2. • It has been just over 100 years since Alexis Carrel first described the concept of operating
on the coronary circulation.
Over this time CABG has gone through three distinct eras :
1st Experimental period, 2nd Vein graft era, and the Current era
of mixed venous and arterial grafting.
• Alexis Carrel was one of the first surgeons to appreciate the relationship
between angina and obstructive coronary artery disease.
• The LITA was used in humans as early as 1945 by Arthur Vinberg, who implanted it directly
in the myocardium of the LV, the “Vinberg Procedure”.
• Robert H. Goetz performed the first successful clinical
CABG on May 2, 1960 using a non-suture technique
to connect the RITA to the coronary artery.
Alexis Carrel
3. • Vasilii Kolesov, who is believed to have been the first to perform a sutured
anastomosis of an internal mammary artery to the left anterior descending artery
25 February 1964.
• Michael DeBakey, who led his team to perform a saphenous vein aorto-coronary
bypass with a continuous suture technique on 23 November 1964.
• Rene Favaloro, who was the first to systematically perform CABG with reproducible
results and is considered to be “the father of bypass surgery”.
4. Arterial Conduit :
Autologous
• Right and left Internal thoracic artery
• Radial artery
• Inferior epigastric artery
• Splenic artery
• Gastroduodenal artery
• Left gastric artery
• Intercostal artery
Non- Autologous
• Bovine Internal thoracic artery.
6. Histology of Blood vessel :
Three coats or Tunica, except in capillaries.
1. Tunica Intima
The internal elastic lamina contains fenestrations.
That allows passage in for perfusion & migration of cells.
7. 2. Tunica Media
Dense connective tissue layer.
Thicker in arteries than in vein.
Smooth muscle are more in arteries.
The external elastic lamina is thinner and
with few fenestrations.
3. Tunica Adventitia
The connective tissue continues and fueses
with the stroma of the organ system.
It may contains vasa vasorum.
8. The tunica intima and adventitia are longitudinally arranged where as the media is
circular.
The endothelium is lined by squamous cells, and secrets chemical mediators for :-
• Diapedesis (leukocytes)
• Blood coagulation (thromboplastin & VW factor, prostaglandins)
• Vascular tone (nitric oxide, EDRF).
Nourishment of blood vessel :
Small & medium blood vessel have their nutrient & gaseous exchange by direct
diffusion from the lumen. A wall thickness up to 350 microns can be easily perfused
through diffusion.
In larger vessel the inner part, up to middle of T. media is by simple diffusion but the
outer layers are by specialized arterioles/venules called vasa vesorum.
10. Internal Thoracic / Mammary Artery (ITA/IMA) :
Origin : From the inferior aspect of the first part
of subclavian artery opposite the thyrocervical trunk,
about 2-3 cm above the sterno-clavicular jn.
Course:
• Above the first costal cartilage, it runs downwards,
forward and medially behind the SC jn.
• Related posterior to subclavian v & phrenic N.
• Below the first costal cartilage, it runs down along
the lateral to edge of sternum.
• Its termination in the 6th ICS by dividing into the
superior epigastric and musculophrenic arteries.
11. Relationships
Anteriorly – Upper six costal cartilages and the internal intercostal muscles of the
spaces.
Posteriorly – Sternocostalis muscle.
12. Branches:
1. Pericardio-phrenic artery – arises at the root of neck and accompanies the phrenic
nerve.
Supplies pericardium and pleura
2. Mediastinal arteries – irregular branches supply the thymus & mediastinal soft
tissue.
3. Two anterior intercostal arteries per space in upper six ICS.
4. Perforating branches to the anterior chest wall.
In females 2,3,4 perforators supply the breast.
5. Superior epigastric artery enters the rectus sheath at the 7th cartilage.
6. Musculophrenic artery runs down and laterally behind the costal cartilages and
gives anterior intercostal arteries.
13. Histology of the ITA :
1. Lined with typical arterial endothelium.
2. Internal elastic lamina has fewer and smaller fenestrations.
3. The media contains fewer smooth muscle cells and 5-9 elastic lamellae.
4. The proximal and distal end 10 to 20 % contains fewer elastic lamellae, and
usually none are distal to the bifurcation.
5. The adventitia contains dense collagen fibers and loose alveolar tissue that
contains adequate vasa vasorum.
6. Wall thickness is about 200 μm, which is well under the 350 μm that can be
nourished by diffusion from the lumen.
