ICL 1.3: Anatomy of Coronary Artery & Conduction System

Question 1

what are the coronary arteries?

Answer 1

the “coronary arteries” are the vessels that bring the blood to the heart muscle

the heart receives no nourishment from blood inside chambers!! the supply of oxygen and nutrients to the heart is from the coronary arteries which is why they’re so important!!

Question 2

where do the coronary arteries originate from?

Answer 2

the 2 coronary artery ostia are located in the center of the left and right aortic sinuses (Sinus of Valsalva) of the aortic valve

the left coronary artery originates from the left aortic sinus where as the right originates from the right aortic sinus

Question 3

what is the course of the right coronary artery?

Answer 3

the right coronary artery emerges from the aorta into the AV groove which is full of fat

it then descends through the groove, then curves posteriorly and continues downward in the posterior interventricular sulcus which is also full of fat

Question 4

what is the course of the left coronary artery?

Answer 4

it is a very short vessel!!

the left coronary artery (left main coronary artery) emerges from the aorta through the ostia of the left aortic cusp within the sinus of Valsalva

then the left coronary artery travels from the aorta, and passes between the pulmonary trunk and the left atrial appendage

then under the appendage the artery divides into the:

1. anterior interventricular artery (left anterior descending artery) (LAD)
2. left circumflex artery

Question 5

what are the branches of the right coronary artery?

Answer 5

1. marginal branch of the right coronary artery**
2. posterior interventricular branch of the right coronary artery (posterior descending artery, PDA)
3. SA nodal branch of the right coronary artery

Question 6

what are the branches of the left coronary artery?

Answer 6

1. circumflex branch of the left coronary artery

posterior interventricular branch of circumflex branch of left coronary artery

2. anterior interventricular branch of the left coronary artery (LAD)

Question 7

what supplies blood to the SA node?

Answer 7

SA node receives blood from the SA nodal branches of the right and left coronary arteries

55% right, 45% left

Question 8

what supplies blood to the AV node?

Answer 8

usually the AV node artery gets its blood supply from the right coronary artery

the AV Node Artery is a major contributor to the arterial supply of the atrioventricular conducting pathway and is an important vessel in the pathogenesis of heart block

Question 9

what supplies blood to the papillary muscle in the left ventricle?

Answer 9

the anterior papillary muscle more frequently receives two blood supplies:

1. LAD (left anterior descending artery)
2. LCX (left circumflex artery)

the posterior papillary muscle is usually supplied only by the PDA

Question 10

what supplies blood to the papillary muscle in the right ventricle?

Answer 10

the anterior papillary muscle more frequently receives two blood supplies:

1. LAD
2. right coronary artery

the posterior papillary muscle is usually supplied by the PDA, right coronary artery, and septals

the septal papillary muscle is usually supplied by 1st, 2nd, 3rd septal arteries

Question 11

what is the crux cordis?

Answer 11

the point where the coronary sulcus meets the interatrial and interventricular sulci

this cross is important in determining coronary dominance

Question 12

what is right dominance?

Answer 12

the right coronary artery supplies the right ventricle, posterior half of the septum and the left posterior ventricle

most people have right coronary dominance!

Question 13

what is balanced dominance?

Answer 13

each ventricle is supplied by the corresponding artery

this is because the two arteries don’t reach the crux cordis!

Question 14

what is left dominance?

Answer 14

the circumflex artery supplies the left ventricle, half of the septum and the right posterior ventricle

this is because the circumflex is the one that crossed the crux cordis!

Question 15

what is collateral circulation in the heart?

Answer 15

a network of tiny blood vessels, which under normal conditions, are not open; there isn’t communication between the right and left circulation in the heart

collateral vessels may enlarge and become active –> this can happen when the coronary arteries narrow to the point that blood flow to the heart muscle is impaired

this allows blood to flow around the blocked artery to another artery nearby or to the same artery past the blockage, protecting the heart tissue from injury

ex. if the right coronary artery is obstructed, the left or the circumflex will start to send some branches to supply that area! this only happens if there’s a long period for it to do so, it won’t happen during acute heart problems

Question 16

what are extramural and intramural coronary arteries?

Answer 16

the left and right coronary arteries and their branches lie on the surface of the heart, and therefore are sometimes referred to as the epicardial coronary vessels

these vessels distribute blood flow to different regions of the heart muscle

when the vessels are not diseased, they have a low vascular resistance relative to their more distal and smaller branches that comprise the microvascular network

as in all vascular beds, it is the small arteries and arterioles in the microcirculation that are the primary sites of vascular resistance, and therefore the primary site for regulation of blood flow

the arterioles branch into numerous capillaries that lie adjacent to the cardiac myocytes

a high capillary-to-cardiomyocyte ratio and short diffusion distances ensure adequate oxygen delivery to the myocytes and removal of metabolic waste products from the cells (e.g., CO2 and H+)

Question 17

when does blood flow through the coronary arteries?

Answer 17

diastole!

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Question 18

how does the the myocardial oxygen supply and demand work?

Answer 18

if you’re in a place of high elevation and you have normal cardiac circulation but mild obstruction of the coronary arteries, you won’t have enough oxygen in machu pichu!

Question 19

what is a myocardial infarction?

Answer 19

obstruction of each major coronary artery results in infarction of specific areas of the myocardium

LAD supplies the wall of the left ventricle which is important for pumping blood through the body so that’s why the LAD is called the widow maker

Question 20

which veins drain the heart?

