Cardiovascular - Cardiac anatomy and function

Question 1

Define and describe the structure of intercalated discs

Answer 1

These are the structures between myocardial cells that allow for cardiac muscle to be electrically, chemically and mechanically coupled together as a ‘functional syncytium’

Structures within intercalated discs

1. Gap junctions - permit direct passage of molecules between cells –> no need for neurotransmission: electrical and chemical coupling
2. Fascia adherens - anchor actin filaments within the cell to the cell membrane
3. Macular adherens - (desmosomes) anchor cardiac cells to one another - mechanical coupling

Question 2

What are gap junctions

Answer 2

Structure within the intercalated discs. These are junctions between cells that permit direct passage of molecules between myocardial cells including intracellular ions and larger molecules. This allows direct electrical spread of action potentials from cell to cell without need for neurotransmission

Question 3

What is the fascia adherens

Answer 3

Structure within the intercalated disc. These anchor actin filaments within sarcomere of cardiomyocytes to the cell membrane

Question 4

What is the macular adherens

Answer 4

Structure within the intercalated disc, also known as desomosomes, that anchor cardiac cells to one another

Question 5

how are the aortic valve cusps kept away from the aortic walls and why is this important

Answer 5

eddies created by the sinuses of valsalva - prevent occlusion of the origins of the coronary arteries

Left coronary - originates left posterior sinus of valsalva (adjacent to left coronary cusp)

Right coronary - originates from left anterior sinus of valsalva (adjacent to right coronary cusp)

Question 6

Describe the path of the left coronary artery

Answer 6

1. Left posterior aortic sinus –> Lateral to pulmonary trunk –> left atrioventricular groove –> divides: 1. left anterior descending (inferiorly into anterior interventricular groove and anastomose at inferior border with posterior interventricular a. Many patients –> diagnonal and septal branches extend across the sternocostal surface of the heart and into the septum
2. left circumflex branch which proceeds in the AV groove towards the left border where it gives off a left obtuse marginal branches and then turns around to the posterior AV groove where it commonly anastomoses with the terminal end of right coronary artery.

Question 7

What does the left coronary artery supply

Answer 7

1. LV
2. LA
3. AV septum
4. Some of RA
5. Maybe SA node (40%)

Question 8

Describe the path of the right coronary artery

Answer 8

1. Left anterior aortic sinus –> passes between pulmonary trunk and RA –> Descends in the AV groove and gives off the following branches
   - SA branch (60% SA node)
   - Right marginal

continues along the AV groove posteriorly until it reaches the posterior interventricular groove where it
- posterior interventricular artery

Question 9

What does the right coronary artery supply

Answer 9

1. SA node (60%)
2 AV node (90%)
3. RA
4. RV
5. Postero-inferior portion of LV

Question 10

What does the left anterior descending artery supply

Answer 10

1. Anterolateral myocardium
2. Apex
3. Interventricular septum

Question 11

What does the left circumflex artery supply

Answer 11

1. SA node (40%)

2. Posterolateral LV

Question 12

What does the right marginal branch of the right coronary artery supply

Answer 12

The right ventricle

Question 13

What does the posterior interventricular artery supply

Answer 13

1. The posterior septum

2. AV node

Question 14

What is left dominance and in what % of the population does this exist

Answer 14

15% of population the posterior interventricular artery is supplied by the left circumflex artery rather than the right coronary artery

Question 15

Summarise the venous drainage systems of the heart

Answer 15

Coronary sinus (85% venous blood) - lies in the posterior part of the atrioventricular groove –> receives tributaries from 5 cardiac veins:

1. • The great cardiac vein (next to LAD)
2. • The middle cardiac vein (Next to PDA)
3. • The small cardiac vein (Next to RCA)
4. • The posterior vein of the left ventricle
5. • The oblique vein of the left atrium (along posterior surface of left atrium.
     All coalesce to form the coronary sinus

The Anterior Cardiac veins (minimal)
The Thebesian veins (causes of shunt)

Question 16

Describe the pathway of the veins that coalesce into the coronary sinus

Answer 16

The great cardiac vein - with LAD

The middle cardiac vein - with PDA

The small cardiac vein - with RCA

The posterior vein of LV

The oblique vein of LA (along posterior surface of LA)

Question 17

Describe the anterior cardiac veins

Answer 17

Arise on anterior RV

Drain into RA directly (not carotid sinus)

