Atrial fibrillation (AF) is a supraventricular arrhythmia associated with an increased risk of stroke, heart failure and all-cause mortality.1 Sinus rhythm control and heart rate control are two commonly used strategies to manage patients with AF, alongside the use of anticoagulants for prevention of stroke. Rhythm control with antiarrhythmic drugs (AADs) has similar survival benefits to rate control and is only advocated for patients with symptomatic AF.2–5 It has been suggested that rhythm control may be superior to rate control if the former can be achieved without the side effects associated with some AADs.6
A growing alternative to AADs for rhythm control is the use of catheter ablation. According to the 2006 American College of Cardiology (ACC)/ American Heart Association (AHA)/European Society of Cardiology (ESC) guidelines for the management of AF, catheter ablation of AF is primarily indicated in patients with symptomatic, drug-refractory AF or patients who are intolerant to at least one class 1 or class 3 AAD, while it may also be suitable in asymptomatic patients with heart failure and/or reduced ejection fraction.7 Catheter ablation has been shown to be superior to and safer than AADs in patients with drug-refractory AF.8–11 The results of large randomised trials, such as the Ablation Versus Anti-Arrhythmic Drug Therapy for AF (CABANA) trial,12 comparing catheter ablation with rhythm control drugs are highly anticipated as they are expected to provide answers to clinical questions, including whether rhythm control with catheter ablation has benefits over AAD therapy or rate control strategies.
Of the various methods of catheter-based ablation, the most common is radiofrequency catheter ablation, which involves the insertion of mapping and radiofrequency ablation catheters via the femoral vein into either the left or right atrium. Mapping catheters are used to identify areas that contain triggers for AF or areas that have wavelets responsible for maintaining AF. Subsequently, radiofrequency energy is delivered through ablation catheters to create ablation lesions around areas (e.g. pulmonary veins [PVs]) containing AF triggers, thereby electrically isolating focal triggers of AF from the atria.13–16 Nowadays, radiofrequency catheter ablation often involves the creation of wide-area circular ablation lesions around the ostia of the PVs, thereby achieving PV isolation (PVI) from the atria. In patients with persistent AF, additional ablations may also be needed, and may involve the placement of linear ablations in the atria.
The efficacy and safety of catheter ablation may be partly linked to the operator’s skills and experience in catheter navigation and ablation as well as the complexity of the cardiac anatomy. These factors may give rise to certain challenges in both the arrhythmia mapping and ablation stages, especially with the conventional catheter ablation approach, which involves the use of manually steerable catheters. Challenges may include the accurate navigation of the ablation catheter around the left atrium (LA) due to the variability of the cardiac anatomy. Another challenge may be achieving stability of the catheter during ablation, especially when producing a confluent line of ablation over the complex 3D surface of the atria or the PV.17,18 Even the arrhythmia mapping stage may be associated with some challenges, especially for inexperienced electrophysiologists, since the signals collected from the mapping catheter can be quite complicated and variable, making interpretation difficult.
Recent years have seen the introduction of two remote catheter navigation systems: one is based on an electromechanical ‘robotic’ navigation system (Sensei® X Robotic Catheter System, Hansen Medical, US), and the other is based on a magnetic navigation system (Niobe® Magnetic Navigation System, Stereotaxis Inc., US). Remote catheter navigation systems may help to overcome the challenges associated with catheter ablation. These systems are intended to achieve precise and stable manipulation of catheters in both the mapping and ablation stages. The robotic navigation system uses electromechanical guidance to robotically manoeuvre the catheter, while the magnetic navigation system allows control of catheters (containing inner magnets) by changing the orientation of a magnetic field. The purpose of this article is to discuss the initial clinical experiences of catheter ablation using the robotic navigation system for the treatment of AF.
Electromechanical Robotic Navigation System
The robotic navigation system seeks to offer improved control, accuracy and stability of navigation of mapping as well as ablation catheters compared with manually steerable catheters. It also aims to reduce radiation exposure for both the patient and the operator and to shorten procedure times. The robotic navigation system has been described in detail previously;19–23 briefly, it consists of three linked components – a physician’s workstation, a remote catheter manipulator (RCM) and a steerable guide catheter. In clinical practice, the physician’s workstation may be placed remotely from the patient’s bedside and the RCM mounted to the bedside, with the guide catheter placed inside the cardiovascular system.
Catheter navigation is achieved through operator-dependent manipulation of a steerable guide catheter that can accommodate any conventional standard ablation catheter. The steerable guide catheter contains an outer and an inner steerable sheath (11.5 and 8.5F, respectively). These sheaths can be manoeuvred via a pull-wire mechanism by the RCM, which responds to the movements of a 3D hand-operated joystick on the workstation.
The physician’s workstation has an integrated non-fluoroscopic imaging system (CoHesion™ 3D Visualization Module, Hansen Medical, US) that combines the rapid generation of high-resolution 3D cardiac anatomy with Cartesian 3D representation of the position of the catheter tip, thereby facilitating instinctive catheter navigation and placement. Catheter navigation may be further facilitated with the use of pre-operative computed tomographic (CT) and intra-operative fluoroscopy images, which are displayed on the screen of the workstation. Finally, the precision of arrhythmia mapping and ablation may be improved with the use of a software system (IntelliSense™ Fine Force Technology, Hansen Medical, US) that can provide continuous proximal feedback on the contact force exerted by the catheter tip on the tissue. This is important as the quality of mapping24 and the size of ablations created may be partly affected by the contact force of the catheter with the tissue.25
Apart from the challenges associated with catheter ablation, a concern is the high exposure of both the patient and the operator to X-ray fluoroscopy. The X-ray exposure is a particular issue when conventional fluoroscopy is used to assist catheter navigation as well as when radiofrequency energy is used to create the ablation lesions. The use of the robotic navigation system allows for reduced X-ray fluoroscopy exposure for both the patient and the operator as catheter navigation may be aided by the use of a non-fluoroscopic electroanatomical system. Furthermore, the exposure of the operator to X-rays may be further reduced with the use of the robotic system since the physician’s workstation can be positioned away from the patient’s bedside.
