Cardiac stent

1. Unit 3
Cardiac Stents

2. Coronary artery
• Coronary arteries supply blood to
the heart muscle.
• The coronary arteries wrap around
the outside of the heart. Small
branches dive into the heart
muscle to bring it blood.
• Any coronary artery disorder or
disease can have serious
implications by reducing the flow
of oxygen and nutrients to the
heart muscle.
• This can lead to a heart attack and
possibly death.

3. • Atherosclerosis (a buildup of
plaque in the inner lining of
an artery causing it to
narrow or become blocked)
is the most common cause
of heart disease.
• Plaque consists of
cholesterol, fatty substances,
waste products, calcium and
the clot-making substance
fibrin.

4. Coronary Angioplasty
• Since the 1980s, a procedure has been used to open partially blocked
coronary vessels before they become totally occluded.
• This procedure, called coronary artery angioplasty.

5. • Coronary artery angioplasty performed as:
– A small balloon-tipped catheter, about 1 millimeter in
diameter, is passed under radiographic guidance into the
coronary system and pushed through the partially occluded
artery until the balloon portion of the catheter straddles (sit)
the partially occluded point.
– The balloon is then inflated with high pressure, which
markedly stretches the diseased artery.
– After this procedure is performed, the blood flow through
the vessel often increases threefold to fourfold.

6. Cardiac Stents
• Stents are small, expandable tubes that treat
narrowed arteries in your body.
• In people with coronary heart disease caused by the buildup
of plaque, they can:
– Open narrowed arteries
– Reduce symptoms, like chest pain
– Help treat a heart attack
• Usually made of metal mesh, they’re put into arteries after a
procedure to expand the artery called a percutaneous coronary
intervention (PCI) or, its more common name, angioplasty.

7. Stent
• Small stainless steel mesh tubes called “stents” are sometimes
placed inside a coronary artery dilated by angioplasty to hold the
artery open.
• Within a few weeks after the stent is placed in the coronary artery,
the endothelium usually grows over the metal surface of the stent,
allowing blood to flow smoothly through the stent.

9. Before & after angioplasty

10. • However, reclosure (restenosis) of the blocked coronary artery
occurs in about 25 to 40 percent of patients with stent replacement
• Restenosis is usually due to excessive formation of scar tissue that
develops underneath the healthy new endothelium that has grown
over the stent.
Restenosis

12. • Current research focuses on the reduction in deposition of
thick smooth muscle after stent placement.
• Substantial improvements have been made, including the use
of more biocompatible materials, anti-inflammatory drug-
eluting stents, resorbable stents, and others.
• Restenosis can be treated with a reintervention using the
same method.

13. Types Of Coronary Stents
• Currently, there are three types of stents available and
commonly called heart stents or cardiac or coronary stents.
1. Bare Metal Stent (BMS)
2. Drug-Eluting Stent (DES)
3. Bioresorbable Vascular Scaffold (BVS)
In 1986, French researchers implanted the first stent into a
human coronary artery. Eight years later, the FDA approved
the first heart stent for use in the U.S.

14. Bare Metal Stent (BMS)
• Bare metal stents (first-generation stent) are made of stainless
steel.
• Although they almost eliminated the risk of the artery
collapsing, they only modestly reduced the risk of re-
narrowing.
• About a quarter of all coronary arteries treated with bare-
metal stents would close up again, usually in about 6 months.

15. Drug-Eluting Stent (DES)
• Drug-Eluting Stents (DES) consist of a standard metallic stent,
a polymer coating, and an antirestenotic drug that is mixed
within the polymer and released over time.
• This prevent the growth of scar tissue in the lining of the
artery.
• This helps the damaged artery to remain smooth and open. It
ensures a good blood flow and reduces the risk of re-
narrowing or restenosis of the artery.
• Due to its slow healing process and risk of stent thrombosis
patients implanted with DES stent are on drug therapy (DAPT)
which helps to reduce the risk of blood clots (stent
thrombosis).

