Efficient Pulmonary Vein Isolation Using a Multi-channel, Duty-cycled RF Generator and Circular Ablation Catheter

Atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice, accounting for approximately one-third of all hospitalizations for cardiac rhythm disturbances.^1,2 For treatment of symptomatic and drug-resistant paroxysmal atrial fibrillation (PAF), catheter ablation using radiofrequency energy (RF) has become a widely accepted therapeutic option. Several landmark clinical studies within recent years have improved our understanding of the mechanisms and origin of AF induction. Depending on disease progression, 60 to 95% of triggers responsible for AF induction originate within the pulmonary veins (PV).^3,4 Therefore, ablation strategies that electrically isolate the PVs have been developed to cure patients of symptomatic paroxysmal AF. In conventional techniques, a 4- or 8-mm electrode-tipped ablation catheter is manually steered under fluoroscopic guidance, often with the aid of a 3-D navigation system. PV isolation is performed by segmental ostial disconnection or circumferential ablation, creating a long linear lesion along the antral region of the veins. However, these techniques can be time-consuming and require a long learning curve, because standard ablation catheters were originally designed to deliver RF in a point-by-point manner. It is also possible to leave small gaps in the desired lesion line, which can result in poor clinical outcome. In this case study, we will describe the use of an RF ablation system (Cardiac Ablation System, Ablation Frontiers, Carlsbad, CA) designed to simplify and shorten the procedure for PV isolation. The system, which recently has become available in Europe, combines a multi-channel RF generator with an over-the-wire, circular, decapolar ablation catheter. This system allows the operator to deliver pre-defined ratios of bipolar and unipolar RF energy to any or all electrodes on the catheter array simultaneously. By utilizing the 3-D circular shape of the catheter to deliver RF, the ablation technique does not require 3-D electroanatomical mapping or robotic-assisted navigation.

Case Presentation

A 60-year-old male with a four-year history of highly symptomatic paroxysmal AF was referred for ablation. Antiarrhythmic medical management, including beta-blockers, sotalol, flecainide, and amiodarone, had proven ineffective for alleviation of tachycardia or was poorly tolerated with side effects, including fatigue and symptomatic sinus bradycardia. The patient presented with a history of hypertension and mild left ventricular hypertrophy, but no hyperthyroidism. Coronary artery disease was excluded by angiography. Echocardiography showed normal left ventricular function and left atrial size (24 cc/m²).

Catheter and Generator Description The Pulmonary Vein Ablation Catheter (PVAC™, Ablation Frontiers) mapping and ablation catheter has an adjustable 25-mm circular electrode array (Figure 1), which is comprised of ten 3-mm platinum electrodes with 3-mm spacing. Catheter navigation and positioning are supported by both bidirectional steering and over-the-wire technique (Figure 2). The circular array can be extended to assume a spiral configuration that allows for various tissue contact positions. Each electrode contains a thermocouple located underneath the most distal surface, presumably the area most likely to make endocardial contact. By rotating the catheter shaft with the distal tip extended and engaged against anatomical structures, the diameter of the circular array can be effectively increased or decreased from 20 mm to 35 mm. Decreasing diameter with clockwise rotation allows electrograms to be recorded and analyzed within the PV. Counterclockwise rotation can increase the array diameter, facilitating mapping and ablation around the antrum of veins with larger diameters. The GENius™ (Ablation Frontiers) is a multi-channel RF generator (Figure 3) capable of simultaneously delivering duty-cycled energy to operator-selected electrodes. The generator has five preset energy settings: bipolar, unipolar, and three ratios of bipolar-to-unipolar energy: 4:1, 2:1 and 1:1. Pre-clinical studies have shown that lesion depth is inversely proportional to the amount of bipolar RF delivered.5 Power is delivered independently to each electrode in a temperature-controlled manner with a maximum of 10 W.

