Ablation of atrial fibrillation

The ablation of atrial fibrillation is an invasive technique that is used in the treatment of Atrial fibrillation (AF in the UK or Afib in the US), one of the most common cardiac arrhythmias. Ablation is the removal or melting away of an unwanted structure or tissue. Ablation of atrial fibrillation can be accomplished with different techniques; the most established approach is via radiofrequency ablation (RFA) around the pulmonary veins, which are the veins that bring oxygenated blood from the lungs back to the upper chambers or atria, in the left side of the heart.

History

In 1987, James L. Cox introduced an open-heart surgical procedure which has been subsequently established as capable of curing Atrial Fibrillation. This procedure was originally called the Maze procedure. It consists in a series of incisions and sutures that create many electrically isolated compartments in the atria. In one of its latest designs, it is called Maze IV. Maze IV, as opposed to Maze III, utilizes radiofrequency or cryoablation and is performed with a medial sternotomy or a lateral thoracotomy and only two small incisions in the atrial muscle. A minimally invasive version, or Minimaze has also been developed. Specialists in cardiac electrophysiology attempted to replicate the Maze procedure results using catheters advanced via the groin or neck veins, and therefore no incisions, as early as the late 1980s. Only in the 1990s the pioneering work of Michel Haïssaguerre's group focused on the role of the pulmonary veins as the trigger of Atrial Fibrillation. More recently, circumferential ablation around the pulmonary veins has become the preferred approach and additional focal sources outside the pulmonary veins have been described in specific groups of patients, such as those affected by persistent or chronic atrial fibrillation, patients with sleep apnea and obesity, older female patients, patients with a weak heart muscle (low left ventricular ejection fraction) and patients with microscopic scars in the left atrium.

Indication

At least 5 million people in the US alone suffer from atrial fibrillation. It represents by far the most relevant heart rhythm-related clinical issue, due to its complications including stroke, heart failure and increased risk of death. These complications are more frequent in less healthy individuals, such as patients over age 75, with diabetes, heart failure or heart valve malfunction. In many cases, the condition can be controlled with medications, either by reducing the heart rate ("rate control") or by maintaining a regular rhythm ("rhythm control"). In a significant proportion of patients, drugs are either ineffective or lead to unacceptable side effects. In those cases, electrophysiology-based treatment modalities such as ablation treatment may be employed. Younger patients with normal cardiac anatomy and function have the highest probability of maintaining normal rhythm while taking antiarrhythmic drugs.

Currently, many high specialization centers on the world, especially in Europe and the US, but also South America, are dedicated to the safe and effective use of this ablation procedure. The procedure is thus performed in many EP labs. It is currently recommended that it be carried out with the help of a 3D mapping system. The most common form is an ablation of the pulmonary veins and surrounding tissue by means of radiofrequency energy.

Methods

Atrial fibrillation ablation can be performed from the inside of the heart via catheters that are introduced from the groin artery or neck artery; in this case, no incisions are made. Alternatively, it can be accomplished from the outside of the heart with either open heart surgery or via a thoracoscopy approach. A mixed or hybrid approach is also available. The most common approach is the first, or only catheter-based. In this case, the catheter that delivers the ablative energy can use radiofrequency, or cryothermic energy. High intensity ultrasound or laser energy had been used in the past. The ablative catheter is able to deliver lesions only from its tip, which is from 4 to 8 mm long, shaped like a match point. The ablation points are centered in the left upper chamber of the heart, or left atrium. A series of ablation points is used to establish a line of lesions. These lines are supposed to block the trigger points of Atrial Fibrillation and create a barrier to the propagation of the arrhythmia. As stated, the lesions target the entrance of the pulmonary veins, of which usually two right and two left ones are found. The lesion points are applied inside the left atrium a few millimeters from the pulmonary vein insertion in the body of the left atrium. This region is known as pulmonary vein antrum. The end point of the procedure is to electrically isolate the pulmonary veins - pulmonary vein isolation or PVI. A less common approach is to encircle both pulmonary vein orifices on one side with a single wider elliptical line, technique called WACA or wide area circumferential ablation. Other lines of lesions and ablation points inside the left and right atrium are often made - mostly on the posterior wall and often also on other targets, such as the coronary sinus, the left atrial appendage base, the superior vena cava, the right atrial isthmus. Currently, area of complex fragmented signals, called CFAE are also treated with ablation points in order to reduce the risk of recurrent AF. The procedure takes between 2 and 4 hours and occasionally needs to be repeated. As a general rule, older patients with more heart disease and more frequent, longer episodes require more extensive ablation procedures. A technique using a cryoablation balloon capable of creating lesions all around its perimeter is also being used with comparable results in patients with paroxysmal atrial fibrillation. The current recommendation for atrial fibrillation ablation requires documentation of successful isolation of the target areas with a circular mapping catheter and proof of block in case ablation lesions are delivered along a line (linear lesions). RFA of atrial fibrillation can also be performed with the help of stereotaxis navigation of the left atrium, which allows the ablator catheter to be moved in the atrial anatomy remotely from the patient's operative bed and using a magnetic field to direct and gently steer the tip of the catheter into the appropriate sites of ablation.

