CVM_Lect-1-9.pptx

UNIT - 6
Cardiovascular Mechanics
1. Fundamental Principles
of Fluid Mechanics
2. Cardiovascular System
3. Heart Valve Dynamics
4. Blood Vessel
Mechanics
5. Blood Flow Models
6. Artificial heart valves
7. Biological and
mechanical valves
development
8. Testing of valves
9. Prosthetic Valve
Dynamics

Fundamental Principles
of Fluid Mechanics

Conservation Laws
• Blood flow must obey the principles of conservation of
mass, momentum, and energy.
• Applied to any given region of space, the principle of
conservation of mass means that whatever flows in
must flow out.
• If flow is confined to blood vessels, then we obtain a
rule similar to Kirchhoff's law of electric circuits:
• At any junction the summation of current flowing into a
junction must be equal to the sum of the currents
flowing out of that junction.
• In a single tube of variable cross section, a steady flow
implies that the average local speed of flow is inversely
proportional to the local cross sectional area.

Conservation Laws
• Conservation of momentum means that the
momentum of matter cannot be changed without
the action of force.
• If there is force acting on a body, then according to
the Newton's law of motion, the rate of change of
momentum of the body is equal to the force.

Reynolds Transport Theorem
• The Reynolds Transport Theorem is a
generalisation of the principles of mass and
momentum conservation.
• A conserved quantity in the system is one whose
rate of change we can quantify in terms of other
physical eﬀect.

Pressure gradient &
divergence of shear stresses

Pressure gradient &
divergence of shear stresses
a) shows a small rectangular element of blood
subjected to equal pressure on all sides. The element
remains in equilibrium.
b) Shows an element subjected to shear stresses that
are equal on all sides. Because the shear stresses are
equal in this case, the fluid element will be distorted
by the shear stresses, but there will be no tendency
to accelerate.
c) shows a steady laminar flow of a fluid in a tube. The
velocity distribution is indicated on the left. To the
right, a series of fluid elements is shown. The shear
stresses acting on these elements are indicated by
arrows, with the magnitude proportional to the
length.

Types of fluids
• We categorise fluids according to the nature of the
relationship between the stress tensor and the strain
tensor:
• Newtonian fluids obey a stress–strain relationship of
the form
σ = 2µε − ρI
• Where, ρ is the pressure, ε is the strain tensor and µ is
the viscosity (which is constant),
• Inviscid fluids obey
σ = − ρI
• while other fluids have a more complicated relationship
between the stress and strain tensors, which may
depend on the history of the fluid motion, as well as
the current state.

Newton's Law of Motion
• Newton's law states that
Mass x acceleration= force
• Applied to a fluid, it takes the following form, which
will be explained in detail below:
Density x (transient acceleration + convective
acceleration) = - pressure gradient + divergence of
normal and shear stresses i.e. viscous stresses per
unit volume
Navier–Stokes equation

Flow of Fluid
• Flow is defined by the field of velocity
vectors of all particles in a domain.
• It is said to be steady if the velocity field is
independent of time.
• It is unsteady if the velocity field varies with
time.

Laminar & Turbulent Flow
• It is turbulent if the velocity field is
stochastic, that is, if the velocity
components are random variables described
by their statistical properties.
• A turbulent flow contains small eddies within
large eddies, and smaller eddies within small
eddies, ad infinitum.
• A laminar flow is one that is not turbulent.

Laminar & Turbulent Flow
Laminar Flow
• A parabolic flow profile.
• Low shear strain rate
• Coefficients of friction or
viscosity is low
• Molecular motion
between the sliding
cylinders
Turbulent Flow
• A profile that is much
blunter at the central
portion of the tube and
much sharper at the wall.
• High shear strain rate
• Coefficients of friction or
viscosity is high
• the molecular transport
• the convection of the
turbulent "eddies"

Laminar (Poiseuille) Flow
• Assumptions of Poiseuille flow
• Flow is axisymmetric
• Flow is fully developed and the vessel is rigid with a
uniform cross-section
• Vessel is straight
• Flow is steady
• Artery is large enough that a Newtonian fluid model is
appropriate

1. Non-axisymmetric flow
• To derive Poiseuille flow, we assumed the flow
was axisymmetric. However, this need not be the
case, as there are other solutions of the equations
with broken symmetry. However, these are only
observed for high Reynolds numbers, when the
flow becomes turbulent.
• Another reason for the flow to become non-
axisymmetric is if the pipe is not perfectly circular.

