Experimental and clinical evidence supporting septectomy in the primary treatment of acute type B thoracic aortic dissection.

Background: We reviewed the mechanics involved in the aneurysmal dilatation of the false lumen (FL) in type B aortic dissection and the experimental and clinical evidence supporting the proposition that the main agent for this dilatation is a differential of pressure between the false and true lumena. This difference in pressure is the consequence of a restricted outflow of the FL. Our aim was to study the relationship between the size of a septectomy that increases the outflow of the FL and its effect on the values of the differential of pressure. Methods: A bench-top model of aortic dissection was used to determine the relationship between the area of the tears and the value of the pressure differential. A range of tear sizes was tested. Results: The highest differential of pressure (6.77 mm Hg) was found with a single proximal tear. The addition of a distal tear decreases the pressure difference. The greater the sum of the areas of proximal and distal tears, the lower the pressure difference between true lumen and FL. This pressure difference approached zero, as the sum of the areas approached 250 mm(2). Conclusions: A septectomy of at least 250 mm(2), initiated from the distal tear to the proximal aorta of an area, should be part of the initial treatment of acute aortic dissection. Concomitant with it, the proximal tear should be occluded with either a bare stent or a stent graft.