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PA20016 > Heart 1 > Flashcards

Heart 1 Flashcards

1
Q

What are the most common cardiovascular diseases?

A

Coronary heart disease and stroke.

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2
Q

How can most cardiovascular diseases be prevented?

A

Addressing behavioural risk factors such as tobacco use, unhealthy diet/obesity, physical inactivity and harmful use of alcohol.

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3
Q

What are some of the risk factors for cardiovascular disease?

A

Hypertension, diabetes, hyperlipidaemia.

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4
Q

What are the main conduction pathways of the heart?

A

Atrial excitation and contraction (rapid - 1m/s) and ventricular excitation and contraction (rapid - 0.3-1m/s).

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5
Q

What is involved in atrial excitation and contraction?

A

SA node excitation, AV node excitation.

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6
Q

What is involved in ventricular excitation and contraction?

A

His bundle and branches, purkinje fibres.

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7
Q

What is sinus rhythm?

A

A regular heart beat driven by the SAN with rate 60-100 bpm.

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8
Q

What is a normal heart rate?

A

60-100bpm.

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9
Q

What is dysrhythmia?

A

An abnormal heart rhythm.

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10
Q

What is arrthymia?

A

No rhythm of the heart.

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11
Q

What is the difference between dysrhythmia and arrhythmia?

A

The terms are used interchangably and mean the same thing.

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12
Q

What is the P wave?

A

Depolarisation of the atria.

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13
Q

What is the QRS complex?

A

Depolarisation of the ventricles.

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14
Q

What is the T wave?

A

Repolarisation of the ventricles.

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15
Q

What does the PR segment represent?

A

The AV delay.

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16
Q

What does the ST segment represent?

A

Ventricular plateau.

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17
Q

What does the PR interval represent?

A

Atrial depolarisation and AV delay.

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18
Q

What does the QT interval represent?

A

Ventricular depolarisation and repolarisation.

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19
Q

What are the two principle types of action potentials of the heart?

A

The pacemaker action potential and the cardiac action potential.

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20
Q

Where does the pacemaker action potential occur?

A

The SAN and AVN.

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21
Q

Where does the cardiac action potential occur?

A

In atrial and ventricular myocytes and in Purkinje fibres.

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22
Q

What are the features of the pacemaker action potential?

A

Starts with slow depolarisation, repolarisation and there is no true baseline - there is spontaenous depolarisation.

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23
Q

What are the features of the cardiac action potential?

A

There is rapid depolarisation, rapid repolarisation, a pleateau, further depolarisation and then a stable baseline.

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24
Q

What causes the depolarisation in the cardiac action potential?

A

Rapid Na+ influx via voltage activated sodium channels.

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25
Q

What causes the rapid repolarisation in the cardiac action potential?

A

Transient K+ efflux.

26
Q

What causes the plateau in depolarisation in the cardiac action potential?

A

K+ efflux is slow, and there is rapid delayed rectifier potassium channels.

27
Q

What causes the stable baseline in the cardiac action potential?

A

K+ efflux via an inwardly rectifying potassium channel.

28
Q

What does the duration of the cardiac action potential determine?

A

The refractoriness of the heart.

29
Q

What is the absolute/effective refractory period?

A

Generation of the 2nd action potential is not possible even at the strongest consecutive stimulus.

30
Q

What is the relative refractory period?

A

When generation of the 2nd action potential is possible, but requires a stronger stimulus.

31
Q

Why are there refractory periods after the cardiac action potential?

A

There is rapid inactivation of the fast voltage-activated sodium channels by maintained depolarisation.

32
Q

What relevance does phase 0 in cardiac action potential?

A

Class I Anti-arrthythmic drugs target this phase.

33
Q

What relevance does phase 2 of cardiac action potential have in terms of drugs?

A

This phase is inhibited by class IV anti-arrythmic drugs.

34
Q

What relevance does phase 2 of cardiac action potential have in terms of drugs?

A

A target for class III anti-arrhythmic drugs.

35
Q

How is the HCN channel activated?

A

Hyperolarisartion-activated. It is a cyclic nucleotide-gated channel.

