LEFT INTERNAL MAMMARY ARTERY

Introduction
LIMA as conduit has proved to be superior and better for early and late survival after CABG.
It is a first choice conduit because of its superior biologic characteristics, unparalleled long term patency, better clinical outcomes.
Anatomy
•    1. It arises from first portion of subclavian artery.
•    2. Travels downwards on the inside of ribcage from approximately a centimeter from sternum.
•    3. It is accompanied by IT vein.
•    4. It divides into musculophrenic artery and the superior epigastric artery at 6th ICS.
•    5. RITA is closer to sternal margin.
Branches
•    1. Mediastinal branches
•    2. Thymic branches
•    3. Pericardiophrenic artery
•    4. Sternal branches
•    5. Perforating branches
•    6. Twelve anterior intercostal branches, two on each side
•    7. Musculophrenic artery
•    8. Superior epigastric artery
Characteristics:
•    1. It has resistance for atherosclerosis development, may be because of resistance of endothelium for injury.
•    2. The internal elastic lamina
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inhibits cellular migration
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prevents initiation of intimal hyperplasia.
•    3. Also, medial layer is thin with few SMCs
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less proliferative response to mitogens like platelet derived growth factor and pulsatile muscular stretch.
•    4. Endothelium of ITA is unique. It produces vasodilators nitric oxide and prostacyclin in abundance
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So has favorable response to drugs in postop period
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eg. Milrinone – dilates it, noradrenaline – does not constrict it, NTG vasodilates it but not SVG.
•    5. “Downstream” effect on the coronary vasculature
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coronary target appears protected distal to anastomosis
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due to this endogenous secretion of vasodilators.
•    6. “Re modelling” seen in ITA
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adapts to demand for flow by this diameter.
•    7. It increases flow in same way as normal coronary by increse in velocity and caliber mediated by endothelium.
Blood supply to:
•    1. ITA supplies blood to pericardium, phrenic nerve, sternum, anterior chest wall, pectoralis major, mammary gland, anterior abdominal wall, diaphragm.
•    2. Pedicle harvesting: into pedicled, semi skeletonized, skeletonized.
Sprayed / wrapped in papavarine solution.

Skeletonization – Only artery is mobilised leaving internal thoracic venous plexus intact, leads to decrease in sternal ischaemia which is seen on LIMA harvest.
In semiskeletonized
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ITA and veins also mobilized
Skeletonization has advantages:
•    1. It increases luminal diameter and free flow compared to pedicled graft.
•    2. Provides larger conduit
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allows more sequential grafts
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more targets are revascularized.
Limitations of skeletonization:
Concerns regarding vascular integrity, vasoreactivity and patency.
Patency:
They demonstrated decreases in MI / reoperation / cardiac events in LIMA.
Patency    LIMA –> LAD    SVG -> LAD
1 yr                 98%                87%
4 yr                 91%                83%
10 yr               95%                61%
15 yr               88%                32%

- by Dr Amarja