16. Sirolimus, Paclitaxel etc. are drug that inhibits vascular smooth-muscle-cell proliferation
/ scar tissue proliferation. To prevent restenosis.
• First-generation: DES include sirolimus-eluting stents (SES; 2003)
and paclitaxel-eluting stents (PES; 2004) (TABLE ).
• Second-generation DES, including zotarolimus- and everolimus-
eluting stents (ZES, EES), were approved for use in the United
States in 2008 (TABLE ).
• The newer stents, EES and ZES, are thinner and more flexible
and have a cobalt-chromium alloy platform, which makes them
more deliverable than the first-generation stents.
• These stents may also be more biocompatible, thereby
generating less inflammatory response and faster vessel
endothelialization.

17. • Although the underlying principle of DES remains constant, each
type may offer variations with respect to
• Deliverability (ease of placement),
• Efficacy (preventing restenosis) and
• Safety (thrombosis rates).

18. For Detail:
https://www.uspharmacist.co
m/article/drug-eluting-stents

19. Bioresorbable Vascular Scaffold (BVS)
• Bioresorbable Vascular Scaffold is similar in appearance to a stent,
but is a non-metallic, non-permanent, mesh implant which gets
absorbed gradually, dissolves over time and allows the artery to
function naturally again.
• This new scaffold disappears over 12-24 months and supports the
vessel until it has the ability and strength to stay open on its own.
• BVS is made of a material commonly used in other medical devices,
such as dissolving stitches.
• This material allows the BVS to break down into elements already
found in your body like water (H2O) and carbon dioxide (CO2),
enabling the artery to return to a more natural state.

20. Bioresorbable Vascular Scaffold (BVS)
• Like DES stents, BVS is also coated with a drug which releases
from a polymer that disappears after the work is done.
• It is approved by the FDA, and widely popular scaffold.
• It reduces the risk of re-narrowing (restenosis) the artery
again.
• The Absorb GT1 BVS, or Absorb, is the first commercially-
available FDA-approved absorbable coronary drug-eluting
stent, also known as a bioresorbable vascular scaffold.
• It consists of a bioresorbable polymer scaffold containing a
drug (everolimus) and bioresorbable polymer coating.
Fully bioresorbable vascular scaffolds: lessons learned and future directions, Nature
Reviews cardiology, 2019. https://www.nature.com/articles/s41569-018-0124-7

22. Unit 3
Valves

23. Heart Valves
Heart consists of:
Right (Atrium and Ventricle)
Left (Atrium and Ventricle)
Two Types of Valves:
Atrioventricular Valve: separates
the atrium from the ventricle
Semi-Lunar Valve: separates the
ventricles from the outgoing
blood vessels

24. Heart Valves
Right Atrioventricular Valve:
Tricuspid Valve
Left Atrioventricular Valve:
Bicuspid Valve
Right Semi-Lunar Valve:
Pulmonary Valve
Left Semi-Lunar Valve:
Aortic Valve
Purpose of Valves: Prevent
backflow, or flow of blood back
into chamber from which it came

25. Heart Valves
When Ventricle expands: atrioventricular
valve allows blood to flow forward to
the atrium into the ventricle while the
semilunar valve prevents blood from
flowing back in heart
When Ventricle contracts:
atrioventricular valve closes to prevent
backflow while semilunar valve allows
blood to body or lungs
Prevention of backflow: ensures the proper
direction of flow and reduces amount of
work heart must do to pump blood

26. When Heart Valves Stop Working
• Heart Valve diseases fall into two categories:
stenosis- hardening of the valve
incompetence- permittence of backflow
3 causes of Heart Disease:
Rheumatic Fever: stiffens valve tissue, causing stenosis
Congenitally defective valves: do not form properly as the heart
develops, but often go unnoticed until childhood
Bacterial infection: causes inflammation of valves, tissue scarring,
and permanent degradation

27. Prosthetic heart valve
• Any valve implanted to replace original
• Mechanical: Metal,
– Lifespan >20 years
– Lifelong anticoagulation agent warfarin, because of
coagulation risk
– costlier
• Bioprosthetic (made of biological tissue)
– Porcine valve, Pig
– Life span 10 years
– No Anticoagulation
– Older Patient

28. Mechanical Valves
• STARR-EDWARDS VALVES
– Ball in a Cage, High risk clots
• TILTING DISC VALVE
– Single disc
– Tilts
• ST JUDGE’S VALVE
– Bileaflet valves
– Two discs
– Least risk clots

29. • The Starr–Edwards caged ball prostheses,
commercially available at the present time, was
successfully implanted in the mitral position in
1961.
• This design uses a spherical occluder, or
blocking device, held in place by a welded
metal cage
• The caged ball prostheses is made of a polished Co–Cr alloy (Stellite
21®) cage and a silicone rubber ball (Silastic®) which contains 2% by
weight barium sulfate.
• The valve sewing rings use a silicone rubber insert under a knitted
composite polytetrafluorethylene (PTFETeflon ®) and polypropylene
cloth.

