Atrial Fibrillation (AF)
Atrial fibrillation (AF) is a well described rhythm disturbance that is more common with advancing age. It is estimated that over 30% of those with atrial fibrillation are > 80 years of age. In the United States, AF is the leading cause of hospitalization in >450,000 cases annually, and contributes to >99,000 deaths annually.
The heart consists of four heart chambers (two atria and two ventricles) connected through four heart valves. Each of these chambers should normally beat in a coordinated manner with the other chambers, thereby ensuring that blood flows efficiently into, thru, and eventually out of the heart.
AF is an abnormal rhythm in which the two atria (smaller chambers of the heart) suffer uncoordinated activation; instead of contracting and pushing blood forward, the atria quiver (fibrillate). This results in loss of coordinated atrial activity and inconsistent filling and pumping of the ventricles (the larger chambers). The effect of AF on individual patients varies greatly, and may manifest as:
- Palpitations (racing of the heart).
- Shortness of breath.
- Light headedness (often the result of low blood pressure).
- Loss of consciousness.
- No symptoms.
Besides these common symptoms, AF can lead to clot formation in the heart itself (most commonly in a portion of the heart known as the left atrial appendage); if this clot becomes detached and mobile, it may travel to the brain, causing a stroke. AF increases the risk of stroke five fold over the general population. It has also been shown that AF-related stroke is likely to be more severe than non-AF-related stroke.
The goals of AF treatment are:
- Conversion of AF back to sinus (regular) rhythm, if possible.
- Control of the overall heart rate if the patient remains in AF.
- Prevention of stroke.
- Prevention of compromised heart structure and function because of long-standing AF.
The first (non-surgical) options of AF treatment are:
- Medications to convert AF back to sinus rhythm or to control heart rate.
- Electrocardioversion (controlled shock) to convert AF back to sinus rhythm.
- Ablation techniques (creating scars in the heart to prevent or trap the electrical activity that leads to AF).
- Anticoagulation (making the blood “thin” with medication to prevent the formation of blood clots in the atria).
Should these treatment options fail to convert and/or prevent further AF, more invasive (surgical) techniques are considered, including:
- The Cox-Maze Procedure
- The Convergent Procedure
- Isolated Left Atrial Appendage Clipping
In 1991 Cox and colleagues originally described a procedure that would interrupt re-entry electrical activity in the atria; this technique was based on the concept of a maze and was named the “maze procedure”. Since that original publication, numerous modifications to the initial ablation technique have been made. Perhaps the most significant modification to the technique is replacement of the original cut-and-sew technique with mostly ablation tools (either freezing or radiofrequency sources that create ablation areas). The success of the maze procedure in curing atrial fibrillation is reported as anywhere from 77% to 99%. The procedure has also clearly reduced the incidence of stroke.
The maze procedure can be performed in isolation, but is usually performed in conjunction with another cardiac surgical procedure, such as a valve repair or coronary artery bypass.
Recurrent AF can be addressed with nonsurgical ablation techniques performed by electrophysiologists (non-surgeons). Should patients continue to have recurrent AF, they may be considered for an adjunctive procedure that also utilizes ablations performed through a small surgical incision. This bringing together of nonsurgical and surgical ablations is known as the Convergent Procedure.
The Convergent Procedure involves making an incision on the lower edge of the sternum. Through this incision, access is gained to the space directly underneath the heart (but inside the heart itself). This bottom area of the heart is the left atrium, the target area for much of the ablation techniques used to treat AF. A radiofrequency ablation tool is used to treat the lower part of the left atrium. Once this surgical procedure is completed, the patient may undergo further evaluation and possibly even further ablations by an electrophysiologist. A patient undergoing a Convergent Procedure may remain in-hospital for a few days for close monitoring.
Left Atrial Appendage Closure
AF involves uncoordinated quivering (fibrillation) of the left atrium (as opposed to a regular, pulsatile movement). This uncoordinated movement may lead to blood pooling and clot formation within the left atrium, most commonly in an area known as the left atrial appendage. Clot within the left atrial appendage may become dislodged and enter the blood stream, leading to a stroke. Patients with AF suffer a five-fold increased stroke risk compared to the general population.
The two common strategies to address the problem of clot formation in the left atrial appendage secondary to AF are:
- Anticoagulation (thinning of the blood to prevent clot formation).
- Left atrial appendage ligation (closing the opening of the appendage so that it no longer communicates with the bloodstream).