Initial Clinical Experience of Catheter Ablation Using the Robotic Navigation System
At the St Bartholomew’s and The Royal London Hospital, catheter ablation procedures using the robotic navigation system have been performed for the treatment of patients with tachyarrhythmias such as AF. According to clinical experience at this centre, catheter ablation using the robotic navigation system has shown a similar efficacy, safety and procedure time to conventional catheter ablation. Importantly, it has been noted that X-ray exposure of both the patient and the operator was reduced with catheter ablation using the robotic navigation system compared with conventional catheter ablation. Because the workstation is placed away from the patient’s bedside, the operator does not need to wear a lead apron during catheter ablation. Consequently, the physician’s experience during procedures using the robotic navigation system has, anecdotally, been one of a reduction in operator fatigue.
A prospective randomised controlled trial to determine whether catheter ablation of AF utilising the robotic navigation system improves outcome compared with manual catheter ablation is currently under way.26 Preliminary results suggest that catheter ablation using the robotic navigation system is as effective as manual catheter ablation for AF and that the use of the robotic navigation system results in less operator fatigue and lower radiation doses to the patient.27 These preliminary results are consistent with data from an earlier prospective randomised trial that evaluated the impact of catheter ablation using the robotic navigation system combined with an intuitively integrated 3D mapping system on fluoroscopy exposure during PVI.28 In this study, patients with paroxysmal AF were randomised to either catheter ablation with the robotic navigation system (n=30) or to a conventional catheter ablation approach (n=30). PVI was achieved in all patients. At a mid-term follow-up of six months, the proportion of patients who were free from AF recurrence was similar in both treatment groups (73 and 77%, respectively; p=0.345). The overall fluoroscopy time was significantly lower in the robotic navigation system group versus the conventional ablation group (9±3.4 and 22±6.5 minutes, respectively; p<0.001). The operator’s fluoroscopy exposure was also significantly reduced in the robotic navigation system group versus the conventional ablation group (7±2.1 and 22±6.5 minutes, respectively; p<0.001).
Non-randomised single-centre studies have reported preliminary experience with the robotic navigation system in patients with drug-refractory paroxysmal AF,29 symptomatic or drug-resistant AF30 and paroxysmal or persistent AF who underwent PVI.31 These earlier studies also suggested that catheter ablation of AF using the robotic navigation system was as safe as conventional catheter ablation and was associated with significantly shorter overall duration of radiofrequency delivery, total procedural time and fluoroscopy exposure.
Saliba et al. have reported their preliminary experience of using the robotic navigation system to perform left and right atrial mapping and radiofrequency ablation of AF and atrial flutter (AFL) in patients with drug-refractory AF.21 A total of 40 patients underwent AF ablation, with 23 of these patients also undergoing additional right AFL ablation. The results of this study showed that acute PVI success rates (100%) and procedure time (163±88 minutes) were similar to those from previously reported data for the conventional catheter ablation approach. Furthermore, one-year follow-up results showed that five patients and 34 patients (86%) were free from atrial arrhythmia on AADs and off AADs, respectively. In terms of safety, a significant number of patients developed pericardial tamponade (5%). However, it should be noted that when this trial was conducted it was not possible to continuously measure the contact force of the catheter tip. More recent studies are utilising the robotic navigation system with the added new feature of software that allows continuous measurement of the contact force of the catheter tip with the tissue and also warns the operator when a pre-set limit is reached.28 The results from these prospective randomised controlled trials will provide more data on the safety profile of catheter ablation using the robotic navigation system with the updated software. Improved awareness of the contact force would provide a more accurate idea of whether, and to what extent, the catheter is in contact with the tissue.
Summary and Future Outlook for Remote Navigation Systems and Catheter Ablation
The remote navigation systems, both robotic and magnetic, have been developed to overcome some of the technical limitations associated with conventional catheter ablation of AF. Initial clinical experience suggests that the robotic navigation system is efficacious, safe and feasible for catheter ablation in the treatment of AF. This system reduces the need for excellent manual navigation skills but may require other skills instead, such as the ability to accurately control the catheter using the 3D joystick.
In terms of clinical evidence, the data available from small randomised and/or non-randomised clinical trials have focused on the clinical feasibility and safety of the robotic navigation system. These data have been positive thus far and suggest that catheter ablation using the robotic navigation system has similar procedural times, efficacy and safety to conventional manual ablation in patients with AF. Additionally, it has been associated with a reduced fluoroscopy exposure to the patient and the operator as well as a shorter fluoroscopy time compared with conventional catheter ablation.
Large randomised trials with long-term follow-up to compare the safety and efficacy of catheter ablation performed with remote navigation systems versus conventional manual navigation will help determine the role of remote systems in the catheter ablation of AF. It is reasonable to suggest that while these systems may not be used too often for simple catheter ablation procedures, they may be expected to become routinely used in centres that carry out complex catheter ablation procedures. In terms of the future role of catheter ablation in the treatment of AF, as data from large randomised trials such as the CABANA trial become available, it is likely that guidelines may change to recommend catheter ablation as a first-line option for patients with paroxysmal AF – especially those with symptomatic disease – if the results for catheter ablation prove positive.