1. Non-axisymmetric flow
• Reynolds number: This is a dimensionless quantity used
to describe a fluid flow. It is probably the most widely used
dimensionless number in fluid mechanics. It is defined by
• where
• ρ is the fluid density,
• U is a characteristic velocity scale,
• L is a characteristic length scale, and
• µ is the viscosity of the fluid.
• The Reynolds number gives a qualitative description of
the flow, and is an order-of-magnitude estimate. The
precise value is usually not important.
• For example, when describing the flow, the difference
between a flow with Re = 60 and one with Re = 80 is
often unimportant, but the difference between one
with Re = 100 and Re = 1000 is important.

2. Non-fully-developed ﬂow
• Arteries are usually long compared with their
diameter and have a regular cross-section, so the
assumption of fully developed ﬂow is often
reasonable. However:
• The cross-section may not be constant along the
pipe, for example due to:
• Arterial taper, which tends to occur in most arteries.
• Elasticity in the arterial walls cause the cross-sectional
area to change in response to a change in pressure,
resulting in non-uniformities in the cross-section along
the pipe.

2. Non-fully-developed flow
• There may be entrance effects due to a change in
the vessel, for example:
• Flow in the ascending aorta is unlikely to be fully
developed, since it is affected by the profile as it leaves
the ventricle.
• Flow in a daughter artery just after a bifurcation is
affected by the splitting of the flow in the parent vessel.
• Entrance effects persist for a distance proportional
to a Re, where a is the radius of the artery and Re is
the Reynolds number.

3. Effect of arterial curvature on the
flow
• The derivation of Poiseuille flow assumes the artery is
straight.
• In reality, most arteries are curved, which has a significant
effect on the flow structure.
• It is still possible to gain some insight using analytical
techniques in the case when the centreline of the artery
(the locus of centres of cross-sections of the pipe) is circular.

3. Eﬀect of arterial curvature on the
ﬂow

4. Effect of unsteadiness in the flow
• Flow in the cardiovascular system is not steady, but
is rather highly pulsatile. This is illustrated in the
graph below, which shows pressure and flow in the
aorta.

4. Effect of unsteadiness in the flow
• Slow oscillations of the pressure gradient
• When the oscillations in the pressure gradient
are sufficiently slow, there is enough time for
Poiseuille flow to develop, meaning the profile
at any fixed time looks like the Poiseuille flow
solution with the same pressure gradient.

5. Unsteady ﬂow: High-frequency
oscillations
• In this case, we cannot neglect the time-derivative
term in the Navier–Stokes equations.
• We still assume:
• Flow is axisymmetric
• Flow is in the axial direction
• Flow is fully developed (independent of z)

5. Non-Newtonian flow
• The blood is a Newtonian fluid. Newtonian fluids
have a stress–strain relationship of the form
σ = 2µε − ρI

• Deformation of cells: As they flow along the arteries,
the red blood cells deform significantly, meaning that a
rigid-particle model to describe them is probably
inaccurate. In order to pass through the narrow
capillaries the cells adopt a completely different shape.
• Particulate nature of cells: The cells have diameter of
around 8 µm, and in small vessels this is a substantial
proportion of the vessel diameter. In the capillaries it
may be larger than the vessel diameter. With such
relatively large particles in a small vessel, a continuum
model may not be justified.

• Observed shapes adopted by red cells when
travelling through a glass capillary of
diameter 7 µm.
• The differences between the shapes of the
three cells are thought to be due to the
position of the cell within the capillary.
• The pictures are reproduced well by a
mathematical model:
• To obtain a similar configuration to that in the top
picture the cell is placed symmetrically.
• To obtain the middle picture the cell is offset by
0.5 µm towards the top.
• Finally to obtain the bottom picture the cell in the
model is offfset by 1 µm.

Importance of Flow Analysis
• Turbulence in blood flow is strongly implicated in atherogenesis.
Atherosclerotic plaques are often found at sites of turbulence in
the aorta.
• Associated with the velocity fluctuations in a turbulent flow are
pressure fluctuations. Pressure fluctuations can excite vibrations
in the eardrum and cochlea, and can be heard if the frequencies
are in the audible range. We can hear the howling of wind
because wind is turbulent. We can hear jet noise if the jet flow is
turbulent.
• The Korotkoff sound at systole is the sound of the jet noise of
rushing blood. A heart murmur is a turbulent noise. Flow
separation at a site of stenosis in an artery often causes
turbulence in the separated region, making it possible to detect a
stenosis by listening to the noise (bruit) in the blood flow with a
stethoscope.

