Cardiac physiology and ECG Flashcards

1
Q

Describe the process of the cardiac cycle?

A

Diastole
- During diastole, the atrioventricular valves are closed.
- Blood flows into the left and right atria from the veins
- As the atria fill, the Atrioventricular valves open allowing the passage of blood from the atria to the ventricles
- The atrioventricular valves then close to prevent the backflow of blood from the ventricles back into the atria
- The ventricles contract and the pressure increases above that of the major arteries and so the semi-lunar valves open. This causes the push of blood from the ventricles into the aorta and the pulmonary artery.

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2
Q

What are they types of valves in the heart and where are they?

A
  • Atrioventricular valves:
    Are found between the atria and the ventricles
    Bicuspid (Left)
    Tricuspid (Right)
    Prevent backflip from the ventricles back into the atria
  • Semi-lunar valves:
    Are found between the ventricles and the major arteries
    Between the right ventricle and the pulmonary artery
    Between the left ventricle and the aorta
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3
Q

What is the end systolic volume?

A

The volume of blood in the ventricles at the end of systole

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4
Q

What is the end diastolic volume?

A

The volume of blood at the end of diastole

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5
Q

What is the stroke volume?

A

Stroke volume = End diastolic volume - end systolic volume
- it is the amount of blood ejected from the heart in a single heart beat

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6
Q

What are the types of intercalated discs incorporated into cardiac muscle and what is their function?

A

The intercalated discs are found in the sarcolemma- the plasma membrane of the cardiac muscle cells

  • Desmosomes- are structures found at the end of the cardiac muscle fibres to anchor them together. They provide mechanical support and prevent the cells from pulling apart during the individual fibres contracting
  • Gap junctions- is a channel between adjacent cardiac muscle fibres that allow the transmission of action potentials from one cardiac muscle cell to the next.
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7
Q

What is the pericardium and what are its functions?

A
  • The pericardium is a fibrous, double-walled sac that encloses and protects the heart and its vessels.

It has 2 main functions;
- It anchors the heart and keeps the heart and its vessels protected
- Also provides lubrication via pericardial fluid that prevents the heart from rubbing against the ribcage and Wreduces the friction generated by the heart as it moves within the thoracic cavity

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8
Q

What is pericarditis?

A

When the pericardial sac becomes infected and inflamed- can have a viral or bacterial cause or can be a result of other inflammatory conditions e.g. rheumatoid arthritis
- it presents itself as chest pain on the left side behind the breast bone.
- When the fluid becomes inflamed, it leads to the person being able to feel the rubbing of the heart against other structures and can be painful

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9
Q

What in the heart is known as the ‘Pacemaker region’?

A

The sino-atrial node

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10
Q

What is the process of transmission of the action potential around the heart?

A
  • The action potential is fired from the pacemaker cells in the SA node
  • It then travels across the atria node to the AV node
  • Once in the ventricles, the action potential followed the Bundle of His down the septum and into the walls of each ventricle
  • These then branch into the purkinje fibres
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11
Q

What are the two cell types that initiate an action potential in the heart?

A
  • Pacemaker cells in the Sino-atrial node
  • Cardiomyoctye cells (don’t actually generate the AP, but can pass it along)
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12
Q

The pacemaker cells in the SA node are ____?

A

Autorhythmic- they generate the action potential themselves without any outside stimulation

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13
Q

What is the process of generating cardiac action potentials in the pacemaker cells and the effect on the membrane? (write like an exam q)

A

Pacemaker cells are found in the Sino-atrial node of the heart. They have autorhythmicity and so generate the action potentials without any nervous stimulation and control the heart rate.

