Morgane Evin

Assessment of left atrial function by MRI myocardial feature tracking

Left atrium (LA) volumes and function are predictors of cardiovascular events. Because LA function cannot be assessed from cardiovascular magnetic resonance imaging (MRI) using the well‐established left ventricular tagging techniques, we hypothesized that adequate feature tracking (FT) applied to conventional cine MRI data could characterize LA function accurately.

Left atrial aging: a cardiac magnetic resonance feature-tracking study.

Importance of left atrial (LA) phasic function evaluation is increasingly recognized for its incremental value in terms of prognosis and risk stratification. LA phasic deformation in the pathway of normal aging has been characterized using echocardiographic speckle tracking. However, no data are available regarding age-related variations using feature-racking (FT) techniques from standard cine magnetic resonance imaging (MRI). We studied 94 healthy adults (41 ± 14 yr, 47 women), who underwent MRI and Doppler echocardiography on the same day for left ventricular (LV) diastolic function evaluation. From cine MRI, longitudinal strain and strain rate, radial motion fraction, and radial relative velocity, respectively, corresponding to the reservoir, conduit, and LA contraction phases, were measured using dedicated FT software. Longitudinal strain and radial motion fraction decreased gradually and significantly with aging for both reservoir (r > 0.31, P < 0.003) and conduit (r > 0.54, P < 0.001) phases, whereas they remained unchanged during the LA contraction phase. Subsequently, the LA contraction-to-reservoir ratio increased significantly with age (r > 0.44, P < 0.001). Longitudinal strain rate and radial relative velocity significantly decreased with age (reservoir: r = 0.39, P < 0.001, conduit: r > 0.54, P < 0.001), and these associations tended to be stronger in women than in men. Finally, associations of LA functional indexes with age were stronger in individuals with lower transmitral early-to-atrial maximal velocity ratio and mitral annulus maximal longitudinal velocity, as well as higher transmitral early maximal-to-mitral annulus maximal longitudinal velocity ratio, highlighting the LV-LA interplay. Age-related changes in LA phasic function indexes were quantified by cine MRI images using a FT technique and were significantly related to age and LV diastolic function.

Cardiac MR Strain: A Noninvasive Biomarker of Fibrofatty Remodeling of the Left Atrial Myocardium

Purpose To determine whether left atrial (LA) strain quantification with cardiac magnetic resonance (MR) imaging feature tracking is associated with the severity of LA fibrofatty myocardial remodeling at histologic analysis. Materials and Methods This prospective case-control study was approved by the institutional review board. LA strain was evaluated with cardiac MR feature tracking between January 2014 and March 2015 in 13 consecutive patients (mean age, 61 years ± 19; nine male) with mitral regurgitation in the 24 hours before mitral valve surgery and 13 age- and sex-matched healthy control subjects. LA strain parameters were compared first between control subjects and patients and then according to atrial fibrillation and mitral regurgitation status. Associations between LA strain and histology of preoperative biopsies were reported by using receiver operating characteristic curve analysis and Spearman correlation. Results Peak longitudinal atrial strain (PLAS) was significantly lower in patients with mitral regurgitation than in healthy control subjects (P < .001). Increased LA remodeling was significantly related to altered LA strain, and the strongest association was found between PLAS and the degree of fibrofatty myocardial replacement at histologic analysis (r = -0.75, P = .017). LA end-diastolic volume was increased in patients with mitral regurgitation when compared with that in healthy volunteers (P < .001) because of volume overload; however, volume did not correlate with the histologic degree of LA fibrofatty replacement (r = -0.35, P = .330). Conclusion LA strain, especially PLAS, correlates strongly with the degree of fibrofatty replacement at histologic analysis. Such functional imaging biomarker in combination with LA volumetry could help to guide clinical decisions, since myocardial structural remodeling is a known morphologic substrate of LA dysfunction leading to atrial fibrillation with adverse outcome.

Differentiation and quantification of fibrosis, fat and fatty fibrosis in human left atrial myocardium using ex vivo MRI

Background Atrial fibrillation is associated with an atrial cardiomyopathy composed mainly of fibrosis and adipose tissue accumulation. We hypothesized that MRI, when used in an optimal ex vivo setting allowing high spatial resolution without motion artifacts, can help characterizing the complex 3D left atrial (LA) wall composition in human myocardial samples, as compared to histology. Methods This prospective case-control study was approved by the institutional review board. 3D MRI acquisitions including saturation-recovery T1 mapping and DIXON imaging was performed at 4.0 T on 9 human LA samples collected from patients who underwent cardiac surgery. Histological quantification of fibrosis and fat was obtained. MRI T1 maps were clustered based on a Gaussian Mixture Model allowing quantification of total, interstitial and fatty fibrosis components. Fat maps were computed from DIXON images and fat fractions were calculated. MRI measurements were performed on the same location as the histological analysis (plane) and on the entire sample volume (3D). Results High correlations and levels of agreement were observed between MRI and histology for total (r = 0.93), interstitial (r = 0.93) and fatty fibrosis (r = 0.98) and fat (r = 0.96). Native T1 correlated with the amount of fibrosis from MRI and histology. The 3D MRI total, interstitial and fatty fibrosis ranges were between 6% and 23%, 4% and 17.3%; and 1.4% and 19.7% respectively. Conclusion High Field ex vivo MRI was able to quantify different LA myocardial components with high agreement in 2D with histology and moreover to provide 3D quantification of such components whereas in vivo application remains a challenge.

