Catheter Ablation Techniques
Catheter ablation techniques are constantly evolving. Early catheter ablations tried to recreate the lesions in the open-chest Cox maze procedure by creating linear ablation lines that interrupted the atrial fibrillation wavelets. However, electrophysiologists (EPs) had difficulty duplicating the Cox maze lesions during closed-chest catheter ablation. The procedure had high complication rates and required long fluoroscopy times.
Research in Bordeaux, France, by Michel Haïssaguerre, MD, and colleagues suggested that electrophysiologists didn’t need to duplicate the Cox maze lesion set. Instead, Dr. Haïssaguerre’s group found that over 90% of atrial fibrillation is triggered (starts) in or near the pulmonary veins. As a result of these findings, a new type of catheter ablation technique, called Segmental Pulmonary Vein Isolation or Ostial Pulmonary Vein Isolation, was created. Dr. Haïssaguerre and colleagues used radiofrequency energy to ablate the pulmonary vein ostium, the opening to the pulmonary veins. When “isolated,” pulmonary veins can no longer trigger atrial fibrillation. As a result, Dr. Haïssaguerre and his colleagues were able to terminate atrial fibrillation and stop antiarrhythmic drugs for 62% (28) of patients in the study1.
This pulmonary vein isolation approach continues to be the cornerstone of catheter ablation strategies for treating paroxysmal atrial fibrillation. However, pulmonary vein isolation can mean different things to different doctors. Indeed, it has become a catch-all term to describe any ablation of the pulmonary veins. This can lead to misunderstandings between doctors and patients and make a big difference in the rate of freedom from afib after ablation.
Perhaps the most crucial difference among doctors is whether the pulmonary veins are isolated or just ablated. For a procedure to be called pulmonary vein isolation, the doctor must confirm that the pulmonary veins are “blocked”—in other words, that conduction block was achieved. This is done with a mapping catheter that can determine whether there is any electrical activity around the pulmonary veins.
There have been several updates to the segmental (ostial) pulmonary vein isolation developed by Dr. Haïssaguerre and his colleagues. First, it was found that ablating tissue in the ostia (opening) of the pulmonary veins could lead to pulmonary vein stenosis (narrowing), which is a severe complication that can obstruct oxygenated blood from flowing from the lungs into the heart. Second, it was found that more extensive lesion sets were better at stopping afib. This is probably because the pulmonary veins aren’t the only area in the heart that can trigger atrial fibrillation. Over time, afib can create new pathways, called macro re-entry sites, to “cycle” in the heart. Macro re-entry sites are different for each patient.
Ablation strategies and techniques continue to evolve, as does the terminology, as doctors learn more about areas of the heart that could act as a trigger or re-entry site. Thus, the term “segmental pulmonary vein isolation” is rarely used today. Instead, we refer to the anatomic area that will be ablated or the technical ablation approach.
Electrophysiologists use a single-point radiofrequency energy catheter to ablate one spot after another, similar to drawing a line by making dots one after the other. However, if all dots are not connected, gaps allow the afib to re-enter the heart. One method to alleviate this issue is to continuously drag the catheter along the tissue. Using this method is thought to result in more uninterrupted lesions with fewer gaps.
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Basic Catheter Ablation Techniques
Here are the most frequently used basic catheter ablation techniques, shown in order of the fewest to the most ablation (lesion) lines:
Antrum Pulmonary Vein Ablation — Because of the issues with the ostia, as mentioned above, the antrum (base) of the pulmonary veins became the site of catheter ablations. The antrum includes the posterior (back) wall of the left atrium. It extends to the anterior (front) of the right pulmonary veins. In essence, it is a wide perimeter around the pulmonary veins. Antrum pulmonary vein ablation entails lesion lines in this area, but doctors do not confirm conduction block.
Pulmonary Vein Antrum Isolation (PVAI or PVI) — Lesion lines are made in the antrum of the pulmonary veins, and doctors confirm that conduction block has been achieved. Some electrophysiologists also make additional lesion lines. These may include the superior vena cava, roof of the atrium, or the septum (the wall that separates the two sides of the heart). You can see these structures in this diagram of the heart. However, the location of the additional lesions varies by doctor. For example, there isn’t a standard requiring all pulmonary vein antrum isolations to include a lesion line along the superior vena cava.
Circumferential Ablation — Similar to pulmonary vein antrum isolation, circumferential ablation entails lesions encircling the pulmonary veins. Some electrophysiologists also make an ablation line that connects the pulmonary veins on the posterior (back) wall of the left atrium or may ablate tissue from the pulmonary veins to the mitral valve. In addition, a mapping catheter is used to identify “potentials,” which are areas that could serve as a trigger or macro re-entry site for atrial fibrillation.2 Some doctors confirm that conduction block has been achieved. In contrast, others look for the elimination of “potentials” or a reduction in electrical activity in the ablated area.
