatially coregistered hemodynamic information noninvasively.4Pelc L.R. Pelc N.J. Rayhill S.C. et al.Arterial and venous blood flow: noninvasive quantitation with MR imaging.Radiology. 1992; 185: 809-812PubMed Google Scholar Electrocardiography-synchronized and respiration-controlled 3-dimensional magnetic resonance (MR) velocity mapping (flow-sensitive 4-dimensional MRI), a state-of-the-art MRI technique, was used to acquire time-resolved, 3-dimensional, morphologic, and 3-directional blood flow data. Visualization was performed with a commercially available software tool initially developed for engineering applications, which allowed for several 3-dimensional visualization modes for a detailed visual inspection of local hemodynamic features associated with complex vascular geometries (Appendix E1).5Frydrychowicz A. Weigang E. Harloff A. et al.Images in cardiovascular medicine Time-resolved 3-dimensional magnetic resonance velocity mapping at 3 T reveals drastic changes in flow patterns in a partially thrombosed aortic arch.Circulation. 2006; 113: e460-e461Crossref PubMed Scopus (15) Google Scholar A homemade software tool was used to quantify blood flow information at multiple locations along the vascular tree. Based on an exemplary patient measurement, the possibilities of time-resolved 3-dimensional flow visualization and MR-based quantitative flow analysis are demonstrated, which might influence therapeutic strategies in individual patients in addition to standard clinical diagnostic testing. In this symptomatic patient MR angiography depicted a moderate coarctation of the aortic arch (Figure 1). However, in addition to the stenosis, unusual origins of the supra-aortic branches were diagnosed. A large right common carotid artery was directly followed by the left internal carotid artery. At the height of the coarctation, both the left and right subclavian arteries originated. The right subclavian artery crossed behind the esophagus to the right side as a lusoric artery (Figure 1, white asterisk). Directly distal to the stenosis, the left external carotid artery (Figure 2) branched from the aorta.Figure 2Middle, surface-rendered image from flow-sensitive 4-dimensional magnetic resonance imaging with cut planes placed orthogonal to the general flow direction. Left and right, Charts displaying blood flow over time in liters per millisecond in the cardiac cycle for 12 acquired time frames. Below, Flow scheme displaying blood flow per cardiac cycle distributed within the vessels of interest. Cut planes used for flow quantification and absolute results, as well as percentage of flow through bypass and arch, are schematically indicated by red bars and red numbers, respectively. AAo, Ascending aorta; CoA, coarctation; DAo, descending aorta; RCCA, right common carotid artery; LICA, left internal carotid artery; LECA, left external carotid artery; LSA, left subclavian artery; LusA, lusoric artery.View Large Image Figure ViewerDownload Hi-res image Download (PPT) The patient was offered surgical repair of the aorta because the atypical aortic branches are associated with an increased risk for complications during endovascular intervention. By using an intercostal approach, a 2-cm Dacron bypass graft was placed between the ascending and descending aortas. Postoperatively, the patient complained about dizziness and became unconscious once. However, cranial computed tomography and color-coded Doppler ultrasonography of the external and internal carotid artery remained unchanged. Four-dimensional MR velocity mapping was performed for an additional overview over the flow alterations and hemodynamic status after the surgical procedure. Figure 1, B, resembles particle traces at late systole. The highly accelerated flow within the bypass graft can be clearly appreciated. Additionally, overt vertical and considerable helical blood flow in the descending aorta distal to the bypass anastomosis were observed. Severe blood flow alterations, even further downstream to the site of the bypass, points toward the effect of the performed surgical procedure and the long-term alteration of vessel wall parameters because the helical flow is associated with altered wall shear rates. Also, the efficiency of vascular filling expressed by the energy loss caused by enhanced transverse kinetic energy is jeopardized and might lead to a changed distribution of blood flow further downstream. (These findings can be appreciated in more detail by viewing the time-resolved particle traces shown in Figure E1.) For a more quantitative analysis, multiple extracted cut planes were evaluated manually by means of individual segmentation of the vascular lumen at all time frames within the cardiac cycle. Results are given in Figure 2 for four 2-dimensional cut planes in the ascending aorta before the bypass, in the descending aorta distal to the bypass, and for both the aortic arch and the proximal bypass (see also schematic analysis, Figure 2, below). The amount of blood flow was readily computed and is displayed as corresponding flow curves with unsuspicious pulse-wave diagrams. Remarkably, about 55% of ascending aortic blood flow volume was directed through the bypass, whereas only 22% was delivered to the aortic arch and thereby to the supra-aortic branches. This “aortic steal” effect led to the decision to introduce α1-mimetics. Using this medication, the patient had a relief of neurological symptoms in her daily life. Despite the limitations, such that MRI is not as widely available as ultrasonography and not ubiquitously available, the technique offers a unique possibility for comprehensive assessment of 3-dimensional vascular hemodynamics, especially in complex vascular geometries. More notably, the added information content not assessable with other imaging modalities has the potential to influence therapeutic decision making, as in the case presented here. However, further serial assessments and patient studies are necessary to evaluate the potential to influence therapeutic decision making and planning of operative procedures in vascular disease. The investigation was performed on a 3T-MR-scanner (TRIO; Siemens Medical Solutions, Erlangen, Germany) using a previously described and modified radiofrequency-pulse spoiled gradient echocardiographic sequence with interleaved 3-directional velocity encoding. Imaging parameters were as follows: velocity encoding, 150 cm/s; spatial resolution, 2.1 × 3.2 × 3.5 mm3; sagittal oblique field of view, 400 × 300 mm2; flip angle, 15°; echo time, 3.5 ms; repetition time, 6.1 ms; bandwidth, 480 Hz per pixel. Respiratory-controlled imaging was performed based on adaptive navigator gating, allowing for free breathing. After the MR scan, the acquired flow-sensitive 4-dimensional MR data underwent fully automated noise filtering and eddy current correction. For visualization, a commercially available software package (EnSight; CEI, Apex, NC) was used. Visualization options included 3-dimensional streamlines, time-resolved 3-dimensional particle traces, and 2-dimensional time-resolved vector fields. With these visualization options, a temporal and spatial description of flow characteristics in 3 dimensions was performed.
Referência(s)