Listen to this patient's heart.


· Mitral valve prostheses can be recognized by their site, metallic first heart sound, normal second heart

sound and metallic opening snap. Systolic murmurs are often also present and it is important to note

that this does not indicate valve mal-function. Diastolic flow murmurs may be heard normally over the

disc valves.

· Aortic valve prostheses may be recognized by their site, normal first heart sound and metallic second

heart sound.

· Both
mitral and aortic valves may be replaced and both the first and second heart sounds will be

metallic. The presence of a systolic murmur does not indicate valve dysfunction. However, the presence

of an early diastolic murmur indicates a malfunctioning aortic valve.

Note. Comment on the mid-sternal, vertical thoracotomy scar, and state whether or not the metallic

valve sounds are audible to the unaided ear (they are most often audible). Some mechanical valves

cause so many clicks that it may not be possible to determine which valve has been replaced solely by

auscultation. Porcine and cadaveric heterografts do not cause metallic clicking or plopping sounds.


This patient has both first and second heart sounds with a metallic quality, indicating that both mitral and

aortic valves are artificial valves (lesion) and the patient is not in heart failure (functional status).


What are the complications of prosthetic valves?

· Thromboembolism.

· Valve dysfunction, including valve leakage, valve dehiscence and valve obstruc-tion due to thrombosis

and clogging. Perivalvular leak is always abnormal. 'Built-in' transvalvular leakage should be less than

10 mi per beat. The loss of expected valve sounds is an important sign of mechanical valve thrombosis.

· Bleeding (such as upper gastrointestinal haemorrhage) due to anticoagulants.

· Haemolysis at the valve, causing anaemia.

· Endocarditis, which carries a mortality rate of up to 60%; patients should be urgently referred to a

tertiary cardiothoracic centre (see pp 57-60).

· Structural dysfunction: fracture, poppet escape, cuspal tear, calcification.

· Non-structural dysfunction: paravalvular leak, suture/tissue entrapment, noise.

What are the causes of anaemia in such a patient?

· Bleeding due to anticoagulants.

· Haemolytic anaemia.

· Secondary to bacterial endocarditis.

What are the advantages of a porcine heart valve?

There is no need for chronic anticoagulation; hence it is sate in women of childbearing

age and in the elderly.

What are the complications of a porcine heart valve

· Degeneration with time.

· Calcification.


What are the indications for valve replacement? x

· Mitral stenosis (see pp 3-7).

· Mitral regurgitation (see pp 8-11).

· Aortic regurgitation (see pp 13-18).

· Aortic stenosis (see pp 18-22).

What are the different kinds of mechanical valves?

Mechanical valves'

· The Start-Edwards valve is a caged ball device and, because blood flows around the ball, there is a

high incidence of haemolysis. This valve was introduced in 1960. The Silastic ball is specially cured to

prevent lipid accumulation (which can result in ball variance). The struts of the modern Starr-Edwards

prosthesis are not covered with cloth.

· The Medtronic-Hall valve is a tilting disc valve made of pyrolytic carbon. The disc tilts to an opening of

75° for aortic prostheses and 70° for mitral prostheses.

· The Bjork-Shiley pivoted single-tilting disc valve has laminar flow and hence a lower incidence of

haemolysis. It was introduced in 1969. In the current model the entire ring and struts are machined from

one piece (i.e. there are no welds). This is referred to as the 'monostrut valve'.

· The St Jude valve is a double-tilting disc valve (bileafiet valve). Other examples of bileafiet prostheses

include the Carbomedics and Duromedics valves.


· Porcine valves (Carpentier-Edwards, Hancock Modified Orifice, C/E Durafiex, Medtronic Intact).

· Pericardial valves mounted on a frame (Mitroflow, Carpentier-Edwards peri-cardial, lonescu-Shiley,

Hancock). A design flaw predisposed the Ionescu-Shiley valve to sudden rupture of the cusps.

Currently, the Baxter pericardial valve is being used but its long-term durability remains to be



These are cadaveric aortic or pulmonary valves. Homografts are considered the valve of first choice in a

young patient requiring aortic valve replacement. They are useful in replacing infected aortic valves as

they are more resistant to reinfection than other prosthetic valves.

What kind of valve would you use to replace the mitral valve?

A mechanical prosthesis. Patients in whom the risk posed by anticoagulants is unacceptably high may

receive a bioprosthesis, but at the increased risk of further operation at a later date.

What kind of valve would you use to replace the aortic valve?

Mechanical valves are used in younger patients in whom the risk of porcine valve failure is higher and for

whom durability of the valve is of paramount importance. Porcine valves may be considered for elderly

patients whose lite expectancy may not exceed that of the prosthesis.

Why are mechanical valves increasingly preferred over bioprosthetic valves?

Two randomized controlled trials have shown a lower rate of reoperation with mechanical prostheses

than with porcine prostheses, and a smaller increased risk of anticoagulant-related bleeding.

What do you know about the convexo-concave model for the Bjork-Shiley prosthesis ?

This was a modification of the previously reliable design which resulted in the strut retaining the tilting disc

becoming liable to fracture several years after implantation, causing fatality. All Bjork-Shiley valves

manufactured after 1975 have a radio-opaque ring marker in the edge of a tilting disc. This ring marker is

missing if the strut is fractured. The disc may be spotted in the peripheral circulation. About two thirds of

the patients with strut fracture die acutely. The risk of strut fracture is 7 per 10 000 per year, but the risk of

another mitral valve replacement exceeds this. This risk is greatest in patients with a large-size mitral

prosthesis (31 and 33 mm) and a weld date between I January 1981 and 30 July 1982.

Is there any difference between the lifespan of a porcine mitral prosthesis and that of a porcine

aortic prosthesis?

Porcine mitral bioprostheses usually fail after about 7 years whereas those in the aortic position fail in

about 10 years owing to degeneration of the valve leaflets. In younger patients, these prostheses tend to

degenerate more rapidly.

Which patients should receive a bioprosthetic valve?

· Those unable to take anticoagulants and those not expected to live longer than the predicted lifespan

of the prosthesis.

· Patients over the age of 70 years who require an aortic valve replacement as the rate of

degeneration is relatively slow in these patients.

In a woman of childbearing age, which kind of valve – bioprosthetic or mechanical - do you


Until recently, bioprosthetic valves were advocated in women of childbearing age to avoid the adverse

effects of warfarin on the fetus. More recently, it has been found that the risk of fetal abnormalities is very

low in pregnant women receiving warfarin, although there is an increased risk of spontaneous abortion.

There also appears to be an accelerated risk of bioprosthetic valve degeneration during pregnancy. Thus

the risks of spontaneous abortion have to be weighed against the operative mortality rate of 10% during

reoperation following valve failure. It is increasingly believed that, if valve replacement is needed, a

mechanical prosthesis should be used (Br Heart J 1994; 71:196-201 ).

If a patient with atrial fibrillation requires a prosthetic mitral valve, which kind of valve would you


A mechanical valve, as these patients need warfarin treatment for atrial fibrillation.

The first aortic valve replacement (caged ball device) was performed by Dr Dwight Harken in March 1960

at Peter Bent Brigham Hospital in Boston. Shortly thereafter, Dr Nina Braunwald, at the National Institutes

for Health, USA, performed a total mitral valve replacement with an artificial flexible leaflet valve.

A. Starr and M.L. Edwards, both US physicians.