The coronary arteries arise from the aorta and supply blood to the heart muscle. The right coronary artery supplies parts of the right side of the heart while the left coronary artery supplies parts of the left side. Coronary blood flow increases during exercise to meet the higher oxygen demands of the heart. Coronary artery disease occurs due to atherosclerosis narrowing the arteries and reducing blood flow, which can lead to angina or myocardial infarction if blood flow is severely reduced.

3. • The main coronary arteries lie on the surface
of the heart and smaller arteries then
penetrate from the surface into the cardiac
muscle mass.
• It is almost entirely through these arteries
that the heart receives its nutritive blood
supply.

4. • Two coronary arteries (right and left) arise
from the root of ascending aorta and supply
blood to the myocardium.

5. Right coronary artery supplies blood to the
• Right ventricle,
• The right atrium,
• The posterior part of left ventricle,
• The posterior part of interventricular septum
• And major portion of the conducting system
of heart including SA node.

6. Left coronary artery supplies blood mainly to
• The anterior part of left ventricle,
• Left atrium,
• Anterior part of the interventricular septum
• And a part of the left branch of bundle of His.

7. • Predominant supply by the right coronary
artery described above is seen in about 50%
individuals.
• In 20% individuals the predominant supply to
myocardium is by left coronary artery.
• In 30% individuals it is the balanced supply,
i.e. equal supply by the two arteries.

8. • Normally, the coronary arteries appear to
function as end arteries.
• However, the presence of an arterial plaque
or occlusion allows the anastomoses present
between vessels to become functional.
• That is why they are also known as functional
end arteries and not true end arteries.

9. • Coronary sinus is a wide vein about 2 cm
long, which drains most of the venous blood
from the myocardium (mainly left ventricle)
into the right atrium.
•Anterior cardiac vein draining venous blood
mainly from the right ventricle opens directly
into the right atrium.

11. • A continuous flow of blood to the heart is
essential to maintain an adequate supply of
O2 and nutrients.
• The resting coronary blood flow in the resting
human being averages 70 ml/min/100 g heart
weight, or about 250 ml/min, which is about
5 percent of the total cardiac output.
• Three to six fold increase in the coronary
blood flow may occur during exercise.

12. • Oxygen consumption by the myocardium is
very high (8 mL/min/100 g at rest).
• Because of this, even at rest 70–80% of the
oxygen is extracted from each unit of the
coronary blood as compared to the whole
body (average of 25%) oxygen extraction at
rest.

13. • The increased oxygen demand of the
myocardium during exercise is met with by
almost total (nearly 100%) extraction of
oxygen and by manifold increase in the
coronary blood flow

14. • During systole, the tension developed in the left
ventricle is so high that it has throttling effect on
the branches of the coronary arteries penetrating
through them
• As a result, the average blood flow through the
capillaries of left ventricles falls to the extent
that during isometric contraction phase, the
blood flow to the left ventricle practically ceases,
i.e. becomes zero.

15. • During diastole, the cardiac muscles relax and
blood flow increases. Thus, most of the
coronary blood flow (over 70%) occurs during
diastole .

16. Nitrous oxide method (Kety method)
• Principle - Nitrous oxide method is the most
common method used for measuring coronary
blood flow. It gives almost accurate value and
is based on the Fick’s principle

17. • Procedure - The individual is made to inhale a
mixture of 15% nitrous oxide and air for 10
min.
• During inhalation of gases, serial samples of
arterial and coronary sinus venous blood
(through a catheter introduced) are taken at
fixed intervals for 10 min.

