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Clinical Physiology > Arrhythmias > Flashcards

Arrhythmias Flashcards

1
Q

What two systems are innervated by the vagus nerve?

A

Heart and GIT

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2
Q

Normal sinus rhythm impulses originate from which node?

A

SA node

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3
Q

Describe the impulse pathways during AF

A

Impulses have random, chaotic pathways

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4
Q

Name three conditions which are associated with AF

A
  • Rheumatic disease
  • Pericarditis
  • Hyperthyroidism
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5
Q

Name three ways a heart can be restored to normal rhythm

A
  • Defibrillation
  • Cardioversion
  • Transcutaneous pacing
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6
Q

What is an AV block?

A

Decreased rate of impulse from atria to ventricle through AV bundle

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7
Q

List four physiological causes of heart block

A
  • Ischaemia
  • Compression
  • Inflammation
  • Extreme vagal excitation (parasympathetic)
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8
Q

What occurs in 1st degree AV block?

A

Atrioventricular conduction is lengthened

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9
Q

Describe the lead II ECG of 1st degree AV block

A

P wave precedes each QRS but PR interval is >0.2s

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10
Q

What occurs on the ECG of both 2nd degree AV blocks?

A

Sudden dropped QRS

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11
Q

Describe the lead II ECG of 2nd degree AV block

A

Intermittently skipped ventricular beat

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12
Q

What occurs in Mobitz 1 AV block?

A

Progressive lengthening of PR interval until there is a dropped QRS

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13
Q

What occurs in Mobitz II AV block?

A

Normal PR interval with a randomly dropped QRS

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14
Q

What occurs in 3rd degree AV block?

A

Impulses originate at AV node and proceed to ventricles. Atrial and ventricular activities are not synchronous

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15
Q

Describe the lead II ECG of 3rd degree AV block

A

Constant rates of P waves and QRS complexes that occur independently of each other

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16
Q

What can be used to rx bradycardia?

A
  • Atropine
    • Blocks parasympathetic nervous system
  • Isoprenaline
    • Activates sympathetic nervous system
  • Adrenaline (last resort)
17
Q

From which node does sinus tachycardia originate?

A

SA node

18
Q

Where do the impulses originate in supraventricular tachycardia?

A

Above the ventricles, usually the atria

19
Q

Where do the impulses originate in ventricular tachycardia?

A

Ventricles

20
Q

Where do narrow complex tachycardias originate?

A

Above the ventricles

21
Q

Where do broad complex tachycardias originate?

A

Usually from the ventricles, though can also be SVT with aberrant conduction

22
Q

What is done to halt broad complex tachycardia?

A

Synchronised cardioversion

23
Q

What can trigger broad complex tachycardia?

A
  • After MI (hypoxia)
  • Drugs/toxins
  • Inflammation
24
Q

What is the most common non-psychogenic narrow complex tachycardia?

A

AV-nodal reentrant tachycardia (AVNRT), accounting for 80-90% of all cases

25
Q

What causes AVNRT?

A

Extra pathways in/around the AV node

26
Q

In AVNRT, does the fast pathway have a short or long refractory period?

A

Long

27
Q

In AVNRT, does the slow pathway have a short or long refractory period?

A

Short

28
Q

Describe the conduction process of AVNRT

A
  • Signal comes down from the SA node and goes down both pathways, reaching the end of the fast pathway before the slow pathway
  • Signal goes down into the ventricles as well as back up the slow pathway to meet the slow signal where they cancel each other out
  • Both pathways enter their refractory periods, with the slow pathway recovering sooner
  • Another signal comes down and starts down the slow pathway while the fast is still in refractory
  • As the signal reaches the end of the slow pathway the fast pathway comes out of refractory
  • The signal continues down into the ventricles as well as travelling back up the fast pathway to the atria and reentering the slow pathway
  • Cycle continues, causing an atrial and ventricular contraction with every loop
29
Q

Describe an ECG of AVNRT

A
  • Narrow complex tachycardia without P waves
    • P waves may not always be visible (may be buried in QRS, as atria and ventricles are contracting simultaneously)
    • May have ‘pseudo-waves’ caused by retrograde P waves
30
Q

How is AVNRT treated?

A
  • Sometimes terminates itself, ending in a QRS
  • Adenosine (transiently blocks AV node)
31
Q

How does adenosine rx SVT?

A
  • Vascular smooth muscle
    • Inhibits Ca++ channels, reducing contraction
    • Opens K+ channels, hyperpolarising the cells
  • SA/AV node
    • Opens K+ channels, hyperpolarising the cells
    • Inhibits release of noradrenaline
32
Q

How does adenosine induce rebound tachycardia?

A

Decreased cardiac output and vasodilation result in hypotension, triggering the baroreceptor reflex

33
Q

What is the long term rx for AVNRT?

A

Catheter ablation - defective tissue is identified then destroyed by high energy (heat, laser, or extreme cold [cryo-ablation]) with a catheter

Clinical Physiology (11 decks)

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