Safety

Possible complications are perforation of the posterior wall of the atrium into the esophagus, perforation of the free wall resulting in a strangling collection of blood around the heart, that is known as cardiac tamponade, and narrowing of a pulmonary vein near its insertion in the heart, which in the worst-case scenario can lead to death of a piece of lung tissue or pulmonary infarction. A possible complication is represented by a blood clot flowing from the heart into the brain causing an embolic stroke. Currently the procedure is accomplished under anticoagulation with oral and intravenous medications, since recent data suggest that performing the procedure without discontinuation of Warfarin or Coumadin can abolish or significantly reduce the risk of such complication. In experienced centers, the major complication rates should not exceed 2%. Other possible complications can affect the integrity of the groin vessels, or femoral arteries used to introduce the catheters inside the large chest arteries and therefore the heart.

Efficacy and advantages

After a single procedure, more than 50% of patients with an otherwise normal heart can enjoy freedom from arrhythmias, according to studies that have followed patients typically for one year. With two or more procedures, the efficacy can be as high as 80-90% in other recent case series. These results compare favorably with data on natural evolution of the disease or success observed with antiarrhythmic drugs

Long-term effects and advantages of the procedure are not fully known. In one 5-year study from Germany, most patients remained in normal rhythm after 5 years. Others have reported better long-term results by more extensive ablation approach suggesting that the procedural strategy could affect the long-term outcome. Efficacy in patients past their 60s is being studied by an ongoing, long-term study, in part sponsored by the US national heart, blood and lung institute. It is advised by leading scientific institutions that anticoagulants could be safely stopped, after careful consideration, a few months – usually 6 months – after a successful procedure, in patients who were taking them before the procedure because AF increases their risk of stroke. Various studies have compared the effects and risks of ablation of Afib versus use of antiarrhythmic drugs All of them have shown that ablation therapy is more effective than antiarrhythmic drugs, in particular in younger patients with a healthy heart and if the ablation is done by highly skilled practitioners.

Alternative techniques

A cure for Atrial Fibrillation can be achieved also with the surgical procedure called Maze or the Minimaze, as described in the History chapter above. This surgical approach can be used as a stand-alone surgery, more often in conjunction with otherwise needed cardiac surgery, or a thoracoscopic procedure, that is without the need to open the patient's chest. The surgical procedure can be carried out as a hybrid, that is to say combined with a catheter approach

Recommendations

International cardiology societies have issued joint recommendations for the selection of patients suitable to undergo this procedure In general, ideal candidates for an ablation for AF, patients should be 1) symptomatic for the arrhythmia (one of the following symptoms: palpitations, shortness of breath, fatigue and or weakness, dizziness); 2) have tried and failed at least one antiarrhythmic drug; 3) should be free of severe lung disease; 4) should not have extensively scarred atria (upper heart chambers). Following ablation, most of these patients are free of recurrent AF at least at one year or later. A recent publication of the New England Journal of Medicine suggested that in patients with paroxysmal atrial fibrillation and no structural heart disease, first line ablation therapy could be acceptable in terms of safety and efficacy. This has been confirmed by the study RAFFT-2, presented at the late breaking trials at the heart rhythm society meeting of 2012.

External links

• [1] Patient oriented information from the Mayo Clinic
• [2] Patient information on Atrial Fibrillation from the American Heart Association at www.heart.org