Four-dimensional flow MRI of stented versus stentless aortic valve bioprostheses

Eur Radiol DOI 10.1007/s00330-017-4953-2 CARDIAC Four-dimensional flow MRI of stented versus stentless aortic valve bioprostheses Floortje van Kesteren 1,2 & Laurens W. Wollersheim 3 & Jan Baan Jr. 2 & 3 Aart. J. Nederveen 1 & Abdullah Kaya & S. Matthijs Boekholdt 2 & Bas A. de Mol 3 & Pim van Ooij 1 & R. Nils Planken 1 Received: 7 April 2017 / Revised: 14 June 2017 / Accepted: 19 June 2017 # The Author(s) 2017. This article is an open access publication Abstract Objectives To evaluate aortic velocity, wall shear stress (WSS) and viscous energy loss (EL) of stented and stentless bioprostheses using 4D flow MRI 1 year after surgical aortic valve replacement. Methods For this cross-sectional study 28 patients with stented (n = 14) or stentless (n = 14) bioprosthesis underwent non-contrast-enhanced 4D-flow MRI at 1.5 T. Analyses included a comparison of velocity, WSS and EL in the ascending aorta during peak systole for both spatially averaged values and a comparison of local differences using per-voxel analysis. Results No significant differences were found in peak and mean velocity (stented vs. stentless: 2.45 m/s vs. 2.11 m/s; p = 0.09 and 0.60 m/s vs. 0.62 m/s; p = 0.89), WSS (0.60 Pa vs. 0.59 Pa; p = 0.55) and EL (10.17 mW vs. 7.82 mW; p = 0.10). Per-voxel analysis revealed significantly higher central lumen velocity, and lower outer lumen velocity, WSS and EL for stentless versus stented prostheses. Conclusion One year after aortic valve implantation with stented and stentless bioprostheses, velocity, WSS and EL were comparable when assessed for averaged values in the ascending aorta. However, the flow profile described with local analysis for stentless prosthesis is potentially favourable with a significantly higher central velocity profile and lower values for outer lumen velocity, WSS and EL. Key Points • Stentless bioprostheses can be implanted instead of stented aortic valve bioprostheses. • Haemodynamic performance of valve prosthesis can be assessed using 4D flow MRI. • Averaged ascending aorta PSV, WSS and EL are comparable 1 year post-implantation. • Centreline velocity is highest, WSS and EL is lowest for stentless prosthesis. Keywords Four-dimensional MRI . Cardiovascular magnetic resonance . Heart valve prosthesis . Stented . Stentless Abbreviations 4D Four-dimensional 3D Three-dimensional MRI Magnetic resonance imaging Floortje van Kesteren and Laurens W. Wollersheim are joint first authors * R. Nils Planken 1 Department of Radiology and Nuclear Medicine, Academic Medical Centre, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands 2 Department of Cardiology, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands 3 Department of Cardiothoracic Surgery, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands Introduction Surgical aortic valve replacement is the standard treatment for patients with advanced aortic valve disease including severe and symptomatic aortic valve stenosis [1, 2]. Nowadays, a bioprosthetic heart valve is used in more than three-quarters of surgical aortic valve replacements [3]. Traditional bioprosthetic valves have a stented framework made of metal, with valve leaflets mounted on the stent to resemble a native tri-leaflet valve. Recently, bioprostheses Eur Radiol have become available that replaced metal stents with polymer stents. Although the stented design facilitates easy implantation, it reduces the effective orifice area and obstructs laminar blood flow [4]. As an alternative, stentless bioprostheses have been introduced. Because of the absence of a space-consuming stent, stentless bioprostheses should improve haemodynamic performance compared to stented bioprostheses. Indeed, transthoracic echocardiography observations revealed lower valvular pressure gradients in stentless valves compared to stented valves [5]. In addition, without obstruction due to space-consuming stents, flow profiles are expected to show lower flow velocities, lower wall shear stress (WSS) and less viscous energy loss (EL). WSS is the tangential force of blood flow on the endothelial cells outlining the vessel wall. High aortic WSS can occur for example by obstructed flow and may lead to aortic dilation [6, 7]. Furthermore, flow obstruction causes energy loss and viscous EL can be used as a measure of aortic blood flow disturbance [8]. Current evidence for a better haemodynamic performance of stentless bioprostheses is limited. Recently, four-dimensional (4D) flow magnetic resonance imaging (MRI) (time-resolved three-dimensional (3D) phase contrast imaging, with velocity encoding in all principal velocity directions) has become available. This technique improves the understanding of blood flow patterns through the heart and large vessels [9, 10]. In addition to echocardiography, 4D flow MRI measurements can be used for visualisation and quantification of blood flow volumes and flow profiles [11]. The aim of this study was to compare the performance of stented and stentless bioprostheses and to reveal differences in local flow velocity, WSS and EL between the prosthesis types using 4D flow MRI at 1 year after implantation. Methods Study population The Institutional Ethics Committee gave their approval for this exploratory cross-sectional study. All consecutive patients who underwent surgical aortic valve replacement within the previous 9–15 months were screened for exclusion criteria. In addition to standard MRI exclusion criteria, patients with a history of multiple heart valve replacements or known persistent atrial fibrillation were excluded. All eligible patients were asked to participate. After informed consent the MRI exam was conducted in 30 patients with either a stented Mitroflow (Sorin, Saluggia, Italy; Fig. 1a) or stentless Freedom Solo (Sorin, Saluggia, Italy; Fig. 1b) bioprosthesis. MRI All participants underwent a cardiovascular MRI at 1.5-Tesla (Magnetom Avanto, Siemens Medical Systems, Erlangen, Germany; software version B17). No contrast agent was used. The examination included a standard-of-care prospective electrocardiogram triggered and respiratory-gated short axis timeresolved (CINE) MRI for the evaluation of cardiac dimensions and function. For the assessment of aortic blood flow, timeresolved 3D phase-contrast MRI with three-directional flow encoding (4D flow) was obtained in a sagittal oblique 3D volume covering the aortic valve bioprosthesis and the thoracic aorta using electrocardiogram gating during free breathing with a respiratory navigator placed at the lung-liver interface. Pulse sequence parameters were as follows: echo time/pulse repetition time = 2.5/5.0 ms; bandwidth = 440 Hz/pixel; flip angle α = 7°; acceleration mode GRAPPA factor 2 with 24 reference lines, temporal resolution = 40 ms (18 phases); field of view (FOV) = 320 mm; spatial resolution 2.0 × 1.7 × 2.2 mm3. Velocity sensitivity was adjusted to minimize velocity aliasing ( (...truncated)