Robotic ablation

Catheter ablation

Until recently, cardiac arrhythmias (heart rhythm disorders) could only be treated with medication, which only relieved symptoms for a few patients. Many others would continue to experience symptoms, particularly breathlessness and palpitations. In addition, some forms of arrhythmia could only be treated with risky open heart surgery.

Over the last 20–30 years, catheter ablation has come to be used for most heart arrhythmia conditions: an electrophysiologist passes thin catheters up through veins in the leg towards the heart. By emitting radiofrequency energy at the tip of these catheters, it is possible to destroy the area of heart tissue causing the arrhythmia. Still, the technique is technically challenging, particularly with atrial fibrillation, with success requiring continuous lines of scar to encircle the pulmonary veins in the left atrium.

Introduction of robotic ablation

To address these technical difficulties, robotic ablation has been developed whereby a sheath capable of steering and manipulating the ablation catheter is inserted into the femoral veins. The doctor then controls this robotic sheath from a control station nearby. Although there are others emerging, the most widely used robotic system is the Sensei Robotic Catheter System by Hansen Medical Inc. (Mountain View, CA, USA). Their robotic sheath capable of catheter manipulation is the Artisan sheath, with the remote controlled station called the Sensei system.

Robotic systems were initially tested in the ablation of SVT and atrial flutter. However, with the exponential increase in catheter ablation of complex cardiac arrhythmia such as AF and VT, there medical benefits are numerous. According to a Hansen Medical press release in June 2009, over 2000 procedures had already been performed around the world using their system.

Potential benefits

Although manual catheter ablation of most arrhythmias has become standardised, low risk and successful, certain challenges remain. Manipulation of catheters to precise locations within the heart and keeping them stable in the desired position can be challenging by hand, and manipulation by the robot can be helpful in this respect. Achieving adequate tissue contact, ideally with a small amount of pressure being applied by the catheter during ablation, is essential to effectively destroy the heart tissue responsible for the arrhythmia. By controlling catheter movement using the robot, the physician can automatically adjust and titrate the contact force to achieve the desired location and position . There is evidence that robotic ablation causes quicker more effective burns.

Use of robotic navigation for catheter ablation was also designed to allow electrophysiologists to perform most of the procedure without being exposed to X-rays, which can be dangerous in the long term. Use of robotic navigation has been shown to reduce fluoroscopy times in catheter ablation of AF, resulting in reduced X-ray exposure for patients and other health care professionals present in the catheter laboratory.

Success rates

Several early studies have demonstrated that robotic ablation can be used to successfully treat arrhythmias such as SVT and atrial flutter. More recent studies have focused on its use in ablation of AF. There are several published series where centres have reported their experience using this equipment. These have shown a single procedure success rate approximately equivalent to that achieved when performing procedures manually.

The Rostock group in Hamburg published a series of 64 patients with paroxysmal AF undergoing catheter ablation using the Sensei system. They were able to isolate 100% of pulmonary veins, with reasonable procedure and fluoroscopy times (180 and 23.5 minutes respectively). They achieved subsequent freedom from AF in 81% at 1 year. There were no procedural complications in this cohort.

One study of 390 consecutive patients compared success rates in those having catheter ablation of AF performed robotically to those performed manually over the same period in a single institution. The cohort was mixed and included patients with paroxysmal and persistent AF. They were able to isolate all pulmonary veins in 100% of patients in both groups. There was no difference in procedure time between manual and robotic ablation, although there was a reduction in fluoroscopy time (X-ray use) with robotic ablation. They reported success rates of 85% with robotic ablation versus 81% if performed manually at 14 months (although this difference did not reach statistical significance). To date there are no completed randomised controlled trials to compare robotic ablation of AF to manual ablation, and so it remains to be seen whether these potential benefits will translate into better success rates.

Robotic ablation of ventricular tachycardia has also been reported. There are no large scale trials comparing robotic and manual ablation of VT as yet. The ability to titrate force and improve catheter-tissue contact is of particular importance in this setting, in that the ventricle can be over a centimetre thick, and producing burns that span the thickness of the wall can be difficult using conventional methods.

Evolution

Several studies have been published describing outcomes of AF ablation using this technology. The critics of robotic ablation cite the high complication rates in the studies reporting 'first in human' experience with the technology. Wazni et al. reported experience with the first 71 catheter ablations for AF in their centre using the Hansen robotic navigation system starting from 2005. They reported complications mainly from 2 problems. Firstly, if used with a short introducer, the thicker robotic sheath may result in bruising and bleeding at or near the site where it enters the vein. Secondly, the increased pressure that can be applied to create burns resulted in a higher than usual rate of perforation, causing leakage of blood from the heart into the sack around the heart (tamponade) which needs to be drained by a tube. These complications can occur during manual ablation of AF, with a major complication rate of approximately 4% accepted as the norm.

There have been subsequent modifications to get around these problems, both in the technology itself and in clinical practice using the robot. Firstly, a long flexible introducer (30 cm 14F sheath) can be inserted into the vein in the leg, which the robotic sheath can then pass safely through to avoid complications. Secondly, in addition to the pressure sensor system called Intellisense that shows the operator on a visual scale how much pressure is being applied, a "tactile vibration feedback" system has been added so that the robotic controller vibrates progressively as more pressure is applied. The pressure sensor technology that has emerged alongside this robotic system is, in itself, an important development in terms of safety and monitoring of tissue contact. Other companies such as Endosense and Biosense Webster have since produced ablation catheters with pressure sensor technology.

