A tribute to Viking O. Björk (1918–2009): A four-decade functioning Björk-Shiley aortic valve prosthesis

February 18th 2014 marks the fifth anniversary since Viking Olov Björk (1918–2009) passed away in Stockholm of internal hemorrhage sustained in a subway accident, at the age of 90. This leading cardiothoracic surgeon, inventor, and personality survives today by his pioneering work in the field of developing an artificial heart valve with excellent mechanical properties and a low rate of complications in an endless pursuit to improve the quality of life of heart valve patients, and especially of children and women of child bearing age (1). We illustrate this lifelong commitment by reporting one of the longest functioning Björk-Shiley aortic valve prosthesis.

In 1976, a 29-year-old man received a 27-mm Björk-Shiley aortic valve prosthesis for severe regurgitation of a bicuspid valve. The prosthesis used was a second generation low-profile mechanical valve with a tilting disc of pyrolytic carbon housed by two tantalum struts. Despite instructions, he was lost from follow-up and took acenocoumarol without measuring the International Normalized Ratio (INR). After 37 years in NYHA class I without embolic or hemorrhagic events, he presented in mid-2013 with atypical chest pain and dyspnea on exertion caused by an ascending aortic aneurysm with a maximal diameter of 6.3 cm. During aortic surgery the prosthetic valve was observed tightly adhered to the aortic annulus with no sign of perivalvular leak. The valve showed no structural deformity, the pyrolytic carbon disk was fully opening and there was no evidence of disk fatigue (Figure 1). The prosthetic valve remained in place and the further course was uneventful.

Figure 1. The Björk-Shiley tilting disk aortic prosthesis is inspected through the dissected aortic root 37 years after implantation. The valve is tightly adhered to the aortic annulus with no evidence of perivalvular leak. The tilting disk and the holding mechanism show no structural deformity or sign of fatigue despite opening for more than 1,3 billion cycles.

Our patient had a Björk-Shiley pyrolytic carbon tilting disc valve with a life of approximately 1.36 billion cycles, assuming that the average heart rate was 70 beats/min. This estimate is far beyond any manufacturer's fatigue test could determine.

Since 1962 the Starr-Edwards silastic-ball valve was the only commercially available heart valve prosthesis in Europe. Viking Björk used this valve and was concerned of the high gradients, reaching up to 70 mmHg, experienced with the valve, especially in older women with narrow aortic roots where the supravalvular crista was pronounced. After a visit to Hokkaido in Japan, he familiarized himself with Wada's invention of a tilting disc valve, the Wada-Cutter valve, which V. Björk considered to be a big step forward. The valve disc was made initially of Teflon, but the poor creep resistance of the Teflon hinge mechanism allowed disc deformation with subsequent disc embolization (2). In 1968, he manufactured together with the American engineer, Donald Shiley, a free-floating disc valve that opened in the aortic position to 60 degrees. This valve provided significant advantage over the bulky Starr–Edwards cage ball valve with a lower transvalvular gradient (3). On January 16, 1969, he implanted this valve in a patient for the first time. It was manufactured initially by Shiley Inc. and later by Pfizer Inc. It is considered to be the first successfully used tilting disc valve. The material component of the occluder disc was a thermoplastic, acetyl resin (Delrin). Delrin had the positive characteristics of biocompatibility, endurance, dimensional stability, ease of fabrication, resistance to impact wear, resilience, and natural lubricity. The disc moved between two metal struts welded to the metallic housing ring—an inflow strut and an outflow strut (4). It has been estimated that approximately 24,000 Björk-Shiley Delrin-Disk heart valves were implanted from 1969 through 1981 with excellent initial clinical results (66% ten-year survival rate).

The eccentric opening of the Delrin disc proved to be effective in avoiding clot formation, but the design apparently contributed to strut fracture and flow turbulence. In 1971, the initial Delrin disc was replaced with a pyrolytic carbon (5). The pyrolytic carbon disc eliminated the problems associated with sterilizing the Delrin disc, which could retain water and swell, and it provided a considerable increase in durability. In 1975, the conical disc was replaced with a spherical disc that incorporated a radiopaque marker. On screening, it was then easy to verify the function of the disc movement (1). This valve showed excellent hemodynamic profile and mechanical properties and was the valve used in our patient.

The rate of thromboembolic complications with Björk-Shiley valves was 4–5.4% per 100 patient years. V. Björk main objective was to improve the valve flow in order to diminish thromboembolic complications. In 1975, he changed the design of the valve. In 1976, he implanted the first convexo- concave disc valves, in which the configuration of the disc was changed mainly to improve the flow through the smaller flow area and thereby diminish thrombo embolic complications. When open, the fluid forces would cause the disc to slide out of the orifice by 2 mm, eliminating the low-flow area caused by the disc edge touching the orifice in the earlier valve models with a flat disc. Additional clearance between the disc and the flange diminished the low flow area behind the disc by 50% and provided for a “washing effect” of the disc. Thromboembolic complications were reduced from 4 to 1% per 100 patient years (6). This model, however, was prone to fracture of the outlet strut that held the tilting disc, leading to potential catastrophic consequences and for this reason the model was recalled in 1986.

The vision of V. Björk to improve the quality of life of patients with heart valve disease remains alive in our days. Our patient is still in NYHA I clinical status after presenting with heart failure in 1976 in the age of 29. The fact that the Björk-Shiley tilting disc aortic valve prosthesis is well-functioning for four decades without taking proper anticoagulant medication (consider that an INR of 3.5–4.5 was required for first generation aortic mechanical prostheses) confirms the excellent mechanical and hemodynamic properties of this type of valve. It is estimated that about 120,000 radial/spherical Björk-Shiley valves have been implanted worldwide (7). V. Björk is still surviving by the lives he saved throughout these years.

Viking Björk is definitely a legend and as Francis Robicsek stated in his obituary in the Journal of Thoracic and Cardiovascular Surgery “he was a visionary that made an everlasting mark in the history of cardiothoracic Surgery” (8).

Declaration of interest: The authors report no declarations of interest. The authors alone are responsible for the content and writing of the paper.