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

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November 1999

MANUFACTURER/MODELS
St Jude Medical Inc/AG-701, AHPS-605, AS-601, AECS-602, MS-601 and MECS-602.

ISSUE
High rate of early thromboembolic complications associated with St Jude Medical's Silzone® (silver coated) mechanical heart valve, particularly among mitral valve patients.

For the attention of:

Health Authorities (England)- Chief Executives
NHS Trusts (England)- Chief Executives

IMMEDIATE ACTION

1. Follow up all patients implanted with Silzone® mechanical heart valves to identify any signs of stroke or transient ischemic attack (TIA) and ensure adequate anticoagulation control.

2. Consider examining patients using Trans-Oesophageal Echocardiography (TOE) to identify any signs of valve thrombus, recognising that there are certain risks associated with TOE. Priority should be given to patients most likely to be at risk, ie those who have suffered thromboembolic complications, those with mitral valve implants, and those who received their implants within the last 6 months.

3. Consider the information contained in this Notice when making a future choice of mechanical heart valve.

4. Report all incidents of thromboembolic complications and/or valve thrombus to the MDA and to the manufacturer.

DISTRIBUTION REQUIRED
Please bring this advice to the attention of all who need to know or be aware of it. This will include distribution by:

TRUSTS to:

• Liaison Officers (for onward distribution)
• Medical Directors
• Directors of Cardiothoracic Surgery
• Cardiothoracic Surgeons
• Directors of Cardiology
• Cardiologists

HEALTH AUTHORITIES to:

• Liaison Officers (for onward distribution)
• Registration Inspection Units
• Independent acute sector

BACKGROUND
St Jude Medical applied a silver coating to the sewing cuff of their range of Silzone® mechanical heart valves with the aim of reducing the risk of infective endocarditis, a life-threatening complication. Over 30 thousand Silzone® coated heart valves have been distributed worldwide since early 1997, over 700 of which are within the UK.

Over the last year MDA has received notification that 7 patients suffered a stroke or peripheral embolism among a group of 51 patients implanted with Silzone® heart valves by a number of surgeons at one UK centre. Six of these patients had received a mitral Silzone® valve (including one who had received both mitral and aortic valves). The adverse events occurred within 3 months of valve implantation, and in two cases extensive thrombus was identified on the valve's silver coated sewing cuff. There have been a further 5 suspected incident of TIA among this patient group.

The 51 patients were enrolled in a clinical study involving different types of prosthetic heart valve, comparing various risk factors for embolic complication. Only one patient among 118 implanted with the standard (uncoated) St Jude heart valve within this study was found to have suffered an embolic complication. There were no significant differences in predisposing risk factors for embolic complications or patient anti-coagulation control between the group of patients with the Silzone® valve and the standard St Jude heart valve. An independent review of these data on behalf of the Society of Cardiothoracic Surgeons of Great Britain and Ireland was requested by the manufacturer to confirm the validity of these events. The review confirmed the statistically greater thromboembolic event rate associated with the Silzone® valve compared with the standard St Jude valve; 22.47 (CI 10.71-47.13) and 0.38 (CI 0.05-2.27) percent per patient year respectively. However, in view of the small number of patients, these data should be interpreted with caution.

The same UK centre has reported a further case of mitral valve thrombosis involving a patient implanted with a Silzone® valve outside the scope of this study. MDA has also received notification of the death of a patient who received a Silzone®; mitral valve at another UK implanting centre, in which thrombus was found on the valve at post-mortem.

In addition a pathologist outside the UK has reported concerns based upon his evaluation of an unexpectedly high number of Silzone® valve explants. This finding led to a review of all patients implanted with Silzone® valves at one North American hospital. Although complete details of this hospital's findings are not yet available as further patient review is underway, there is concern arising from the high number of thromboembolic complications which have been identified. However, St Jude Medical has informed MDA that their survey of Silzone® patients at two other North American hospitals demonstrated no unusually high complication rates.

St Jude Medical is currently sponsoring a 4,000 patient prospective randomised clinical trial (AVERT) to compare the standard and Silzone® versions of their mechanical heart valve. The aim of this study was to investigate the efficacy of the silver coating in reducing endocarditis, although details of all major complications are being collected. To date this study has not identified a significant difference between the thromboembolic complication rates among patients with the Silzone® and the standard St Jude valve. It will, however, be some time before this study yields adequate data to enable an assessment of the valve's thrombogenicity. Further information will be reviewed as it becomes available enabling additional advice to be provided as necessary.

ENQUIRIES

Enquiries to the MHRA should quote reference number 04/01/98122131.