Atrial Fibrillation Surgery - Maze Procedure
The MAZE Procedure is performed by Cardiothoracic surgeons on the left and right atrium for the treatment of atrial fibrillation. Atrial fibrillation is an abnormality of the electrical system of the heart. Normally, the heartbeat is triggered by an electrical impulse which starts in the Sinoatrial (SA) node. This structure resides in the right atrium and is the normal "pacemaker" of the heart. The electrical signal to contract starts in the SA node and normally moves evenly across the atrium, triggering it to contract all at once. The impulse then travels across the atrioventricular ( AV ) nodeand triggers the ventricles (the main pumping chambers of the heart) to contract. This is called sinus rhythm. Atrial fibrillation occurs when this electrical impulse no longer travels from SA node to the AV node in the normal manner. Instead of the impulse traveling evenly across the atrium straight from the SA node to the AV node, the impulse is "side-tracked" such that the atrium is no longer triggered evenly and in synchrony, but is triggered one small region at a time. The atrium no longer contracts in a coordinated manner, but instead it fibrillates irregularly. The electrical signal to ventricle through the AV node is therefore irregular and hence the heartbeat is irregular.
A variety of conditions can lead to atrial fibrillation. The most common cause of atrial fibrillation is simply aging. Our risk of atrial fibrillation increases as we grow older and areas of scarring or fibrosis develop in our atrial tissue as a result of simple "wear and tear." Abnormalities of the valves in the heart, most often the mitral valve, can also cause "wear and tear" and lead to atrial fibrillation. Some specific conditions, such as thyroid disease, may be treatable with medications alone. Other conditions may be treatable by our colleagues the cardiologists in the cardiac catheterization laboratory. In a small number of cases, atrial fibrillation appears to be inherited - which is to say that it runs in some families - while in many cases its cause is unknown.
Atrial fibrillation results in :
- An irregular heartbeat that may be too slow at times, and racing at others.
- Loss of the atrial contraction that normally contributes to filling of the ventricle (the main pumping chamber of the heart) and improves pump performance --in some ways analogous to a automobile engine supercharger.
- Abnormal flow of blood through the atrium with areas of stagnation (eddies) which increase the risk of stroke.
The surgical procedure consists of creating a number of incisions in the atrium that disrupt the re-entrant circuits. Once the incisions are made, they are sewn together again. The atrium can then hold blood on its way to the ventricle and can squeeze or contract to push the blood in to the ventricle, but the electrical impulse cannot cross the incisions. The result is what looks like a children's maze in which there is only one path that the electrical impulse can take from the SA node to the AV node. The atrium can no longer fibrillate, and sinus rhythm (the normal rhythm of the heart) is restored.
|The surgical procedure looks schematically like a children's maze with only one path from the SA node to the AV node. (Click on the illustration to enlarge it.)|
|The arrangement of incisions on the heart is complex. This drawing shows the heart seen from back-to-front after the MAZE procedure. (Click on the illustration to enlarge it.)|
The MAZE procedure is not necessary in most patients with atrial fibrillation. Many patients are not bothered by the rhythm or the medications required to control it. In some cases, cardiologists are able to disrupt the circuits with catheters. Some patients, however, are so troubled by the way they feel when they are in atrial fibrillation or by the medications they must take that a surgical option is appropriate. In addition, individuals in atrial fibrillation who have experienced a stroke are at significant risk for another stroke. The MAZE procedure may be indicated in these individuals as well.
The MAZE procedure is an "open heart" procedure requiring cardiopulmonary bypass (the heart-lung machine). Accordingly, it carries risk of stroke, kidney failure, other organ failure, and death. The risk of this procedure is felt to be low in general, but the risk will be affected by each individual's specific health conditions (heart function, lung function, kidney function, etc.). In addition, some patients require a permanent pacemaker postoperatively. This is thought to be due to underlying disease of the SA node.
The MAZE procedure is highly effective in restoring sinus rhythm. Success rates vary by center, but are generally reported in the range of 80-100%.