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Foundation Year MBChB > Electrophysiology of CVS > Flashcards

Electrophysiology of CVS Flashcards

1
Q

What is the anatomy of the heart?

A

Superior Vena Cava
Inferior Vena Cava
Right Atrium
Tricuspid Valve
Right Ventricle
Pulmonary Valve
Pulmonary Artery
Pulmonary Vein
Left Atrium
Mitral Valve
Left Ventricle
Aortic Valve
Aorta

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2
Q

What is the difference between the heart’s chambers?

A

The atria are the receiving chambers of the heart and receive blood
The ventricles are the discharging chambers of the heart and discharge blood from the heart

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3
Q

Why is there an anatomical difference between the ventricles of the heart?

A

The left ventricle is thicker than the right ventricle as it pumps blood to the entire body and so need more force
Left has more cardiac cells

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4
Q

How is blood oxygenated via the heart?

A

Superior vena cava carries deoxygenated blood from the head, neck and upper limb
Inferior vena cava carries deoxygenated blood from lower parts of the body
Deoxygenated blood from the right atrium enters the right ventricle through the tricuspid valve
Deoxygenated blood form the right ventricle enters the lungs through the pulmonary artery
Oxygenated blood from the lungs is supplied to the left atrium
Oxygenated blood from the left atrium enters the left ventricle through the mitral/bicuspid valve
Arch of aorta arises from left ventricle which pumps oxygenated blood to all parts of the body

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5
Q

What are the three types of events of the cardiac cycle and how can they be measured?

A

Electrical: ECG (read to find out what is occurring electrically)
Mechanical: Pressure and volume changes
Acoustic: Heart sounds (first and second)

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6
Q

What is the definition of membrane potential?

A

The difference in charge between the inside and outside of the cell

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7
Q

What is the definition of polar?

A

Having ‘“poles” both positive (+) and negative (-) poles/sides

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8
Q

What is the definition of depolarisation?

A

Membrane potential going from more negative to less negative (or positive)
The difference in charge across the membrane, i.e. the poles, getting smaller

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9
Q

What is the definition of repolaristation?

A

Becoming polarised again
Positive and negative sides become more different

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10
Q

What is the definition of ion channels?

A

Proteins which act as openings to let specific ions move through
May be “gated”- open in response to certain stimuli

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11
Q

What is a key difference between cardiac muscle and skeletal muscle?

A

Skeletal muscle is stimulated by the nervous system, but cardiac muscle is stimulated by its own electrical stimulation

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12
Q

How is a cardiac contraction initiated?

A

By the generation of action potentials at SA (Sino-atrial) nodes

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13
Q

What does depolaristion of the cardiac cells cause?

A

Electrical activity across the atria and down to ventricles (apex of the heart) which causes cardiac contraction

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14
Q

What is the meaning of automaticity?

A

The generation of a spontaneous action potential by cardiac cells
Is not identical in all parts of the heart

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15
Q

How does the SA node compare to the other components of the heart?

A

The SA node has the highest degree of automaticity and so generates the impulses at the highest frequency and so suppresses all the other elements

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16
Q

Can other elements take over if the SA node was suffering difficulties with automaticity?

A

Yes, but at an expense of a lower heart rate

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17
Q

What is the heart rate that each element generates due to its automaticity?

A

SA node: 60-100 bpm
AV node: 40-60 bpm
Bundle of His: 40 bpm
Purkinje fibres: 15-20 bpm

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18
Q

When are some moments that the AV node may takeover from the SA node to maintain heart function?

A

Heart attack as SA node may not function properly
Blockage in artery (AV node receives no oxygen so won’t function)

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19
Q

What is the location of the SA node in the heart?

A

Autorhythmic cells (main pacemaker) in the right atrium near the entry of superior vena cava

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20
Q

What is the location of the AV node?

A

Autorhythmic cells near the floor off the right atrium

21
Q

How is the action potential conducted to the AV node from the SA node?

A

Internodal pathways connect SA & AV nodes
Electrical activity spreads rapidly to AV node via internodal pathways
Depolarization spreads more slowly across atrial muscle
Conduction slows within AV node (allows atria to completely empty)

22
Q

What happens if there is an internodal delay?

A

Herat block, first degree

23
Q

How is the action potential conducted from the AV node to the Purkinje fibres?

A

Action potentials pass into Bundle of His
(Wall of the septum between the ventricles)
Bundle divides into left & right bundle branches
Fibres continue downward and divide into many small Purkinje fibres that spread outward among the contractile cells
Will then go to the base of ventricles (apex of heart) and so cause contraction of the heart

24
Q

What do the different waves on an ECG represent?

