Balloon Catheters for Ablation
Balloon catheters can ablate larger areas of tissue than traditional, single tip catheters, which require point-by-point ablation. Balloon catheters are used to perform pulmonary vein isolation for paroxysmal atrial fibrillation. They are not used in more advanced ablation techniques and generally are not used to treat persistent and longstanding persistent afib.
After inserting the balloon catheter, the electrophysiologist inflates the balloon and then delivers cryo, laser, or radiofrequency energy. With balloon catheters, doctors don't need expensive real-time mapping systems, so this could put catheter ablation within the reach of any facility with electrophysiology equipment. In addition, balloon catheters could decrease ablation time since a large area of tissue can be ablated at the same time. Shorter ablation time means less exposure to radiation related to the use of fluoroscopy. However, the time needed to perform ablation varies by doctor. In general, electrophysiologists who have performed a large number of ablations are faster, and have higher success rates, than doctors who have limited experience with ablations.
We'll look at the two main balloon catheters, the Arctic Front Cardiac CryoAblation System and the HeartLight Endoscopic Ablation System, as well as an early stage radiofrequency energy balloon, called the Hot Balloon, which is being developed in Japan.
Cryoballoon — Arctic Front
The Cardiac CryoAblation System (Medtronic) uses nitrous oxide gas (cryo energy) to ablate tissue by freezing it. The included Arctic Front balloon catheter comes with two balloon sizes (23mm and 28mm) to accommodate different pulmonary vein sizes. Each balloon is actually composed of two balloons. Nitrous oxide gas is delivered to the inner balloon. The outer balloon is a safety cushion, so the gas doesn't come into direct contact with heart tissue. After positioning the catheter in the pulmonary vein, the doctor inflates the balloon and delivers the cryo energy to the balloon, as shown in this video.
The system also includes a single point cryo-catheter, similar in design to traditional radiofrequency catheters, to make additional lesion lines or to perform "touch ups". A mapping catheter is typically used in procedures to confirm that pulmonary vein isolation has been achieved. However, Arctic Front doesn't require sophisticated real time mapping or guidance systems.
The Arctic Front cryoballoon received European regulatory approval in 2005 and has been used to treat over 20,000 patients worldwide since it was first introduced. In December 2010, Arctic Front became the first balloon catheter to receive FDA approval for afib treatment in the US.
In the US clinical trial, STOP AF, Arctic Front did better than antiarrhythmic medication in stopping atrial fibrillation in patients with paroxysmal afib. Of the patients who had cryoablation, 58% were free from afib episodes and were able to discontinue taking antiarrhythmic drugs one year after the procedure (69.9% were free of AF, but some remained on an antiarrhythmic medication). Comparatively, only 7.3% of patients who only took antiarrhythmic drugs were free of atrial fibrillation at 12 months.
Individuals who had an Arctic Front ablation also had fewer complications, with a Major Atrial Fibrillation Event rate of only 3.1% compared with 8.5% for patients who took antiarrhythmic drugs. However, there was one stroke that was related to the procedure, and seven patients developed pulmonary vein stenosis. Some people who had cryoablation suffered from phrenic nerve palsy, a serious complication that makes it difficult to breathe normally. Most of the 29 phrenic nerve palsies resolved within three months, and nearly all had stopped after 12 months, without the need for another procedure.
The rate of phrenic nerve damage may have been related to learning curve, or a doctor's experience with the Arctic Front cryoballoon. Electrophysiologists are accustomed to placing and manipulating single point radiofrequency catheters, but balloon catheters are new. At the Boston Atrial Fibrillation Symposium in January 2011, Dr. Jeremy Ruskin, conference organizer and STOP AF investigator, presented data showing how learning curve affected STOP AF success and safety. Doctors who had performed 12–23 cryoablation cases had higher success rates than those who had performed only one or two procedures. Similarly, there were no major adverse events when the procedure was performed by an experienced operator compared to a 7% serious adverse event rate for those using Arctic Front for the first time.
As doctors become more familiar with the cryoballoon, the incidence of phrenic nerve injury could decrease. Dr. Ruskin reported that the incidence of phrenic nerve damage was halved in the 80 patients who received cryoablation after the official trial. Procedure times should improve as well. The average procedure time was six hours in STOP AF, with experienced doctors having much lower procedure times than less experienced doctors. However, the average ablation and fluoroscopy time was just over an hour, which underscores how quickly a balloon catheter can ablate a large area of tissue.
Patients who have had an Arctic Front ablation have reported a vast improvement in their quality of life. Individuals participating in the STOP AF trial completed a questionnaire on symptoms prior to the procedure and took the same questionnaire one year after the ablation. Before treatment, all patients had afib symptoms, such as palpitations, fatigue, and shortness of breath. One year after the procedure, only 20% of patients reported having symptoms. See how Arctic Front improved patients' lives.
Laser Balloon — HeartLight
The HeartLight Endoscopic Ablation System (CardioFocus), which was approved in Europe in June 2009 and is in a clinical trial in the US, uses laser energy to ablate tissue. The laser balloon offers real time visualization, meaning the electrophysiologist can see where the balloon is positioned and where the energy is delivered. Doctors who spoke about their experience with the laser balloon at the Heart Rhythm Society meeting said that its visualization capability is a large step forward for catheter ablation. Dr. Moussa Mansour, of Massachusetts General Hospital, reiterated the importance of this feature at the Boston Atrial Fibrillation Symposium. He stated that the real time visualization becomes more important when a patient has complex anatomy. He noted two other advantages: doctors can see whether there are any gaps in the ablation lines, which could increase effectiveness, and they also can see when tissue starts to overheat and adjust the power accordingly, which may reduce some complications.