Deceleration as a Generator of
Pressure Gradient
• If there is no turbulence and if the
gravitational and frictional forces are small
enough to be ignored,
Density x acceleration = -pressure gradient

Pressure – Volume Loop
A plot of the pressure and volume in a ventricle during a cardiac cycle

Principle of Heart Valve Closure

• The mitral valve is composed of two very flexible,
thin membranes. These membranes are pushed
open at a stage of diastole when the pressure in
the left atrium exceeds that of the left ventricle.
• Then a jet of blood rushes in from the left atrium
into the left ventricle, impinges on the ventricular
wall, and is broken up there.
• Thus, the blood stream is decelerated in its path
and a positive pressure gradient is created.

• Toward the end of diastole, the pressure acting on
the ventricular side of the mitral valve membranes
becomes higher than that acting on the side of the
membranes facing the left atrium.
• The net force acts to close the valve. In a normal
heart, closure occurs without any backward flow or
regurgitation.
• The papillary muscles play no role at all in opening
and closing of the valve. They serve to generate
systolic pressure in the isovolumetric condition by
pulling on the membranes, and to prevent
inversion of the valves into the atrium in systole.

THE AORTIC VALVE
• composed of three leaflets
• attach at their base in a semilunar manner to the
aortic wall
• not muscularized
• moves passively according to changes in blood flow
and pressure

THE AORTIC VALVE
During diastole, left ventricular pressure is
less than the pressure in the aorta, and the
leaflets coapt at their tips to close the valve
and prevent retrograde flow
During systole, the pressure gradient
drops to zero and the leaflets relax,
allowing the valve to open

THE AORTIC VALVE
• The leaflets must withstand substantial
backpressure of 80 mmHg in normotensive
individuals and more than 100 mmHg in
hypertensive individuals, resulting in the leaflets
stretching 10% in the circumferential direction and
as much as 30% in the radial direction, with values
of circumferential mechanical stress in the range of
300–600 kPa.
• Movement of the blood into the aorta creates high
oscillatory shear stress varying between –5 and
7 Pa on the ventricular side of the leaflet, while the
aortic side experiences lower shear stress peaking
at 2 Pa, with flows that are generally thought to be
more disturbed and complex.

Aortic Valve Diseases
• Aortic Stenosis
• the narrowing of the AV opening during systole
• producing an obstruction of the left ventricular outflow
• caused by a congenital abnormality of the valve or by
progressive calcification
• elevated pressures in the left ventricle during systole
• left ventricular wall thickens

• Aortic Insufficiency (aortic regurgitation)
• the valve does not close completely in diastole
• Allowing blood to flow in the reverse direction (leak)
• Causes might be, aortic dilatation, congenital
abnormality of the valve, and calcification etc.
• The blood reflux from the aorta into the left ventricle
increases the ventricular workload through pressure and
volume overloads
• these overloads trigger a hypertrophic dilatation of the
left ventricle

• Aortic Valve Malformations
• represent different cases of congenital malformations
involving various numbers of cusps, from one to five
• Some of these cusps can be fused with a raphe (the
conjoined area between two underdeveloped cusps that
turns into a malformed commissure)
• complete or incomplete fusions of the cusps
fusion of two anatomical
cusps into a functional cusp
with a raphe (in brown)

• Aortic Valve Malformations

Three-dimensional illustration of a
type 1 bicuspid aortic valve

Failure Mechanisms of the Aortic
Valve with Aortic Insufficiency
• Classifications of AI failure mechanisms have been
proposed to provide cardiac surgeons with a better
understanding of the diseased AV and help them
guide the approach to be used for treatment.
• Because stenotic valves cannot usually be surgically
repaired (they need to be replaced instead), more
efforts have been devoted to regurgitant AVs.
Existing classifications are generally based on the
distinction between two underlying causes for AI,
issues with the aortic root, and issues with the
cusps.

Failure Mechanisms of the Aortic
Valve with Aortic Insufficiency

Mitral Valve
• A medical view cross-section of the mitral valve is
shown in figure.

