Arrhythmias

Question 1

What is an arrhythmia?

Answer 1

An irregular heart beat

Question 2

How are arrhythmias classified?

Answer 2

Site (atrial,nodal, ventricular) and type (irregular, tachycardia brachycardia)

Question 3

How can irregular heart beat progress?

Answer 3

Flutter then fibrillation

Question 4

Which sort of arrhythmia has greatest impact on cardiac output, how can they progress?

Answer 4

Ventricular arrhythmias, can progress to ventricular fibrillation (fatal)

Question 5

What is the most common type of arrhythmia?

Answer 5

Atrial fibrillation

Question 6

What happens in bradycardia, what can cause it?

Answer 6

Slow heart rate e.g. sinus dysfunction or heart slowing drugs e.g. beta blocker

Question 7

What can bradycardia lead to?

Answer 7

Atrial fibrillation, cardiac arrest

Question 8

What is treatment for bradycardia?

Answer 8

Ach receptor (M2) antagonist (e.g. atropine) to prevent slowing vagal stimulation of heart.
Implantation of pacemaker device.

Question 9

What is atrial fibrillation, what’s the role of ectopic sites?

Answer 9

Irregular, rapid atrial contraction.

Ectopic sites where action potentials and thus atrial systoles are initiated from all over.

Question 10

What is the effect of atrial fibrillation on ventricles?

Answer 10

AVN only intermittently activated by chaotic activity of atria so irregular ventricular function

Question 11

How is atrial fibrillation treated?

Answer 11

Slow atrial contractions (e.g. verapamil, amiodarone, beta blocker, ivabradine)
Electrical shock treatment to restore normal rhythm

Question 12

What is heart block?

Answer 12

Toxic effect of cardiac glycosides or, infarct encompasses AVN so wave of activity not transmitted from atria to ventircles

Question 13

What happens to beating of atria and ventricles in heart block?

Answer 13

Atria beat at pace set by SAN but ventricles beat independently at pace set by ventricular pacemaker cells

Question 14

What happens to hearts pumping in heart block?

Answer 14

Loss of efficiency

Question 15

What happens in 1st degree heart block?

Answer 15

Slower conduction through AVN

Question 16

How do you diagnose 1st degree heart block?

Answer 16

Prolonged PR interval (>0.25 secs)

Question 17

What is 2nd degree heart block?

Answer 17

Block of AVN so partial conduction (not all impulses conducted through AVN)

Question 18

How do you diagnose second degree block on ECG?

Answer 18

P wave blocked from initiating a QRS complex

Question 19

What happens in 3rd degree block?

Answer 19

No conduction, ventricles contract independently of atria (at intrinsic rate of 30-40bpm)

Question 20

How do you treat heart block?

Answer 20

Artificial pacemaker

Question 21

How can ectopic pacemaker activity arise?

Answer 21

Ischaemic damage to SAN so other cells undertake pacemaker activity

Question 22

Where do secondary pacemakers arise?

Answer 22

AVN and purkinjie fibres

Question 23

What assumes pacemaker role when SAN is blocked?

Answer 23

AVN

Question 24

What assumes pacemaker role when AVN blocked?

Answer 24

Funny current in Purkinje fibres can initiate slow pacemaler potential

Question 25

List some anti dysrhythmic drugs?