14. Features of IMA suitable as coronary conduit :
1. It is a artery of medium-small caliber, with predominant elastic component,
especially in its
proximal part.
2. It has preserved network of vasa vasorum, residual periadventitial connective
tissue, and
nervous fibers without plexus.
This outlines ITA as a “living” conduit even after its skeletonization.
3. There is a weak possibility of spasms in response to adrenergic stimuli.
But, the endothelial integrity secures the reflex release of nitric oxide and other
vascular
relaxing factors.
4. The prevalent elastic fibers explains its good compliance and increased cross-
sectional
15. 5. As an arterial conduit, it is used to arterial pressures therefore lesser intimal
hyperplasia
is seen in longer duration.
6. The anatomical location is suitable for coronary grafting.
7. Suitable diameter – 3.5 mm matches coronary.
8. The intact endothelium produces EDRF (NO) and prostacyclin thus resistant to
spasm and
blockage.
9. Interestingly, it is rarely affected by atherosclerosis.
It has been observed that the degenerative process of elastolysis causes
fragmentation in fibers of the tunica media and internal elastic membrane.
But here, this is followed generation of muscle-like cells which is not of vascular
origin. Thus there is no migration on vascular smooth muscle cells through the
lamina.
16. Role NO in vascular hemodynamics :
NO is produced by the enzyme nitric oxide synthetase and it relaxes the smooth
muscle
tissue by promoting the synthesis of cGMP
.
The ITA endothelium releases more prostaglandin I-2 (prostacyclin)
and shows greater NO mediated vasodilation than veins.
Extraluminal NO causes relaxation of vascular smooth muscle.
Intraluminal NO inhibits platelet aggregation & adhesion.
Downstream travel of NO from the ITA can cause coronary
vasodilation.
Because NO inhibits mitogenesis and smooth muscle proliferation,
17. In ITA Histamine is a potent stimulus for NO release.
Serotonin-induced vasoconstriction is inhibited by NO.
The serotonin from platelets, mast cells and damaged endothelium are implicated in
acute coronary spasm and may contribute to venous graft spasm but are unlikely to
cause ITA spasm.
Harvesting Techniques :
1. Intra thoracic 2. Extra thoracic.
1. Pedicle graft : There is an entire pedicle of veins, muscle and fascia.
Conventional technique, simple and feasible for daily practice.
However, the wide-pedicled graft with surrounding muscle and
fascia has
limited arterial length, especially in case of multiple anastomoses.
18. 2. Skeletonization : Only the artery is isolated.
Improve conduit flow with larger vessel diameter, has increased
length,
and can reduce risk of deep sternal infection specially in
diabetic pts.
However, the skeletonization can cause injury to the artery,
require
more time and skill.
3. Semi skeletonized: With just accompanying veins.
Semi skeletonization provides a lean-
pedicled graft with max length,
without lengthening the operative time.
19. Perioperative spasm : IMAs with poor perioperative flow rates are more likely to
occlude.
An adequately dilated IMA graft facilitates proper placement of
sutures.
To relieve the spasm vasodilating substances are applied to the outside of the pedicle
or can be injected intra-luminally with or without hydrostatic dilation.
Hydrostatic dilation with papaverine and saline provides good dilation but carries
risk of
mechanical damage to the media and intima caused by cannulation and
overstretching and chemical damage (acidity).
Blood with dissolved papaverine was less acidic and thus preferred.
20. Grafting strategy :
Unilateral :
A. LIMA to LAD - Well accepted, gold standard.
B. LIMA to circumflex (marginal branches).
C. RIMA to RCA, RIMA to LAD.
Bilateral :
1. RIMA to LAD + LIMA to LCx marginal branches.
2. LIMA to LAD + RIMA through transverse sinus LCx marginal br.
3. Composite Y graft with free RIMA to LIMA.
With LIMA to LAD and RIMA to Cx marginal branches.
1. 2.
3.
21. Patency :
LITA to LAD = 92 to 97 percent at end of 1st year.
88 to 96 percent at 5 years
88 to 93 percent at 10 years.
RITA patency is less by 5 to 10 percent
(but if only RITA to LAD is considered, patency rates are comparable.)
The failure rate for ITA grafts is 0.5 to 1.0 percent per year between 1st yr and 10th yr.
Unlike saphenous vein grafts, ITA grafts rarely develop arteriosclerosis.
Less than 4% of ITA have clinical evidence of arteriosclerosis, and less than 1% have
significant luminal narrowing by the end of 1st year.
