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
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