Arrhythmias and Anti-arrhythmics

Question 1

How long does it typically take for an AP to propagate from the AVN to myocytes?

Answer 1

0.2s

Question 2

What is the funny current?

Answer 2

current activated by hyperpolarisation
sends K out and Na in
causes depolarisation

Question 3

Upon sufficient depolarisation in the SAN, which calcium current activates?

Answer 3

ICaT

Question 4

Which calcium current generates the AP upstroke in the SAN?

Answer 4

ICaL

Question 5

What is the Calcium Clock?

Answer 5

• the spontaneous release of calcium from from areas of the SR just below the cell membrane
• contribute to the initiation of the upstroke of the AP in the SAN

Question 6

What K currents are involved with the repolarisation in the SAN?

Answer 6

IKir and IKs and IKach

Question 7

What is the role of ICNX at RMP in the SAN?

Answer 7

3Na in for Ca out…depolarising influence - reverses at peak of AP

Question 8

How is the membrane potential stabilised in the Ventricular myocytes during diastole?

Answer 8

Kir

Question 9

Which sodium channels mediate the upstroke in the ventricular AP?

Answer 9

Nav1.5

Question 10

what is the notch in the ventricular AP caused by?

Answer 10

simultaneous inactivation of N and opening of rapid activating K channels

Question 11

What does the P wave in the ECG symbolise?

Answer 11

atrial depolarisation

Question 12

What does the QRS complex in the ECG symbolised?

Answer 12

rapid ventricular depolarisation

Question 13

What does the T wave represent in the ECG?

Answer 13

ventricular repolarisation

Question 14

How is current transmitted between cardiac muscle cells?

Answer 14

gap junctions

Question 15

What would be considered a normal cardiac electrical vector direction?

Answer 15

5o’clock (anything between 3-7o’clock)

Question 16

When measuring the ECG, which vector provides the best recording method?

Answer 16

RA ->LL

Question 17

How long should a p-wave last?

Answer 17

0.08-0.15s

Question 18

How long should the Q-T interval be?

Answer 18

~300ms

Question 19

Why is the P wave an upward deflection?

Answer 19

the current is moving in the direction of the recording electrode

Question 20

Why is the Q a downward deflection?

Answer 20

L->R depolarisation of the intraventricular septum moving towards 7/8 o’clock away from recording electrode

Question 21

Why is the R an upward deflection?

Answer 21

ventricles depolarise towards the recording electrode

Question 22

Why is the T wave an upward deflection?

Answer 22

repolarisation from out to in

2 negs make a positive so upstroke

Question 23

Which other feature do some individuals have on their ECG?

Answer 23

a U wave (purkinje fibre repolarisation)

Question 24

What are the potential disruptions to electrical function of the heart?

Answer 24

defects in impulse formation - altered automaticity

defects in impulse conduction - re-entrant arrhythmias

Question 25

what usually controls automaticity in the heart?

Answer 25

ANS

Question 26

what can happen in altered automaticity?

Answer 26

a latent pacemaker subverts the SAN function and overdrive suppression is lost

Question 27

When may altered automaticity occur?

Answer 27

- if the firing frequency of the SAN is low or conduction is impaired - if the latent pacemaker fires at a rate faster than the SAN

Question 28

What may occur if the SAN firing frequency is low?

Answer 28

escape beats - latent pacemaker forms the impulse | escape rhythms - series of escape beats

Question 29

What may occur if the latent pacemaker fires faster than the SAN?

Answer 29

ectopic beats | ectopic rhythm

Question 30

What make cause an ectopic rhythm?

Answer 30

ischemia, hypokalaemia, fibre stretch

Question 31

What is triggered activity?

Answer 31

afterdepolarisations triggered by a normal AP | EAD or DAD

Question 32

When does an EAD occur?

Answer 32

Phase 2 terminal plateau | Phase 3 repolarisation

Question 33

What causes EAD during phase 2?

Answer 33

Ca Channels

Question 34

What causes EAD during phase 3?

Answer 34

Na channels

Question 35

What are EADs associated with?

Answer 35

prolongation of the AP

Question 36

When does a DAD occur?

Answer 36

after a complete repolarisation

Question 37

What is a DAD associated with?

