A system for the treatment of a vessel defect, the system comprising: a hybrid prosthesis comprising: a distal end graft portion configured to extend from the aortic arch into the descending aorta and including a tubular main body comprising a support structure , the distal graft portion having a proximal end , a distal end , and a main lumen extending therebetween, at least one tubular branch extending from the main body of the distal graft portion near the proximal end thereof and having a first end , a second end , and a branch lumen extending therebetween, the branch lumen being in fluid communication with the main lumen, the tubular branch extending from the main body at an acute angle whereby the distal graft portion has a generally Y shaped configuration; and a proximal graft portion extending from the distal graft portion, wherein the main body of the distal graft portion and the body of the proximal graft portion are formed from a single piece of graft material, the proximal graft portion including a tubular body , the body of the proximal graft portion being crimped and entirely unstented, having a proximal end , a distal end , and a lumen extending therebetween and being configured for placement within the ascending aorta and extending into the aortic arch; and an introducer comprising a central catheter and an auxiliary catheter , wherein at least a portion of the distal graft portion of the hybrid prosthesis is retained in a compressed configuration on the central catheter of the introducer for endoluminal delivery to a site of the vessel defect, and wherein the auxiliary catheter is positioned within the branch . a hybrid prosthesis comprising: a distal end graft portion configured to extend from the aortic arch into the descending aorta and including a tubular main body comprising a support structure , the distal graft portion having a proximal end , a distal end , and a main lumen extending therebetween, at least one tubular branch extending from the main body of the distal graft portion near the proximal end thereof and having a first end , a second end , and a branch lumen extending therebetween, the branch lumen being in fluid communication with the main lumen, the tubular branch extending from the main body at an acute angle whereby the distal graft portion has a generally Y shaped configuration; and a proximal graft portion extending from the distal graft portion, a distal end graft portion configured to extend from the aortic arch into the descending aorta and including a tubular main body comprising a support structure , the distal graft portion having a proximal end , a distal end , and a main lumen extending therebetween, at least one tubular branch extending from the main body of the distal graft portion near the proximal end thereof and having a first end , a second end , and a branch lumen extending therebetween, the branch lumen being in fluid communication with the main lumen, the tubular branch extending from the main body at an acute angle whereby the distal graft portion has a generally Y shaped configuration; and a proximal graft portion extending from the distal graft portion, wherein the main body of the distal graft portion and the body of the proximal graft portion are formed from a single piece of graft material, the proximal graft portion including a tubular body , the body of the proximal graft portion being crimped and entirely unstented, having a proximal end , a distal end , and a lumen extending therebetween and being configured for placement within the ascending aorta and extending into the aortic arch; and an introducer comprising a central catheter and an auxiliary catheter , wherein at least a portion of the distal graft portion of the hybrid prosthesis is retained in a compressed configuration on the central catheter of the introducer for endoluminal delivery to a site of the vessel defect, and wherein the auxiliary catheter is positioned within the branch . <EOS>