421 - Aortic Valve Replacements

ing the heart to work harder. To compensate, the left ven- tricle increases in muscle mass leading to chest pain. 8 Valve stenosis can be congenital, but also can be caused by calcium buildup, rheumatic fever, endocarditis, trauma or rare condi- tions such as Marfan syndrome and lupus. 7,8 T H E H I S T O R Y O F T H E A V R A N D T H E T Y P E S O F V A L V E S As early as the 1920s, valvular heart disease was corrected by valvuloplasty. Surgeons tried to decalcify the leaflets, while some attempted to attach artificial leaflets. Regardless of the method, results were less than ideal. The calcified leaflets still were stenosed, and the artificial leaflets ruptured. 2 Dr. Hufnagel, a surgeon from Georgetown University, per- formed the first heart valve replacement on a human patient in 1952. The patient presented with aortic regurgitation. Dr. Huf- nagel’s solution was to place a prosthesis, which he created, in the patient’s descending thoracic aorta. 1 This prosthesis, essen- tially a ball in a plexiglass cage, was implanted to decrease the patient’s regurgitant flow by 75%. Patients who underwent this procedure ended up with improvements in their symptoms of congestive heart failure. 1 Dr. Hufnagel replaced more than 200 aortic valves with his design; some of the valves lasted around 30 years. 5 Since Dr. Hufnagel, more than 80 different types of mechanical metal or plastic valves have been created and surgi- cally implanted. These include the ball-in-cage design, single- tilting-disk design and bileaflet-tilting-disk design. 3 The Harkin-Soroff ball valve was first used in 1960. Dr. Dwight Harkin created a ball valve with a double cage made of stainless steel and a ball made of silicone. Two of the first seven patients Dr. Harkin operated on using this valve sur- vived, however, they both needed a second valve replace- ment. One was redone after 22 years, with the ball show- ing no signs of deterioration. 5 Following Dr. Harkin’s valve were several more types of ball-in-cage valves, essentially the same design with different materials. Several types of disc valves were created throughout the 1960s, many of which were used on mitral valves. Toward the end of the 1960s, Dr. Viking Bjork and Donald Shiley created a single-tilting-disc valve. 5 This valve was immobile, allowing blood to flow through the aorta without falling back into the left ventricle. It was an exceptionally successful invention that was used around the world on about 300,000 patients between 1969 and 1986. 5 Bileaflet disk valves were introduced in the early 1960s, start- ing with the Gott-Daggett bileaflet valve which was implanted in more than 500 patients. 2 The idea of a bileaflet design was to create a lower profile compared to the ball-in-cage valve. The Gott-Daggett valve had a heparin coating, but had an issue with stagnant blood flow which led to thrombosis and was dis- continued in 1966. 5 In 1977, the St. Jude Medical bileaflet valve was invented as a result of collaboration between doctors and engineers. The leaflets rest on hinges that allow them to open and close with the flow of blood. The first one was implanted in October 1977, and they are still used today, with more than 1.3 million valves used since its inception making it the most popular mechanical valve in the world. 5 While the mechanical valve has a rich history, the history of the tissue valve is less extensive. The first source of tissue valves was from human cadavers, but this practice didn’t last long due to logistical issues with the supply. 4 Currently, the most common type of tissue valves are xenografts, usually porcine or bovine origin. 13 The first xenograft aortic valve replacement was in 1965 performed by Dr. Carpentier in Paris. Two and a half years later, Dr. Car- pentier had replaced 61 valves in 53 patients with a very poor success rate. While there were issues with the technical aspect of the valve replacements, most failures were due to an immune response to the xenografts. 13 Following these failures were studies to determine how to decrease the immune response. The studies revealed washing the valves in various chemicals decreased the immune response. The valves were washed in sodium periodate and ethylene glycol that denatured and neutralized the soluble proteins of the xenograft, respectively. The valves were then soaked in glutaraldehyde that reduced the antigenicity of the valves. 13 Washing the valves increased their functionality at one year to 82%, an increase of 37% from before the studies. 13 Today, when purchased and delivered, the tissue valves come soaked in a glutaraldehyde solution. In 1977, the St. JudeMedical bileaflet valve was invented as a result of collaborationbetweendoctors andengineers. ... The first one was implanted in October 1977, and they are still used today, with more than 1.3million valves used since its inceptionmaking it the most popularmechanical valve in theworld. 5 | The Surgical Technologist | JANUARY 2019 14