The laser balloon is made of a special material that allows it to conform to a variety of pulmonary vein sizes and shapes. Inside the balloon, there is an endoscope (miniature camera), an optical fiber that delivers laser energy, and a lumen (small tube) that circulates a liquid coolant. The endoscope is what enables the electrophysiologist to see where the balloon is placed and where the laser energy is delivered. The doctor positions the catheter at the ostia (opening) of a pulmonary vein and inflates the balloon, and then delivers the laser energy, which is visible as a green light, to create lesions. When one area has been ablated, the doctor turns the balloon to ablate another area. You can see a HeartLight laser ablation by clicking on this clinical procedure video.
Advanced mapping systems aren't needed for the procedure, but intracardiac echocardiography (ICE), which provides real time ultrasound images, is typically used. A mapping catheter is also used to confirm that the pulmonary veins have been isolated.
The laser balloon was used to treat 27 patients with paroxysmal atrial fibrillation in a small study at Homolka Hospital in Prague, Czech Republic. After ablation, a circular mapping catheter was used to verify that the pulmonary veins had been electrically isolated (blocked). The laser balloon isolated all pulmonary veins, although some veins needed more than one ablation during the procedure. Three months later, 18 patients returned for follow up, and nearly 90% of pulmonary veins remained isolated. Four patients (17%) continued to have afib symptoms. Interestingly, two of these patients were experiencing symptoms even though re-mapping confirmed that the pulmonary veins were isolated. This suggests that, for them, atrial fibrillation was being triggered in a different part of the heart. None of the patients had pulmonary vein stenosis of more than 30%, and there were no major complications, such as stroke or damage to the phrenic nerve or esophagus.
Results on the first 200 patients treated by the HeartLight laser balloon were presented at the Heart Rhythm Society meeting in May 2011. At that time, 107 patients had reached six months of follow up, and 65% were free from atrial fibrillation and off antiarrhythmic medication after a single procedure.
The laser balloon feasibility (safety) clinical study in the US completed enrollment in February 2011. CardioFocus could begin enrollment in a larger pivotal trial investigating effectiveness and safety of the laser balloon in 2011.
Radiofrequency "Hot" Balloon
Another balloon catheter, which uses radiofrequency energy, is in early stages of development in Japan. Its inventor, Dr. Shutaro Satake, of the Hayama Heart Center, spoke on the hot balloon at the Heart Rhythm Society meeting. The balloon is made of compliant material, which can conform to a variety of pulmonary vein sizes and shapes, and is filled with a solution of saline and ionized contrast medium. Inside the balloon, there is a coil electrode, which is the source of radiofrequency energy, and a thermocouple to measure temperature. When the radiofrequency energy is delivered to the balloon, the coil electrode gets hot. The balloon has a special agitation system that constantly mixes the saline solution and keeps the entire balloon at a single temperature, which could reduce charring.
Dr. Satake and his colleagues published their results on hot balloon ablation of 63 paroxysmal and 37 persistent patients. Patients received pulmonary vein antral isolation. In addition, the roof and posterior (back) wall of the left atrium were ablated. The balloon's malleable material helped to identify when a complication could arise. For instance, by looking at how the balloon's shape changed at the pulmonary veins, doctors surmised the balloon was inserted too deeply in the veins, which could result in pulmonary vein stenosis. Similarly, by watching the shape of the balloon, doctors could avoid damage to the esophagus. Dr. Satake and his colleagues also used a pacing device near the right superior pulmonary vein in order to avoid damage to the right phrenic nerve, which is one of the nerves that makes the diaphragm contract automatically during breathing. As a result, the complication rate was very low. There were no cases of severe pulmonary vein stenosis, though three people (3%) had asymptomatic pulmonary vein stenosis, and there was one incident of phrenic nerve palsy.
The single-center study showed very high success rates. At 11 months, 60 (95%) paroxysmal patients and 32 (86%) persistent patients were free from afib and off antiarrhythmic drugs. Follow up monitoring began three months after the ablation. Patients were instructed to use a mobile ECG (electrocardiogram) at the same time every day for three months. In addition, patients were instructed to activate the ECG if they were experiencing atrial fibrillation. This follow up is more rigorous than the minimum in the Heart Rhythm Society guidelines. However, it's possible that asymptomatic afib events were not captured by the mobile ECG since it was activated just once a day. In addition, the authors of the study did not define what constituted "freedom from AF". The Heart Rhythm Society guidelines state that any episode that lasts 30 seconds or more should be considered an afib event, but some studies characterize an event as atrial fibrillation once it lasts several minutes. Without knowing how they classified events, we can't judge the hot balloon's high success rate. The hot balloon is not yet in clinical trials either in the US or Europe.
Comments on Balloon Catheters
Balloon-based systems may improve success rates and lower the procedure time. However, it can be difficult to position some balloon catheters in the right pulmonary veins. If the balloon is positioned too deeply, pulmonary vein stenosis could develop. In addition, some balloon catheters have difficulty reaching the right inferior pulmonary vein, so the doctor may need to use a single point catheter to ablate this vein.
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