30. • Natural heart valves allow blood to flow straight through the center
of the valve (central flow)
• Caged-ball valves completely blocked central flow and collisions
with the occluder ball caused damage to blood cells
• Finally, these valves stimulated thrombosis, or formation of blood
clots
• The relatively large profile design of caged ball or disc construction
also increases the possibility of interference with anatomical
structures after implantation.

31. Mechanical Valves:
Single Leaflet Disc Valves
• Uses a tilting occluder disk to
better mimic natural flow
patterns through the heart
• tilting pattern allow more
central flow while still
preventing back flow
• Some damage still occurs to
blood cells
• Reduces thrombosis and
infection, but does not eliminate
either problem

32. Bjork-Shiley Standard Aortic Valve
Model: Bjork-Shiley Standard
Type: Aortic Tilting Disc
Materials: Disk-Pyrolytic
Carbon, cage-Haynes 25,
sewing ring-Teflon
HAYNES® 25 alloy is a cobalt-nickel- chromium-tungsten alloy that combines excellent
high-temperature strength with good resistance to oxidizing environments

33. Bjork-Shiley Valve:
Initial Fracture Assessment
• Investigators determined that the
floating disc opens and slams shut
at least 70 times per minute or 40
million times per year, causing
fatigue failure
• Although changes were made,
fractures continued to occur
• Finally, in 1984, Shiley discovered
the source, known as “Bimodal
Closure Phenomenon”

34. Mechanical Valves:
Bileaflet Disc Heart Valves
• Consists of two semicircular
leaflets that pivot on hinges
integrated onto the flange
• Carbon leaflets and flange
exhibit high strength and
excellent biocompatibility
• Provide closest
approximation to central flow
• Allows small amount of
backflow as leaflets cannot
close completely

35. St. Jude Bileaflet Valve
Model: St. Jude Valve Standard
Design :Mitral, Aortic, Tricuspid
Bileaflet Valve
Materials-Cage and disk-
pyrolytic carbon, sewing ring-
double velour knitted
polyester

36. Complication with Mechanical Valve
• Thrombus formation
– Blood Stagnates, slowing of blood flow
– Risk of Embolus, an unattached mass that travel through
the bloodstream and capable of creating blockage
– Stroke
• Infective Endocaroitis
– Infection in valve
– High mortality
• Haemolysis
– Blood churned in Valve
– Break down RBCs (Anaemia, Low Hb)

37. Animal Tissue Valves
• Heterograft or Xenograft
Vavles
• A transplant of tissue
taken from one species
and grafted into another
• Most commonly used
tissues are the porcine
(pig) valve tissue and
Bovine (cow) pericardial
tissue

38. Porcine (pig) Valves
• Two major brands of
porcine available today,
Hancock and Carpentier-
Edwards
• Has good durability and
and good hemodynamics
• Materials: Porcine valve
tissue, stents made of wire,
Elgiloy(cobalt-nickel alloy),
sewing ring-knitted Teflon

39. Pericardial (cow) Valves
• Lasts as long as standard
porcine valves at 10 years
• The pericardial valve has
excellent hemodynamics,
even in smaller
sizes(19mm to 21mm)and
has gained a large market
share (about 40% of US
tissue valves) in this group
of patients

40. Homografts (Human to Human)
• Homografts are valves transplanted from one human to
another
• After donation, valves are preserved in liquid nitrogen
(cyropreserved) until needed
• Since the valve must be thawed overnight, the patient’s size
must be known beforehand
• As with heart transplants, homograft availability is limited by
donor availability

41. Animal Tissue Valves vs. Mechanical Valves
• With the animal tissue, patients do not need lifelong
anticoagulant therapy required with mechanical valves
• Animal tissue is also inexpensive and mass-produced
• However, animal tissue has uncertain durability (5-15 years)
that will inevitably require a risky re-operation
• Mechanical valves can also fail suddenly and catastrophically
• Have serious problem with thromboembolism