Although radiofrequency (RF) energy reliably makes transmural lesions, it does have drawbacks. It can damage structures near the pulmonary veins, like the esophagus, or make tears or rips in the heart. In addition, traditional single-point radiofrequency catheters require point-by-point ablation, which is time-consuming. If there is a gap in the lesion line, afib could re-enter the heart.
Multielectrode catheters, which have an array of electrodes, may address some of these drawbacks. Studies provide strong evidence that multielectrode catheters provide similar safety and efficacy to conventional single point catheters, with significant reductions in procedure time and exposure to fluoroscopy.1,2
Multielectrode catheters can deliver bipolar and unipolar energy. It is thought that bipolar radiofrequency energy may reduce complications seen with unipolar radiofrequency energy, but there is still limited data.
Medtronic has three multiple-electrode catheters in various shapes to perform different catheter ablation techniques. This could improve success rates as electrophysiologists can use specially designed tools for lesions in various parts of the heart instead of using one catheter in all areas. These three catheters are:
These catheters can deliver both unipolar and bipolar radiofrequency energy, which is sometimes called phased RF. Bipolar simply means that the radiofrequency energy is transmitted from two places—in this case, two electrodes—to a single target. As a result, bipolar radiofrequency energy is lower power, so lesions are less deep than unipolar. However, since bipolar radiofrequency energy is sent to both sides of the tissue (top and bottom), high temperatures aren’t needed.
Since there are many radiofrequency electrodes on these catheters, EPs can use bipolar radiofrequency energy in half, some, or none of the electrodes, depending on the area of the heart being ablated. This may help achieve transmurality while reducing complications. Bipolar radiofrequency energy is usually applied to thicker heart tissue. In contrast, unipolar can be used on thinner tissue, such as that found at the septum. In addition, these catheters cycle the radiofrequency energy on and off (called duty-cycled RF), allowing tissue to cool, which may help prevent char formation. This is different from single-point irrigated radiofrequency catheters, which use saline solution to cool the tissue.
A study in the Netherlands3 used the first-generation Pulmonary Vein Ablation Catheter (PVAC) to treat 90 paroxysmal afib patients and 12 with persistent afib. The PVAC was able to isolate 95% of pulmonary veins at the time of the procedure. In addition, the procedures were fast. Paroxysmal afib patients were only exposed to an average of 17 minutes of radiation from the fluoroscopy used to help the EPs guide catheter placement.
During follow-up visits, pulmonary veins in 11 paroxysmal afib patients were reconnected due to gaps in the original lesion lines. These patients underwent a second ablation with a single-point radiofrequency catheter. At about 12 months, 64.4% of all paroxysmal patients were free from afib and off antiarrhythmic drugs. There was no charring and no damage to the phrenic nerve or esophagus.
The success rate was lower than reported in many studies, which may be because study monitoring was very rigorous. Patients had 24–48 hour Holter monitoring at three, six, and 12 months. To record asymptomatic afib episodes, they had a seven-day afib “alarm” at six months. Thus, all afib events should be captured, not just those patients felt (symptomatic episodes). Not all studies have such an active monitoring protocol.
In addition, success in this study was defined as patients being free from afib episodes and off antiarrhythmic medication. When including patients who continued to take antiarrhythmic medication, the success rate was almost 88% versus the reported rate of 64.4%.
In this study, patients with persistent atrial fibrillation did not fare as well as paroxysmal patients. Half of the persistent patients (6) had afib episodes during follow-up visits, and four underwent a second procedure. Even with a second procedure, none remained in normal sinus rhythm without antiarrhythmic drugs. The 50% success rate underscores how difficult it is to treat persistent afib with catheter ablation. To find out why persistent AF is so challenging to treat, see Can Catheter Ablation Successfully Treat Persistent AF.
Clinical studies have demonstrated improvement in afib ablation with PVAC. For example, a study comparing PVAC to single point catheter ablation (THERMOCOOL) in 102 paroxysmal afib patients showed that success rates were similar for both. However, the use of PVAC resulted in significantly shorter procedure times, resulting in reduced fluoroscopy exposure time than for the conventional point-by-point catheter. No serious complications were noted with either catheter.1
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Of concern was that in an early multicenter study in Europe, 37.5% of patients who had a PVAC procedure showed new cerebral emboli (clots in the brain) on magnetic resonance imaging (MRI) scans taken after the procedure compared to only 7.4% of patients who had traditional irrigated radiofrequency ablation and only 4.3% of patients who had cryoablation.4
These “silent” cerebral emboli were evident on MRI images but didn’t affect speech, gait, or cognitive function. It’s unclear whether they may lead to a stroke or transient ischemic attack (mini-stroke). However, it is known that patients with silent brain infarcts (areas of the brain that are cut off from blood supply and oxygen but do not result in noticeable neurocognitive impairment) have a higher risk of dementia or cognitive decline.5
PVAC Gold is the newest generation of PVAC. In the PRECISION Gold trial evaluating the PVAC Gold in 51 patients with paroxysmal afib, only one patient (2.1%) had a cerebral embolism. It resolved and was not detected on an MRI 30 days after the procedure. In addition, the PVAC Gold demonstrated a lower complication rate than the previous generation, which seems to address the previous safety issues.6
The Postmarket Evaluation of the Phased Radiofrequency Ablation System (Gold AF Registry) is a clinical study currently being conducted. It will provide real-world insights into the treatment outcomes of the PVAC Gold and other Medtronic multielectrode catheters in patients with paroxysmal or persistent afib.
The nMARQ catheter (Biosense Webster) is a circular mapping and ablation catheter for use with the CARTO system. It contains ten open irrigated electrodes and can deliver both unipolar and bipolar radiofrequency energy.
The nMARQ catheter was first used in humans in 2013. However, it was recalled from clinical use in 2015 related to three deaths confirmed to be esophageal fistulas. As a result, the catheter was re-designed, and the next prototype is currently under investigation.
A recently published clinical study compared the safety and effectiveness of the nMARQ catheter to single-point ablation with the THERMOCOOL NAVISTAR catheter. In ablation of 81 paroxysmal afib patients, the nMARQ catheter was three times faster in isolating the pulmonary veins, with a shorter procedure time. In addition, the use of the nMARQ catheter was not associated with any major complications. This study demonstrated the advantage of a multielectrode catheter over a single electrode catheter in reducing procedure time and exposure to fluoroscopy.2
To learn about other advancements in catheter design, see Contact Force Sensing Radiofrequency Catheters and Balloon Catheters.
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