Download Coronary circulation mgmc

Coronary circulation
Dr. S. Parthasarathy
MD., DA., DNB, MD (Acu),
Dip. Diab. DCA, Dip. Software statistics
PhD (physio)
Mahatma Gandhi medical college and
research institute , puducherry – India
• The left main and right coronary arteries arise
from the aorta behind the left and right aortic
valve leaflets
Right Coronary Artery (RCA)
•
•
•
•
•
•
•
•
•
•
The right coronary artery branches into:
Right marginal artery
Posterior descending artery
The right coronary artery supplies:
Right atrium
● Part of the left atrium
● Right ventricle
● Posterior interventricular septum
● Sino-atrial node (in 60%)
● Atrioventricular node (in 80%)
• Circumflex artery
• left anterior descending
• Left posterior descending
• Dominant ??
•
•
•
•
•
•
The left coronary artery supplies:
● Left atrium
● Left ventricle
● Anterior interventricular septum
● Sino-atrial node (in 40%)
● Atrioventricular node (in 20%)
•
•
•
•
•
•
Four veins lead into the coronary
sinus:
● Great cardiac
● Middle cardiac
Small cardiac
Oblique
• Penetrate
• epicardial plexus
• Subendocardial plexus
Blood flow
• The resting coronary blood flow in human
being averages about 225 ml /min, which is
about 4 to 5 percent of the total cardiac
output.
• Six to seven times CO increased yet the
coronary blood flow is increased 3 – 4 times
• 3- 4times is the Coronary reserve !!
Extraction high ??
• The energy requirements of the myocardium
are provided almost aerobically with little
capacity for anaerobic metabolism.
• During resting condition, 70 to 80 % of oxygen
carried by coronary blood is extracted by the
myocardium.
• Extraction cant increase on stress but the
cardiac output / coronary flow can increase
• Collateral channels are blood vessels
(usually small) which allow blood to
flow directly from one artery to another.
• A coronary collateral circulation may also arise
from different branches of the same coronary
artery or from branches of two different
coronary arteries
Collateral
• Usually negligible because the driving
pressure at the two ends of the anastomoses
is nearly equal.
• if the artery supplying one branch of this
collateral circulation becomes occluded, the
large pressure reduction will divert blood flow
through the patent artery and into the
distribution of the occluded artery through
these collateral vessels.
Micro circulation
• coronary microcirculation, formed by vessels
with < 300 microns in diameter.
• Rich network of capillaries
• One / myocyte
• But less in IV septum and AV node.
Micro circulation
Myocardial contrast echocardiography
• technique capable of providing information on the
anatomy and function of the microcirculation in vivo.
It employs an intravascular tracers with rheologic
properties similar to red blood cells. This tracers freely
flows into the coronary microcirculation, without ever
leaving the vascular compartment, and it is detectable by
ultrasound procedures during its passage into the micro
vessels.
Coronary circulation
• Coronary blood flow is phasic,
• In diastole
Phasic variations
• More for subendocardial vessels
• More for LV
•
•
•
•
•
•
•
The relative maintenance of
subendocardial blood flow
may also be related to the
extensive number of redundant
arteriolar and capillary
anastomoses
in the subendocardium.
Phasic more for left coronary
Coronary circulation
• Blood supply to the LV is directly dependent
on the difference between the aortic pressure
and LV end-diastolic pressure (coronary
perfusion pressure)
• inversely related to the vascular resistance to
flow,
• Two other determinants of coronary flow are
vessel length and viscosity
Assumptions
• The physiology of coronary blood flow is
based upon the assumption that coronary
arteries are non distensible tubes, and that
blood is a homogeneous fluid.
CPP = DBP – LVEDP … What happens
when ??
• LVH – end diastolic pressure rise – CPP
decrease
• Tachycardia – diastole time decrease – flow
decrease
• Aortic regurgitation – diastolic pressure
reduced - CPP decrease
CPP = DBP – LVEDP
Factors affecting circulation
• The myocardial metabolism is aerobic, an
• increased O2 demand quickly has to lead to
vasodilatation.
• The following factors are involved in the
coronary vasodilatation
REGULATION – metabolic factors
• Oxygen is a mild vasoconstrictor
• Hypoxia
vasodilation
AMP ---- MORE AMP – ADENOSINE
• Hypoxia
ATP
• Accumulation of lactate and H+ ions
• Prostacyclins
Neuro humoral factors:
• Nor epinephrine released from sympathetic
nerve endings and adrenal epinephrine have a
vaso dilatory effect on the distal coronary
vessels via beta 2 adrenoceptors.
Endothelial factors:
• ATP (e.g., from platelets),
• bradykinin, histamine and acetylcholine are
vasodilators.
• They liberate nitric oxide (NO) from the
endothelium, which diffuses into vascular
muscle cells to stimulate vasodilatation
Endocardial viability ratio
• EVR = DPTI / TTI = oxygen supply / demand
• 1 or above is ok
• 0.7 – subendocardial ischemia
EVR
Steal
• Coronary artery steal is an absolute decrease
in collateral dependent myocardial perfusion
at the expense of an increase in blood flow to
a normally perfused area of myocardium, as
may follow the drug-induced vasodilation of
coronary arterioles.
• Eg. Ischemia , collaterals , isoflurane
Normal – collateral - Steal
Summary
•
•
•
•
•
•
•
•
Anatomy
Extraction and flow
Collateral
Microcirculation
Phasic flow
Determinants
EVR
Steal
Thank you all
• Is it clear or have you to
Put fingers in the face
and get confused ??