Box-lesion set during modified Cox maze significantly improves patient outcomes

April 11, 2008

St Louis, MO - Placing an additional ablation set during the Cox-maze procedure, a short step that adds between 10 and 20 seconds to surgery performed to treat atrial fibrillation, significantly improves clinical outcomes, according to a new report[1]. Isolating the entire posterior left atrium by creating a "box lesion" resulted in a significantly lower incidence of early atrial arrhythmias and higher freedom from atrial fibrillation at one and three months, say investigators.

Publishing the findings in the April issue of the Journal of Thoracic and Cardiovascular Surgery, lead investigator Dr Rochus Voeller (Washington University School of Medicine, St Louis, MO), along with senior author Dr Ralph Damiano, explain that the box lesion is created by making an additional ablation line across the dome of the left atrium between the superior right and left pulmonary veins. This surrounds and isolates the pulmonary veins and the posterior left atrial wall from the rest of the left atrium.

First introduced into clinical practice in 1987, the Cox-maze procedure has been modified over the years, with Damiano and colleagues replacing the surgical incisions with linear lines of ablation on the atria. Initially, the authors note, the right and left pulmonary vein lesions were connected inferiorly with a single ablation line, leaving the "posterior left atrium in electrical continuity with the remaining atrium."

To test the effect of completely isolating the posterior left atrium with the box lesion, the group investigated the difference in outcomes between patients who underwent the Cox-maze procedure with or without the additional box-lesion set in the posterior left atrium. From April 2002 to September 2006, 137 patients underwent a bipolar radiofrequency ablation-assisted Cox-maze procedure at Barnes-Jewish Hospital in St Louis.

Overall, freedom from atrial fibrillation recurrence at one and three months was significantly higher among those who received the box-lesion set. By six and 12 months, all patients who received the box-lesion set were free from atrial fibrillation, report the authors. The use of antiarrhythmic drugs was also significantly lower among those who had their pulmonary veins and the posterior left atrial wall electrically isolated from the rest of the left atrium with the box-lesion set.

Results comparing box-lesion set with single bipolar ablation lesion

End point Box-lesion set , n=81 (%) Si ngle connecting ablation lesion, n=56 (%) p
Freedom from atrial fibrillation recurrence at 1 mo 87 69 0.015
Freedom from atrial fibrillation recurrence at 3 mo 96 85 0.028
Use of antiarrhythmic drugs at 3 mo 35 58 0.018
Use of antiarrhythmic drugs at 6 mo 15 44 0.002

"The most dramatic finding of this study was that isolating the entire posterior left atrium instead of only the individual pulmonary veins during the Cox-maze IV procedure resulted in a significant decrease in the incidence of early postoperative atrial tachyarrhythmia. The incidence was decreased by 48%," write Voeller and colleagues. "This likely was the reason for the shorter median length of hospital stay in the box-lesion group, because the management was simplified without the occurrence of postoperative atrial tachyarrhythmias."

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