Single point radiofrequency (RF) catheters are widely used in catheter ablations. These catheters transmit energy from a single point at the catheter’s tip. Thus, the radiofrequency energy is “unipolar.” With these catheters, electrophysiologists make lesions by ablating one spot after another, similar to drawing a line with a sequence of dots. However, if all dots are not connected, gaps can allow afib to re-enter the heart. One method to alleviate gaps is to continuously drag the catheter along the tissue to create uninterrupted lesions.
In general, high temperatures are needed to make sure that all layers of tissue are ablated. However, these high temperatures can also lead to blood and tissue accumulating on the catheter tip. This is known as char formation. When charring occurs, only the outer layer of tissue may be ablated, which means the lesion isn’t transmural. In addition, heat generated by radiofrequency energy can cause blood around the ablated area to clot. If a clot were to dislodge from the heart, a stroke could occur.
Most EPs who use radiofrequency energy use irrigated catheters (sometimes called “cooled RF”). This decreases the likelihood of thrombus and char formation.1 Irrigated catheters have tiny holes at the tip that spread cooled water, usually a saline solution, to the ablation area. In this way, the EP can deliver high levels of radiofrequency energy while moderating the temperature where the catheter connects with heart tissue.
A multicenter trial compared antiarrhythmic drugs and radiofrequency catheter ablation using the THERMOCOOL Irrigated Tip Catheter (Biosense Webster) in 167 patients with paroxysmal atrial fibrillation.2 Patients who had failed at least one antiarrhythmic medication were randomized to receive either ablation or antiarrhythmic drugs.
The results showed that the THERMOCOOL catheter ablation was more effective than antiarrhythmic medication in controlling afib. Of the patients who had the ablation, 66% were free from atrial fibrillation at 12 months. However, a few remained on antiarrhythmic medication. Conversely, only 16% of patients who were treated with drugs were free of afib episodes. The THERMOCOOL catheter ablation was also safer, with only 5% for those who had an ablation having serious adverse events compared to 9% on an antiarrhythmic drug. In addition, patients who had an ablation had a significant improvement in quality of life. For more information about the trial’s results, see our video interviews with Dr. David Wilber, the principal investigator, and Dr. Steven Hao, a trial investigator.
The THERMOCOOL trial results 3 proved that catheter ablation could successfully treat afib and set a standard for FDA approval so this catheter could be used for comparison in other afib catheter ablation clinical trials.
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Unipolar radiofrequency energy has been associated with complications, such as cardiac tamponade (filling the heart with fluid), cardiac perforation (rips or tears in the heart), damage to the esophagus or phrenic nerve (one of the nerves that makes the diaphragm contract automatically during breathing), and pulmonary vein stenosis (narrowing of the vein). But, there are ways to help minimize catheter ablation risks,
To learn more about other energy sources and technologies in development or use, some of which may help reduce risks, see Multielectrode Radiofrequency Catheters, Contact Force Sensing Radiofrequency Catheters, and Balloon Catheters.
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