Internally Cooled RF Ablation of Atrial Fibrillation Using a Basket Mapping Catheter in a Patient with a Left Common Pulmonary Vein

Case Presentation

A 54-year-old man was referred for radiofrequency (RF) ablation of atrial fibrillation. Paroxysms of atrial fibrillation started four years ago, and were refractory to antiarrhythmic drug treatment with sotalol hydrochloride, flecainide acetate, and amiodarone hydrochloride. Atrial fibrillation became persistent one year ago, and the patient underwent a total of seven electrical cardioversions. However, atrial fibrillation recurred within weeks, despite a high dose of amiodarone medication. He had no other history of cardiovascular disease, and a recent echocardiogram was normal, except for a left atrial size of 4.9 cm. A magnetic resonance angiography was performed prior to the ablation, in order to define the individual pulmonary vein (PV) anatomy. The angiography revealed the anatomic variant of a left common PV trunk, with an ostial size of 31 mm in the coronal view (Figure 1). Separation into the superior and inferior branches was observed 23 mm behind the ostium. The anatomy of the right-side PV was normal. The chronic anticoagulation with warfarin was discontinued five days before the ablation, and low molecular heparin (enoxaparin) was given subcutaneously during the three days preceding the procedure. The patient was brought to the electrophysiology lab after written informed consent was obtained. A quadripolar electrode catheter was placed at the His bundle region, and a decapolar electrode catheter was placed in the coronary sinus; both through the left femoral vein. A 4 French (Fr) arterial line was placed in the right femoral artery for invasive blood pressure measurement and monitoring of IV anticoagulation. Two long, 8 Fr SL 1 sheaths (Diag, Minnetonka, Minnesota) were introduced through the right femoral vein and advanced into the superior vena cava. Double left atrial access was obtained using the standard Brockenbrough technique for transseptal catheterization. An 8.5 Fr EPT Convoy sheath with a 120 º curve then replaced one of the SL 1 sheaths. For this, a 0.032´´ extra stiff guidewire was advanced through the SL 1 sheath (still containing its dilator), and placed fairly deeply into the left common PV. The SL 1 sheath was removed, keeping the wire in the left superior PV. The EPT Convoy sheath was then advanced over the wire into the left atrium. A bolus of a 7,000 unit of heparin was given, followed by repetitive doses administered to keep the activated clotting time (ACT) between 330-350 seconds. The ACT was measured every twenty minutes after reaching its target range. A 31 mm, 64-pole basket catheter (Constellation, Boston Scientific, Natick, Massachusetts) was advanced through the EPT convoy sheath and positioned into the left common PV (Figure 2). Attention was paid so only the distal two-thirds of the basket catheter were positioned in the vein. This allowed bracketing and mapping of the electrical potentials at the orifice between the distal two-thirds and the proximal third of the catheter. The initial ostial mapping result is shown in Figure 3A. The recordings represent bipolar electrograms, between adjacent electrodes of the same spline. The basket catheter has 8 splines, each containing 8 electrodes, thus allowing the recording and displaying of a total of 56 bipolar electrograms. Figure 3 shows only the proximal three bipoles of each spline, which reveal pulmonary vein potential at the A, G and H spline. The atriovenous junction around these splines was targeted with RF energy, using an internally cooled ablation catheter (Chilli, Boston Scientific). Radiofrequency was applied in a temperature-controlled mode with a temperature limit of 39 ºC and a maximum power of 35 Watts. Twenty-one RF applications, each lasting sixty seconds, were required to obtain electrical isolation of the PV (Figure 3B). The right-sided PVs were also mapped with the basket catheter. The right superior vein exhibited 3 distinct electrical connections, which were successfully ablated with a total of seven radiofrequency applications. The right inferior vein exhibited no intrinsic electrical activity. The transseptal sheaths were drawn back into the right atrium and no more heparin was given. A 20-pole HALO catheter, positioned next to the tricuspid annulus, replaced the basket catheter. Internally cooled-tip radiofrequency was applied to the cavotricuspid isthmus with resultant bidirectional conduction block. This flutter-line ablation was considered to be beneficial because of the common association of atrial fibrillation and flutter, especially on antiarrhythmic drug treatment and the very low risk of complications. All catheters were then removed, allowing the ACT to normalize before the sheaths were removed. Enoxaparin, twice daily in a weight-adapted dose (1 mg/kg), was restarted four hours after sheath removal. It was continued until the international normalized ratio (INR) was above 2. Warfarin was restarted in a maintenance dose that same evening, and amiodarone was continued for four weeks, in a lower dose of 200mg/day, and then discontinued. It is now more than three months after the procedure was performed, and the patient has had no further recurrences of atrial fibrillation.

Discussion

This case illustrates the superiority of two technologies. (1) The internally cooled ablation catheter has several benefits in this setting. It reduces coagulum formation, especially important on the left side, and makes similar size lesions as standard RF catheters at low power settings. Furthermore, the internally cooled RF catheter at higher power settings is superior to conventional RF ablation catheters for ablating the cavotricuspid isthmus. (2) The basket-mapping catheter has several advantages for RF ablation of common pulmonary vein trunks. The left common PV trunk of this patient measured 31 mm in the coronal view. Because no circumferential "Lasso" catheter is available that covers a PV ostium of this size, only the basket catheter allows mapping of the complete atriovenous junction. Based on the basket mapping results, we were able to deliver RF at the site of the earliest pulmonary vein potentials representing the atriovenous junction of the common PV, thus minimizing the risk of pulmonary vein stenosis. In our experience, the stability of the basket catheter employed with its distal 2/3 in the PV, electrically bracketing the atriovenous junction, and visually identifying the PV chamber is favorable in comparison to circumferential catheters. This is particularly true in very large pulmonary veins.