Posterior Wall Isolation — In some patients with paroxysmal afib, pulmonary vein isolation alone might undertreat afib, and in those with persistent and longstanding persistent afib, pulmonary vein isolation might not be a sufficient treatment. One strategy is to use a box lesion set to target the posterior wall. That can be achieved by performing a linear ablation of the left atrium roof joining the superior pulmonary veins and the left atrium floor joining the inferior pulmonary veins.2
Advanced Catheter Ablation Techniques
Over time, atrial fibrillation can lead to atrial remodeling, which is also known as substrate modification. Remodeling means that afib can change the deeper layers of heart tissue (substrate) or the way electricity is conducted within the heart.
Advanced catheter ablation techniques, which are primarily used to treat persistent and longstanding persistent afib, target electrical remodeling and structural remodeling. However, clinical data is inconclusive, meaning that it is not clear whether these techniques can stop persistent or longstanding persistent afib for most patients.
The most commonly used advanced catheter ablation techniques are:
Stepwise Ablation — Stepwise ablation is the only ablation strategy with a stated goal of terminating afib. It involves isolation of the pulmonary veins and entails additional lesion lines and sequences, which may differ with each electrophysiologist. It is sometimes called sequential ablation because additional ablation lines are performed in a specified order. After isolating the pulmonary veins, many EPs make a lesion line along the roof of the left atrium and then pace or use a mapping catheter to determine whether conduction has stopped. If afib continues, the EP will ablate the next area in the sequence. Some may ablate the coronary sinus, the vessel between the left atrium and the left ventricle. In contrast, others may ablate the mitral isthmus, the area where the mitral valve and the left inferior pulmonary vein meet. There isn’t a specific sequence proven to have the best results, mainly because clinical trials haven’t been performed on this.
Complex Fractionated Atrial Electrograms — EPs occasionally ablate complex fractionated atrial electrograms (CFAE, pronounced cafe) to treat persistent and longstanding persistent afib. A complex fractionated atrial electrogram is a site with an unusual electrical pattern that could be due to the length of the electrical wave (long or short), the frequency of electrical activity (a lot or a little), or the speed of conduction (fast or slow). Complex fractionated atrial electrograms appear to represent macro re-entry sites. In theory, ablating these sites should stop afib. However, clinical studies haven’t shown that eliminating CFAEs eliminated afib, even after extensive ablation.2 None of the HRS Expert Consensus Statement authors identified as routinely using CFAE-based ablation for paroxysmal afib patients, and only 10% used it for persistent and longstanding persistent afib patients. Therefore, the HRS Expert Consensus Statement says that the usefulness of CFAE-based ablation is not well established for persistent and longstanding persistent afib and is not recommended for paroxysmal afib.2
Non-Pulmonary Vein Triggers — Targeting non-pulmonary vein triggers can be added to pulmonary vein isolation.2 Although pulmonary vein isolation is the cornerstone of catheter ablation, up to 11% have afib that starts from outside the pulmonary veins.3 Most commonly, these sites are located in the posterior (back) wall of the left atrium, the left atrial appendage, and other thoracic veins. Isolating these triggers with focal ablation at the site of origin has been associated with improved arrhythmia-free survival. In the HRS Expert Consensus Statement, 35% of the authors identified targeting non-pulmonary veins when ablating persistent and longstanding persistent afib with radiofrequency energy, and 46% identified using this strategy for redo procedures.2
Focal Impulse and Rotor Modulation (FIRM) ablation —Another advanced ablation mapping strategy allows EPs to target rotors, electrical sources in the atrium that help maintain afib. The precise location of rotor and focal sources can be determined with specialized probes and software and ablated within minutes. A key benefit is that this ablation is faster than conventional ablation. The CONFIRM trial demonstrated that rotors and focal sources were present in almost all (97%) paroxysmal or persistent afib patients and FIRM-guided ablation nearly doubled freedom from afib at one year (82.4% with FIRM versus 44.9% traditional ablation alone). While some studies have shown the superiority of FIRM ablation over conventional strategies, others have shown varying results.
Ganglionated Plexi Ablation — Another advanced strategy is ablating the ganglionated plexi (GPs), which are “fat pads” in the heart. Nerves in the ganglionated plexi control automatic functions such as breathing and initiate electrical activity in the heart. It is thought that when one ganglionated plexus is activated, another nearby will also be activated. Some EPs use mapping catheters with high-frequency electrodes to identify ganglionated plexi. In contrast, others simply ablate the four primary ganglionated plexi in the left atrium. However, EPs have not widely adopted ablation of the ganglionated plexi, which may be because there is little research data available.
Hybrid ablation — Hybrid ablation is a treatment for patients with more severe atrial fibrillation, typically persistent or longstanding persistent afib. It is a joint ablation where a cardiac surgeon ablates the outside of the heart, and an electrophysiologist ablates the inside of the heart. This may improve the prospects of transmurality, where ablation lines fully penetrate all layers of the cardiac tissue to create a conduction block that stops afib. In addition, with each specialty ablating areas best suited to their different approaches, higher success rates and fewer complications could be possible.
To learn more about the technology used in catheter ablations, see Catheter Ablation Technology.
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