Characterization of complex flow patterns in the ascending aorta in patients with aortic regurgitation using conventional phase-contrast velocity MRI

Int J Cardiovasc Imaging DOI 10.1007/s10554-017-1239-3 ORIGINAL PAPER Characterization of complex flow patterns in the ascending aorta in patients with aortic regurgitation using conventional phasecontrast velocity MRI Odd Bech‑Hanssen1,5 · Frida Svensson3 · Christian L. Polte2,5 · Åse A. Johnsson4,6 · Sinsia A. Gao1,5 · Kerstin M. Lagerstrand3 Received: 30 June 2017 / Accepted: 31 August 2017 © The Author(s) 2017. This article is an open access publication Abstract Ascending aorta (AA) flow displacement (FD) is a surrogate for increased wall shear stress. We prospectively studied the flow profile in the AA in patients with aortic regurgitation (AR), to identify predictors of FD and investigate whether magnetic resonance imaging (MRI) phase-contrast flow rate curves (PC-FRC) contain quantitative information related to FD. Forty patients with chronic moderate (n = 14) or severe (n = 26) AR (21 (53%) with bicuspid aortic valve) and 22 controls were investigated. FD was determined from phase-contrast velocity profiles and defined as the distance between the center of the lumen and the “center of velocity” of the peak systolic forward flow or the peak diastolic negative flow, normalized to the lumen radius. Forward and backward volume flow was determined separately for systole and diastole. Seventy percent had systolic backward flow and 45% had diastolic forward flow in large areas of the vessel. AA dimension was an independent predictor of systolic FD while AA dimension and regurgitant volume * Odd Bech‑Hanssen odd.bech‑ 1 Departments of Clinical Physiology, The Sahlgrenska Academy at the University of Gothenburg, Gothenburg, Sweden 2 Departments of Cardiology, The Sahlgrenska Academy at the University of Gothenburg, Gothenburg, Sweden 3 Departments of Diagnostic Radiation Physics, The Sahlgrenska Academy at the University of Gothenburg, Gothenburg, Sweden 4 Departments of Radiology, The Sahlgrenska Academy at the University of Gothenburg, Gothenburg, Sweden 5 Institute of Medicine at the Sahlgrenska Academy, Sahlgrenska University Hospital, Gothenburg, Sweden 6 Departments of Clinical Sciences, The Sahlgrenska Academy at the University of Gothenburg, Gothenburg, Sweden were independent predictors of diastolic FD. Valve phenotype was not an independent predictor of systolic or diastolic FD. The linear relationships between systolic backward flow and systolic FD and diastolic forward flow and diastolic FD were strong (R = 0.77 and R = 0.76 respectively). Systolic backward flow and diastolic forward flow identified marked systolic and diastolic FD (≥0.35) with a positive likelihood ratio of 6.0 and 10.8, respectively. In conclusion, conventional PC-FRC data can detect and quantify FD in patients with AR suggesting the curves as a research and screening tool in larger patient populations. Keywords Aortic regurgitation · Cardiovascular magnetic resonance · Flow displacement · Aortic aneurysm Introduction A diversity of flow patterns in the ascending aorta (AA) has been documented in mainly patients with a bicuspid aortic valve [1–3]. Flow displacement (FD) with high velocity close to the vessel wall is a hallmark and has been proposed as a surrogate for increased wall shear stress that might serve as a quantitative parameter for risk-stratifying patients regarding development of AA aneurysm [4]. It is well known that patients with bicuspid aortic valve frequently develop AA aneurysms and the risk of aortic dissection or rupture is markedly increased compared with patients with tricuspid aortic valve [5]. Still, AA aneurysm is a frequent finding in patients with moderate and severe AR and, importantly, a majority of patients with dilated AA and AR have a tricuspid aortic valve [6]. Previous studies on the flow profile in the AA excluded [7–9] or had only a few [1, 3, 4, 10] patients with significant AR. From flow mechanics [11, 12] and previous studies [7, 13] it is conceivable that 13 Vol.:(0123456789) Int J Cardiovasc Imaging apart from valve phenotype we can expect that AA dilatation in itself and significant AR due to increased velocity are determinants of FD, but this has not been verified. The high-resolution four-dimensional (4D) magnetic resonance imaging (MRI) acquisition needed for the most comprehensive description of flow is time-consuming and requires highly specialized expertise. The conventional method to measure aortic regurgitation (AR) from the amount of backward flow during diastole, is based on net through-plane phase contrast flow rate curves (PC-FRC). Such curves are derived from a cross-sectional plane typically in the proximal AA at the sino-tubular junction. Using the same cross sectional plane, the two-dimensional velocity profile across the vessel area for different phases of the cardiac cycle can be visualized (2D-PC). FD defined as the distance between the center of the lumen and the “center of velocity” normalized to the lumen radius can be described using conventional 2D-PC data [9]. Complex flow patterns leads to regions of simultaneous forward and backward flow across the vessel area [14, 15]. By decomposing the net PCFRC, the forward and backward volume flow throughout the cardiac cycle can be visualized and quantified separately for systole and diastole [14]. In the present study, we selected patients with moderate to severe AR in order to investigate both forward and backward flow through the entire heart cycle. We hypothesized that the PC-FRC contains quantitative information about FD in both systole and diastole. Thus, the aims of the study were threefold; (1) to study the systolic and diastolic flow profile in patients with moderate or severe AR, (2) to identify predictors of FD and (3) to investigate whether PC-FRC contain quantitative information related to FD. Materials and methods Study population This prospective study comprised 40 patients with chronic AR and 22 controls. The patients were either investigated prior to valve surgery (n = 23) or as part of follow-up due to moderate (n = 14) or severe regurgitation (n = 3). Exclusion criteria were ≥moderate regurgitation in any other valve, presence of a cardiac shunt, any other form of significant cardiac disease and irregular heart rhythm. The controls were students or recruited from the hospital staff. They did not have any symptoms or history of cardiovascular disease. The study was conducted according to the Declaration of Helsinki. The Regional Ethics Review Board gave ethical approval for the study protocol, and written informed consent was obtained from all participants. 13 MRI examination The MRI examination was performed on a 1.5 T scanner (Achieva, Philips Healthcare, Best, The Netherlands) using a five-channel phased-array cardiac coil. After standardized patient-specific planning, a series of cine-images was performed, first in the short-axis view covering the whole heart without gap (slice thickness 8 mm) from the atrioventricular ring to the ape (...truncated)