Lecture – 8
DR ZAHOOR ALI SHAIKH
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CORONARY CIRCULATION
Heart is supplied by TWO CORONARY
arteries:
1- Right coronary artery---(RCA)
2- Left coronary artery---(LCA)
 These coronary arteries arise at the root
of the aorta.

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Coronary artery & their branches
LCA---- -Lt Anterior Descending (LAD)
-Marginal Artery
-Circumflex Artery
 RCA ---- -Marginal Artery
-Posterior descending
branch

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Left coronary artery (LCA) –Divides in
Anterior Descending (LAD)
Circumflex artery
LAD--- Supplies anterior and apical
parts of heart ,and Anterior 2/3rd of
interventricular septum.
 Circumflex branch-- supplies the lateral
and posterior surface of heart.

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Right coronary artery(RCA) supplies:
 Right ventricle
 Part of interventricular septum (posterior
1/3rd)
 Inferior part of left ventricle
 AV Node
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Diagram of coronary circulation
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
Venous return of Heart
Most of the venous blood return to
heart occurs through the coronary sinus
and anterior cardiac veins, which drain
into the right atrium
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Blood flow to Heart during Systole &
Diastole
 During systole when heart muscle
contracts it compresses the coronary
arteries therefore blood flow is less to
the left ventricle during systole and more
during diastole.
 To the subendocardial portion of Left
ventricle it occurs only during diastole
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
As we know blood flow to
subendocardial surface of left ventricle
during systole is not there, therefore,
this region is prone to ischemic damage
and most common site of Myocardial
infarction.
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
Coronary blood flow to the right side is
not much affected during systole.
Reason---Pressure difference
between aorta and right ventricle is
greater during systole than during
diastole, therefore more blood flow to
right ventricle occurs during systole.
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
CORONARY
BLOOD FLOW
DURING
SYSTOLE
AND
DIASTOLE
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
Effect of Tachycardia on coronary blood flow:
During increased heart rate, period of
diastole is shorter therefore coronary blood
flow is reduced to heart during tachycardia.
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
Other causes of decreased blood flow to
left ventricle
1-Aortic stenosis
Reason---As left ventricle pressure is
very high during systole, therefore, it
compresses the coronary arteries more.
2-When aortic diastolic pressure is low,
coronary blood flow is decreased
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CORONARY BLOOD FLOW
Coronary blood flow in Humans at rest is
about 225-250 ml/minute, about 5% of
cardiac output.
 At rest, the heart extracts 60-70% of
oxygen from each unit of blood delivered
to heart [other tissue extract only 25% of
O2.

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CORONARY BLOOD FLOW
Why heart is extracting 60-70% of O2?
 Because heart muscle has more
mitochondria, up to 40% of cell is
occupied by mitochondria, which
generate energy for contraction by
aerobic metabolism, therefore, heart
needs O2.
 When more oxygen is needed e.g.
exercise, O2 can be increased to heart
only by increasing blood flow.
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
Factors Affecting Blood Flow to
CORONARY ARTERIES
-Pressure in aorta
-Chemical factors
-Neural factors

NOTE—Coronary blood flow shows
considerable Autoregulation.
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Chemical factors affecting Coronary blood
flow

Chemical factors causing Coronary
vasodilatation (Increased coronary blood flow)





-Lack of oxygen
-Increased local concentration of Co2
-Increased local concentration of H+ ion
-Increased local concentration of k + ion
-Increased local concentration of Lactate,
Prostaglandin, Adenosine, Adenine nucleotides.
 NOTE – Adenosine, which is formed from ATP
during cardiac metabolic activity, causes coronary
vasodilatation.
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Neural factors affecting Coronary Blood
Flow
1. -Effect of Sympathetic stimulation
2. -Effect of Parasympathetic stimulation

Sympathetic stimulation
 Coronary arteries have
 Alpha Adrenergic receptors which mediate
vasoconstriction
 Beta Adrenergic receptors which mediate
vasodilatation
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Sympathetic stimulation------Cont
 Effect of sympathetic stimulation in intact
body---Epinephrine and Norepinephrine
causes VASODILATATION.
HOW ?
 But the Direct effect of sympathetic on
Coronary arteries is VASOCOSTRICTION.
WHY ?

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
Effect of Parasympathetic stimulation
 -Vagus nerve stimulation (Parasympathetic)
causes coronary vasodilatation
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NEUTRIENT SUPPLY TO
HEART

Heart uses primarily free fatty acids and
to lesser extent glucose and lactate for
metabolism.
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CORONARY ARTERY HEART DISEASE
ISCHEMIC HEART DISEASE (IHD) (ANGINA
PECTORIS)
 MYOCARDIAL INFARCTION

ANGINA PECTORIS:
 THERE IS REDUCED CORONARY ARTERY BLOOD
FLOW DUE TO ATHEROSCLEROSIS
(CHOLESTROL DEPOSITION
SUBENDOCARDIALLY -- Plaque)
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CAUSES OF IHD:
 CIGARETTE SMOKING
 HYPERTENSION
 DIABETES MELLITUS
 INCREASED LIPIDS ( CHOLESTROL)
 OTHER FACTORS: LACK OF EXERCISE,
ANXIETY etc.
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IHD:
 IHD IS USED TO DESCRIBE DISCOMFORT IN
THE CHEST DUE TO DECREASED CORONARY
BLOOD FLOW (TRANSIENT MYOCARDIAL
ISCHEMIA).
 PATIENT COMPLAINS OF TIGHTNESS OR PAIN
IN THE MIDDLE OF CHEST (RETROSTERNAL)
FOR FEW MINUTES. PAIN OFTEN RADIATES TO
INNER SIDE OF LEFT ARM.
 PAIN IS PRECIPETED BY EFFORT AND
RELIEVED BY REST.
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MYOCARDIAL INFARCTION (MI):
 IT IS DUE TO OBSTRUCTION TO THE CORONARY
BLOOD FLOW, ATLEAST 75 % OF LUMEN OF
CORONARY ARTERY IS BLOCKED BY THROMBUS.
 MI IS THE COMMEN CAUSE OF DEATH.
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Applied Aspect
THE C A D.
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Electrocardiographic changes during
exercise test. Upper trace – significant horizontal ST
segment depression during exercise.
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
INVESTIGATIONS:
 ECG
 CARDIAC ENZYMES e.g. CK, LDH, TROPONIN etc.
 ECHOCARDIOGRAPHY
 TREADMILL EXERCISE TEST
 THALLIUM STRESS TEST
 CORONARY ANGIOGRAPHY
 NOTE:
○ ECG CHANGES IN IHD:
 ST DEPRESSION OCCURS IN ECG IN RESPECTIVE LEADS
○ ECG CHANGES IN MI:
 ST ELEVATION OCCURS IN ECG IN RESPECTIVE LEADS
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TREATMENT:
 CORONARY DILATORS E.g. NITRATES
 BETA-BLOCKERS
 ANGIOPLASTY (DILATE AREA OF
CONSTRICTION)
 STENT
 BYPASS SURGERY
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Percutaneous transluminal coronary angioplasty (PTCA). (a) Coronary
angiography demonstrates a severe stenosis in the proximal left anterior
descending artery. (b) During PTCA a soft guidewire is passed across the
stenosis and then a balloon is expanded that dilates the stenosis. (c)
Post-PTC
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An intracoronary stent.
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CORONARY ARTERY BYPASS
SURGERY
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THANK YOU
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