Answer 20

the anterior interventricular vein will drain into the great cardiac vein and then into the coronary sinus which returns to the right atrium

the middle cardiac vein in the posterior interventricular septum is in the sulcus with the posterior descending coronary artery which drains into the coronary sinus as well

1. great cardiac vein
2. middle cardiac vein
3. small cardiac vein
4. anterior interventricular vein

Question 21

what is the coronary sinus?

Answer 21

a collection of veins joined together to form a large vessel that collects blood from the myocardium of the heart

Question 22

what is the valve of the coronary sinus?

Answer 22

a semicircular fold of the lining membrane of the right atrium, at the orifice of the coronary sinus

it can be absent, double or perforated

Question 23

which veins drain into the coronary sinus?

Answer 23

1. anterior interventricular vein –> great cardiac vein
2. middle cardiac vein
3. small cardiac vein

then the coronary sinus in the posterior coronary sulcus drains to the right atrium directly!

Question 24

what is the conduction system of the heart?

Answer 24

a group of specialized cardiac muscle cells in the walls of the heart that send signals to the heart muscle causing it to contract

Question 25

which structures are part of the conduction system of the heart?

Answer 25

1. SA node
2. AV node
3. bundle of His
4. bundle branches
5. purkinje fibers

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Question 26

what is the SA node? where is it located?

Answer 26

SA = sinuatrial node

it’s the pacemaker of the heart and initiates heart beat!!

it’s located along upper end of sulcus terminalis, near the superior vena cava

the SA node is supplied by both sympathetic and parasympathetic nerves

Question 27

where is the AV node located?

Answer 27

the atrioventricular node is located in interatrial septum adjacent to ostium(opening) of coronary sinus

located in interatrial septum adjacent to ostium of coronary sinus inside the Triangle of Koch

Question 28

where is the bundle of His located?

Answer 28

the atrioventricular bundle extends from the AV node along the interventricular septum and ends in the Purkinje fibers

then the AV bundle divides into right and left bundle branches in the septum near junction of membranous and muscular part of septum

Question 29

what are the 4 interatrial/internodal conduction tracts?

Answer 29

1. Bachmann’s bundle
2. anterior intermodal tract (James’)
3. middle internal tract (Wenckebach’s)
4. posterior internodal tract (Thorel’s)

these are all in the RA and originate from the SA node!

Question 30

what is Bachmann’s bundle?

Answer 30

SA node to left atrium

it’s the interatrial/internodal conduction tract that originates in the sinoatrial node and is the only tract that conducts action potentials to the left atrium

Question 31

what is James’ tract?

Answer 31

SA node to AV node

interatrial/internodal conduction tract that runs from the SA node anteriorly around the superior venae cava to join Bachmann’s bundle and continues to join the superior end of the AV node

Question 32

what is Wenckebach’s tract?

Answer 32

interatrial/internodal conduction tract that from the SA node directly to the AV node passing thru the middle margin of the crista terminalis

Question 33

what is Thorel’s tract?

Answer 33

interatrial/internodal conduction tract that runs from the posterior margin of the SA node along the crista terminalis and Eustachian ridge around the coronary sinus ostium into the posterior margin of the AV node

Question 34

what is the AV node?

Answer 34

an electrical relay station between the atria and the ventricles

electrical signals from the atria must pass through the AV node to reach the ventricles

the AV node serves as a gate that slows the electrical current before the signal is permitted to pass down through to the ventricles

this delay ensures that the atria have a chance to fully contract before the ventricles are stimulated

Question 35

what is the bundle of His?

Answer 35

a collection of heart muscle cells specialized for electrical conduction that transmits the electrical impulses from the AV node to the point of the apex of the fascicular branches

Question 36

what is the course of the bundle of His?

Answer 36

the bundle of His branches into the three bundle branches: right, left anterior and left posterior

the bundle branches run along the interventricular septum

then the bundles give rise to thin filaments known as Purkinje fibers which distribute the impulse to the ventricular muscle

the bundle branches and Purkinje network comprise the ventricular conduction system!

Question 37

if your SA node isn’t working, which other parts of the heart can act as ectopic pacemakers?

Answer 37

1. atria
2. AV junction
3. ventricles

Question 38

what are the intervals seen in an EKG?

Answer 38

P wave: the sequential activation (depolarization) of the right and left atria

QRS complex: right and left ventricular depolarization (normally the ventricles are activated simultaneously)

ST-T wave: ventricular repolarization

U wave: origin for this wave is not clear - but probably represents “after depolarizations” in the ventricles

PR interval: time interval from onset of atrial depolarization (P wave) to onset of ventricular depolarization (QRS complex)

QRS duration: duration of ventricular muscle depolarization

Question 39

what is the sympathetic innervation of the heart?

Answer 39

upper thoracic spinal cord, through sympathetic chain to cardiac nerves

directly to ventricular myocardium

can raise heart rate to 230 bpm

Question 40

what is the parasympathetic innervation of the heart?

Answer 40

right vagal nerve to SA node

left vagal nerve to AV node

vagal tone normally slows heart rate to 70 - 80 bpm

Question 41

what is the cardiac plexus?

Answer 41

the cardiac plexus receives contributions from both the sympathetic and parasympathetic systems!

the superficial plexus located near the aortic arch gets input from the left inferior cervical branches of CN X and the superior cervical sympathetic branches

the deep plexus located near the tracheal bifurcation gets sympathetic input and parasympathetic input from CN X

Question 42

why do you get referred pain of the heart in the left arm?

Answer 42

nerves from the heart and nerves from the arm synapse together on the middle cervical ganglion before traveling up the spinothalamic tract to the brain

the innervation of the skin in the arm comes to the same middle cervical ganglia as the heart

the brain has to decide where the pain is coming from but there are more nerve endings in your arm so your brain just decides the pain is more likely to be coming from the arm