Arryhthmias (ignore)

Question 1

Define what a cardiac arrhythmia is

Answer 1

It is a disturbance of heart rate, or rhythm (regularity of beats)

Question 2

Define what bradycardia and tachycardias are

Answer 2

• Bradycardias = HR ˂ 60 b.p.m.
• Tachycardias = HR ˃ 100 b.p.m.

Question 3

What is meant by supraventricular or ventricular arrhythmias ?

Answer 3

1. Supraventricular simply tells you the origin of the arryhthmia is above the AV node
2. Ventricular simply tells you the origin of the arrythmia is in the ventricle either the ventriclar muscle (common) or fascicles of the conducting system (uncommon)

Question 4

What causes an arrythmia to arise ?

Answer 4

By either changes in impulse formation, or impulse conduction

Question 5

List the clinical causes of arrythmias

Answer 5

Abnormal anatomy:

• left ventricular hypertrophy
• accessory pathways
• congenital HD

Autonomic nervous system (ANS):

• Sympathetic stimulation: stress, exercise, hyperthyroidism
• Increased vagal tone causing bradycardia

Metabolic:

• Hypoxia: chronic pulmonary disease, pulmonary embolus
• Ischaemic myocardium: acute MI, angina
• Electrolyte imbalances: K+, Ca 2+, Mg2+

Inflammation: viral myocarditis

Drugs: direct electrophysiologic effects or via ANS

Genetic: mutations of genes encoding cardiac ion channels e.g. the congenital long QT syndrome

Question 6

What are the 4 main electrophysiological mechanisms of arrythmia formation ?

Answer 6

1. Ectopic beats: Beats or rhythms that originate in places other than the SA node
2. Re-entry: requires more than one conduction pathway, with different speed of conduction (depolarization) and recovery of excitability (refractoriness)
3. Conduction block - may be partial (incomplete), or complete. In partial block there is slowed conduction: tissue conducts all impulses, but more slowly than usual
4. Accessory pathways - some individuals possess electrical pathways in parallel to the AV node

Question 7

What are the 2 ways in which ectopic beats may occur and give examples of causes ?

Answer 7

1. Altered automaticity e.g. ischaemia, catecholamines
2. Triggered activity, e.g. digoxin, long QT syndrome

Question 8

Define what altered automaticity is

Answer 8

This is when the function of the SA node as the normal pacemaker is taken over by another ‘latent pacemaker’

Question 9

Describe what is meant by triggered activity

Answer 9

This is when a normal AP triggers abnormal oscillations in membrane potential termed afterdepolarizations (ADs), these may occur during, or after, repolarization. Termed either:

1. Early afterdepolarizations (EADs)
2. Delayed afterdepolarizations (DADs)

Question 10

A tachycardia being life threatening or not depends on what?

Answer 10

On how they affect the cardiac output.

Question 11

What is the underlying mechanism causing arrythmia in digoxin toxicity, Torsades de Pointes in the long QT syndrome and hypokalaemia?

Answer 11

Triggered activity

Question 12

Give some examples of re-entry problems which may result in arrythmias

Answer 12

1. Structural abnormalities: accessory pathways, scar from MI, CHD
2. Functional: Conditions that depress conduction velocity or shorten refractory period promote functional block, e.g. ischaemia, drugs

Question 13

Give the 3 main examples of conduction block type arrythmias

Answer 13

1st, 2nd and 3rd degree AV node block

Question 14

Give an example of a common accessory pathway and the arrythmia it can result in

Answer 14

Bundle of Kent:

1. Impulse through bundle of Kent is conducted more quickly than that through the AV node
2. Ventricles receive impulses from both the normal and accessory pathways – can set up the condition for a re-entrant loop predisposing to tachyarrhythmias