Durability has always been a crucial performance indicator for artificial heart valves. There is the intrinsic durability of the valve itself, as constructed by the manufacturer, but it is the durability of the implanted valve in the individual patient which is the real issue, particularly, but not solely, for the patient. Progress in the design and manufacture of artificial heart valves has arisen from information gained from pulse duplicator studies, from fatigue testing, and from animal implants—but the bottom line is durability once implanted in the patient, and the longer the follow up the better.
The Edinburgh heart valve study of 533 patients, who had their valve implant(s) between 1975 and 1979, now reports comparative clinical outcome for mechanical versus bioprosthetic valves at 20 years.1 The present report supplements a 12 year follow up, published in 1991.2 The original study was prospective and randomised. The study design was modified in January 1977 in those patients randomised to receive a porcine bioprosthesis. Initially, the porcine valve used was the Hancock prosthesis, but, after January 1977, the Carpentier-Edwards valve was used because of its “substantial cost advantage”.
The authors are to be congratulated over the length and completeness of follow up. Six patients were lost to follow up and the remaining survivors were followed up beyond 1 January 1988, giving a mean follow up of 20.4 years. The patient population in the study is younger than current patient demographics, with a mean age at operation of 54 years. Data from the UK Heart Valve Registry (UKHVR), which commenced data collection across the UK in 1986, reported a mean age at operation of 59 years in 1986,3 with progressive increase to a mean of 66 years for first time valve replacement patients in 2000.4 In 2000, approximately 40% of first time valve replacement patients were 70 years old or older.4
The question of the change in bioprosthetic valve of choice midway through patient recruitment must be addressed. The authors indicate that analyses comparing the two porcine valve types produced “very similar” results. Although no data are provided in this manuscript relating to this issue, the assumption of the relative equivalence of these two porcine bioprosthetic valves is probably acceptable for the purposes of this study.