Answer 25

``` By modifying AP: Local anaesthetics (lidocaine) Beta blockers Amiodarone Verapamil Ivabradine Adenosine ```

Question 26

How does use of beta blockers and amiodarone vary based on time frame?

Answer 26

Beta blocker: acute | Amiodarone: chronic

Question 27

How do L.A treat arrhythmias?

Answer 27

Bind VGNC Reduce abnodmal propagation Reduce abnormal impulses

Question 28

How do LA reduce abnodmal propagation?

Answer 28

Extend effective refractory period (until drug dissociates from channel) so reduces risk of propagating abnodmal impulses and prevent ectopic beat occuring after sinus rhythm

Question 29

How do LA reduce abnormal impulses?

Answer 29

Reduce excitability (decreased open Na+ channel so reduce spontaneous depolarisation)

Question 30

In what state does Lidocaine bind sodium channel?

Answer 30

Active state

Question 31

When do sodium channels reactivate (lidocaine)?

Answer 31

When lidocaine begins to dissociate

Question 32

How is lidocaine's efficiency frequency dependent?

Answer 32

High frequency impulses (e.g. tachycardia, fibrilaiton) should be suppressed more than low frequency ones (e.g. sinus rhythm) as an impulse arriving soon after drug begins to dissociate will be suppressed more than impulse arriving later

Question 33

What are the risks of lidocaine?

Answer 33

Reduced contractility of myocardium Block Na+ entry, so more Na+ comes in via NCX to compensate, so more Ca2+ pumped out, less Ca2+ in cell so less contractility and heart failure

Question 34

How can lidocaine actually cause dysrhythmia?

Answer 34

Less Ca2+ in cell (due to NCX activity) so decreased contractility and cardiac failure Reduced perfusion of coronary arteries and ischaemia so dysrhythmia.

Question 35

Examples of beta blockers?

Answer 35

Atenolol, propanolol

Question 36

By reducing sympathetic drive, what do beta blockers do?

Answer 36

Reduce myocardial oxygen demand and debt Reduce pacemaker currents induced by sympathetic stimulation Reduce disaprity and shortening of action potentials associated with sympathetic drive

Question 37

What are the chronic effects of beta blockers?

Answer 37

Increase AP length Reduce cardiac workload and debt Reduce platelet stickiness (reduce thromobosis and risk of myocardial ischaemia)

Question 38

How can beta blockers increase action potential length?

Answer 38

Decrease K+ current that repolarises cell, increase effective refractory period, so antidsyrhythmic

Question 39

What does ischaemia and sympathetic drive contribute to?

Answer 39

Arrhythmias

Question 40

What is the side effect of beta blockers?

Answer 40

Fall in contractility (block SNS inotropic effects)

Question 41

What does Amiodarone do?

Answer 41

Lengthen AP Reduce cardiac workload Enhances LA activity Effective refractory period

Question 42

How can amiodarone lengthen APs?

Answer 42

Decrease K+ current that repolarises membrane (stage 3 cardiac AP)

Question 43

How does reducing cardiac workload help treat arrhythmias?

Answer 43

Reduce myocardial infarction

Question 44

What are side effects of amiodarone?

Answer 44

Reduced cardiac contractility, skin photosensitivity, thyroid disturbances

Question 45

What is verapamil used for?

Answer 45

Nodal (i.e. when ca2+ current causing arrhyhmias) and ischaemic arrhythmias

Question 46

What does Verapamil block?

Answer 46

L-type Ca2+ channels

Question 47

What are the effects of verapamil?

Answer 47

Reduce excitability of ischaemic cells (in which depolarising current carried by Ca2+) Reduces effect of calcium in cell (causes cell uncoupling through impacting gap junctions) increase conduction and decreased spontaneous depolarisation of purely indivdual cells to encourage heart to act as syncytium

Question 48

Why are most anti arrhythmia drugs potentially dangerous?

Answer 48

Negatively inotropic | Reduce coronary perfusion and thus may lead to future dysrhythmias

Question 49

How can adenosine treat arrhythmias?

Answer 49

Parasympathomimetic acting on A1 receptors to activate IKAch so hyperpolarises membrane and decreasing heart rate by blocking AVN

Question 50

What does ivabradine bind to?

Answer 50

Block HCN4 if channels in the SAN

Question 51

How does ivabradine treat angina and arrhythmias?

Answer 51

Slows cardiac pacemaker activity, reducing myocardial oxygen demand

Question 52

What is adenosine used for?

Answer 52

Supraventricular tachycardia originating in the AVN

Question 53

Why can cardiac glycosides be used for arrhythmias, how?

Answer 53

Slow down heart rate, slow down refracory period of AVN

Question 54

What sort of arrhythmia can atropine treat?

Answer 54

Bradycardia | 2nd or 3rd degree heart block

Question 55

What are the discharge rates of AVN and purkinje fibres?

Answer 55

40-60bpm and 20-40bpm

Question 56

What does flecainide do?

Answer 56

Inhibits Na+ channel, slowing upstroke of cardiac action potential

Question 57

Why use flecainide over lidocaine?

Answer 57

Stronger blocker of Na+ channels

Question 58

A compound that opens K+ channels in the atrioventricular node

Answer 58

Adenosine

Question 59

What arrhythmia are cardiac glycosides used to treat?

Answer 59

Atrial fibrillation