Ablation Procedure

To aid navigation and allow for the measurement of any asymptomatic PV stenosis, magnetic resonance imaging (MRI) was performed pre-procedure and scheduled for six-month follow-up. Pre-procedure transesophageal echocardiogram was performed to rule out intracardiac thrombi. The patient entered the catheterization laboratory in sinus rhythm. Conscious sedation was achieved with midazolam. Vascular access was obtained through a femoral vein. A steerable decapolar catheter was positioned in the coronary sinus for recording electrograms and atrial pacing. A steerable transseptal sheath (9 French Bard® Channel, Bard Electrophysiology, Lowell, MA) was introduced via the right femoral vein and maneuvered across the fossa ovalis into the left atrium via standard transseptal puncture guided by transesophageal echocardiography. Systemic anticoagulation was achieved with intravenous heparin to maintain an activated clotting time (ACT) of ≥250 seconds. Direct selective angiography of all pulmonary veins was performed to obtain a geometric reference for positioning the PVAC. After PV angiography, a 0.032” guidewire was inserted into the left superior pulmonary vein (LSPV). The PVAC was deployed in the left atrium and advanced over-the-wire to the antrum of the vein. By using steering mechanisms available on both the PVAC and the sheath, the electrode array could be positioned at the superior aspect of the vein. Antral ablation of the anterior and superior aspect of the LSPV was performed. Energy was delivered to anterior-superior electrode pairs that showed high quality electrograms, presumed to be in good contact with atrial tissue, in a 4:1 ratio (80% bipolar, 20% unipolar) for 60 seconds. The posterior and inferior electrodes were inactive. After RF application, PV potentials were significantly diminished and the catheter was rotated slightly to gain a new position, and RF was again applied in a segmental fashion until local PV potentials were eliminated. A typical example of electrograms pre- and post-RF application is shown in Figure 4. For ablation of the inferior aspect of the large LSPV, the guidewire was repositioned into an inferior branch to achieve a stable catheter position. Segmental ablation was again performed until local PV potentials were eliminated. Complete isolation of the LSPV was proven by forwarding the PVAC to a position distal the ablation line. Atrial stimulation from the distal coronary sinus as well as stimulation via the PVAC was performed to reveal any LA-PV connection. After confirmation of isolation, the PVAC and the guidewire were pulled back in the LA, and the guidewire was forwarded into the left inferior vein (LIPV). As before, the PVAC was positioned at the antral region of the vein and isolation of the LIPV was achieved by performing three circular ablations with good electrode contact along the circumference of the vein. Presumably some of the lesions from ablation of the LSPV provided block along the superior aspect of the LIPV. Pacing maneuvers revealed one remaining LA-PV connection in a posterior position. A single segmental ablation in the 2:1 mode (66% bipolar, 33% unipolar) successfully achieved disconnection. The right superior (RPSV) and right inferior veins (RIPV) were isolated using circumferential and additional segmental ablation with 4:1 mode. Prior to ablation in the RSPV, maximum output pacing was performed to exclude phrenic nerve capture. After all RF applications, AF could not be induced with atrial burst pacing up to 200 ms and isoproterenol infusion (at a maximum dose of 20 µg/min). Procedure time was 110 minutes, fluoroscopy time was 28 minutes, and there was a total delivery of 21 RF applications.

Post-Ablation Management

The patient was treated with intravenous heparin and phenprocoumon during his overnight stay. Heparin was continued until the international normalized ratio was ≥2.0.

Follow-Up

The patient was seen in outpatient clinic at three and six months post procedure. At both follow-up visits, the patient reported improvements in quality of life as well as no symptoms of disease. No silent AF episodes were noted during 72-hour Holter monitoring at both visits, and MRI at the six-month follow-up excluded asymptomatic PV stenosis.

Discussion

Electrical disconnection between the PVs and left atrium is the cornerstone of AF ablation strategies.6 Conventional techniques for disconnection require two transseptal punctures: one for a therapeutic ablation catheter and one for a diagnostic circular mapping catheter. Often, sophisticated 3-D mapping systems are used for catheter localization, and complex robotic systems may be used to assist in steering. This case study describes the use of a catheter ablation system that combines mapping and ablation in one catheter that is capable of delivering RF in a multi-channel, duty-cycled manner. This combination allows a single operator to efficiently create long contiguous lesions around the veins with a single catheter. Isolation can be verified by mapping and pacing with this catheter or a standard reference catheter placed in the CS. Moreover, the procedure time is relatively short, the technique requires only conventional imaging, and no investment in complex imaging or navigation equipment is required. In addition to these practical considerations with regards to efficiency, several features of this technique for AF ablation may improve the safety profile. First of all, operators ablate with ratios of bipolar:unipolar energy, which allow for tailored lesion depth. Combined with the power limit of 10W per electrode, this may reduce complications due to collateral heating damage, such as esophageal fistula, phrenic nerve palsy, and PV stenosis. Third, because each electrode has a thermocouple placed close to the tissue interface, both power delivery and temperature control are very precise, possibly reducing the chance of char and thrombus. Finally, the relatively large surface area, or “footprint,” of the catheter tip may help reduce the risk of complications such as perforation or tamponade. Since October 2007 we have performed approximately 60 ablations using this system and have noted significant improvements, with both a reduction in adverse events and a boost in lab productivity. So far, our safety and efficacy outcomes are remarkably similar to reports by other centers using this technology from both the 2008 Heart Rhythm Society meeting in San Francisco and the European Society of Cardiology congress in Munich.7,8 We will present the results from our initial series of patients at the American Heart Association (AHA) Scientific Sessions in November.

Conclusion

Electrical disconnection of pulmonary veins can be performed safely, efficiently and effectively using a circular ablation catheter and multi-channel RF generator. Due to the single-operator, single-catheter technique, and no requirement for 3-D mapping or robotic-assisted steering, this system may improve productivity for centers offering AF ablation.