18. • The coronary blood flow (CBF) is then
determined from the amount of nitrous oxide
taken up per minute (N2O/ min) and the
difference of nitrous oxide content of arterial
(A) and venous (V) blood, i.e.
• CBF = N2O taken up/min
(A − V)

19. • Principle - The radioactive tracers are pumped
into cardiac muscle cells by the enzymes Na+–
K+ ATPase and equilibrate with the
intracellular K+ pool.
• Distribution of radioactive tracers is directly
proportional to myocardial blood flow and
this forms the basis of this technique

20. Coronary angiographic technique
Electromagnetic flowmeter technique

21. Autoregulation.
• Coronary circulation shows well developed
phenomenon of autoregulation
• 60-200 mmHg

22. • Metabolic local factors are the most important
factors which regulate the coronary blood flow.
• Direct effect of O2. It has been proposed that a
decrease in the tissue PO2 could also act directly
on the arterioles and cause vasodilation.
• Oxygen Demand as a Major Factor in Local
Coronary Blood Flow Regulation

23. • Adenosine is considered the major factor in
production of coronary vasodilation during
hypoxic states.
• In myocardial ischaemia

25. • Role of other local metabolites. Hydrogen
ions, bradykinin, CO2 and prostaglandins are
the other suggested vasodilator substances

26. • Autonomic nerves control the coronary blood
flow directly as well as indirectly.

27. • Parasympathetic nerve fibres to coronary
vessels through vagus are so less that the
parasympathetic stimulation has very little
direct effect, causing vasodilation

28. • Sympathetic nerve fibres extensively
innervate the coronary vessels.
• The transmitters released at their nerve
endings are epinephrine and norepinephrine.
• The net result of direct effect of sympathetic
stimulation is vasoconstriction.

29. Mean aortic pressure.
• Rise in mean aortic pressure increases the
blood flow and vice versa.
Emotional excitement.
• During emotional excitement states, the CBF
is increased due to increased sympathetic
discharge

30. Muscular exercise.
• Normal CBF at rest is about 70 mL/100 g
tissue/min. During exercise, CBF increases
about four times because of sympathetic
stimulation by the following mechanisms:
• Increased activity of heart
• Increased cardiac output (> 5 folds)
• Increase in mean arterial pressure

31. Hypotension.
• There occurs reflex increase in noradrenergic
discharge during hypotension which produces
coronary vasodilation to increase CBF.

32. Hormones affecting CBF are:
• Thyroid hormones increase CBF because of
increase in metabolism.
• Adrenaline and noradrenaline cause increase
in CBF indirectly.
• Acetylcholine may increase CBF by its action
on heart similar to parasympathetic
stimulation.
• Nicotine is reported to increase CBF through
the liberation of norepinephrine.

33. • Coronary artery disease (CAD) also known as
ischaemic heart disease results due to the
insufficient coronary blood flow.
• It is a condition associated with development of
atherosclerosis in the coronary arteries, which
supply the heart muscles (myocardium). With
atherosclerosis, the arterial wall is hardened and
its lumen becomes narrow due to plaque
formation

34. • Definition. Angina pectoris refers to a
transient form of myocardial ischaemia,
especially occurring during increased Oxygen
demand (e.g. during exercise) in patients with
coronary artery disease having about 60–70%
narrowing of coronary arteries.

35. Characteristic features.
• Typically, the angina is described as a feeling
of uncomfortable pressure, fullness,
squeezing or pain in the substernal region,
which may be localized or may be referred to
the inner border of left arm, neck or jaw.

36. • Myocardial infarction (MI) or acute myocardial
infarction (AMI), commonly known as a ‘heart
attack’ refers to a degree of myocardial
ischaemia (due to interruption of blood
supply) that causes irreversible changes
(necrosis i.e. cell death or infarction) in the
myocardium.

37. Signs and symptoms
• Sudden severe chest pain is a classical
symptom of MI. Pain lasts for more than 30
min and typically may radiate to left arm and
left side of neck.
• Associated symptoms with pain, often
complained by patients are shortness of
breath, nausea, vomiting, palpitation,
sweating and anxiety

38. • Approximately 25% of all myocardial infarction
are ‘silent’ i.e. without chest pain or other
symptoms. Silent MI usually occurs in
diabetics with associated autonomic
neuropathy in elderly.