A

P wave: Atrial depolarisation
QRS complex: Ventricular depolarisation and atrial repolarsation
T wave: Ventricular repolarisation
PR interval: Delay in the AV node; atria electrical activity
QT interval: Ventricular electrical activity

25
How is the cardiovascular generally regulated?
Local: auto-regulation Neural: automatic nervous system Humoral: numerous constrictors and dilators
26
What are the mechanisms of hormone release?
Humoral: in response to changing levels of ions or nutrients in the blood Neural: stimulation by nerves Hormonal: stimulation received from other hormones
27
What occurs if there is a change in stroke volume?
A change in heartbeat
28
What are the two nervous systems that the heart is associated with, and what are they broadly responsible for?
Parasympathetic nervous system: rest and digest Sympathetic nervous system: fight or flight
29
What is the function of the automatic nervous system?
Consists of motor neurones that: Innervate (supply with nerves) smooth muscle, cardiac muscle, internal organs and skin Makes adjustments to ensure optimal support for body activities Operates via subconscious control (sometimes changes)
30
How is visceral activity controlled?
Most visceral organs are innervated by both sympathetic and parasympathetic fibres, which results in dynamic antagonisms that precisely control visceral activity
31
How can heart activity be controlled by both sympathetic and parasympathetic fibres?
Sympathetic fibres: Increase heart and respiratory rates, and inhibit digestion and elimination Parasympathetic fibres: Decrease heart and respiratory rates, allows for digestion and discharging of waste
32
How do catecholamines affect heart rate?
Sympathetic effect so increases heart rate Increases slope of pacemaker potential Increasing rate of depolarisation by increasing Ca^2+ entry
33
How does acetylcholine affect heart rate?
Parasympathetic affect so decreases heart rate Reduces slop of pacemaker potential Hyperpolarises pacemaker cell membrane (increasing K^+ removal) via muscarinic receptors
34
What is electrophysiology on a cellular level?
Rapid signals can be sent through the body via action potentials Changes in the voltage across cell membrane (membrane potentials) Caused by the entry/exit of ions (Atoms/molecules with extra or fewer electrons) Ions entering/leaving make the inside of the cell more positive or negative
35
What are action potentials?
Rapid depolarisations and repolarisations in the cell membrane, via voltage gated ion channels, which are transmitted down the length of the cell
36
What are cardio myocytes and what are their function?
Cardiac muscle cells Conduct the signal through the heart using action potentials whilst also contracting
37
How is the action potential conducted in cardiac muscle?
Signal passes through gap junctions of intercalated discs, where the cytoplasm is continuous between cells
38
What is Phase 0 of the cardiomyocyte action potential?
Phase 0 - Depolarisation Action potential from SA node opens fast Na+ channels Large, but transient (1-2 msec), increase in Na+ permeability - Na+ enters Accompanied by dramatic reduction in K+ conductance - prevents K+ efflux and repolarization
39
What is Phase 1 of the cardiomyocyte action potential?
Phase 1 – Early Repolarisation Fast Na+ channels close Membrane potential begins to fall - reflects partial repolarization
40
What is Phase 2 of the cardiomyocyte action potential?
Phase 2 - Plateau Despite closure of fast Na+ channels, potential remains positive or near 0 for ~300 msec Largely due to opening of voltage-gated slow Ca2+ channels Ca2+ entry is involved in excitation-contraction coupling
41
Why is there a plateau in phase 2?
Na+ influx from slow Na+ channels Slow leakage of K+ out of cell keeps potential from rising
42
What is Phase 3 of the cardiomyocyte action potential?
Phase 3 - Repolarisation Intracellular K+ moves down concentration gradient - leaves cell causing it to repolarize Repolarization facilitated by closure of Ca2+ and slow Na+ channels
43
What is Phase 4 of the cardiomyocyte action potential?
Phase 4 – Resting Membrane Potential Cell repolarized and ready for the next stimulus
44
What is the importance of troponin?
Check if a heart attack has occurred which will be indicated by high troponin levels Will remain high for 1-2 weeks post heart attack
45
When is troponin also present?
Released when heart is damaged/ no perfusion Need to also check SVT (accessory pathway) between nodes; over long time/over exhorting so troponin may be present Pericarditis also leads to an increase in troponin levels
46
How do action potentials spread between the cells?
Gap junctions: direct transfer of ionic current from one cell to the next
47
What does it mean for cells to be "electrically coupled"?
Cells are connected by a gap junction Flow of ions from cytoplasm to cytoplasm Very fast, fail-safe transmission Almost simultaneous AP generation
48
How do skeletal myocytes and cardio myocytes differ?
Skeletal: Dependent of action potential on neural activity Resting membrane potential= -85mV Action potential lasts 2.5msec No extracellular Ca2+ for contractions Cardiac: No dependency of action potential on neural activity Resting membrane potential= -90mV Action potential lasts ~300msec Have extracellular Ca2+ for contractions

Foundation Year MBChB (27 decks)

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