The goal of any catheter or energy source is to create a transmural lesion while minimizing complications. A transmural lesion—scar tissue that completely penetrates the heart tissue from the inside to the outside—is key to a successful ablation by preventing errant electrical signals.
Making a transmural lesion is as much of an art as it is a science. It depends on the temperature generated by the energy source, how much pressure is applied to the catheter (contact force), and how long the catheter remains in contact with the tissue. Different energy sources can be used in various types of catheters, and each has advantages and disadvantages. Thus, patients may want to be aware of the multiple options.
Here are the energy sources being used or tested today in atrial fibrillation catheter ablations:
Radiofrequency (RF) energy is radio waves that are converted to heat to ablate and create scar tissue. RF is the most widely used energy source in catheter ablations and reliably achieves transmurality. In general, high temperatures are needed to ensure the ablation of all layers of tissue. Traditional RF catheters are unipolar, which means the energy is transmitted from a single point at the catheter’s tip.
Cryothermy, or cryo energy, is intense cold. Cryo forms ice crystals in the tissue, causing cells to die and create scar tissue. Lesions may be easier to make since the cold temperature causes tissue to stick to the catheter. Cryo energy can be used in single-point catheters and balloon catheters. Animal studies2 have shown less thrombus (clot) formation with cryo energy than RF energy, suggesting that cryothermy could lower the risk of a stroke. However, phrenic nerve injury is more common with cryoballoon ablation. In the FIRE AND ICE trial, cryoballoon ablation was associated with more phrenic nerve injury (2.7%) than radiofrequency ablation (0%). However, most injuries were resolved within three months.1
Laser energy is light waves that are converted to heat to ablate and create scar tissue. Laser may be a safer heat-based energy than unipolar RF energy. The catheter doesn’t need to be in direct contact with tissue with laser energy, which could mean fewer complications. Unlike other energy sources, contact force is not a factor in whether a laser lesion is transmural. In addition, laser energy can be adjusted to tissue thickness, with higher energy applied to thicker tissue and lower energy to thinner tissue.
Ultrasound technology uses high-frequency sound waves to produce heat in atrial tissues to create lesions. High-intensity focused ultrasound (HIFU) showed early promise, but clinical studies showed high complication rates and low effectiveness. A novel method being investigated uses low-intensity collimated ultrasound (LICU), a narrow beam of energy delivered from a catheter tip that creates lesions in the tissue without direct contact.
Electroporation uses non-thermal direct current energy to create holes in cell membranes that mainly target active cells. One frequently-cited benefit of this new technology is the lack of collateral damage to surrounding tissues, thus improving safety and decreasing complications. This technology is still being investigated, though it is approved in Europe.
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Catheter design and functionality constantly evolves. Today, most atrial fibrillation ablations use single-point radiofrequency energy catheters, with a success rate—freedom from atrial fibrillation—of about 70%. It’s believed that different types of catheters could have higher success rates or fewer complications. Here are different types of catheters available today for atrial fibrillation catheter ablations:
Single point radiofrequency catheters emit radiofrequency energy from a single point at the catheter tip. In making lesions, EPs ablate one spot after another, similar to drawing a line by making dots one after the other. If all the dots are not connected, afib could re-enter the heart through the unablated space (gap).
Multielectrode radiofrequency catheters have several electrodes, each of which can transmit radiofrequency energy. These catheters can ablate larger areas of tissue than single-point radiofrequency energy catheters, which could decrease procedure times. In addition, multielectrode catheters may be better than single-point catheters at making contiguous lesions (lesion lines without any gaps).
Contact force sensing radiofrequency catheters. Contact force is a variable that affects transmurality. Without enough pressure, the lesion may not fully penetrate the tissue and thus allow afib to re-enter the heart. With too much pressure, complications can occur. These catheters tell the EP how much pressure is being applied to the catheter and tissue.
Balloon catheters. After the balloon catheter is inserted into the left atrium, the EP inflates the balloon at the catheter tip. Balloon catheters can ablate a larger area of tissue than single-point radiofrequency catheters, shortening procedure time and enhancing the prospects that lesions will be contiguous (without gaps). There are balloon catheters using cryothermy, laser energy, and even radiofrequency energy. In general, balloon catheters have difficulty reaching the right-sided pulmonary veins.
To learn more about catheters used in atrial fibrillation treatment, see Single Point Radiofrequency Catheters, Multielectrode Radiofrequency Catheters, Contact Force Sensing Radiofrequency Catheters, and Balloon Catheters.
To learn more about whether catheter ablation is appropriate for you, see Are You a Candidate for Catheter Ablation.
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