6. Cardiac Arrhythmias

Question 1

How do class 1 drugs act?

Answer 1

Block Na channels
Marked slowing conduction in tissue
Minor effects on action potential duration

Question 2

How do class 2 drugs act?

Answer 2

Beta blockers
Reduction in effluent of Ca
Diminish phase 4 depolarisation and automaticity

Question 3

How do class 3 drugs act?

Answer 3

Block K channels
Increase action potential duration
Longer refractor period

Question 4

How do class 4 drugs act?

Answer 4

Calcium channel blockers
Decrease inward Ca currents resulting in a decrease of phase 4 spontaneous depolarisation
Affect plateau phase of action potential

Question 5

What are the effects of Ca channel blockers on slow action potential (SAN, AVN)?

Answer 5

Extend slope of phase 0
Increase refractory period
Harder for node to beat again

Question 6

Where are fast action potentials found?

Answer 6

Cardiac and atrial myocytes

Question 7

Where are slow action potentials found?

Answer 7

SA or AV node

Question 8

What causes a re-entry rhythm?

Answer 8

1. An accessory pathway in heart connecting atrium to ventricle
   - Present only in small populations
   - Wolf-Parkinson-White syndrome (WPW)
2. Two pathways within AVN
   - causes supraventricular tachycardia (AVNRT)
3. Scarring

Question 9

In general, what do drugs work to do in arrhythmias?

Answer 9

Reduce abnormal impulse generation
Slow conduction through tissue
Block AV node to terminate some rhythms

Question 10

Give 2 examples of class 1b agents

Answer 10

Lidocaine (IV)

Mexiletine (oral)

Question 11

What are the effects of class 1B agents on cardiac activity?

Answer 11

No change in phase 0 in normal tissue
Action potential duration slight decreased
Increase threshold (Na+)
Decrease phase 0 conduction in fast beating or ischaemic tissue

Question 12

What are the effects of class 1B agents on ECG?

Answer 12

None in normal heart

In fast beating or ishcaemic heart, prolongation of QRS

Question 13

What are the uses of class 1B agents?

Answer 13

Acute - ventricular tachycardia

Not used in atrial arrhythmias or AV junctional arrhythmias

Question 14

What are the side effects of class 1B drugs?

Answer 14

Less pro arrhythmic than class 1A
Dizziness, drowsiness
Abdominal upset

Question 15

Name 2 class 1C agents

Answer 15

Flecanide 
Propafenone (used less)

Question 16

What are the effects of class 1C agents on cardiac activity?

Answer 16

Substantially decreased phase 0 (Na+) in normal heart
Decreased automaticity (increased threshold)
Increased action potential duration and increased refractory period

Question 17

What are the effects of class 1C agents on ECG?

Answer 17

Prolonged PR, QRS and QT

Question 18

What are class 1C agents used for?

Answer 18

Wide spectrum
Used for supraventricular arrhythmias (fibrillation and flutter)
Premature ventricular contractions (ectopic beats)
WPW syndrome

Question 19

What are the side effects of class 1C agents?

Answer 19

Pro-arrhythmia and sudden death especially with chronic use and in structural heart disease
Increase ventricular response to supraventricular arrhythmias
CNS and GI effects

Question 20

Name some class II agents

Answer 20

Propranolol
Bisoprolol
Metoprolol
Esmolol (very short acting)

Question 21

What are the effects of class II agents on cardiac activity?

Answer 21

Increase action potential duration and refractory period in AV node to slow AV conduction velocity
Decrease phase 4 depolarisation

Question 22

What are the effects of class II agents on ECG?

Answer 22

Prolonged PR

Slower heart rate

Question 23

What are class II agents used for?

Answer 23

Treating sinus and catecholamines dependent tachycardia
Converting reentrant arrhythmias at AV node
Protecting the ventricles from high atrial rates in atrial flutter or atrial fibrillation

Question 24

What are the side effects of class II agents?

Answer 24

Bronchospasm

Hypotension

Question 25

Name some class III agents

Answer 25

Amiodarone | Sotalol

Question 26

What are the cardiac effects of amiodarone?

Answer 26

``` Increase refractory period and action potential duration Decrease phase 0 and conduction Increase threshold Decrease phase 4 Decrease speed of AV conduction ```

Question 27

What are the effects of amiodarone on ECG?

Answer 27

Prolonged PR, QRS and QT | Decreased heart rate

Question 28

What is amiodarone used for?

Answer 28

Effective for most arrhythmias

Question 29

What are the side effects of amiodarone?

Answer 29

``` Increase with time Pulmonary fibrosis Hepatic injury Increase LDL cholesterol Thyroid disease Photosensitivity Optic neuritis ```

Question 30

What are the cardiac effects of sotalol?

Answer 30

Increased Acton potential duration and refractory period in atrial and ventricular tissue Slow phase 4 Slow AV conduction

Question 31

What are the ECG effects of sotalol?

Answer 31

Prolonged QT | Reduced heart rate

Question 32

What are the uses of sotalol?

Answer 32

Supraventricular and ventricular tachycardia

Question 33

What are the side effects of sotalol?

Answer 33

Proarrhythmia, fatigue, insomnia

Question 34

Name 2 class IV agents

Answer 34

Verapamil | Diltiazem

Question 35

What are the cardiac effects of class IV agents?

Answer 35

Slow conduction through AV Increased refractory period in AV node Increase slope of phase 4 in SA to slow HR

Question 36

What are the effects on ECG of class IV agents?

Answer 36

Prolong PR | May increase or decrease heart rate depending on blood pressure response and baroreflex

Question 37

What are the uses of class IV agents?

Answer 37

Control ventricles during supraventricular tachycardia Convert supraventricular tachycardia Can be used in asthma patients when beta blockers can’t

Question 38

What are the side effects of class IV agents?

Answer 38

Caution when partial AV block present, can get asystole if beta blocker is on board Caution when hypotension, decreased cardiac output Some GI problems (constipation)

Question 39

What is the mechanism of adenosine?

Answer 39

Natural nucleoside that binds A1 receptors and blocks adenylyl cyclase thus reducing cAMP which in turn activated K+ currents in AV and SA node, causing hyperpolarisation Therefore leads to decrease in heart rate

Question 40

What are the cardiac effects of adenosine?

Answer 40

Slows AV conduction

Question 41

What are the uses of adenosine?

Answer 41

Convert re-entrant supraventricular arrhythmias

Question 42

What is the mechanism of ivabradine?

Answer 42

Blocks If ion current which is highly expressed in sinus node

Question 43

What are the cardiac effects of ivabradine?

Answer 43

Slows the sinus node but does not affect blood pressure

Question 44

What are the side effects of ivabradine?

Answer 44

Flashing lights | Teratogenicity not known (avoid in pregnancy)

Question 45

What are the uses of ivabradine?

Answer 45

Reduce inappropriate sinus tachycardia | Reduce heart rate in heart failure and angina

Question 46

What is the mechanism of digoxin?

Answer 46

Enhances vagal activity | Slows AV conduction and slows HR

Question 47

What are the uses of digoxin?

Answer 47

Treatment to reduce ventricular rates in atrial fibrillation and flutter

Question 48

What is the mechanism of atropine?

Answer 48

Selective muscarinic antagonist

Question 49

What are the cardiac effects of atropine?

Answer 49

Block vagal activity to speed AV conduction and increase HR

Question 50

What are the uses of atropine?

Answer 50

Treat vagal bradycardia