Stereotactic magnetic resonance guidance for anatomically targeted ablations of the fossa ovalis and the left atrium.

Introduction: Targets for radiofrequency ablation (RFA) of atrial fibrillation are increasingly being selected based on anatomic considerations. Because fluoroscopy provides only limited information about the relationship between catheter positions and cardiac structures, we evaluated whether stereotactic catheter guidance might facilitate anatomical catheter navigation and RFA to the great vessels, the fossa ovalis and the left atrium (LA).

Methods And Results: An electromagnetic catheter's position system was superimposed on three-dimensional (3D) MR images using fiducial markers. This allowed the dynamic display of the catheter position on the true anatomy of previously acquired MRI in real-time. To assess the reproducibility of RFA, repeat ablations were created at the identical anatomic site in the inferior vena cava (IVC) in 5 swine. Average distance of the repeated ablations was 4.4 +/- 2.4 mm.In five swine the catheter was anatomically guided with the MRI to the fossa ovalis and a single RFA was performed. On the pathological specimen all ablation sites were located within the fossa ovalis with an average distance of 3.9 +/- 2.1 mm from its center. In two of the experiments the ablation catheter was passed into the left atrium and anatomically targeted ablation performed in the lateral wall of the left atrial appendage. Catheter location and ablation site were confirmed by autopsy and histology.

Conclusion: Real-time display of the catheter position on 3D-MRI allows anatomically targeted catheter navigation and RFA in the IVC, the fossa ovalis, and the left atrium. This may facilitate anatomically based interventions like septal puncture or pulmonary vein ablation and decrease fluoroscopy times.