CARDIOVASCULAR JOURNAL OF AFRICA • Vol 23, No 3, April 2012
126
AFRICA
Cardiovascular Topics
The design and development of a stented tissue
mitral and aortic heart valve replacement for human
implantation
MURRAY LEGG, EDWARD MATHEWS, RUAAN PELZER
Abstract
A study was conducted into the development of a mitral and
aortic heart valve replacement that caters for patients having
suffered valve damage due to stenosis or rheumatic fever. The
appeal of the valve is that it is constituted from a solid frame
housing pericardial tissue leaflets, and allows the patient
freedom from post-operative blood-thinning medication. The
valve is designed to appeal to patients in developing areas
of the world, as it features a clip-in mechanism to secure
the valve assembly into the sewing ring, which is stitched in
independently of the frame and leaflets. Re-operative valve
replacement would then be made possible when the pericar-
dial leaflets began to calcify. Novel aspects of the design added
value to the science of heart valve replacements, through the
use of sintered chrome cobalt in the valve components, the
insights gained into mechanical testing of pericardium, and
the patient benefits offered by the complete design. Further
work is planned to fatigue test the assembly, undergo animal
trials and make the valve available for commercial use.
Keywords:
aortic valve replacement, mitral valve replacement,
tissue valve
Submitted 13/5/10, accepted 16/8/10
Cardiovasc J Afr
2012;
23
: 126–130
DOI: 10.5830/CVJA-2010-065
Two main but divergent solutions address heart valve
replacements, namely bioprosthetic types and mechanical valve
replacements. Rapid advances in the chemical treatment of tissue
valves by glutaraldehyde fixation
1
and the progression from ball-
and-cage valves
2
to tilting disc
3
and bi-leaflet
4
designs were all
limited to a few exciting, pioneering years.
Current valve designs, particularly those of the mechanical
form, create turbulent blood flow. This turbulence leads to the
formation of blood thromboses and haemolysis and ultimately
a thrombo-embolic event. Blood-thinning medication must be
prescribed on an ongoing basis. This is a major logistical and
financial limitation to patients in outlying and impoverished
areas.
Tissue valves do not present the risk of stroke to the patient,
but are constructed from porcine or bovine pericardial tissue. The
body’s immune response to this generally causes calcification
and tissue hardening, ultimately detracting from the ideal
functioning of the heart valve replacement and it requires
re-operative surgery within a 10- to 15-year period.
It has been estimated that worldwide, around 380 000 valve
replacements take place annually.
5
The majority of these patients
are elderly and from first-world countries. Developing countries,
however, actually face a greater need for valve replacements
due to high instances of rheumatic fever. It is purely a socio-
economic limitation that prevents valve surgery being more
commonplace in these developing countries.
Long-term follow-up studies focusing largely on elderly
recipients may skew the opinions on favourable valve-
replacement methodologies because minimal emphasis is
given to patients’ long-term follow up in developing countries.
Unger and Ghosh
5
discuss this, noting that 85% of all open-
heart procedures are performed in countries representing 11%
of the current world population. Lack of education and the
distances from healthcare facilities may still impede evasion of
post-operative complications associated with anti-coagulation.
Therefore, there is a need for a valve replacement that requires
little or no ongoing supportive treatment.
Heart valve replacements
Two main failure modes are experienced in natural mitral and
aortic valves, namely stenosis and regurgitation. These can occur
in isolation or together at both valve positions. Mitral stenosis
occurs where the mitral valve obstructs flow from the left atrium
into the left ventricle. Mitral regurgitation occurs when the mitral
valve allows reverse flow of blood to the left atrium, rather than
it all being pumped during systole through the aortic valve into
the aorta.
Developing countries, because of infrastructural limitations
in the use of antibiotics, generally have high instances of aortic
regurgitation induced by rheumatic fever. Such occurrences
in the developed world are typically limited to the elderly
who contracted rheumatic fever in their youth but were not
administered antibiotics.
Mechanical valves
The largest load placed on mechanical valves is that of
transvalvular pressure, which occurs just after valve closure.
This causes two types of wear stress, namely impact- and
Centre for Research and Continued Engineering
Development, North West University, Pretoria, South Africa
and consultant to TEMM International (Pty) Ltd
MURRAY LEGG, PhD
EDWARD MATHEWS, PhD
RUAAN PELZER, PhD,
