Download Cardiac Valves - 02-28-2013

Cardiac Valves
Jeffrey R. Scott, Ph.D.
Heart – The primary pump
Anatomy / Function – Heart Facts
The Average Heart:
• Weighs ~7-15 ounces (200 – 425 grams)
• Is slightly larger than the size of a persons fist.
• Beats ~100,000 times each day.
• Pumps ~2,000 gallons (7,571 liters) of blood each day.
• Will beat ~3.5 billion times in a lifetime.
Anatomy - Heart
Anatomy – Chambers
4 Chambers
• Right Atrium
• Right Ventricle
• Left Atrium
• Left Ventricle
(largest and strongest)
Definition
Cardiac Valve
One of the four structures within the heart
that prevent backflow of blood by opening
and closing with each heartbeat. They
include the tricuspid, pulmonary, mitral (or
bicuspid), and the aortic valve.
Anatomy – Valves
4 Valves
• Tricuspid Valve:
Between Right Atrium and Right Ventricle
• Pulmonary Valve: Between Right Ventricle and Pulmonary
Artery
• Mitral Valve:
Between Left Atrium and Left Ventricle
• Aortic Valve:
Between Left Ventricle and Aorta
Anatomy – Heart Valves
The primary function of Cardiac Valves is to ensure unidirectional blood flow.
Anatomy – Heart Valves
Anatomy – Heart Valves
Number of Leaflets
• Tricuspid Valve:
3
• Pulmonary Valve: 3
• Mitral Valve:
2
• Aortic Valve:
3
During Systole
(Ventricle Contraction)
Heart – Pattern of Blood Flow - Video
What Problems Can Occur?
1. Valvular Stenosis
- stiff or fused leaflets which cause narrowing of
the valve opening.
2. Valvular Insufficiency / Regurgitation
- inappropriate valve seal or closure causing leakage.
Cardiac Valve Disease
- Scope of the Problem
~5 million people in the U.S. are diagnosed with cardiac valve
disease per year.
Types: 1. Congenital
2. Acquired Over Time
3. Result of an Infection
(Present at Birth)
(Most Common)
(i.e. Rheumatic Fever)
Note:
Rheumatic fever (RF) is an illness which arises as a complication of untreated or inadequately treated
strep throat infection, which can seriously damage the valves of the heart. Throat infection with a
member of the Group A streptococcus (strep) bacteria is a common problem among school-aged
children. It is easily treated with a ten-day course of antibiotics by mouth. However, when such a throat
infection occurs without symptoms, or when a course of medication is not taken for the full ten days,
there is a 3% chance of that person developing rheumatic fever.
Cardiac Valve Disease - Types
Valve Involved
Stenotic disease
Insufficiency/
Regurgitation disease
Aortic valve
Aortic valve stenosis
Aortic insufficiency/regurgitation
Mitral valve
Mitral valve stenosis
Mitral insufficiency/regurgitation
Tricuspid valve
Tricuspid valve stenosis
Tricuspid insufficiency/regurgitation
Pulmonary valve
Pulmonary valve stenosis Pulmonary insufficiency/regurgitation
Both Tricuspid and Pulmonary Valve Disease are less common than Aortic and
Mitral Valve Disease due to lower pressures on the right side of the heart.
Diagnosis - Echocardiogram
An echocardiogram is a diagnostic test which uses ultrasound
waves to capture images of the heart chambers, valves and
surrounding structures. It can measure cardiac output, is a
sensitive test for inflammation around the heart (pericarditis),
and can be used to detect abnormal anatomy or infections of the
heart valves.
Valve Disease - Video
Etiology of Disease
Aortic Stenosis
• Calcification of tricuspid aortic valve with age (>50%)
• Calcification of bicuspid aortic valve (30-40%)
• Rheumatic fever (<10%)
Risk Factors that may accelerate disease:
• Hypertension
• Diabetes mellitus
• Hyperlipoproteinemia (High Lipids)
• Uremia (High Nitrogen)
Result:
Causes increased pressure in the left ventricle and impaired
flow through the aorta.