  • The ion channels known as ‘Funny channels’ open which allow the entry of Na+ into the cell.
  • This causes the inside of the cell to become more positive and an increase in the membrane potential (slow depolarisation- slow influx of Na+ ions). this is known as a slow drift to threshold potential.
  • As this membrane potential nears threshold potential, the long-lasting transient calcium channels open. This causes Ca2+ ions to move into the cell, leading to a more rapid depolarisation of the membrane.
  • At this point, rectifier K+ channels are opened, this causes K+ ions to move out of the cell and leads to rapid repolarisation of the membrane.
  • In the pacemaker cells, there is no resting potential, so as soon as repolarisation has occurred, the process restarts immediately and the funny channels are reopened.

DRAW A PICTURE OF THE MEMBRANE POTENTIAL V TIME GRAPH AND LABEL IT WITH THE IONS.

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14
Q

How are action potentials transmitted in cardiomyocytes (Write like an exam question)?

A

Cardiomyocytes are muscle cells that are found in the heart. They cannot generate action potentials like the pacemaker cells can, but can pass them along purkinje fibres to the next cardiomyocyte cells via gap junctions.

  • The Na+ channels open, leading to rapid influx of sodium ions and rapid depolarisation of the membrane.
  • This leads to the opening of K+ channels, causing K+ ions to be pumped out- causing a slight repolarisation of the membrane.
  • This leads to a plateau phase. As K+ is slowly being pumped out and Ca2+ channels are opened, causing calcium to be pumped in slowly. These two actions balance the charges out and so leads to a plateau in the membrane potential.
  • The K+ ions then begin to rapidly efflux from the cell (via rectifier K+ channels) causing rapid repolarisation of the membrane.
  • The cell then remains at resting potential until the next action potential is fired.

DRAW A PICTURE OF THE MEMBRANE POTENTIAL V TIME GRAPH AND LABEL IT WITH THE IONS.

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15
Q

Explain the differences between generating an action potential in the cardiomyocytes and the pacemaker cells? (Answer like an exam Q)

A

Pacemaker cells are found in the Sino-atrial node of the heart. They have autorhythmicity and so generate the action potentials without any nervous stimulation and control the heart rate.

  • The ion channels known as ‘Funny channels’ open which allow the entry of Na+ into the cell.
  • This causes the inside of the cell to become more positive and an increase in the membrane potential (slow depolarisation- slow influx of Na+ ions). this is known as a slow drift to threshold potential.
  • As this membrane potential nears threshold potential, the long-lasting transient calcium channels open. This causes Ca2+ ions to move into the cell, leading to a more rapid depolarisation of the membrane.
  • At this point, rectifier K+ channels are opened, this causes K+ ions to move out of the cell and leads to rapid repolarisation of the membrane.
  • In the pacemaker cells, there is no resting potential, so as soon as depolarisation has occurred, the process restarts immediately and the funny channels are reopened.

DRAW A PICTURE OF THE MEMBRANE POTENTIAL V TIME GRAPH AND LABEL IT WITH THE IONS.

Cardiomyocytes are muscle cells that are found in the heart. They cannot generate action potentials like the pacemaker cells can, but can pass the potentials along to the next cells via gap junctions.

  • The Na+ channels open, leading to rapid influx of sodium ions and rapid depolarisation of the membrane.
  • This leads to the opening of K+ channels, causing K+ ions to be pumped out- causing a slight repolarisation of the membrane.
  • This leads to a plateau phase. As K+ is slowly being pumped out and Ca2+ channels are opened, causing calcium to be pumped in slowly. These two actions balance the charges out and so leads to a plateau in the membrane potential.
  • The K+ ions then begin to rapidly efflux from the cell (via rectifier K+ channels) causing rapid depolarisation of the membrane.
  • The cell then remains at resting potential until the next action potential is fired.

DRAW A PICTURE OF THE MEMBRANE POTENTIAL V TIME GRAPH AND LABEL IT WITH THE IONS.

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16
Q

What is excitation-contraction coupling?

A

EC-coupling refers to the events that link the excitation of the cardiomyocytes via the generation of action potentials with the contraction of the muscle. This is due to the action potentials causing changes in levels of the secondary messenger molecule Ca2+ which is crucial in muscle contraction.

