Quantification of global and regional left atrial function in paroxysmal atrial fibrillation using CMR derived 4-D wall motion analysis

Methods Eight healthy volunteers (6 male, mean 29.7 yrs) and 6 patients (6 male, mean 61.7 yrs) with paroxysmal AF underwent imaging during sinus rhythm on a 1.5 T scanner. Steady state free procession imaging of the LA, acquired in an axial stack and parasagittal at 6 mm slice thickness with no interslice gap, was retrospectively reconstructed into 25 phases per R-R interval. Segmentation of the LA wall was performed manually using ARGUS software (Siemens Medical Solutions). The following landmarks were identified manually at each phase and used to construct a spherical coordinate system: four pulmonary vein ostia and four points on the mitral annulus (superior, inferior, left, right). Using MATLAB, contour points were fitted with a 16-element mesh to obtain a continuous description of changes in atrial radius through space and time. LA volume and radial fractional shortening of each element were calculated for each phase and subject. Elements were separated into superior, inferior, septal and free walls for regional analysis. Differences between patients and volunteers were determined with an unpaired t-test.