(Data from : Long-Term Results of Internal Thoracic 12 Artery Grafting J.F. Sabik III, F.D. Loop, Arterial Grafting for Coronary Artery Bypass
Surgery, https://link.springer.com/)
22. Factors influencing conduit patency
a) Intimal fracturing and thrombosis.
b) Profound spasm with secondary thrombosis.
c) Faulty anastomotic technique.
d) Severe calcific coronary disease.
e) Competitive coronary flow causing thrombosis.
24. Radial Artery :
Alain Carpentier first used the RA in 1971.
However, within 2 yrs there were reports of early failure &
significant intimal hyperplasia, which resulted in almost
complete abandonment of its use as a graft.
Techniques of early RA skeletonization combined with the use of mechanical
dilatation resulted in vessel trauma and spasm and subsequent early graft failure.
Christopher Acar in 1992, used a more refined “no-touch” method of harvesting &
used pharmacological vasodilatation.
This better understanding of graft physiology and protection of the endothelium led to
100% RA patency on early postoperative angiography.
A number of RCT that have compared the RA to SVG and free RITA as the graft for non-LAD targets
showed the RA to have superior patency on 5-year angiographic follow-up.
(RAPS (Radial Artery Patency Study), Radial Artery Versus Saphenous Vein Patency – RSVP trails)
25. Origin and course:
The radial & ulnar arteries originate as a bifurcation
of the axillary A in the cubital fossa.
It runs along the lateral aspect of the forearm between
the brachioradialis and flexor carpi radialis muscles.
Proximal to the wrist, it splits into
the superficial & deep palmar branch
forming an anastomosis with the distal
branches of the ulnar artery in the hand
(Palmer Arches).
26. Histology of RA :
It is a medium sized muscular artery.
With relatively more fenestrations in the
elastic laminas.
T. Media has more smooth muscle cells
than elastic fibres.
T. adventitia has more fatty-fibrous tissue
and less concentration of vasa vasorum.
27. Features of RA suitable as coronary conduit :
PROS :
• It has an adequate length to reach any coronary vessel.
• Proper diameter (2–3 mm without size mismatch to the coronary arteries).
• Robust structure, and relative resistance to kinking.
• Has higher patency rates compared to SVGs.
• Superficial anatomical location and easy to manipulate surgically.
• Can be harvested with the IMA and SV at the same time.
• Is less risky for sternal wound infection and mediastinitis.
28. CONS :
• The tendency for vasospasm is its most important negative characteristic.
• Elastic laminae have multiple fenestrations. This is the reason why the RA presents
a
vulnerability to atherosclerosis.
• Diabetes mellitus and renal dysfunction aggravate vascular wall morbidity leading
to intimal hyperplasia in RA grafts.
• It produced less NO than the ITAs.
• Intense reactivity to endothelin I, angiotensin II, nor-epinephrine, serotonin etc,
released after any endothelial damage or platelet aggregation.
This possibly also explain its spastic character.
• Flow competition phenomenon with mildly stenotic native coronary arteries is
common in RA grafts (string sign).
29. RA harvesting technique :
RA harvest can be: 1. Open or Endoscopic.
2. Pedicled or Skeletonized.
Conventional harvesting is with the accompanying veins and fat, minimal handling,
limited use of electrocautery. Avoiding probing or hydrostatic dilation.
Modified harvesting technique using ultrasonic scalpel / harmonic scalpel , can cut
and coagulate causing minimal thermal injury of the graft.
Endoscopic harvesting technique
A 3 cm incision on the wrist crease, parallel to the RA.
7 mm scope, the harvesting cannula and bipolar scissors
are used.
Vasoview 7 System
30. Skeletonization of the RA is superior to the pedicled technique in terms of patency
rates.
However, there are also disadvantages, such as irreversible injury to the RA or
spasms.
Management of RA conduit spasm :
The gold standard to prevent RA spasm is systemic administration of systemic
diltiazem,
in combination with topical papaverine.
The intraluminal injection of warm arterial blood and papaverine is also favored.
Other topical RA antispasmodic in clinical use are calcium channel blockers,
verapamil with nitroglycerin (VG solution), and phenoxybenzamine.
Avoidance of cold saline or ice slush in the pericardium is also significant to prevent
spasm.
31. Preoperative exclusion criteria for RA harvesting :
Allen test is the most widely used clinical test for preoperative evaluation of
sufficient ulnar collateral circulation to the hand.
A Barbeau test using a pulse oximeter on (1st or 2nd finger), contributes to assure an
intact palmar arch observing the pulse and saturation.
