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Physiology for Anaesthetists > Cardiovascular - Cardiac anatomy and function > Flashcards

Cardiovascular - Cardiac anatomy and function Flashcards

1
Q

Define and describe the structure of intercalated discs

A

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
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2
Q

What are gap junctions

A

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

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3
Q

What is the fascia adherens

A

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

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4
Q

What is the macular adherens

A

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

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5
Q

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

A

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)

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6
Q

Describe the path of the left coronary artery

A
  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.
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7
Q

What does the left coronary artery supply

A
  1. LV
  2. LA
  3. AV septum
  4. Some of RA
  5. Maybe SA node (40%)
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8
Q

Describe the path of the right coronary artery

A
  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

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9
Q

What does the right coronary artery supply

A 
1. SA node (60%)
2 AV node (90%)
3. RA
4. RV
5. Postero-inferior portion of LV
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10
Q

What does the left anterior descending artery supply

A
  1. Anterolateral myocardium
  2. Apex
  3. Interventricular septum
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11
Q

What does the left circumflex artery supply

A
  1. SA node (40%)

2. Posterolateral LV

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12
Q

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

A

The right ventricle

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13
Q

What does the posterior interventricular artery supply

A
  1. The posterior septum

2. AV node

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14
Q

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

A

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

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15
Q

Summarise the venous drainage systems of the heart

A

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

    • The great cardiac vein (next to LAD)
    • The middle cardiac vein (Next to PDA)
    • The small cardiac vein (Next to RCA)
    • The posterior vein of the left ventricle
    • 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)

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16
Q

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

A

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)

17
Q

Describe the anterior cardiac veins

A

Arise on anterior RV

Drain into RA directly (not carotid sinus)

18
Q

Describe the Thebesian veins

A

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

19
Q

Where does the coronary sinus open and where is it

A

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

20
Q

What associated findings may be associated with inferior wall iscahemia

A

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

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

21
Q

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

A

Lateral wall ischaemia –> LV dysfunction

22
Q

What does STE/STD mean in V1 and V2

A

Septal ischaemia –> occlusion of septal branch of LAD

23
Q

What does STE/STD mean in V3 and V4

A

Apical ischaemia –> distal LAD

24
Q

What ECG findings will be present in anterior wall ischaemia

A

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

25
Q

What are the ECG findings in posterior wall ischaemia

A

STD in v1 —–> v4

STE in V7, V8, V9

26
Q

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

A

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)
27
Q

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

A

Skeletal muscle = 25%
Cardiac muscle = 65%

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

28
Q

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

A

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

29
Q

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

A

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

30
Q

What is the autoregulatory range for coronary autoregulation

A

Coronary Perfusion Pressure 60 - 180 mmHg

31
Q

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

A

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.

32
Q

Describe the autonomic control of coronary blood flow

A

Minor direct effect

PSNS –> weak Vd

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

33
Q

How do nitrates improve coronary blood flow

A
  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)

34
Q

How do beta blockers affect coronary blood flow

A
  1. Reduce HR –> reduce O2 demand. Increase diastolic time –> increased blood flow to LV
  2. Inhibit inotropy by SNS –> reduced demand
35
Q

How do Ca channel blockers influence coronary blood flow

A

Nifedipine

  1. –> coronary vasodilatation
  2. Peripheral VD –> reduced afterload and reduced O2 demand
36
Q

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

A

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

Physiology for Anaesthetists (61 decks)

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