PO-03-104 MRI VERSUS ULTRASOUND: EXPLORING THE INFLUENCE OF IMAGING MODALITY ON THE FIDELITY OF NON-CONTACT CHARGE DENSITY MAPPING

Abstract

Non-contact charge density mapping of atrial fibrillation (AF) relies on an inverse algorithm and accurate representation of atrial geometry. Current clinical systems utilize intrachamber ultrasound (US) for endocardial surface mesh reconstruction. To compare intrachamber US and MRI derived left atrial (LA) reconstructions and investigate the impact of any geometric discrepancy on non-contact mapping derived conduction metrics. Five patients underwent LA ablation for persistent AF. Intrachamber US data was analyzed with AcQMap 8.5 (Acutus Medical) to produce individual LA surface meshes. Cardiac MRI was acquired up to 6 weeks prior to their procedure on a 3T clinical MR scanner. A proprietary graphical interface tool implemented in Matlab R2014a enabled 3D surface mesh reconstruction from 2D MRI slices. Prior to registration of MRI and US generated surface meshes, the mitral valve (MV), left atrial appendage, and pulmonary veins (PVs) were excluded. Registration was achieved with a two-step approach, using the iterative closest point algorithm followed by a rigid registration using 5 anatomic landmarks: center of 4 PVs and MV holes. Subsequently, non-contact intrachamber voltage measurements from the individuals’ procedures were processed to inversely derive cardiac activation on all surface meshes and measure the resulting conduction speeds (Figure 1A and B). The average distance between surfaces of intrachamber US and MRI reconstructed surface meshes was measured as 3.4±4.0mm. Histograms of non-contact mapping determined conduction speed over surface mesh area for each participant displayed similar overlapping distributions for intrachamber US and MRI (Figure 1C). Conduction speed statistics across the entire population did not show a significant difference between the two modalities (0.66±0.26m/s and 0.63±0.22m/s respectively) (Figure 1D). LA surface reconstructions produced by intrachamber US and cardiac MRI compare favorably. We demonstrate concordance between both modalities in subsequent application of the inverse algorithm required for non-contact charge density mapping and calculation of conduction speed.