Arrhythmia's

Question 1

What is an arrhythmia?

Answer 1

Disturbances of heart rate or rhythm which can be caused by changes in impulse formation or impulse conduction

Question 2

What do alternations in impulse conduction involve?

Answer 2

• changes in automaticity

- triggered activity

Question 3

What do abnormalities in impulse conduction arise from?

Answer 3

• re-entry
• conduction block
• accessory tracts

Question 4

What is overdrive suppression?

Answer 4

the SA node pacemaking is normally dominant over latent pacemakers such as the AV node and purkinje fibres

Question 5

How might overdrive suppression by lost?

Answer 5

• SA node firing frequency is pathologically low
• latent pacemaker fires at an intrinsic rate faster than the SA node rate
• can occur in response to tissue damage

Question 6

How might an ectopic rhythm occur?

Answer 6

• latent pacemaker generates a series of ectopic beats

- can result from ischaemia, hypokalaemia, increased sympathetic activity, fibre stretch

Question 7

What is an afterdepolarization?

Answer 7

• abnormal oscillations in membrane potential triggered by a normal AP
• if they reach threshold can cause premature APs and beats

Question 8

EADS are most likely to occur when HR is fast and they occur in the purkinje fibres T/F?

Answer 8

False

they are most likely to occur when it is slow but they are most likely to occur in the purkinje fibres

Question 9

Where in the AP do EADS occur?

Answer 9

phase 2 and phase 3

Question 10

Where in the AP do DADs occur?

Answer 10

• after complete repolarization

- they are caused by large increases in [Ca]i

Question 11

DADs are most likely to occur when HR is fast T/F?

Answer 11

True

Question 12

What does the re-entrant circuit require?

Answer 12

• unidirectional block (ante retrograde conduction prohibited, retrograde conduction allowed)
• slowed retrograde conduction velocity

Question 13

Describe partial conduction block and give an example?

Answer 13

• All impulses are conducted but more slow than usual

- e.g. First degree AV block

Question 14

Describe intermittent conduction block and give an example?

Answer 14

• tissue conducts some impulses but not others

- second degree AV block

Question 15

Describe Mobitz type I and II second degree AV node block?

Answer 15

I - PR interval gradually increases from cycle to cycle until AV node fails completely and a ventricular beat is missed
II - PR interval is constant but every nth ventricular depolarisation is missing

Question 16

Describe complete conduction block and give an example?

Answer 16

• no impulses are conducted through the affected area

- 3rd degree AV block

Question 17

Describe 3rd degree heart block?

Answer 17

• atria and ventricles beat independently
• ventricular pacemaker is the Purkinje fibres - fire slowly and unreliably
• manifests as bradycardia and low CO

Question 18

What is an accessory tract pathway?

Answer 18

• electrical pathway in parallel to the AV node

- e.g. Bundle of Kent

Question 19

Describe conduction through the bundle of Kent?

Answer 19

• conducted more quickly than through the AV node

- ventricles receive impulses from both the normal and accessory pathways - leads to tachyarrhythmias

Question 20

Give an example of class Ia, Ib and Ic drugs used to treat arrhythmias?

Answer 20

IA = Disopyramide 
IB = Lignocaine 
IC = Flecainide

Question 21

Give an example of a Class II drug?

Answer 21

Metoprolol

Question 22

Give an example of a class III drug?

Answer 22

Amiodarone

Question 23

Give an example of a class IV drug?

Answer 23

Verapamil

Question 24

How do class I agents work?

Answer 24

• bind preferentially to voltage activated Na+ channels and slow the rate of AP and prolong refractory period