36
Q

What structure do HCN channels have?

A

They are tetramers. Each subunit is composed of 6 transmembrane helixes.

37
Q

What is the channel type of the funny current?

A

It is a hyperpolarised activated cyclic nucleotide-gated channel.

38
Q

What is the selectivity of the funny current?

A

Non-selective cation current, permeable to both Na+ and K+ but at physiological potentials it is mainly sodium influx.

39
Q

What is the activation of the funny current?

A

By membrane repolarisation and directly by increased intracellular cAMP.

40
Q

What is the modulation of the funny current?

A

Sympathetic positive via beta1 and beta2 adrenoceptors (beta2 are mainly at the SAN and atria) and parasympathetic negative modulation by muscarinic M2 receptors.

41
Q

What is the role in the funny current in the heart?

A

Cardiac automaticity and the heart rate is controlled by the autonomic NS and by circulating adrenaline.

42
Q

What is the pharmacology of the funny current?

A

Direct inhibition - selectivity of ivabradine and indirect effects via a decrease in sympathetic or an increase in parasympathetic input.

43
Q

How can the pacemaker potential be modified by sympathetic stimulation?

A

An increase in sympathetic stimulation increases the magnitude of the inward directed funny current, hence speeding up depolarisation as a consequence of its activation.

44
Q

What does an increased action potential frequency result in?

A

An increased heart rate.

45
Q

How is the pacemaker potential modified by parasympathetic stimulation?

A

The smaller the funny current, the more time is required to reach the threshold and the frequency of the action potential is reduced.

46
Q

What are arrhythmias that affect heart rate?

A

Bradycardia and tachycardia.

47
Q

What are arrthythmias that are classified by heart rhythm?

A

Regular and irregular.

48
Q

What are arrhythmias that classified by the site of origin in the heart?

A

Supraventricular (SAN, atria and AVN) and ventricular (bundles of His, Purkinje fibres and ventricles).

49
Q

What are arrhythmias that are classified by the type of QRS complex?

A

Narrow and broad.

50
Q

What are the signs of arrhythmias?

A

Feeling heartbeats/palpitations, shortness of breath and fatigue, chest pain, dizziness and feeling faint, blackouts/syncope and cardiac arrest.

51
Q

What are the physiological causes of sinus bradycardia?

A

Increased vagal tone (activity of the vagus nerve) which is common in trained athletes.

52
Q

What are some non-cardiac causes of bradycardia?

A

Endocrine disorders such as hypothyroidism, an electrolyte imbalance such as severe hyperkalemia, hypo/hyper calcaemia, anti-arrhythmic drugs (beta blockers, CCBs, digoxin), antihypertensives and hypothermia.

53
Q

What are some intrinsic causes of bradycardia?

A

Sick sinus syndrome - ischaemia and infarction of the SAN, atrioventricular blockade or heart block (ischaemia; fibrosis, congenital heart defects, infections and inflamamtons such as myocarditis, diptheria and rhematic fever)

54
Q

In the case of hypothermia induced bradycardia, why are drugs such as atropine not useful?

A

The cause is due to reduced metabolism rather than parasympathetic activities, so would not be responsive.

55
Q

What is sick sinus syndrome?

A

A group of heart rhythm disorders due to the malfunction of the SA node that may be present on the ECG as: sinus pause, sinus arrest, bradycardia-tachycardia syndrome.

56
Q

What are the different degrees of atrioventricular block in bradycardia?

A

First degree (slower AV conduction), second degree (missed beats to the ventricles), third degree (no

57
Q

What are drugs that may cause bradycardia?

A

Drugs that block the funny current directly, heart rate control drugs that act on the SAN and AVN and drugs that are used in the treatment of bradycardias.

58
Q

What is a drug that directly blocks the funny current?

A

Ivabradine.

59
Q

What are heart rate control drugs that act on the SAN & AVN?

A

Beta blockers (as anti-arrhythmic agents) and digoxin.

60
Q

What are some drugs that are used in the treatment of bradycardias?

A

Atropine and isoprenaline.

PA20016 (10 decks)

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