Mitral Valve
• The mitral valve are composed of four primary
elements. These elements include the valve
annulus, the valve leaflets, the papillary muscles,
and the chordae tendineae.
• The bases of the leaflets form the annulus, which is
an elliptical ring of dense collagenous tissue
surrounded by muscle. The circumference of the
mitral annulus is 8 to 12 cm during ventricular
diastole when blood is flowing through the mitral
valve from the left atrium to the left ventricle.
• During ventricular systole the mitral valve closes
and the circumference of the mitral annulus is
smaller.

A superior view of a mitral valve

Mitral Valve
• The mitral valve is a bicuspid valve and has an
aortic (or anterior) leaflet and a mural (or posterior)
leaflet.
• Because of the oblique position of the valve, strictly
speaking neither leaflet is anterior or posterior. The
aortic leaflet occupies about a third of the annular
circumference and the mural leaflet is long and
narrow and lines the remainder of the
circumference.
• When the valve is closed the view of the valve from
the atrium resembles a smile. Each end of the
closure line is referred to as a commissure.

Mitral Valve
• Each leaflet is composed of collagen reinforced
endothelium. Striated muscle, nerves fiber, and
blood vessels are also present in the mitral valve.
Muscle fibers are usually present on the aortic
leaflet but rarely on the mural leaflet.
• The aortic (anterior) leaflet is slightly larger than
the mural (posterior) leaflet. The combined surface
of both leaflets is approximately twice the area of
the mitral orifice, allowing for a large area of
coaptation permitting effective valve sealing.

Mitral Valve
• The chordae tendineae for both leaflets attach to the
papillary muscle. Chordae tendineae consist of an inner
core of collagen surrounded by loosely meshed elastin
and collagen fibers with an outer layer of endothelial
cells.
• There is an average of about 12 primary chordae
tendineae attached to each papillary muscle. The
anterolateral and the posteromedial papillary muscle
attach to the ventricular wall and tether the mitral
valve into place.
• The chordae tendineae prevent the mitral valve from
inverting through the annular ring and into the atrium.
That is, in normal physiologic situations they prevent
mitral valve prolapse. Improper tethering results in
prolapse and mitral regurgitation.

Mitral Valve
• Stresses in mitral valve leaflets of up to 0.22 MPa
have been estimated when the left ventricular
pressure reaches up to 150 mmHg during
ventricular systole.
• Mitral velocity flow curves show a peak in the curve
during early filling. This is known as an E wave. Peak
velocities are typically 50 to 80 cm/s at the mitral
annulus. A second velocity peak occurs during the
atrial systole and is known as an A wave.

Mitral Valve
• In healthy individuals, velocities in the A wave are
lower than the velocities during the E wave.
• Diastolic filling of the ventricle shows a peak inflow
during diastolic filling followed by a second peak
during atrial systole.

Mitral Valve Failure
• Chordae tendineae rupture and papillary muscle
paralysis can be consequences of a heart attack.
• This can lead to bulging of the valve, excessive
backward leakage into the atria (regurgitation), and
even valve prolapse.
• Valve prolapse is the condition under which the
valve inverts backward into the atrium. Because of
these valve problems, the ventricle does not fill
efficiently.
• Significant further damage, and even death, can
occur within the first 24 h after a heart attack
because of this problem.

Anatomy of the Arterial
bed
Mean Radius of Various Arteries

Arterial Radius related to Age
The radius and wall thickness of human arteries for young ( Y) and old (0) persons

Modulus of Elasticity related to Age
(a) Thoracia aorta (b) Iliac artery
Incremental modulus of elasticity of arteries of normal
young and old persons at a pressure of 100 mm Hg

Vascular Branching
Mother Branch
Daughter Branch

Pulsatile Blood Flow
• In pulsatile blood flow the transient inertial force
term may become important when compared with
the viscous force term.
• To make an estimate, let U = a characteristic
velocity, ω = a characteristic frequency, and L = a
characteristic length.
• This is a dimensionless number. If it is large, the
transient inertial force dominates. If it is small, the
viscous force dominates.

• The dimensionless number ωL2/ν is a frequency
parameter, and is called the Stokes' number
because its significance was pointed out by George
Stokes in 1840. It is better known by its square
root,
• which is called Womersley number in honor of J. R.
Womersley, who made extensive calculations on
pulsatile blood flow in 1950s. If L is taken to be the
radius of the blood vessel, then Womersley's
number is often written as α:

• The ratio of the radius of the tube to the wall layer
thickness (δ) is
• if α is large , the effect of the viscosity of the fluid
does not propagate very far from the wall and
pulsatile flow will be relatively blunt, in contrast to
the parabolic profile of the Poiseuillean flow, which
is determined by the balance of viscous and
pressure forces.

