Imitation of Radiofrequency ablation scars with laser system for MR guided ablation of Atrial Fibrillation

INTRODUCTION: Atrial Fibrillation (AF) is among the most common cardiac arrhythmias with a high risk of mortality and morbidity [1-2]. There are several minimally invasive catheter approaches that are performed under imaging guidance. These methods imitate the linear and transmural cuts and sutures along the atrial walls as in the widely accepted surgical Cox Maze procedure to block undesired currents. Cryotheraphy, microwave ablation, radiofrequency (RF) ablation, and laser ablation are common techniques used in these procedures. Catheter delivery of RF energy to the cardiac chamber is widely used and approved as safe and successful [4]. The operation is commonly performed under x-ray, which suffers from poor soft tissue contrast. In addition, the surgeon has to decide whether the local ablation is successful by looking at the simultaneous ECG data, which makes the operation technically difficult and time consuming. Due to the long exposure times, x ray burns may occur. MR imaging during RF ablation is possible with proper matching and tuning circuits [3]. However, during the operation RF and ECG catheters may cause artifacts in the image for some orientations. On the other hand, fiber delivery of laser energy has no MR compatibility issues and is used with MR guidance in the field. It is not widely used in treatment of AF, since there is a risk of perforating the myocardial wall. Several diffusing tip designs have been proposed to emit light in cylindrical symmetry [7] to produce a more even effect, but, due to its orientation with respect to the cardiac chamber, common RF delivery methods cannot be applied directly. Here, we propose a novel multiple fiber scheme for delivery of laser beam that imitates the scars created with RF probes under MR guidance. This scheme imitates the ablation pattern of RF delivery and as such is expected to have quick adaptation by physicians. As a preliminary demonstration, we used a 3-fiber scheme supported by real-time MR thermometry maps of the ex-vivo and in-vitro ablation zones during laser delivery.