Transcript heart valve prosthesis - New Technologies Research Center (NTRC)

Cardiovascular Implants
• The total cost (direct and indirect) for CVD in the
United States was almost 450 billion USD in 2008
• CVD is also the leading cause of death worldwide
and is projected to remain so for decades
HEART VALVE PROSTHESIS
Heart valves open and close over 40 million times a year
and they can accumulate damage sufficient to require
replacement in many individuals.
More than 80,000 replacement valves are implanted
each year in the United States .
There are many types of heart valve prostheses and they
are fabricated from carbons, metals, elastomers, plastics,
fabrics and animal or human tissues
HEART VALVE PROSTHESIS
Generally, almost as soon as the valve is implanted, cardiac
function is restored to near normal levels and the patient
shows rapid improvement.
In spite of the overall success seen with replacement heart
valves, there are problems that may differ with different
types of valves; they include induction of blood clots,
degeneration of tissue, mechanical failure, and infection.
Coronary heart disease
Atherosclerosis
• A chronic, progressive, multifocal disease of the vessel wall
intima
• Affects the large elastic arteries and large and medium-sized
muscular arteries
• At points of branches, sharp curvatures
• Mature atherosclerotic plaques consist of:
– A central core of lipid and cholesterol crystals and cells
such as macrophages and smooth muscle cells along with
necrotic debris, proteins and degenerating blood elements
• Complications of atherosclerosis:
– Obstruction of a vascular
– Disruption of a plaque followed by thrombus formation
– Destruction of the underlying vascular wall
Atrial Septal Defect closure that will close the hole in the heart wall.
Vascular grafts
• Synthetic grafts:
– Perform well in large-diameter, high-flow, low-resistance locations
such as the aorta
– Synthetic small-diameter vascular grafts (<6 to 8 mm in diameter)
generally perform less well with 5-year patency less than 50%
• Natural grafts:
– The iliac and proximal femoral arteries, with grafts used for
aortofemoral bypass having 5- to 10-year patency rates of 90%
– The saphenous vein (superficial vein in the leg) is typically removed
surgically and moved to the site needed to bypass blockages in the
coronary circulation (for coronary artery bypass grafting)
Vascular graft research
• Resolving one problem may introduce another
• Eliminating the underlying cause of the chronic foreign body
response by using resorbable materials
• Introduction new elastomers
• Implanting dense, tissue-engineered tubes of smooth muscle
cells
• Endothelium detachment in vein grafts
• Surface modifications for:
– Prevent coagulation, prevent platelet adhesion/aggregation,
promote fibrinolysis, inhibit smooth muscle cell
adhesion/proliferation, and promote endothelial cell adhesion
and proliferation.
Example:
The 5.0-mm ID, 7-cm-long graft implantation in the
common carotid artery
• advantages over polyester and Teflon:
elasticity and ease of handling
Major complications of vascular grafts
• Failure of small-diameter vascular prostheses due to:
– Occlusion by thrombus formation
– Fibrous hyperplasia (excessive cell reproduction)
• Thrombosis
• Thromboembolism
• Infection
• Pseudoaneurysm (an extravascular hematoma that
communicates with the intravascular space)
• Intimal hyperplasia, and structural degeneration
Stent implantation often follows
balloon angioplasty
Characteristics of an ideal stent ?
• Ability to hold on the balloon catheter supported by a guide wire
• Good expandability ratio
– After insertion at the target area and the balloon is inflated, the stent should
undergo sufficient expansion and conform to the vessel wall
• Sufficient radial strength
– Implanted, the stent should be able to overcome the forces imposed by the
atherosclerotic arterial wall and should not collapse
• Sufficient flexibility
– It should be flexible enough to travel through even the smaller diameter
atherosclerotic arteries
• Adequate radiopacity/magnetic resonance imaging (MRI) compatibility
– To assist clinicians in assessing the in-vivo location of the stent
• Thromboresistivity
– The material should be blood compatible and not encourage platelet adhesion
and deposition
• Drug delivery capacity
– Essential requirements for stents of the modern era to prevent restenosis
Future Stents
• Material used for making stents:
– Mechanical properties
– Suitable surface characteristics
– Excellent haemo-compatibility
– Good biocompatibility
– Drug delivery capacity
• Drug eluting stent: future of coronary stents: FDA approved
• Percutaneous transluminal coronary angioplasty cannot be
performed without damaging blood vessels and eliciting
restenosis
– Drug elution at the target site is a clear solution to this problem.
• Developing new polymer materials
– Hemocompatibility, hydrophobicity, anti-inflammatory, conformability
to the stent size, sterilizability and biodegradability
Intravascular filter
Venous thromboembolic disease:
Significant cause of mortality due to the complication of
pulmonary embolism Formation:
– Thrombus detached from the wall of the vein
– Travel through the inferior vena cava to the right side of the
heart
– Embolus in one of the large branches of the pulmonary
Artery
• Therapy:
– Anticoagulation drug such as warfarin and/or heparin
– High risk of bleeding
• Vena caval filters: (A): A, The stainless steel Greenfield filter; B,
the
• modified-hook titanium Greenfield filter; C, the bird’s-nest filter; D,
the Simon nitinol filter; E, the Vena Tech filter (alloy of cobalt,
chromium). (B): Photo of vena caval filter at autopsy demonstrating
some thrombus at the filter site
• RAPEASE® Permanent Vena Cava Filter
• OPTEASE® Retrievable Vena Cava Filter
• Pulmonary Valved Conduit
• Contegra®
– Natural alternative for reconstruction
or replacement of the natural right
ventricular outflow tract (congenital heart valve defects)
– An animal jugular vein that
contains a valve with three leaflets (to correct or reconstruct
the path that blood takes to travel from the heart to the lungs).
– Similar to a human heart valve.
Pacemaker