Left atrium MRI 4D-flow in atrial fibrillation: Association with LA function

Left atrium (LA) is a principal site of thrombus formation inducing thromboembolic events, which have been associated with LA low flow velocities. Recent developments in magnetic resonance imaging (MRI) 4D flow analysis enable a non-invasive visualization of LA flow patterns. Our main objective was to investigate modifications of the main vortices in the LA with regards to LA functional indices in 4 patients with atrial fibrillation (AF) and 6 healthy volunteers. Vorticity threshold and Q-criterion indices were computed from the centered vorticity calculation on filtered 4D velocity MRI images. Phasic LA longitudinal strains were computed on cine MRI images using LA feature tracking algorithm. LA dilation in AF came along with a drop in LA longitudinal strains. Best correlations between LA flow and functional changes were found for velocity vs. longitudinal strains corresponding to reservoir and LA contraction phases (r=0.69 and r=0.81, p<;0.03). Similarly, the highest correlation was found during LA contraction phase for associations between LA longitudinal strains and Q-criterion (r=0.52). In AF, LA functional changes are tightly associated with flow disorganization during the cardiac cycle especially during LA contraction phase.

Inter-study repeatability of left ventricular strain measurement using feature tracking on MRI cine images

Feature tracking (FT) is a novel approach for myocardial strain evaluation from standard cine MRI. Conversely to tagging, an original feature of FT is its ability to analyze all heart chambers, independently of their wall thickness. However, few technical challenges, including its inter-study repeatability need to be investigated and this is the aim of our study. We studied 10 healthy individuals (59±9 years), who underwent 2 MRI exams, separated by two weeks. For each exam, cine short-axis slices corresponding to left ventricular (L V) basal, mid-L V and apical locations were analyzed, by the same operator, using a custom FT software to extract global peaks of 1-radial thickening (Er), 2-circumferential strain (Ec), and 3-endocardial radial motion (Erm). Briefly, the FT, based on spatial correlation, was applied to myocardial contours initially drawn on a single time phase. Bland-Altman analysis revealed low bias for comparison between the 2 exams (mean bias [±1.96·standard deviation] were: 0.02 [-0. 11,0. 14]% for Er, 0.00 [-0.04,0.05]% for Ec, 0.00 [-0.05,0.06]% for Erm). As expected, strain magnitudes decreased with age. The application of an automated FT on data systematically acquired during MRI provided consistent and reproducible LV myocardial strain measurements.

CMR left atrial characterization in Cushing's syndrome: a feature tracking study

Background The aim of this study was to automatically assess global and regional left atrium (LA) strain in Cushing’s syndrome (CD). Modifications of LA and LV function in patients have been highlighted followed by the restoration of myocardial function after radical treatment and cortisol normalization. Our hypothesis was that a feature-tracking method could improve the understanding of the mechanisms of LA alteration concerning its reservoir, conduit, and atrial contraction phases.

Functional left atrial CMR parameters are early predictors of left atrial alterations in hypertension and strongly associated with lv remodeling

Background Left atrial (LA) structural and functional changes are determinant steps on the pathway toward heart failure with preserved ejection fraction in hypertensive (HT) patients. Most LA studies are based on LA volumes evaluation in CMR and echocardiography or on echocardiographic speckle tracking estimation. Since LA functional evaluation by CMR is now emerging we aimed at 1) evaluating LA function by CMR in controls and hypertensive patients (moderate and severe HT) using feature tracking technique on conventional cine data; 2) evaluating the relationship between the components of LA function (reservoir, conduit, atrial contraction) and left ventricular (LV) remodeling.

Left atrium dysfunction by CMR in aortic valve stenosis

Background Cardiac Magnetic resonance (CMR) imaging is able to characterize with high accuracy left atrial (LA) size and volumes as well as dense myocardial fibrosis. The addition of functional parameters such as LA myocardial strain would enhance CMR usefulness for a comprehensive LA characterization. Our aim was to evaluate the ability of strain values obtained by CMR to characterize LA functional alterations in the setting of aortic valve stenosis (AVS).

Pixel-wise absolute pressures in the aortic arch from 3D MRI velocity data and carotid artery applanation tonometry

A pixel-wise method for absolute and local aortic pressures estimation using 3D velocities in MRI and carotid pressure curves to set-up reference pressure values is presented. This method is based on the Navier-Stokes equation and a fast iterative algorithm. Its reliability was demonstrated: 1) in a synthetic phantom by comparison against simplified Bernoulli equation applied at peak velocities, and 2) in a healthy subject and a patient with aortic coarctation, in which absolute pressure distribution within the aortic arch was consistent with established physiopathological knowledge. Such local absolute aortic pressures may be useful in the understanding of hemodynamic changes secondary to cardiovascular alterations. Also, their addition to the already available indices of risk of aortic complications such as dilatation and dissection definition may prove of major clinical usefulness.