Aortic Valve Stenosis – Examples
Normal
Congenital (Bicuspid) Stenosis
Rheumatic Stenosis
Calcified Stenosis
Etiology of Disease
Aortic Regurgitation
Acute
• Infective Endocarditis
• Trauma
Chronic
• Primary valvular disease caused by:
Rheumatic fever, bicuspid aortic valve, Marfan's
syndrome, Ehlers–Danlos syndrome, ankylosing
spondylitis, systemic lupus erythematosus.
Result:
Causes backflow of blood into the left ventricle during diastole.
Aortic Valve Stenosis / Insufficiency
Aortic Valve Stenosis / Insufficiency
- Symptoms
Aortic Valve – Repair Options
Etiology of Disease
Mitral Stenosis
• Primary cause is Rheumatic Heart Disease
Risk Factors that may accelerate disease:
• Pregnancy
Result:
Causes increased pressure in the left atrium and the
pulmonary circulation. Congestion may cause
thromboembolism, and atrial hypertension may cause
atrial fibrillation.
Etiology of Disease
Mitral Regurgitation
Acute
• Endocarditis - primarily due to S. aureus.
• Papillary muscle rupture or dysfunction, including mitral
valve prolapse
Chronic
• Rheumatic fever
• Marfan's syndrome
• Cardiomyopathy
Result:
Causes backflow of blood into the left atrium during systole.
Mitral Valve Insufficiency - Symptoms
Mitral Valve – Repair Options
Open Cardiac Valve Replacement
Open Cardiac Valve Replacement
Open Cardiac Valve Replacement
Open Cardiac Valve Replacement
Percutaneous Valve Replacement
Valve Replacement
Mechanical / Tissue Valves
Reasons for getting a Mechanical Valve
Child or adolescent
•
Needs a valve to last a lifetime
•
Experiences highest rate of failure for tissue valves
Adults up to age 60
•
Need a valve to last 20–30 years and beyond
•
Experience a higher rate of failure for tissue valves
than older adults
People are already taking blood-thinning medication(s)
•
No advantage in tissue valve
Mechanical Valves - Types
Starr-Edward’s Caged Ball Valve
Ball valves
•
Starr-Edward’s valve
• Only ball valve implanted in US
Disk valves
•
Single leaflet
• Bjork-Shiley valve
• No longer sold in US
• Medtronic-Hall valve
• Omniscience valve
St. Jude Medical Bi-leaflet Valve
Bileaflet
• St. Jude valve
• 90% of market
• Carbomedics valve
• Edwards-Duromedics valve
• No longer available in US
Medtronic-Hall
Single
Leaflet
Edwards (9 Commandments) of
Cardiac Valves
1.
Embolism Prevention.
2.
Durability and corrosion resistance had been improved by forming the struts from stainless steel
instead of Lucite.
3.
Ease and Security of Attachment. Ease and security of attachment had been improved by changing the
shape of the sewing ring from that of a doughnut to a flange; the new shape allowed greater contact with
the annulus.
4.
Preservation of Surrounding Tissue Function. Preservation of surrounding tissue function had been
improved via 2 modifications: the profile of the cage was made rounder where it had previously been
conical, and a porous silicone-rubber sponge was inserted into the body of the sewing ring to provide
flexibility and an antibiotic reservoir.
5.
Reduction of Turbulence. Turbulence had been reduced by increasing the orifice-to-ball ratio.
6.
Reduction of Blood Trauma. The mesh size of the Teflon fabric was enlarged to encourage neointima
formation and to reduce blood trauma.
Edwards (9 Commandments) of
Cardiac Valves
7.
Reduction of Noise. Hufnagel's early valves had a nylon poppet that made a distinct clicking noise that
was audible to the patient and to people around the patient. Hufnagel later covered the poppet with
silicone to reduce the noise. The poppet of the Starr-Edwards valve was made of a solid piece of
compressed silicone. The Starr-Edwards valve was quieter than Hufnagel's valve, but it could still be
heard in thin-chested people if the observer placed his or her ear a few inches away from the patient's
naked chest.
8.
