Developments in cardiovascular valve technology - Biomaterials and Devices for the Circulatory System - page 84

4
Developments in cardiovascular
valve technology

A. H. OLIVENCIA-YURVATI, R. T. MALLET
and J. FERNANDEZ, University of North
Texas Health Science Center, USA

Abstract : This chapter reviews clinical indications for valve replacement,
with emphasis on the aortic, mitral, and tricuspid valves, as well as the
physiology associated with valve replacements. Another section describes
valve biomaterial and the effects of these materials on thrombogenicity,
resistance or susceptibility to infection. Finally, an introduction to newer
biomaterial and valve designs will further pique the reader, with the
intent of spawning new approaches in the ongoing refi nement of cardiac
valves.

Key words : heart valve, cardiac surgery, valve replacement, valve
biomaterials.

4.1 Introduction: cardiac valvular disease

The heart's atrioventricular and semilunar valves ensure the effi cient, uni-
directional fl ow of blood through the cardiac chambers and into the great
arteries. The valve cusps are thin, fi brous structures that move passively in
response to pressure gradients across their respective apertures. The mitral
and tricuspid valves, respectively positioned in the left and right atrioven-
tricular orifi ces, swing open to accommodate the movement of blood from
the atria to the ventricles during diastole, then close with the abrupt increase
in ventricular pressure during systole, preventing blood regurgitation into
the atria. When pressures within the contracting ventricles exceed those of
the aorta and pulmonary artery, the aortic and pulmonic valves open, per-
mitting forceful ejection of blood into the systemic and pulmonary circula-
tions. Thus, normal valvular function coordinates the forward movement of
blood and is therefore essential for mechanically effi cient blood pumping
by the beating heart.
In general, valvular dysfunction manifests as valvular insuffi ciency, i.e.
regurgitation due to incomplete closure of the cusps, or valvular stenosis, a
thickening of the leafl ets impeding their passive motion and restricting
forward blood fl ow. These conditions compromise cardiac performance and
provoke myocardial remodeling and hypertrophy. The most common
valvular abnormality is stenosis of the aortic valve, usually caused by

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