Changes in Left Atrial and Pulmonary Venous Anatomy During Respiration
A 4-Dimensional Computed Tomography–Based Assessment and Implications for Atrial Fibrillation Ablation
The possibility of integrating 3D models of the left atrium (LA) and pulmonary veins (PVs) in 3D mapping systems has recently provided a detailed anatomic reference for electrophysiologists performing atrial fibrillation (AF) ablations. Single-breathhold contrast-enhanced computed tomography (CT) or MRI images are reconstructed to a static 3D surface and registered to the LA geometry acquired by a roving catheter during the procedure. Respiratory changes in LA and PV anatomy, however, can reduce registration accuracy, especially when preprocedural CT images are acquired during inspiration.1
A 46-year-old man was referred for catheter ablation of drug-resistant paroxysmal AF. One day before the procedure, 64-slice cardiac CT was performed during both held inspiration and end-expiration. Images were not gated to the cardiac cycle to reduce patient radiation exposure. Nonrigid image registration2 between inspiratory and expiratory data sets with custom software resulted in a dynamic 3D (ie, 4D) sequence of the combined changes in LA, PV, and pulmonary anatomy during the respiratory cycle. Automatic intensity-based segmentation and surface reconstruction was performed with commercial software (Amira 4.0, TGS Template Graphics Software, Inc, Chelmsford, Mass).
Figure 1 shows the 3D anatomy of the LA and surrounding pulmonary anatomy (upper pane) and the changes in left atrial geometry during respiration (middle and lower panes). The remarkable absolute and relative anatomic changes during respiration are illustrated as a 4D sequence in the supplemental movie file. During inspiration, the inferior PVs show a larger downward movement than the superior PVs, which results in splaying of the ipsilateral PVs.
One day later, lasso-guided electrical isolation of the 4 PVs was performed under general anesthesia with propofol and mechanical ventilation. Merging of the LA 3D surfaces with biplane fluoroscopic imaging was performed as outlined previously3 to assist catheter navigation and ablation. In brief, LA 3D models are shown as an overlay on the fluoroscopic images after registration with a combined angiographic image of the 4 PVs acquired during apnea (ie, expiration; Figure 2). Although the 3D surface acquired during expiration resulted in a near-perfect registration with the angiographic images, the inspiratory 3D surface could not be registered correctly owing to the relative changes in PV and LA geometry, especially in the region of the inferior PVs (yellow dotted circles).
The observed respiratory changes in LA-PV anatomy are concordant with observations made by other authors1 and include splaying of the PVs during inspiration, with larger variability in the position of inferior PVs during respiration. The present 4D analysis for the first time directly relates these changes to the respiratory movements of surrounding pulmonary and diaphragmatic structures.
Sources of Funding
Dr Ector is a research assistant of the Fund for Scientific Research, Flanders. Stijn De Buck acknowledges the support of the IWT OZM 080511 research project.
Dr Heidbüchel is a member of the scientific advisory board of Biosense Webster, Inc, and is holder of the AstraZeneca Chair in Cardiac Electrophysiology, University of Leuven. The remaining authors have nothing to disclose.
The online-only Data Supplement, consisting of a movie, is available with this article at http://circ.ahajournals.org/cgi/content/full/115/23/e617/DC1.
Loeckx D, Maes F, Vandermeulen D, Suetens P. Nonrigid image registration using free-form deformations with a local rigidity constraint. In: Barillot C, Haynor DR, Hellier P, eds. Lecture Notes in Computer Science: Medical Image Computing and Computer-Assisted Intervention: MICCAI 2004. 7th International Conference, Saint-Malo, France, September 26–29, 2004. Proceedings, Part I. Berlin, Germany: Springer; 2004; 3216: 639–646.
Ector J, De Buck S, Adams J, Dymarkowski S, Bogaert J, Maes F, Heidbuchel H. Cardiac three-dimensional magnetic resonance imaging and fluoroscopy merging: a new approach for electroanatomic mapping to assist catheter ablation. Circulation. 2005; 112: 3769–3776.