Womersley's number
The theoretical velocity profiles computed for a straight circular
cylindrical tube in which a sinusoidally oscillating pressure gradient acts.
As (α increases from 3.34 to 6.67, the profiles are seen to become flatter
and flatter in the central portion of the tube.

Pressure and Blood velocity patterns

Transient motion
velocity changing with time
• a recording of blood velocity of a single patient

Transient motion
• an ensemble average of many experiments

Transient motion
• a sample of turbulence velocity of a single patient

Transient motion
• the root-mean-square of the turbulence velocity, or
the so-called turbulence intensity

Blood Flow Model
• Since the pioneering work of Otto Frank in 1899,
there have been many types of mathematical models
of blood flow.
• The aim of these models is a better understanding of
the biofluid mechanics in cardiovascular systems.
• Raines et al. in 1972 observed that patients with
severe vascular disease have pressure waveforms
that are markedly different from those in healthy
persons.
• By developing a model that would predict which
changes in parameters affect those pressure
waveforms in what way, the scientists might provide
a means for diagnosing vascular disease before it
becomes severe.

Electrical Analog Model of Flow
in a Tube
• The electrical schematic of a circuit representing a length
of artery, terminating in a capillary bed.
• The values for resistance, capacitance, and inductance for
each resistor, capacitor, and inductor, respectively, are
calculated from the blood vessel properties on a per unit
length basis.

• For this type of discretized model, the resistance in
each discrete resistor can be written as
• The inductance in the vessel for each discrete
inductor element becomes
• The capacitance of the vessel is the compliance of
the vessel, or dA/dP, and depends on the pressure
at the point where the capacitor is located.
Electrical Analog Model of Flow
in a Tube

Modelling of Flow through
the Mitral Valve
• Assessment of ventricular function and
quantification of valve stenosis and mitral
regurgitation are important in clinical practice as
well as in physiological research.
• Noninvasive assessment of diastolic function that
does not require the use of intracardiac pressure
has been an important goal, and in recent years,
Doppler electrocardiography has become the
“diagnostic modality of choice” to assess diastolic
function.
• The goal of the research that created this model
was development and validation of a mathematical
model of flow through the mitral valve during early
diastolic ventricular filling.

the Mitral Valve
• The model of early ventricular filling, or the
E-wave portion of a single heartbeat, begins
at the time when pressures are equal in the
atrium and the ventricle, i.e., it begins from
the instant of mitral valve opening.
• The model then describes flow and pressures
during ventricular filling up to the point of
atrial systole.

the Mitral Valve
• A schematic of the atrium and ventricle with
the mitral valve in-between. Afluid cylinder
of length L is shown.

the Mitral Valve
• Rv, Rc, M, Ca, Cv are described in greater detail in the
text following.
• The first differential equation describing flow rate
through the mitral valve is shown below.

the Mitral Valve
• The second differential equation is written as
follows:
• where Ca represents atrial compliance in m5/N
(m3/N/m2). The pressure inside the atrium is
related to its volume through atrial compliance. Ca
= d(volume)/dt.
• The volume is also related to flow rate. In one
sense, the flow intro the atrium determines its final
volume and therefore the final atrial pressure.

the Mitral Valve
• Similarly, the third equation describing the system is
the equation for change in ventricular pressure with
time. The ventricular pressure is similarly related to the
ventricular volume and the ventricular compliance, Cv.
The change in pressure of the ventricle is also related to
“active relaxation.”
• In all three equations, q represent flow rate in m3/s,
dq/dt represents the time rate of change of flow rate in
m3/s2, Pa represents left atrial pressure in N/m2, Pv
represents left ventricular pressure in N/m2, and M
represents the inertance term, which is analogous to
inductance in the electrical circuit and has the units of
kg/m4.

CAGED BALL VALVE
• Early mechanical prosthetic heart valves
were ball valves. In 1952, Dr. Charles
Hufnagel implanted the first ball and cage
valve into a patient with aortic valve
insufficiency.
• Although the design of mechanical
prosthetic valves has progressed significantly
over the past 50 years, ball and cage valves
are still the valve of choice by some
surgeons.

