Surgical "maze" procedure
Surgical management of atrial fibrillation has gone through many stages of development. In the 1980's, the idea that the atria of the heart could be cut and sewn back to together (the so-called cut-and-sew technique) to create barriers to electrical conduction led to the development of the "maze" procedure (see figure below). This procedure required extensive open heart surgery so relatively few patients were enrolled in early studies. Despite a high reported success rate, the initial maze operation has not been widely adopted because of the need for such an extensive surgery. More recently, newer techniques of creating these barriers in the heart have been developed, including radiofrequency ablation (high frequency electrocautery injury), cryoablation (freezing-induced injury), or microwave ablation. These surgical techniques still require direct visualization of the heart with open heart surgery to accomplish the full array of barriers deemed necessary for long-term success. Limited surgical procedures tout the ability to treat atrial fibrillation without open heart surgery but through thorocoscopic techniques (inserting instruments through smaller holes in the chest). However, these techniques can only achieve barriers in the area of the pulmonary veins which may only be a component of what is necessary for long-term success (see discussion below). In addition, despite wide availability of these procedures around the country, there is very limited rigorous study of the outcomes of these procedures.
Catheter ablation, initially developed in the 1990's emulated the surgical maze procedure by utilizing radiofrequency ablation (electrocautery injury) to produce linear lines of electrical isolation in the atrial endocardium. With catheter-based ablation, a procedure can be performed entirely through intravenous catheters inserted into the veins in the leg and sometimes the shoulder. No open heart or even minimally-invasive surgery is necessary. In addition, the entire heart can be accessed so that a full complement of ablation barriers or "lines" can be made. In the late 1990's, a key observation that electrical activity within the pulmonary veins which drain into the left atrium often provoked AF led to alternative techniques for catheter-based treatment of AF. The techniques of ablation over the last 10 years have continued to evolve with a primary focus being to create barriers to electrical conduction around the pulmonary veins although other approaches are often used in conjunction.
To achieve the creation of these lines in the heart, an anatomical picture or "map" of the heart is first created. This is made using sophisticated 3-dimensional software guided by a CT scan of the heart obtained beforehand.
Once the anatomy of the heart is created, a catheter which can create radiofrequency lesions is manipulated around the right and left atria to create lines of electrical block.
These lines serve to eliminate both the triggers of atrial fibrillation as well as the substrate necessary to maintain atrial fibrillation once it starts. Using these techniques, catheter ablation of atrial fibrillation has proven to be much more effective long term at maintaining normal rhythm compared with antiarrhythmic medications (as discussed here).
In some people, particularly those with underlying structured heart disease (SHD) and/or episode of atrial fibrillation that are long-lasting, it is sometimes necessary to undergo more than one ablation procedure to achieve a desired efficacy. Nevertheless, in a patient with significant symptoms of atrial fibrillation, catheter ablation has the best hope of eliminating or reducing the number and length of episodes of atrial fibrillation.
Risks of catheter ablation
Although catheter ablation of atrial fibrillation as described above is an efficacious procedure, it is generally considered as an option for therapy only after an attempt of antiarrhythmic medications has been made. This is primarily due to the inherent risks of any invasive procedure. Although the risks of catheter ablation are low, the benefit of ablation must be weighed against the risk prior to undergoing the procedure. The risks of catheter ablation include:
- Bruising (hematoma) at the site of catheter insertion (right or left groin, left shoulder in some cases). This is generally relatively benign and resolves over time rarely requiring a blood transfusion.
- Heart puncture sometimes resulting in blood accumulation in the sac around the heart (cardiac tamponade). This is managed by removing this blood with a needle and temporary drain. Although this may lead to a longer length of stay in the hospital, there are rarely any long-term consequences.
- Stroke (cerebrovascular accident). Many precautions are taken to reduce the risk of stroke including giving blood thinner during and immediately after the procedure. However, the risk of stroke cannot be eliminated. If a stroke occurs, depending on the size and location of the stroke, this can have long-term consequences.
- Constriction of a vein which leads to the left atrium (pulmonary vein stenosis). This is a rare complication but can lead to shortness of breath if it occurs. These can usually be managed by stenting (scaffolding) open the vein through a minimally invasive approach with catheters.
- Esophageal injury. The esophagus (food pipe) is located immediately behind the heart. To avoid damaging the esophagus, a temperature monitor is placed in the esophagus during the procedure so that it can be visualized and avoided while making catheter ablation lesions. This is an exceedingly rare complication but has lead to death on some occasions.