Arterial Diseases & Grafts What Can Go Wrong and How to Fix It Lecture #9 Ref: Harloff, Jan, Are Biomaterials the Limiting Factor in the Progress of Arterial Prosthesis? Termpaper, BE 512, introduction to Biometerials, University of Berlin, 4 September 1995.
Importance Most common causes of morbidity and mortality in people of middle age and later life Two groups Degenerative Extremely common arteriosclerosis Inflammatory Rare arteritis
Thrombosis Blood should clot when it escapes a blood vessel but not when it is flowing within one thrombosis: clotting within a vessel thrombus: clot platelets, fibrin, red blood cells Causes slowing of blood flow changes in vessel wall changes in blood itself Usually occurs in veins Can eventually lead to either ischemia embolism
Ischemia and Embolism Ischemia loss of blood supply due to total closure of vessel lumen loss of oxygen anoxia gradual death of affected cells and replacement by scar tissue organ loss of power/function extremity gangrene Embolism Thrombus that becomes detached Venous side no obstruction usually until entering lung Arterial side often formed in left ventricle can block carotid artery kidney, brain, heart, spleen extremity
Atherosclerosis Arteriosclerosis general term for a variety of conditions that cause thickening and loss of elasticity in arterial walls Atherosclerosis one type inner layer of wall made thick and irregular fatty deposits - plaque major underlying cause for high incidence of arterial disease Affects large arteries mainly but also small arteries Predisposition to thrombosis Artery lined with plaques and still be functional up to 2/3 occlusion and still functional may be fully occluded and functional if occlusion occurs over time body has time to develop alternate routes collateral circulation
Pathogenesis of Atherosclerosis In spite of frequency and lots of research, little is know about the cause Factors influencing formation of plaques known but common mechanism is not Some important factors Age Progresses more rapidly in women after menopause More severe in men than women under age 40 Worldwide differences more common in highly developed societies Special factors hypertension, obesity, cigarette smoking, high fat intake, coincidental diseases, e.g. diabetes Exercise, or lack thereof
Arteritis Inflammation Possible manifestations of an allergic reaction
Others Collagen vascular diseases Attempt to group a number of diseases with unknown origins but with similar manifestations Affects small arteries of internal organs Strong evidence that it is a type of hypersensitivity Thromboangitis obliterans thrombic occlusion of vessels in legs ofyoung men gangrene loss of toes/feet allergic hypersensitivity in artery wall Syphilis heavy smoking attacks aorta and cerebral arteries
Others Aneurysm localized or diffuse dilitation of arterial wall due to damage to elastic tissue Two types saccular outpouching of arterial wall at single point fusiform uniform dilatation of the arterial wall Dissecting aneurysm hemorrhage in media of aorta spreads along vessel John Ritter
Arterial Surgery Aim To deal with the ischemia resulting from occlusion or interruption To correct abnormalities that threaten the integrity of the vessel wall Surgical treatment five general ways Remove diseased artery if possible Reopen an occluded or narrow artery by cutting out plaque endarterectomy Reopen occluded or narrowed artery by dilatation balloon catheterization Develop or promote collateral circulation Replace or bypass narrowed or occluded artery Removal and replacement Bypass Extra-anatomical route
The Ideal Arterial Graft Durable life expectancy greater than that of the host Should not cause undesirable reactions in host Inner surface must be nonthrombogenic Patency of graft should be 100% - occlusion not caused by graft Same mechanical properties as undiseased artery Incorporated into and anchored to surrounding tissue Readily sterilizable with a method that does not degrade properties Readily available material in variety of sizes and lengths Easy for surgeon to handle Nice if material were inexpensive
Natural Arterial Grafts Unprocessed Biological Grafts from patient Greater Saphenous Vein longest vein in the body begins on the medial side of foot and passes up medial side of the leg, across medial side of knee, continues upward to end in the femoral vein in the femoral triangle structurally strong wall thickness in adults is comparable to medium size arteries endothelial cells on lumen surface compliance similar to arteries Arterial Autografts Ideal endothelial lining maintain viability Limited availability not all arteries can be sacrificed
Natural Arterial Grafts II Processed biological grafts nonautogenous likely to attack by immune system processed and tanned leather-like, weakened structural integrity human umbilical cord vein
Synthetic grafts polyester -O(CH 2 ) 2 OCOØOC- large and medium sized vessels woven tight low porosity no preclotting stiff knitted more flexible porous pre-clotting required polytetrafluoroethylene -CF 2 CF 2 - inert two types textile woven or knitted microporous film
Problems Autogenous greater saphenous vein 35% occlude over 3-5 years due to structural changes rapid aging harvesting technique important Umbilical cord marked degeneration after 5 years Synthetic good for large and medium arteries, smal diameter grafts not available thromboresistance of luminal surface compliance mismatch inflexible infections durability