  • In the plateau phase of action potential transmission in cardiomyocyte, Ca2+ is entering the cytosol via long-lasting calcium channels
  • This calcium binds to ryanodine receptors on the external surface of the sarcoplasmic reticulum
  • This leads to calcium-induced calcium release from the SR and causes an increase in intracellular concentration
  • This leads to the activation of troponin and the cross-bridge formation, leading to muscle contraction
  • To switch off the contraction, calcium ions need to be removed via ATPase pumps on the SR e.g. SERCA2 and Na+:Ca2+ exchangers which move calcium ions from the cytosol to the extracellular space.
17
Q

What are the potential effects of abnormal K+ levels in the cardiomyocytes?

A

Altering the levels of K+ will change the resting potential of the membrane. An increase or decrease leads to decreased excitability and contractility.

If levels of EC K+ are increased (hyperkalemia):
- The membrane resting potential will be decreased= depolarisation
- Can lead to arrhythmias and can even be fatal

If levels of EC K+ are decreased (hypokalaemia):
- The resting membrane potential is increased = depolarisation
- Can lead to bradycardia, and cardiac rhythm abnormalities

18
Q

What is the impact of changes in extracellular calcium concentrations?

A

Changes in extracellular Ca2+ concentration causes alterations in the membrane permeability and therefore can lead to cardiac rhythm abnormalities.

19
Q

What is are inotropes and chronotropes?

A

Inotrope- a medicine that changes the force of contraction
can be positive (increase) or negative (decrease)

Chronotrope- A medicine that affects the heart rate
can be positive (increase) or negative (decrease)

e.g. Digoxin is a positive inotrope as it increases contractility and a negative chronotrope as it decreases heart rate.
e.g. CCBs have negative chronotropic and inotropic effects

20
Q

What is the cardiac refractory period?

A

The refractory period is the time after an action potential has been fired that the neurone can NOT yet fire another action potential.

21
Q

What is an ECG?

A

Electrocardiogram
- Looks at the rhythm, rate and electrical activity of the heart
- Involves attaching 10 electrodes to the body to record 12 different views of the heart’s electrical activity- 1 on each ankle, 1 on each wrist and 6 to the chest.
- Produces a trace that shows the electrical activity of the heart

22
Q

What are the letters shown on an ECG trace?

A

PQRST
LOOK AT A DIAGRAM AND BE ABLE TO DRAW AND LABEL AN ECG TRACE!

23
Q

What do each of the PQRST parts of an ECG trace represent?

A

P- Depolarisation of the atria in response to the SA node triggering an action potential. Causes atrial contraction.
P-R interval- The delay of the spread of the AP reaching the AV node, allowing the ventricles to fill.
QRS complex- represents a wave of depolarisation spreading deep into the myocardium of the ventricles. leading to ventricular depolarisation and therefore ventricular contraction
ST segment- the time interval between ventricular depolarisation and repolarisation.
T-wave-Ventricular repolarisation- restoring membrane potential to resting level.

24
Q

What does the P-wave represent in an ECG and how long does it last for?

A

Depolarisation of the atria in response to the SA node triggering an action potential and it spreading through both of the atria. Causes atrial contraction.
- Lasts <120 ms

25
Q

What does the P-R represent in an ECG and how long does it last for?

A

The delay of the spread of the electrical activity (action potential) from the SA node to reach the AV node. (CHECK)
120-200 ms

26
Q

What does the QRS complex represent in an ECG and how long does it last for?

A

Represents a wave of depolarisation spreading deep into the myocardium of the ventricles. leading to ventricular depolarisation and therefore ventricular contraction
60-100 ms

27
Q

What does the T-wave represent in an ECG and how long does it last?

A

Ventricular repolarisation- restoring membrane potential to resting level.
160 ms

28
Q

What does the ST segment represent in an ECG and how long does it last for?

A

Represents the time between ventricular depolarisation and ventricular repolarisation.
80-120 ms