The pericardial heart valve was invented by Marian Ionescu, a British surgeon working at the General Infirmary in Leeds, England. He created this artificial bioprosthetic heart valve as a three-cusp structure made of chemically treated bovine pericardium attached to a Dacron cloth-covered titanium frame.
The Realisation of a concept The experimental and in vitro testing of this novel device took place in 1970, and in March 1971, Ionescu began, for the first time, the implantation of the pericardial valve in all three cardiac positions in humans. Between 1971 and 1976 the valves had been made in Ionescu's own hospital laboratory. Throughout these five years of usage in 212 patients the performance of the pericardial valve was thoroughly evaluated. The results showed that this original valve exhibited the best haemodynamic performance, at rest and during exercise, when compared with the reported results of all other artificial valves in existence. It demonstrated a very low risk of embolisation even in the absence of long term anticoagulation treatment of the patients. There were no cases of valve thrombosis, intra-vascular haemolysis or sudden, unexpected valve failure. The durability of the valve was good at 5 years of follow-up.
Based on these results, the Shiley Laboratory in Irvine, California, began to manufacture this valve and to distribute it worldwide under the name of the 'Ionescu - Shiley Pericardial Xenograft.' From 1976 onwards a series of modifications were made in order to improve the qualities and the performance of the pericardial xenograft. The selection and preparation of the bovine pericardium were standardised and rigorously controlled. For tissue fixation at zero pressure a solution of 0.5% purified glutaraldehyde was used. It contained an optimal proportion of monomers and polymers and an ideal cross-link density was obtained by controlling the concentration and the pH of the solution as well as its temperature and exposure time of the tissue to its action. The thickness and pliability of the pericardium were standardized and the direction of macroscopically visible fibres matched for each three cusps of a particular valve. The supporting stent was changed. The titanium was replaced with machined Delrin which is an acetyl homopolymer with low 'creep' properties due to a stable molecular memory. It is flexible and shock absorbent, essential qualities for a tissue heart valve support. This new stent contained a radio-opaque marker at its base for easy identification. The contour of the scalloped posts was modified and the height of the stent reduced. The entire Delrin structure was covered with seamless Dacron velour and at a later stage, the margins of the scalloped edges were covered with a thin layer of pericardium in an attempt to prevent or reduce the abrasion of the leaflets when in contact with this margin during valve closure. The sewing rim was bolstered for better and safer attachment to the heart annuli and its shape was anatomically contoured into two different configurations to better fit in the aortic and the atrio-ventricular positions. Two other additions were made: an integral valve holder which prevents the touching of the valve's cusps, and a 'freeze-watch' indicator as a safe—guard against exposing the valves during transportation or storage at temperatures below 4 degrees Celsius. The geometry of the valve was slightly modified due to changes in the shape of the stent and by removing the outside pledgets around the posts. This gave a more streamlined shape of the whole structure. These modifications had been progressively introduced and all of them were incorporated in the 'Ionescu - Shiley Low Profile Pericardial Xenograft' valve, which became available in 1983.
Approximately 200,000 pericardial valves manufactured by Shiley Laboratories were distributed around the world between 1976 and 1987 and it is presumed that most of them were implanted in patients. The use of this valve generated a lot of interest expressed in several specialist symposia, academic meetings, and numerous scientific articles published over the years. The appropriation and organisation of this enormous material and the classification and interpretation of data has been a very difficult and complex task, especially because - contrary to what it is claimed - there remains a great deal of variation in standards of reporting in all essential chapters of a scientific work. In some cases it is quite impossible to follow such standards as it will be described later. Despite all these difficulties and impediments, a general view of the performance of the pericardial valve as close to reality as possible could be obtained. One should however keep in mind that any single investigator should resist the temptation to write a review of such a complex matter as tissue heart valves, and to cover the subject completely and fairly. One should also remember that if we study complex and variable conditions, averages must be rejected because they confuse while aiming to unify, and distort while aiming to simplify. From the material available it is evident that the reported hospital mortality and, up to a certain point, late mortality are similar among the various publications of different authors, and do not directly reflect on the quality of the valve used.
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