Fashioning of aortic isthmoplasty patch. A mathematical model

Background. Patch enlargement of the aortic isthmus in congenital coarctation of the aorta (aortic isthmoplasty) has been extensively performed since its introduction in 1957. Even after forty years, the size and shape of the prosthetic patch used as an on a graft is still determined, most of the time, empirically through eyeballing. Not infrequently, it has resulted in an ugly looking repaired aortic segment or with a significant residual systolic gradient across it. These twin problems have called for a mathematical model for designing the patch more precisely. Methods. The model envisages a patch of the shape of an asymmetric octagon whose cranio-caudal length equals the distance from a point 8 mm on the proximal aorta to a point 8 mm on the distal dilated aorta on either side of the coarcted segment. The side to side length of the patch is determined by first subtracting the circumference of the narrowest part of the coarcted segment from the circumference of the distal dilated portion of the aorta and then adding 4 mm more. The larger slant sides of the octagon are obtained by joining the four smaller sides, of 8 mm in length each. Since July 1993 this mathematical model has been employed in 7 patients to prepare the exact size and the shape of the tightly woven low porosity Dacron patch. Results. In each instance a neat cylindrical aorta was obtained without any measurable post-repair systolic pressure gradient across the repaired site. Conclusions. In view of these very satisfying results, we believe that this mathematical model of tailoring the patch has succeeded in converting the patch-aortoplasty procedure for coarctation of the aorta into a precise and hemodynamically fully corrective operation.