Arrhythmias

Question 1

What two systems are innervated by the vagus nerve?

Answer 1

Heart and GIT

Question 2

Normal sinus rhythm impulses originate from which node?

Answer 2

SA node

Question 3

Describe the impulse pathways during AF

Answer 3

Impulses have random, chaotic pathways

Question 4

Name three conditions which are associated with AF

Answer 4

• Rheumatic disease
• Pericarditis
• Hyperthyroidism

Question 5

Name three ways a heart can be restored to normal rhythm

Answer 5

• Defibrillation
• Cardioversion
• Transcutaneous pacing

Question 6

What is an AV block?

Answer 6

Decreased rate of impulse from atria to ventricle through AV bundle

Question 7

List four physiological causes of heart block

Answer 7

• Ischaemia
• Compression
• Inflammation
• Extreme vagal excitation (parasympathetic)

Question 8

What occurs in 1st degree AV block?

Answer 8

Atrioventricular conduction is lengthened

Question 9

Describe the lead II ECG of 1st degree AV block

Answer 9

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

Question 10

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

Answer 10

Sudden dropped QRS

Question 11

Describe the lead II ECG of 2nd degree AV block

Answer 11

Intermittently skipped ventricular beat

Question 12

What occurs in Mobitz 1 AV block?

Answer 12

Progressive lengthening of PR interval until there is a dropped QRS

Question 13

What occurs in Mobitz II AV block?

Answer 13

Normal PR interval with a randomly dropped QRS

Question 14

What occurs in 3rd degree AV block?

Answer 14

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

Question 15

Describe the lead II ECG of 3rd degree AV block

Answer 15

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

Question 16

What can be used to rx bradycardia?

Answer 16

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

Question 17

From which node does sinus tachycardia originate?

Answer 17

SA node

Question 18

Where do the impulses originate in supraventricular tachycardia?

Answer 18

Above the ventricles, usually the atria

Question 19

Where do the impulses originate in ventricular tachycardia?

Answer 19

Ventricles

Question 20

Where do narrow complex tachycardias originate?

Answer 20

Above the ventricles

Question 21

Where do broad complex tachycardias originate?

Answer 21

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

Question 22

What is done to halt broad complex tachycardia?

Answer 22

Synchronised cardioversion

Question 23

What can trigger broad complex tachycardia?

Answer 23

• After MI (hypoxia)
• Drugs/toxins
• Inflammation

Question 24

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

Answer 24

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

Question 25

What causes AVNRT?

Answer 25

Extra pathways in/around the AV node

Question 26

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

Answer 26

Long

Question 27

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

Answer 27

Short

Question 28

Describe the conduction process of AVNRT

Answer 28

* 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

Question 29

Describe an ECG of AVNRT

Answer 29

* 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

Question 30

How is AVNRT treated?

Answer 30

* Sometimes terminates itself, ending in a QRS * Adenosine (transiently blocks AV node)

Question 31

How does adenosine rx SVT?

Answer 31

* 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

Question 32

How does adenosine induce rebound tachycardia?

Answer 32

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

Question 33

What is the long term rx for AVNRT?

Answer 33

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