CAGED BALL VALVE
• The first artificial heart valve was the caged-
ball, which utilizes a metal cage to house a
silicone elastomer ball.
• When blood pressure in the chamber of the
heart exceeds that of the pressure on the
outside of the chamber the ball is pushed
against the cage and allows blood to flow.
• At the completion of the heart's contraction,
the pressure inside the chamber drops and is
lower than beyond the valve, so the ball
moves back against the base of the valve
forming a seal.

CAGED BALL VALVE
• Advantages
• Oldest prosthetic valve.
• Durabilty upto 40 yr
• Disadvantages
• High profile
• Hemolysis
• High thrombogenecity
• Poor hemodynamics in small sizes
• Unique features
• Occluder travels completely out of the orifice, reduces
thrombus & pannus growing from the sewing ring.
• Continuously changing points of contact of the ball
reduces the wear & tear in any one area
• Thrombogenic risk 4-6% per year.

TILTING DISC VALVE
• Björk-Shiley designed the first tilting disk, or
single leaflet, valve around 1969. Those
valves used a tilting disk occluder that was
held in place by a retaining strut.
• However, the development of the bileaflet
valve by St. Jude in 1978, has led to the
predominance of this type of bileaflet valve
in the mechanical valve market.

TILTING DISC VALVE
• Tilting disk valves have a single circular occluder
controlled by a metal strut.
• They are made of a metal ring covered by an PTFE-
coated high translucency (ePTFE) fabric, into which
the suture threads are stitched in order to hold the
valve in place.
• The metal ring holds, by means of two metal
supports, a disc which opens and closes as the
heart pumps blood through the valve.
• The disc is usually made of an extremely hard
carbon material (pyrolytic carbon), in order to allow
the valve to function for years without wearing out.

TILTING DISC VALVE
• Advantages
• Low profile
• Good hemodynamics even in small sizes
• Excellent durability
• Permit central laminar flow.
• Disadvantages
• Anticoagulation mandatory
• Higher risk of thrombosis than cage ball
• Sudden catastrophic valve thrombosis.

BILEAFLET VALVES
• They have two semicircular leaflets retained
within the ring by hinges. The potential for
impeded leaflet movement due to
interference with cardiac structures is slim,
as the open leaflets are positioned in the
middle of the blood stream and enclosed
within the ring in the closed position.
• Bileaflet valves are the most protected as the
leaflets hardly protrude from the valve ring,
even during maximum opening.

BILEAFLET VALVES
• Advantages:-
• Low bulk - flat profile.
• Less thrombogenicy.
• Central laminar flow.
• Two semicircular discs that pivot between open
and closed positions.
• No need for supporting struts.
• Good hemodynamics even in small sizes.
• 2 lateral, 1 central minor orifice , no chance of
sudden catastro thrombosis.
• Disadvantages:-
• Anticoagulation mandatory risk of thrombosis.

TISSUE (BIOLOGICAL) HEART VALVES
• Tissue valves (also called biologic or bioprosthetic
valves) are made of human or animal tissue. Some
valves may have some artificial parts to help give
the valve support and to aid placement.
• Once the tissue is removed from the animal, it is
chemically treated to preserve the tissue and
prevent immulogic reactions once it is placed in a
patient.
• There are three types of tissue valves:
• pig tissue (porcine),
• cow tissue (bovine), and
• human (allografts or homografts).

Porcine Stented valves
• The porcine stented valve was the first generation
of porcine tissue valves. They have been available
for more than 30 years.
• The valves are made from natural porcine aortic
valves, but may be used for aortic or mitral valve
replacement. They are trimmed and then fixed in
buffered glutaraldehyde at high pressure.

Porcine stentless valve
• The porcine stentless valve is used for aortic valve
replacement. The valve is made from a natural
porcine aortic valve and is fixed in buffered
glutaraldehyde solution at a low pressure.
• No stents or synthetic sewing rings are used.
Therefore, these valves are very similar to the
homograft valve.
• These valves are technically
more difficult to implant but
are useful in patients with
small hypertrophied hearts.

Pericardial valves
The Carpentier-Edwards PERIMOUNT Pericardial
Bioprosthesis
• Pericardial valves include the Perimount series valves
(Edwards LifeSciences). Ionescu-Shiley pericardial valves
have been discontinued.
• More recently, stentless porcine valves have been used.
• They offer improved hemodynamics with a decreased
transvalvular pressure gradient when compared with older
stented models.