Question 18

Describe the Thebesian veins

Answer 18

Smallest
Drain directly into 4 chambers of heart
Predominantly in RA and RV
(Thebesians that drain into left contribute toward physiological shunt)

Question 19

Where does the coronary sinus open and where is it

Answer 19

Posterior aspect of heart adjacent to right coronary artery

The sinus opens into the right atrium between the inferior vena cava and the tricuspid valve

Question 20

What associated findings may be associated with inferior wall iscahemia

Answer 20

Inferior heart supplied by RCA
RCA often also supplies SA node
RCA also supplies RV

SA node –> bradycardia
RV –> hypotension (reduced LV preoload)

Question 21

What is the result of infarction in leads I, aVL, V5 and V6

Answer 21

Lateral wall ischaemia –> LV dysfunction

Question 22

What does STE/STD mean in V1 and V2

Answer 22

Septal ischaemia –> occlusion of septal branch of LAD

Question 23

What does STE/STD mean in V3 and V4

Answer 23

Apical ischaemia –> distal LAD

Question 24

What ECG findings will be present in anterior wall ischaemia

Answer 24

STE/STD: I, aVL, V1 —-> V6
LAD !
Associated with severe LV dysfunction

Question 25

What are the ECG findings in posterior wall ischaemia

Answer 25

STD in v1 —–> v4

STE in V7, V8, V9

Question 26

When is cardiac re-synchronization therapy and when is it indicated

Answer 26

EF < 35% and wide complex conduction defect –> CRT can improve atrial and ventricular synchrony through the use of three pacemaker wires

1. RA (via SCV –> SVC)
   2 RV (via SCV –> SVC)
2. LV (via SCV –> SVC –> coronary sinus and great cardiac vein)

Question 27

Compare Oxygen extraction in the heart and in skeletal muscle and state the implications of this

Answer 27

Skeletal muscle = 25%
Cardiac muscle = 65%

This makes the heart susceptible to ischaemia (less of a buffer or zone for compensatory increased O2 extraction)

Question 28

Is blood flow to the LV and RV continuous or intermittent. Describe the left coronary blood flow during systole and diastole –> graph

Answer 28

LV - Intermittent

• -> Nil perfusion during isovolumetric contraction
• -> During diastole –> dichrotic notch (systemic arterial elastance) –> sharp rise in coronary blood flow during diastole.

RV - continuous blood flow throughout cardiac cycle with a dip (not to zero) during isovolumetric contraction

Question 29

What is the mechanism for increased coronary blood flow in response to increased O2 demand?

Answer 29

Exercise –> increased cardiac work –> reduction cytosolic ATP –> increase AMP and Adenosine –> vasodilation –> coronary arterioles increasing coronary blood flow (also K, H, CO2 and NO)

Question 30

What is the autoregulatory range for coronary autoregulation

Answer 30

Coronary Perfusion Pressure 60 - 180 mmHg

Question 31

What is the effect of increased heart rate on coronary blood flow

Answer 31

Increase heart rate encroaches on the diastolic time more than on the systolic time resulting in decreased left coronary blood flow. Right coronary blood flow is relatively unaffected.

Question 32

Describe the autonomic control of coronary blood flow

Answer 32

Minor direct effect

PSNS –> weak Vd

SNS –> increase coronary blood flow due to increased O2 demand due to increased HR and inotropy

Question 33

How do nitrates improve coronary blood flow

Answer 33

1. VD coronary arteries
2. VD arterial beds –> reduced afterload –> O2 demand falls
3. VEnodilation –> reduced preolad –> O2 demand falls

So overall coronary blood flow is reduced (with demand)

Question 34

How do beta blockers affect coronary blood flow

Answer 34

1. Reduce HR –> reduce O2 demand. Increase diastolic time –> increased blood flow to LV
2. Inhibit inotropy by SNS –> reduced demand

Question 35

How do Ca channel blockers influence coronary blood flow

Answer 35

Nifedipine

1. –> coronary vasodilatation
2. Peripheral VD –> reduced afterload and reduced O2 demand

Question 36

How does the drug Nicorandil work with regard to coronary blood flow

Answer 36

K+ channel opener
Increased efflux of K out of cells –> hyperpolarization of cell membranes smooth muscle cells –> reduced cytosolic calcium –> smooth muscle relaxation of coronary vasculature. —> increased coronary blood flow