Use of Materials Compatible with Blood and Tissue. All of the materials used by Starr and Edwards
had been shown to be nonreactive with blood and tissue. These materials included Stellite 21 (a mix of
cobalt, chromium, molybdenum, and nickel), Teflon cloth, Teflon suture, methyl methacrylate, stainless
steel type 302, and compression-molded silicone rubber.
9.
Development of Methods of Storage and Sterilization. For sterilization, the valve was cleaned with
detergent and autoclaved before it was implanted in the patient. The valve could be stored and
autoclaved again, if necessary.
Issues with Ball Valves
Primary issues
• Ball larger than opening in valve to properly
occlude valve when valve shut
• Suboptimal Hemodynamics
• Obstruction of blood flow by large ball
 Attempts to decrease relative size of ball
From the following article
The artificial heart valve
Albert Starr
Nature Medicine 13, 1160 - 1164 (2007)
doi:10.1038/nm1644
Leaflet Valves
Single leaflet
• Single leaflet
• Bjork-Shiley valve
• No longer sold in US
• Medtronic-Hall valve
• Omniscience valve
Bi-leaflet
• St. Jude valve
• 90% of market
• Carbomedics valve
• Edwards-Duromedics valve
• No longer available in US
(a)
(b)
(c)
(d)
The first animal implant: a bi-leaflet valve with a Dacron single-layer sewing ring.
A left atrial view of thrombotic occlusion two days after implantation in a dog.
A modified bi-leaflet valve with enhanced sewing ring and rearranged leaflets.
Thrombosis two days after implantation of the modified valve.
Bi-leaflet Valve – St. Jude
•
•
Cage - pyrolytic carbon
Sewing ring - velour
polyester
Non-rotatable (sutured)
• Rotatable
•
•
Valves - pyrolytic
carbon
Mechanical Valves:
Advantages / Disadvantages
Advantages
• High durability
• Mechanical heart valves placed
in young patients because they
typically last for the lifetime of
the patient
Disadvantages
• Increased risk of blood clotting
• Anti-coagulant drugs (sodium
warfarin)
• Suitable for people who do not
want additional valve
replacement surgery in the
future
Tissue (Biologically-derived) Valves
Xenografts
• Porcine
• Bovine
Allografts
Tissue (Biologically-derived) Valves
Porcine
•
•
Hancock (Medtronic,
Inc.)
Carpentier-Edwards
(Baxter, Inc.)
Bovine Pericardial
•
Carpentier-Edwards
Stentless
•
•
St. Jude Toronto
Medtronic
Porcine Valves
Hancock (Medtronic, Inc.)
•
•
•
Single porcine valve sewn
(glut. processed) into
polypropylene stent
Stent reinforced with CoCr-Ni alloy
Sewing ring-polyester
with silicone insert
Bovine Pericardium Valves
•
•
•
•
Carpentier-Edwards
Baxter Healthcare,
Edwards CVS
Division
Durability-12 years
Stented valve
•
Similar to porcine
valve except for
tissue used
Bovine Pericardium Valves
Advantages:
•
•
•
Good hemocompatibilty
40% of US tissue valves
Most often used to replace aortic valve because of
small size
Disadvantages:
Based upon experience with Ionescu-Shiley PC valve
6-8 year failure rate
• Tearing of pericardial tissue from stent posts (high
stress regions)
•
•
• Addressed by CE valves resulting in increased wear rate of
12 years
Porcine (Stentless) Valves
St. Jude Toronto
•
•
•
•
•
•
•
Removal of entire aortic
root and adjacent porcine
aorta as a block
Coronary arteries tied off
Entire unit implanted
Dacron covering for ease
of sewing/implantation
More blood flow through
valve due to lack of stent?
Difficult to implant
Special measurements
Human-derived Valves
Homografts
•
•
Cadaveric graft
No immunosuppression required
•
•
•
•
Donated valves preserved in liquid nitrogen
Thawed directly before transplant
Sizing must be predetermined by MRI
Limited supply
Tissue Valves: Disadvantages
•
•
•
•
Calcification
Wear and tear
Infection
10-15 years
Cardiac Valves
Jeffrey R. Scott, Ph.D.