Biomedical Engineering Reference
In-Depth Information
5
Mechanical and bioprosthetic heart valves
M . N . H E L MU S , Biomedical Consultant, USA and
C . M . C U N A N A N , Cunanan Consulting, USA
Abstract: Replacement heart valves routinely save thousands of lives each
year, to replace damaged or diseased native valves and restore sufficient
cardiac function for the patient. The clinician has a number of factors to
consider when choosing an appropriate prosthetic valve for a patient,
including their age and life expectancy, lifestyle and quality of life, and
other comorbidities. The two main types of tissue heart valves include a
valve fabricated from a native porcine aortic valve, or one fabricated with
leaflets made from bovine pericardium. Clinical experience demonstrates that
pericardial valves have a longer duration than porcine valves. There have
been significant developments in both types of valves over the years,
including improvements on valve design, materials, treatments, and
fabrication methods. Future advances in heart valves include mechanical
valves with improved hemodynamics and reduced damage to blood
elements, percutaneous heart valves which can be implanted minimally
invasively, and tissue engineered heart valves which have the ability to
repair and grow.
Key words: heart valve, mechanical, tissue, bioprosthesis, prosthesis,
replacement, pyrolytic carbon, porcine, bovine pericardium, xenograft, suture
ring, biomaterials, biocompatibility.
5.1 Introduction
There are four valves in the heart which help direct the one-way flow of blood
through the body. Figure 5.1 shows these four valves, and replacement valves
have been made for each of them. Which valve(s) need replacement is a function
of the patient's disease and history. Historically, the most common disease to
affect the heart valves is rheumatic fever, which primarily attacks the mitral
valve. Congenital defects can also require valve replacement for correction, and
depending upon the severity of the defect, it may not become symptomatic until
the patient is in their 40s. Aortic stenosis is the most common valve disease in
developed countries, where calcification of the native valve results in a stiffen-
ing of the leaflets and overall degeneration of function. Stenosis of the aortic
valve is a progressive condition with many similarities to coronary artery disease
and patients typically become symptomatic in their fifth or sixth decade of life.
