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New Mini Maze Procedure Shows Promise for Treating Persistent Atrial Fibrillation

New Five Box Approach Gets Closer to the Gold Standard for Afib

By Christine Welniak

October 12, 2010 – A new mini maze procedure shows promise in treating persistent atrial fibrillation. Developed by Dr. John Sirak, assistant professor of cardiac surgery at Ohio State University, this totally thoracoscopic surgical ablation for afib closely replicates the "gold standard" Cox Maze III lesion set in the left atrium.

Dr. Sirak has performed roughly 300 total thoracoscopic maze procedures since 2006. In November 2008, he developed the “five box” procedure, which he has performed on 100 patients and describes as being “incredibly effective”.

Cox Maze III: The Gold Standard

When it comes to treatments that could cure atrial fibrillation, the Cox Maze III procedure remains the gold standard. Although radiofrequency energy and cryothermy have replaced the “cut and sew” method first performed by Dr. James Cox in 1987, it is the lesion set itself that is important. As its name implies, the Cox Maze III lesions create a maze that forces electrical impulses to move correctly through the heart—from the sinoatrial node in the upper part of the right atrium to the atrioventricular node at the bottom of the left atrium. The Cox Maze III lesion set using ablation energy sources—this is sometimes called Cox Maze IV—continues to be performed in open heart surgeries.

However, surgeons and electrophysiologists have found it difficult to replicate the Cox Maze III lesion set in the minimally-invasive mini maze procedure and in catheter ablations. That’s because it can be difficult to reach certain parts of the heart in a closed chest procedure. Pulmonary vein isolation, which is the cornerstone of the mini maze procedure and catheter ablations, essentially creates “boxes” around the four pulmonary veins. Although pulmonary vein isolation successfully treats paroxysmal atrial fibrillation 70–75% of the time, it’s widely accepted that longstanding persistent afib requires more extensive lesion sets.

Five Box Thoracoscopic Maze

Dr. Sirak’s five box technique may be what’s needed. The operation not only isolates both the left and right pulmonary veins, but also creates two additional compartments on the dome and floor of the left atrium.

Unique to this procedure, these additional compartments isolate arrhythmic tissue in the left atrium, which is critical in treating persistent AF. Additionally, the superior vena cava and coronary sinus, both important potential sources of atrial fibrillation, are isolated. (This diagram of the heart shows where the pulmonary veins and superior vena cava are located.) All of the ablations are enclosed within discrete, but contiguous, compartments. The integrity of each box—that is, whether afib has been isolated—is verified in real-time by using a pacing probe to confirm that electrical signals entering and exiting each compartment are “blocked”.

Unlike the original mini maze procedure, the five-box thoracoscopic maze is approached entirely through pencil-sized port incisions on each side of the chest. No open incisions are made. The advantage is not only less discomfort for the patient, but better visualization of and access to the key anatomy. It takes about four hours to complete the procedure.

Early results of the five box technique were recently published in the Annals of Thoracic Surgery. Of 36 patients with longstanding persistent AF who had the procedure, 34 were free of AF and off antiarrhythmic medication at three months. Only 19 patients had reached the six-month follow-up period at the time of publication, and all were free of afib without antiarrhythmic drugs. Similarly, all four patients who had been followed for 13 months remained in normal sinus rhythm. Of note, all patients had a seven-day event monitor at three, six, and 13 months. This is more rigorous monitoring than what is recommended in the Heart Rhythm Society guidelines.

The complication rate was remarkably low. There were no instances of pulmonary vein stenosis or perforation to the esophagus, which are relatively common complications of radiofrequency catheter and surgical ablations. However, one patient suffered injury to the right pulmonary artery during the procedure and had to undergo an open-heart procedure to repair the artery.

In data updated through June of this year, the success rates have continued to be very good: 44 of 46 patients and 25 of 26 were free of AF and off antiarrhythmic drugs at three and six months, respectively. All seven patients who had been followed for 13 months remained in normal sinus rhythm. The one patient considered a "failure" at six months remains in sinus rhythm on low-dose antiarrhythmic medication.

What About the Right Atrium?

Unlike the Cox-Maze III, the five box technique only includes lesions in the left atrium. It’s not clear whether the Cox Maze III lesions in the right atrium are “essential” to stopping atrial fibrillation. A Cleveland Clinic study of different lesion sets used to treat permanent afib didn’t show a benefit to performing ablation in the right atrium. However, an analysis of results from 69 clinical studies showed that patients who had biatrial lesions (in both left and right atria) had better freedom from afib than patients who had ablation in the left atrium only.

Dr. Sirak says, “The right atrial components of the Cox Maze III are endocardial [inside the heart] and, thus, cannot be performed in a closed-chest, off-pump procedure. Fortunately, in the vast majority patients with atrial fibrillation, the right atrium plays a negligible role. In fact, in my 300 patients who have undergone a thoracoscopic maze, only 1% have recurred with a right atrial flutter. These patients were easily treated with a short catheter ablation procedure, which has ready access to the right atrial flutter pathways. On the other hand, none of my patients has recurred with left atrial flutter, which is a common problem following the typical 'mini maze' operation."

Technique Is Promising But More Data Is Needed

The five box thoracoscopic maze shows early promise. However, data on a large number of patients is needed to validate the technique. In addition, it will be important to see whether other surgeons can replicate Dr. Sirak’s efficacy and safety results. Dr. Sirak is confident, saying, "This operation offers an electrophysiologically complete, and intuitively very compelling, procedure based on our current understanding of atrial fibrillation. The expectation is that the five-box patients will experience outcomes every bit as durable as the original Cox Maze III.”

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Christine Welniak writes about atrial fibrillation and other heart diseases/conditions for patients, medical professionals, and investors.

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Last Modified October 12, 2010

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