Non-active cardiovascular implants

Device-specific incident reporting guidance
Vigilance guidance and guidance for users is located in Other devices regulatory guidance.

---

 Relevant product standards

• Published standards

1. Prosthetic heart valves:
(i) ISO 5840:1996 (E) Cardiovascular Implants - Cardiac valve prostheses. Published November 1996 (new version due out shortly, see below).
(ii) EN 12006-1:1999 Non-active surgical implants - Particular requirements for cardiac and vascular implants - Part 1: Heart valve substitutes. Published July 1999. Level II Standard.

2. Vascular grafts:
(i) ISO 7198:1998 Cardiovascular Implants - Tubular vascular prostheses. Published August 1998.
(ii) EN 12006-2:1998 Non-active surgical implants - Particular requirements for cardiac and vascular implants - Part 2: Vascular prostheses including cardiac valved conduits. Published February 1998. Level II standard.

3. Endovascular devices (including vascular stents, prostheses for aortic aneurysms and vena cava filters:
(i) ISO 25539-1:2003 Cardiovascular implants - Endovascular device - Part 1: Endovascular prostheses. This is the first part of a series of standards applying to endovascular prostheses. It was based upon the Technical Report : TS 15539, which has since been withdrawn.
(ii) EN 12006-3:1998 Non-active surgical implants - Particular requirements for cardiac and vascular implants - Part 3: Endovascular devices. Published March 1999. Level II Standard.
(iii) EN 14299:2004 Non-active surgical implants - Particular requirements for cardiac and vascular implants - Specific requirements for arterial stents. Published May 2004. This is a Level III Standard in which the Level II Standard is EN 12006-3:1998 Non-active surgical implants - Particular requirements for cardiac and vascular implants - Part 3: Endovascular devices, and the Level I Standard is EN ISO 14630:1997 Non-active surgical implants - General requirements.

• Standards under development

Prosthetic heart valves
A revision to the current ISO Standard covering prosthetic heart valves (ISO 5840:1996), which began in October 1999 is completed and currently awaiting publication.

---

Safety-related information published by the Medical Devices Agency

1999
AN 1999(06) November 1999. 'Thromboembolic complications involving Silzone mechanical heart valves'.

2000
DA 2000(01) January 2000. 'Silzone prosthetic heart valves and annuloplasty rings: Recall'.

---

Bjork-Shiley heart valves
Latest patient management advice was issued to clinicians by the Bowling-Pfizer Supervisory Panel, who are responsible for implementing the settlement arising from the class action over these valves, entitled 'Amended Guidelines To Assess Patients with BSCC valves for Elective Explantation'. Prior to this the Medical Devices Agency (MHRA's predecessor) issued a letter to all cardiothoracic surgeons, cardiologists, and GPs following UK patients implanted with Bjork Shiley convexo-concave (BSCC) heart valves, referencing the (2000) amended guidelines for patient management.

The primary purpose of these guidelines is to determine which patients qualify for financial compensation if elective replacement surgery is undertaken, under the terms of the settlement. In summary those patients for whom the risk of valve fracture exceeds their own personalised risk associated with reoperation are likely to qualify for compensation.

Background information
Worldwide situation
The Bjork-Shiley 60° convexo-concave (C-C) valve, manufactured in the USA, was first introduced into the UK in 1979. It was originally marketed in 7 sizes (21 to 33mm) for use in both the aortic or mitral position. The design featured a pyrolitic carbon 'tilting disc' retained within a metal housing ring by two struts. The larger strut (on the inlet side of the valve) and the housing ring were machined from a single piece of metal. The smaller (outlet) strut was welded to the housing ring.

Since the early 1980s, a number of instances have been reported of mechanical failure of these valves. All of these have been related to fracture of the outlet strut in the vicinity of the weld. A fracture in one leg of the strut (single leg separation) is thought to lead to fatigue failure of the second leg at some varying time later. This allows the disc to escape, resulting in loss of valve function which frequently leads to the death of the patient.

The manufacturer progressively withdrew certain models of the valve from 1982, and in 1986 stopped all manufacture and supply on a world-wide basis. In total, some 82,000 of these valves were implanted world-wide. In the United Kingdom about 5,000 C-C valves were implanted.

Risk factors
Investigation and research, carried out mainly by the Shiley Heart Valve Research Centre, has concentrated on refining estimates of the risk of failure and on developing methods to detect early signs of failure.

Statistical analysis of data relating to the manufacture, implantation and structural failure of the valves has enabled failure risks to be calculated for valves in relation to their size, anatomical position, manufacture date/lot, identity of welder and weld date, and most recently patient age. Analysis of such data requires that the serial number of each failed valve be known. Large mitral valves manufactured in 1981 and 1982 carry the greatest risk of failure. Younger patients (i.e. under 55 years of age at the time of operation) appear to be at an increased risk. The basis for this is not known, although it may be due to haemodynamic factors. There are no diagnostic methods available to determine which valves are likely to fail in the long term.

Provision of advice
The Department of Health policy is that medical specialists (in this case cardiothoracic surgeons and cardiologists) are in the best position to inform and advise patients of the risks and benefits of heart valve replacement procedures and to discuss with them the options available. It has therefore ensured, as far as possible, that these professionals have been kept fully informed of the latest information regarding these valves. The Shiley company has kept relevant medical professionals informed, since 1982, of their best estimates of the risk of mechanical failure for the whole range of valves. The Department of Health has also provided advice in the form of letters sent periodically since 1983 to relevant medical staff or health service managers. The most recent of these, issued in July 2000, identified the fact that the relative risk of outlet strut fracture of the smaller, mostly aortic valves does not appear to be decreasing as is the case for the larger mitral valves.

The nature of the advice given to an individual patient is a matter for professional judgement by the clinician involved. The risks of valve failure have to be weighed against those of re-operation which vary from case to case, dependant on the age and clinical condition of the patient. Each patient's particular circumstances must be considered and the need to inform has to be balanced against possible creation of unnecessary anxiety.

MedicAlert register
Shiley funded the charitable foundation, MedicAlert, to establish a voluntary register of UK patients implanted with C-C valves. This database enhances communication with relevant professionals and allows appropriate information to be passed on to the patient through his or her doctor. The vast majority of UK patients implanted with these valves have now been identified.

Patients who register with MedicAlert are provided with a pendant or bracelet which identifies them to healthcare professionals as having a C-C valve implanted. A letter has been sent to all UK ambulance services by MedicAlert which gives them information on where to take such patients who present as a cardiovascular emergency.

Related initiatives
In order to monitor the use and success of artificial heart valves in the UK, the Department of Health has funded a heart valve registry at Hammersmith Hospital, which was set up in January 1986 the year after the withdrawal of C-C valves from the UK market. This has indicated that about 5,000-6,000 heart valves are implanted in UK patients each year, and among some 66,000 valves implanted since the registry started, acute failures have been very rare.

The Department of Health has also funded an in vitro heart valve evaluation programme at an independent research centre in Sheffield. It has become customary, in recent cases of mechanical failure, for the Department of Health to arrange, on behalf of coroners or other interested parties, for explanted valves to be examined at an independent centre.