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 cellssuch as macrophages and smooth muscle cells along withnecrotic 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 foraortofemoral bypass having 5- to 10-year patency rates of 90%– The saphenous vein (superficial vein in the leg) is typically removedsurgically and moved to the site needed to bypass blockages in thecoronary circulation (for coronary artery bypass grafting)

Vascular graft research• Resolving one problem may introduce another• Eliminating the underlying cause of the chronic foreign bodyresponse by using resorbable materials• Introduction new elastomers• Implanting dense, tissue-engineered tubes of smooth musclecells• 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 thatcommunicates with the intravascular space)• Intimal hyperplasia, and structural degeneration

Stent implantation often followsballoon 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 filterVenous thromboembolic disease: Significant cause of mortality due to the complication ofpulmonary embolism Formation:– Thrombus detached from the wall of the vein– Travel through the inferior vena cava to the right side of theheart– Embolus in one of the large branches of the pulmonaryArtery

• 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 rightventricular 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