Answer 37

Ca overload, provoked by catecholamines, digoxin and HF

Question 38

What is a DAD caused by?

Answer 38

a transient inward Na Current

Question 39

What can several ectopic rhythms lead to?

Answer 39

VF

Question 40

How is VF different to tachycardia?

Answer 40

VF doesnt allow blood to be pumped from the ventricles

Question 41

What can sustained EADs lead to?

Answer 41

torsades de pointes - twisting of the QRS complexes

Question 42

What are re-entry arrhythmias?

Answer 42

self-sustaining electrical stimulations that stimulate an area of myocardium repeatedly and rapidly

Question 43

What is required for a re-entrant circuit?

Answer 43

unidirectional block and slow retrograde conduction velocity

Question 44

What are the potential types of conduction block?

Answer 44

Partial Intermittent Complete

Question 45

What happens in partial block?

Answer 45

the tissue conducts all impulses however more slowly than usual - first degree block

Question 46

What are the forms of intermittent block?

Answer 46

Mobitz type I | Mobitz type 2

Question 47

What happens in mobitz type I?

Answer 47

PR interval gradually increases from cycle to cycle until a beat is missed

Question 48

What happens in mobitz type II?

Answer 48

PR interval normal but every 'n' th beat is missed

Question 49

What happens in complete block?

Answer 49

no impulses are conducted through the affected area and the atria and ventricles beat independently bradycardia and low CO are signs

Question 50

What can happen with accessory tract pathways?

Answer 50

pathways that bypass the AVN and set up conditions for re-entrant loops - Wolf-Parkinson-White Syndrom

Question 51

What is a common accessory pathway?

Answer 51

Bundle of Kent

Question 52

What system is used to classify anti-arrhythmics?

Answer 52

Vaugn-Williams Classification

Question 53

Which drugs do not fit into the V-W classification

Answer 53

adenosine and digoxin

Question 54

What describes Class 1A?

Answer 54

Na channel affected associate and dissociate at a moderate rate slow the rise of the AP and prolong the refractory period

Question 55

Give an example of a class I A drug

Answer 55

disopyramide

Question 56

How is class IB descibed?

Answer 56

Na channel associate and dissociate at a rapid rate prevents premature beats binds preferentially to inactive state

Question 57

What is the advantage of Class IB?

Answer 57

doesn't affect normal myocardium

Question 58

How is class IC described?

Answer 58

Na channel | slow association and dissociation

Question 59

Give an example of class IB?

Answer 59

lignocaine

Question 60

Give an example of class IC?

Answer 60

flecainide

Question 61

What do class II drugs target?

Answer 61

b-adrenoceptors | antagonists

Question 62

How do Class II drugs act?

Answer 62

to decrease the rate of depolarisation in SA and AV nodes

Question 63

How do Class III drugs act?

Answer 63

prolong the AP increasing the refractory period

Question 64

How do Class IV drugs act?

Answer 64

slow conduction in SAN or AVN decreasing force of contraction

Question 65

Which ion channels do Class III drugs affect?

Answer 65

Kv

Question 66

Which ion channels do Class IV drugs affect?

Answer 66

Ca

Question 67

Give an example of a class III drug

Answer 67

Amiodarone

Question 68

Give an example of a class IV drug

Answer 68

Verapamil

Question 69

Where do classI drugs primarily act?

Answer 69

the muscle not the nodes

Question 70

How do class I agents block Nav channels?

Answer 70

by use-dependent block

Question 71

What mechanism do class I agents block the Na channels?

Answer 71

stabilising the inactive state

Question 72

When do class I agents dissociate from Na channels?

Answer 72

in the resting state

Question 73

What are the differences in how class I A B and C affect the AP?

Answer 73

A - moderately blocks and prolongs the repolarisation B - mildly blocks and shortens repolarisation C - markedly blocks but not much effect on repolarisation

Question 74

Which drugs are using to control the rate of SVT in the atria?

Answer 74

Class IC and III

Question 75

Which drugs are used to target the ventricles?

Answer 75

Class IA, IB and II

Question 76

Which drugs target the rhythm of the SVT in the AVN?

Answer 76

Class II, Class IV, digoxin and adenosine

Question 77

Which drugs target the atria, ventricles and accessory pathways?

Answer 77

Amiodarone, Class IA, IC