Atrial fibrillation is the most common irregular heart rhythm, affecting about 2.5 million people in the US, with more than 200,000 new cases of atrial fibrillation are diagnosed each year. Atrial fibrillation is an abnormal heart rhythm originating in the upper chambers of the heart (atria). Several impulses begin and spread throughout the atria, causing a rapid, irregular and disorganized heartbeat.
Ablation is proving to be successful for many patients with atrial fibrillation. The procedure is indicated for those:
Not all patients may be appropriate candidates for catheter ablation of atrial fibrillation. A thorough evaluation will be conducted to see if this procedure is appropriate. Pre-testing includes a history and physical, electrocardiogram (ECG) and possible holter/event monitor. A transesophageal echocardiogram (TEE) may be needed within 24 hours of the procedure to rule out blood clots in the left atrium. Other tests, such as a spiral computed tomography (CT) or MRI, may be required if you have had previous procedures to treat your arrhythmia.
Radiofrequency (RF) energy is radio waves that are converted to heat to ablate and create scar tissue. It reliably achieves transmurality and is the most widely used energy source in catheter ablations. In general, high temperatures are needed to make sure that all layers of tissue are ablated. Traditional catheters use unipolar radiofrequency energy, which simply means that the radiofrequency energy is transmitted from a single point at the catheter’s tip.
Cryo energy, is intense cold that is used to form ice crystals within the tissue, causing the cells to die and creating scar tissue. It may be easier to make lesions using cryothermy since the cold temperatures cause tissue to stick to the catheter. In addition, cryo energy may have fewer major complications. Animal studieshave shown cryo energy to have a much lower incidence of thrombus (clot) formation than radiofrequency energy, which suggests that cryothermy could lower the risk of a stroke. Cryo energy can be used in single point catheters or balloon catheters.
Laser energy is light waves that are converted to heat to ablate and create scar tissue. It may be a safer heat-based energy than unipolar radiofrequency energy. With laser energy, the catheter doesn’t need to be in direct contact with tissue, which could mean it will have fewer complications than radiofrequency energy. Unlike other energy sources, contact force is not a factor in whether a laser lesion is transmural. In addition, laser energy can be adjusted when ablating tissues of varying thickness, with higher energy applied to thicker tissue and lower energy applied to thinner structures in the heart.
Other energy sources, such as microwave and high intensity focused ultrasound (HIFU), have been studied but these energy sources aren’t widely used in catheter ablation.
The design and functionality of catheters is constantly evolving. Most atrial fibrillation ablations today use single point radiofrequency energy catheters, which have 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 the different types of catheters available today for atrial fibrillation catheter ablations:
Single electrode radiofrequency catheters emit radiofrequency energy from a single point at the catheter tip. To make lesions, electrophysiologists 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 in the unablated space (gap).
Multi-electrode radiofrequency catheters have several electrodes, each of which can deliver radiofrequency energy. These catheters can ablate a larger area of tissue than single point radiofrequency energy catheters, which could decrease procedure times. In addition, multielectrode catheters may be better at making contiguous lesions (lesion lines without any gaps) than single point catheters. Finally, these catheters can also deliver superficial bipolar radiofrequency energy, which may reduce injury to deeper tissues in certain areas of the heart. However, there is limited clinical data on multielectrode catheters, which means that complications arising from these procedures may not be fully known or understood.
IRRIGATED TIP CATHETERS
Saline is perfused via a pump mechanism through the catheter tip, turns around within the catheter tip, and returns back to the pump. This represents a closed system because no saline is infused into the blood pool
Open irrigation overcomes the limitations of non-irrigated ablation by lowering electrode and tissue surface temperature, bringing together the efficacy of power delivery with the safety of reduced char formation.
Open Irrigation multi-electrode catheter
nMARQ™ This new open irrigation multielectrode catheter is in clinical trail in the US for treatment of Atrial fibrillation.
Each nMARQ™ Catheter boasts 10 irrigation holes per electrode completely surrounding the electrodes for more efficient cooling.Uniform irrigation occurs immediately at the site of tissue contact reducing trade-offs between precision and safety.
CONTACT FORCE SENSING RADIOFREQUENCY CATHETERS
During cardiac ablation, the contact force sensing Catheter enables the measurement of catheter tip contact force and direction inside the heart. If there is not enough force or pressure, the lesion formation may not be deep enough, which would allow recurrence of arrhythmia. If there is too much pressure, complications, such as steam pops, can occur. These catheters tell the electrophysiologist how much pressure is being applied to the catheter and tissue.
After the balloon catheter is inserted into the left atrium, the electrophysiologist inflates the balloon at the tip of the catheter. Balloon catheters can ablate a larger area of tissue than single point radiofrequency catheters, which enhances the prospects that lesions will be contiguous (without gaps) and could shorten procedure times. There are balloon catheters using cryothermy, laser energy, and even radiofrequency energy.
Disadvantage are that balloon catheters are bulky, lesions are less precise/accurate, they may have difficulty reaching the certain areas of the heart (right pulmonary veins). These catheters do-not allow ablation of areas other than tissues around the pulmonary veins.
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