Doppler study not only allows for the evaluation of the ulnar collateral circulation to
the hand, but also for the preoperative assessment of RA.
33. Patency & Comparison :
RA conduits appear to be superior to SV grafts in terms of early and late mortality
and morbidity, and also in long term survival and freedom from cardiac events.
Graft patency
Short term = 96–100%,
Mid term= 94–97%
Long term = 84–96%
Radial Artery vs. Saphenous Vein Graft Patency (RSVP) trial proved that the graft patency of the RA to the circumflex coronary artery at 5 years
(98.3%) was better than that of the SV (86.4%) and graft narrowing happened in 10% and 23% of patent RA and SV grafts, respectively.
(Kaplan-Meier estimates of event-free survival and over all survival of RA vs. SV patients
Results of a randomized trial. Eur J Cardiothorac Surg 2008;34:113-7)
34. Complications after RA harvesting :
Most common are bleeding, hematomas and wound infection.
Sensory nerve injuries, causing sensory abnormality and numbness in 3–10% of
patients.
Motor impairments are usually a early finding.
Less common is hand ischemia.
35. Right Gastroepiploic Artery :
The GEA is the largest & terminal branch of the gastroduodenal A.
It runs along the posterior surface the prox duodenum, anterior of
the pancreas head, then along the greater curvature of the stomach.
Bailey et al in late 1960s used RGA for indirect myocardial
revascularization for the posterior or inferior wall of the heart.
Direct anastomosis of GEA to the RCA was attempted by Sterling Edwards in early
1970s.
Histologically it is very similar to ITA.
This artery undergoes less arteriosclerosis and demonstrates physiological
adaptability as seen in ITA.
36. GEA is more strongly contracted by KCl, serotonin, and norepinephrine than the ITA,
therefore it is important to prevent spasm of the GEA provoked by platelet
aggregators, adrenergic stimulation, or depolarizing agents.
GEA harvesting technique :
Median sternotomy incision is extended to the xiphoid & umbilicus.
After harvesting the pedicle is raised up through the hole in the
diaphragm passing the liver and the stomach anteriorly, and the end
of the pedicle is fixed to the anterior edge of the diaphragm.
Grafting strategy :
As a in situ graft to RCA or
as free graft as per requirement.
37. Patency
Perrault et al with 51 right gastroepiploic in situ grafts with a patency rate of 90% in
prior to hospital discharge.
At the end of 1st year patency rate of 80% .
With improvement in technique Suma et al showed a10 year patency 87%.
38. Inferior Epigastric Artery :
The inferior epigastric artery is a branch of the FA.
Passes supero-medially from inguinal canal towards the midline.
In 1988, Puig et al. reported the use of the IEA as a bypass conduit.
PROS :
Its superficial course makes harvest easy.
Near perfect match with the branches of RCA or LCx.
Resistance to arteriosclerosis. Its internal elastic lamina has minimal fenstrations.
CONS :
Proximal anastomosis is difficult, wall thickness mismatch. So, composite graft is preferred.
The most frequent complication is an abdominal or retroperitoneal hematoma
Although rare, cases of skin and rectus muscle necrosis are reported.
Its use is favoured on unavailability or unsuitability of
SVG or IMA or RA or a desire of preserving one IMA for the future.
40. Course :
Formed by the dorsal venous arch of the foot, and the dorsal vein
of the great toe.
It ascends up the medial side of the leg, passing anteriorly to the
medial malleolus, and posteriorly to the medial condyle at the knee.
It receives tributaries from other small superficial veins.
The great saphenous vein terminates by draining into the
femoral vein immediately inferior to the inguinal ligament.
41. Histology of the GSV :
The wall of the saphenous vein contains a thin intima, separated from the media by a rudimentary internal
membrane.
The media consists of two distinct layers of muscle cells, outer circular with abundant collagen fibers and inner
longitudinal with few elastic fibers. The longitudinal muscle layers continues into the valve of the veins.
Prominent tunica adventitia with poor vasa vasorum.
The elastic lamina is very poor and interrupted.
42. As a conduit :
PROS :
1. Superficial and easy to harvest.
2. Less time consuming.
3. Suitable size.
4. Adequate length can be easily achieved.
5. Less scaring, quick healing and less complications.
CONS :
1. Development of Vein Graft Disease.
2. Low potential to secrete intrinsic NO & prostacyclin.
3. Not adapted to high arterial pressures.
4. Poor intra luminal perfusion, and thus skeletonized graft can be considered a “dead graft”
5. Diseased veins.
Contraindications :
Varicosities, DVT, PVD, skin disease, diabetic ulcers, recent leg trauma etc.