Other types of biological valves
• Xenografts are tissue valves (eg,
bioprostheses, heterografts); most are from
pigs (porcine), but valves from cows (bovine)
may also be used. Their viability is 7 to 10
years.
• They do not generate thrombi, thereby
eliminating the need for long-term
anticoagulation.

• Homografts, or allografts (ie, human valves),
are obtained from cadaver tissue donations.
• The aortic valve and a portion of the aorta or
the pulmonic valve and a portion of the
pulmonary artery are harvested and stored
cryogenically.
• Homografts are not always available and are
very expensive.

• Autografts (ie, autologous valves) are
obtained by excising the patient’s own
pulmonic valve and a portion of the
pulmonary artery for use as the aortic valve.
• Anticoagulation is unnecessary because the
valve is the patient’s own tissue and is not
thrombogenic.
• The autograft is an alternative for children (it
may grow as the child grows), women of
childbearing age, young adults, patients with
a history of peptic ulcer disease, and those
who cannot tolerate anticoagulation.

Radiologic Identification
• Starr-Edwards caged ball valve :
• Radiopaque base ring
• Radiopaque cage
• Three struts for the aortic valve; 4 struts for the
mitral or tricuspid valve

Cinefluoroscopy
• Structural integrity
• Motion of the disc or poppet
• Excessive tilt ("rocking") of the base ring - partial
dehiscence of the valve
• Aortic valve prosthesis
Fluoroscopy of a normally
functioning CarboMedics
bileaflet prosthesis in mitral
position
A=opening angle
B=closing angle

MRI
• Not useful in assessing prosthetic-valve
structure
• Used only when prosthetic-valve
regurgitation or para valvular leakage is
suspected but not adequately visualized by
echocardiography

Cardiac Catheterization
• Measure the transvalvular pressure gradient,
from which the EOA can be calculated
• Can visualize and quantify valvular or
paravalvular regurgitation

Echocardiography of Stentless
Aortic Homografts
• Doppler flow characteristics similar to native valve.
• Only 2-D evidence: Increased Echo intensity, and
Thickness of aortic annulus.

Patient-prosthesis mismatch
• When the effective prosthetic valve area, after
insertion into the patient less than that of a normal
valve (Rahimtoola in 1978)
• Effective Orifice Area (EOA) indexed to Body
Surface Area (BSA) is less than 0.85 cm2/m2
• EOA (echo) differs from geometric orifice area
(measured directly)
• EOA for each prostheses type & size obtained in
literature from pts normally functioning prostheses
• Average if > 1 value
• mild (0.9 - 1 cm² /m²
• moderate (0.6 - 0.9 cm2/m²
• severe (iEOA < 0.6cm²/m² (Rahimtoola)

Three-step algorithm
• Step 1: Calculation of the patient BSA.
• Step 2: Reference to the specific table for
identification of the adequate valvular EOA
according to the patient BSA.
• Step 3: Selection of the most appropriate
type and size of valve prosthesis according to
the target iEOA

Valve thrombosis
• Incidence of 0.1 to 5.7 % per patient/year
<0.2% per year for mechanical valves
<0.1% bioprosthetic valves
• small thrombus, at the hinge portion of a bileaflet valve
→ obstruct the mechanism
• tilting disk -- a much larger thrombus to prevent
function
• Ball and cage valves – less susceptible → occluder has
no contact at all with the valve housing for a portion of
every cycle
• Clinical
• Non obstructive- incidental/embolic phenomenon
• Partial obstruction- dyspnea,systemic embolism , fever
• Severe obstruction- overt heart failure

Fibrinolytic therapy
• Rt sided thrombosis 80-100% success rate
• Surgery for fibrinolysis failure/symptoms > 3
wk
• Surgery – Lt sided thrombosis, large clot
burden

Embolization
• Cerebral embolization → CT normal/infarct
→ warf & heparin – 72 hrs APTT lower
therapeutic level → till the desired INR
• Anticoagulantion delayed for at least 7 to 14
days - ICH, extensive cerebral infarction →
OAC

Paravalvular Regurgitation
• Mild or moderate paravalvular leakage –
asymptomatic, may have only a mild
haemolytic anemia.
• can be observed carefully with serial echo
• Severe paravalvular leakage - usually have
symptoms of heart failure or severe anemia.
• should be treated with surgical repair or
replacement of the valve

CVM_Lect-1-9.pptx

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