Towards a quantitative MRI-based measure of disease burden in patients with atrial fibrillation
Maurce Pradella1, Sven Knecht2, Michael Kühne2, Aline Mühl2, Tobias Reichlin2, Gian Voellmin2, David Conen2, Jens Bremerich1, Stefan Osswald2, Christian Sticherling2, and Bram Stieltjes1

1Department of Radiology, University of Basel Hospital, Basel, Switzerland, 2Department of Cardiology, University of Basel Hospital, Basel, Switzerland

Synopsis

Atrial fibrillation (AF) is a common disease and associated with myocardial infarction, stroke and dementia. We propose a new approach based on the sphericity of fitted ellipsoids in left atriums of patients with AF. Our results show a strong correlation between sphericity of these ellipsoids and burden of disease and may serve as an objective surrogate parameter in the future.

Introduction

Atrial fibrillation (AF) is a common disease affecting approx. 1 % of the adult population in first world countries. It is associated with myocardial infarction, stroke, dementia and chronic kidney disease and its incidence is estimated to increase dramatically within the next decades [1]. Chronic changes of blood flow due to AF affect 3D appearance of the left atrium (LA) and a model to describe these changes by sphericity was previously described [2]. Here, we propose a new approach to quantitatively assess this chronical change and to correlate it with descriptive clinical parameters that aim to encompass disease burden.

Materials and Methods

Population: Between Mai 2010 and December 2013 a total of 130 patients were included in our study. Average age was 61.6 years. All patients received pulmonary vein isolation (PVI) using radiofrequency via a 3D-electroanatomic mapping system. Overall disease burden was assessed prior to PVI according to Koci et al. and the specific risk for a cerebrovascular insult via the CHA2DS2-VASc-score [3, 4].

MRI: MRI was performed at 1.5T (Magnetom Avanto / Magnetom Espree, Siemens, Erlangen, Germany). Breath-hold, T1-weighted spoiled gradient echo sequence (FLASH) were acquired pre- and post-contrast in coronar orientation after bolus testing was performed. Contrast agent was injected intravenously at a 2 ml/s flow rate (Multihance, 0.1 mmol/kg, Bracco, Milan, Italy). MRI parameters: TR 3.7 s, TE 1.3 ms, flip angle 25°, Bandwidth 63.6 kHz. Acquisition matrix was 380 x 380 pixels, reconstruction matrix 512 x 512 pixels, voxel size 2.25 x 2.25 x 1.2 mm. Slice thickness 1.2 mm with 20% overlap. 80 images were acquired for each series followed by automatic subtraction of pre- from post-contrast images. Total time for acquisition was approx. 20 minutes.

Post-processing: 3-D reconstruction was performed blinded to clinical parameters and performed with a semiautomatic, threshold-based region growing algorithm using Aqaurius Intuition (Terarecon, Foster City, USA; Figure 1). Pulmonary veins and LA appendage were excluded at their ostia. The surface of the left atrium was processed using the open source software Meshlab (Visual Computing Lab - ISTI – CNR, Italy) to eliminate inner points and saved as point cloud. Assessment of sphericity as deviation from an ideal sphere was evaluated with a custom-written code (Matlab R2009b, Mathworks, Natick, MA, USA; Figure 2). To evaluate repeatability two readers performed intra- und inter-reader agreement tests on a subpopulation of 5 randomly selected patients.

Statistics: Analysis was performed using SPSS (IBM SPSS Statistics for Windows, Version 22.0. Armonk, USA). For continuous variables, Student’s T-test or Mann-Whitney U test were used, as appropriate. Discrete variables were compared using Fisher’s exact test. A p-value <0.05 was considered to indicate statistical significance. Reader agreement was evaluated using intra-class correlations (ICC).

Results

Sphericity of the ellipsoid correlated significantly with burden of disease (.369 respectively, p<.001; Figure 3A and 3B). This correlation was stronger when compared to the previously presented method (.265, p<.001). The CHA2DS2-VASc-Score showed a significant correlation to sphericity which was stronger for our score (.392, p<.001 versus .265, p=.004). ICC for intra- and inter reader agreement was strong with 0.93 and 0.84 respectively.

Discussion

Our model of sphericity of the atrium in AF based on a fitted ellipsoid shows a significant correlation between sphericity and individual burden of disease with an excellent repeatability. Additionally it correlates with CHA2DS2-VASc-Score and thus to the specific risk of CVI. Our ellipsoid model based on subtracted MRI-Angiography may serve as an objective surrogate parameter for the evaluation the clinical burden of AF. In future studies, we will evaluate the use of this measure as therapy outcome predictor before pulmonary vein isolation.

Acknowledgements

No acknowledgement found.

References

1. Rahman, F., G.F. Kwan, and E.J. Benjamin, Global epidemiology of atrial fibrillation. Nat Rev Cardiol, 2014. 11(11): p. 639-54.

2. Bisbal, F., et al., Left atrial sphericity: a new method to assess atrial remodeling. Impact on the outcome of atrial fibrillation ablation. J Cardiovasc Electrophysiol, 2013. 24(7): p. 752-9.

3. Koci, F., et al., New classification scheme for atrial fibrillation symptom severity and burden. Am J Cardiol, 2014. 114(2): p. 260-5.

4. Lip, G.Y., et al., Refining clinical risk stratification for predicting stroke and thromboembolism in atrial fibrillation using a novel risk factor-based approach: the euro heart survey on atrial fibrillation. Chest, 2010. 137(2): p. 263-72.

Figures

Figure 1: substraction image of left atrium

Figure 2: point cloud and fitted ellipsoid

Figure 3A: Correlation of sphericity of the fitted ellipsoids to the patients Burden of Disease (acc. to Koci et al).

Figure 3B: Correlation of sphericity of the fitted ellipsoids to the patients Burden of Disease (acc. to Koci et al).



Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)
0461