Adjustments to clinical practice with the robotic system include an increasing trend for operators to use slightly less radiofrequency energy (a lower power setting) when performing robotic ablation compared to manual settings. Many centres, particularly in the USA also advocate use of oesophageal temperature monitoring. These adaptations have limited the rate of tamponades subsequently.

These early studies have allowed others to incorporate changes to their technique, and hence recent work has produced complication rates for catheter ablation of AF very comparable to procedures performed manually. The field of robotic ablation is growing and evolving rapidly, and randomised controlled trials comparing robotic to manual ablation are ongoing in Europe and the USA to see if these potential advantages will translate into better clinical outcomes.

Other emerging robotic technologies

Catheter Robotics, Inc. (New Jersey, USA) founded in 2006 has developed a remote catheter system called Amigo. This system has a robotic sheath to steer catheters which is controlled at a nearby work station, in a manner similar to the Sensei system. The first in human use of this system was in April 2010 in Leicester UK, where it was used to ablate atrial flutter. Further studies are awaited to confirm its safety and efficacy.

Magnetecs Corp. (Inglewood, CA, USA) founded in 2009 has produced their ‘Catheter Guidance Control and Imaging’ (CGCI) system. This has 4 large magnets placed around the table (the patient’s bed), with customised catheters containing magnets in the tip. The catheter is again moved by the magnetic fields and is controlled at a nearby work station. This system has undergone initial in-human testing, and is currently undergoing clinical evaluation at the Hospital Universitario La Paz in Madrid starting September 2010. Magnetecs have already stated their intention to market their CGCI system for use in AF.

The use of magnetic fields to guide catheters is another recent innovation. The system was initially developed at the University of Virginia, and was acquired by Stereotaxis Inc. (St. Louis, Missouri, USA) in 2005 and named the Niobe system (now the Niobe II). Although this system may not meet everyone’s definition of a robotic system it has elements in common with the other systems described. The patient is placed in a magnetic field, generated by large magnets on either side of them (0.08 Tesla). The operator is again at a control station nearby, and controls the movement of the catheters with the click of a mouse. The catheter which has a small magnet in the tip is then moved inside the patient by magnetic fields, and hence although the ablation is controlled remotely there is no actual robot moving the catheter. The Niobe system is being marketed for electrophysiology procedures including catheter ablation, coronary intervention, and placement of left ventricular leads for pacemakers.

Theoretical advantages of the Niobe system again include steering of catheters to precise locations within the heart, and subsequent stability at that location. The force the magnetic fields can apply to place catheters in contact with the heart tissue is lower than that achieved with true robotic systems, which on the one hand may reduce the potential to perforate structures, but on the other may reduce the effectiveness of ablation. To accommodate the Niobe system, catheter laboratories must be specially fitted without ferrous metals that might cause difficulties with the powerful magnets. Stereotaxis Inc sell a range of compatible equipment, including a new compatible irrigated catheter.

The Pappone group reported early experience with the Niobe II system in 40 patients undergoing catheter ablation for AF. They reported longer procedure times than manual procedures but nevertheless completed pulmonary vein isolation (although isolation was not demonstrated with circular mapping catheters). They reported no complications in this cohort. A subsequent study included 45 consecutive patients undergoing catheter ablation of AF using the Niobe II system reported more difficulty achieving pulmonary vein isolation (in this study isolation was demonstrated with circular mapping catheters). They were able to isolate only 8% of pulmonary veins using the system, having to complete procedures manually in the remainder. Although charring was noted on the catheter tip in a third, there were no complications. Success was reported in 45% at 11 months.

A very recent study by the Kuck group reported on use of the Niobe II system in 56 consecutive patients undergoing catheter ablation for AF. The authors reported that the procedures were feasible, although more time consuming than those they performed manually. They again reported difficulty isolating the pulmonary veins in 7% (confirmed with a circular mapping catheter), requiring the procedure to be completed manually. In the first 28 patients there was some charring noted on the catheter tip which may have contributed to the 1 myocardial infarction and 1 transient ischaemic attack (a minor stroke which resolves quickly) within 2 weeks of their procedure. The ablation catheter was then redesigned, and there was no subsequent charring or embolic complications in the subsequent 28 patients. Overall the success rate was 70% at approximately 18 months which was comparable to their results achieved with manual ablation. The Bordeaux group have published in abstract form a similar experience using the stereotaxis system in 28 patients, and comparing its use to manual procedures over the same period. They again found longer procedure times and fluoroscopy times, and had difficulty isolating veins in 14% of cases which were then completed manually. They reported no complications other than haematomas in the stereotaxis group, with similar success rates at 1 year.

Further reports are awaited to confirm whether the redesign of the Stereotaxis irrigated ablation catheters has overcome the issues of char formation, and whether further developments in the Niobe II system will make pulmonary vein isolation achievable for a greater proportion of patients than is currently the case. Likewise, experience with the Magntec and Amigo systems is awaited.

Robotic ablation has proven feasible in ablating arrhythmias such as atrial flutter and SVT. There is great interest in the cardiology community as to whether it may help overcome difficulties with catheter ablation for AF in particular. The principal problem with catheter ablation for AF is the failure to create lasting pulmonary vein isolation. It is hoped that the increased catheter stability, and in the case of the Hansen system the ability to titrate force through monitoring of tissue contact, may improve outcomes of ablation. Further evidence for these various systems, currently at different stages of development, will clarify whether their theoretical advantages translate into safer more effective ablation procedures for patients.