Diagnostic tests : Doppler, venography and mapping.
43. Harvesting Techniques :
1. Open technique - Continuous incision.
- Interrupted bridging skin incision.
2. Endoscopic.
Harvest with adequate fat pad.
Maintain a proper luminal uniformity.
Avoid hydrostatic dilation, blood is preferred.
Excessive pressure may cause intimal injury.
44. Saphenous Vein Graft Disease
Saphenous vein graft disease is composed of three discrete processes:
1. Thrombosis, 2. Intimal hyperplasia, 2. Atherosclerosis.
1. Thrombosis
About 3%-12% within the 1st month.
Combination of alterations in the vessel wall, blood coagulability, and flow dynamics.
The harvesting of venous conduits is associated with focal endothelial disruption.
Loss of the endothelial monolayer results in the accumulation of fibrin on the
surface, the adherence of platelets and neutrophils.
It also activates the extrinsic coagulation cascade by tissue factor that is
expressed in the exposed sub-endothelium.
Inherent anti-thrombotic properties of veins are comparatively weak.
45. 2. Intimal Hyperplasia
Intimal hyperplasia, defined as the accumulation of smooth muscle cells and extracellular
matrix in the intimal compartment.
Major disease process b/w 1month to1 yr, which may reduce the lumen by 25% & above.
Initially, medial smooth muscle cells proliferate in response to growth factors and cytokines
from platelets, endothelial cells and macrophages.
This followed by migration of smooth muscle cells into the intima.
Later synthesis and deposition of extracellular leads to a progressive increase in intimal
fibrosis.
Explained by transient ischemia to the veins during explanation and reperfusion after grafting.
Loss of the vasa vasorum blood supply, on which veins are relatively more dependent than
arteries, may also promote a continuing cycle of ischemia and fibrosis
46. 3. Atherosclerosis
Dominant process beyond the first year after bypass surgery.
Angiographic studies indicate that among patients who had unstable angina, the culprit
lesion in
70% to 85% of cases is an atherosclerotic vein graft stenosis with thrombosis.
Chronic endothelial cell injury and dysfunction lead to rapidly progressive nature of the
atherosclerotic.
Vein graft atheroma has more foam cells and inflammatory cells, including multinucleate
giant cells suggestive of immune-mediated atherosclerosis.
Morphologically, vein graft atherosclerosis tends to be diffuse, concentric, and
friable with a poorly developed or absent fibrous cap and little evidence of calcification,
promoting plaque rupture and thrombosis.
47. Risk factors for vein grafts disease :
a) Smoking
b) Hypertension
c) Diabetes
d) Dyslipidemia (T triglyceride and cholesterol)
e) Female gender
48. Recent Advances :
The e SVS mesh is a flexible extravascular nickel-titanium mesh designed to
reinforce SVGs exposed to the higher arterial pressure in CABG.
It give some physiological attributes of an artery to the SV grafts, thus claimed to
prevent reactive intimal hyperplasia.
Although long-term patency studies are not yet available, first safety reports and
short-term results have been recently published are encouraging.
49. Alternative conduits for CABG
The ideal graft characteristics :- Non-thrombogenic, Sufficient mechanical
strength, Similar compliance to native vessels, Spontaneous
endothelialisation, Resistance to intimal hyperplasia and Compatibility with
the host tissue.
PTFE : Inert fluorocarbon polymer, non-biodegradable, electronegative luminal
surface that is anti-thrombotic. Widely used in lower-limb bypass grafts (7–9 mm)
with excellent results.
In CABG, these grafts are found to be rigid compared with the elastic host artery.
This poor mechanical compliance and the lack of endothelial cells (ECs) lining the
lumen are major factors contributing to their poor patency.
Dacron : Polyester of multiple filaments either woven or knitted into vascular grafts.
50. Attempts to improve synthetic grafts have included embedding them with anti-
thrombotic drugs like heparin, hirudin, tissue factor pathway inhibitor, non-
thrombogenic phospholipids.
Others : Cryopreserved allograft veins, Autologous endothelialized vein allograft,
Synthetic biomaterials and polyurethanes & tissue engineered grafts.
Currently only considèred when traditional autologous conduits are unavailable or
unsuitable.
In the future, the search for an ideal coronary bypass conduit "off the shelf” will
continue
to evolve.
