Pharmacology - Heart

Question 1

Explain the conduction pathway in the heart

Answer 1

SA Node excitation

AV Node excitation

HIS Bundle and Branches

Purkinje Fibres

Question 2

What does each part of an ECG mean?

Answer 2

P Wave –> Depolarisation of the atria

QRS Complex –> Depolarisation of the ventricles

T Wave –> Repolarisation of the ventricles

Question 3

Why can the pacemaker of the heart undergo spontaneous depolarisation?

Answer 3

Because its 4th phase has no true baseline (creaps upwards)

This is due to sodium influx via hyperpolarisation-activated, cAMP-gated, non-selective channels (funny channel)

Question 4

What occurs at the 4 (5) phases of the Cardiac Action Potential?

Answer 4

Phase 0 –> Rapid depolarisation

Due to rapid sodium influx via voltage-activated Na+ channels

Phase 1 –> Rapid repolarisation

Phase 2 –> Plateau

Due to slow Ca2+ influx via L-type channels, and efflux via K+ channels (both voltage-gated)

Phase 3 –> Repolarisation

Due to increased K+ efflux via voltage-gated K+ channels

Phase 4 –> Stable baseline

Question 5

What’s the difference between an Absolute and an Relative refractory period?

Answer 5

Absolute/Effective –> When a second AP isn’t possible regardless of the strength of the stimuli (as phase 0 can’t be reached)

Relative –> If a very strong stimulus is created, then a second AP can be caused

Question 6

How is the if ‘funny’ channel modulated?

And what drug inhibits it?

Answer 6

Stimulates –> Sympathetic NS via B1/2 receptors

Inhibits –> Parasympathetic (vagus nerve) NS via M2 receptors

Ivabradine

Question 7

What are Channelopathies?

Answer 7

Cardiac ion channel genetic diseases

Question 8

What are the classifications and types of Cardiac Arrhythmias?

Answer 8

Site of Origin in the Heart

Supraventricular (SAN/AVN/Atria)

Ventricular (HIS Bundles/Purkinje Fibres/Ventricles)

Effect on the Heart Rate

Bradycardia (below 60bpm)

Tachycardia/arrhythmia (above 100bpm)

Effect on the Heart Rhythm

Regular

Irregular

The type of QRS complex

Narrow

Broad (>120ms in duration of the ECG)

Question 9

What can cause Cardiac Arrhythmias?

Answer 9

Existing heart diseases/myocardial iscaemia

Drugs –> eg, digoxin

Electrolyte disturbances (K+/Ca2+)

Hyper/hypothyroidism

Phenocrymocytoma (increased circulating catecholamines)

Genetic disorders –> eg, channelopathies

Question 10

What different parts of the heart do Rate controlling and Rhythm controlling drugs act on?

Answer 10

Rate Controlling –> The Pacemaker AP

Rhythm Controlling –> The Cardiac AP

Question 11

What is the Vaughan Williams Classification of antiarrhythimic drugs?

Answer 11

Class 1 –> Sodium channel blockers (preventing depolarisation….phase 0)

Class 2 –> Beta-Blockers (inhibits phase 2 and 4)

Class 3 –> Drugs that prolong the AP duration (inhibits repolarisation…..phase 3)

Class 4 –> Calcium Channel Blockers (inhibit the plateau….phase 2)

Question 12

Explain Class I antiarrhythmic drugs

Answer 12

Sodium channel blockers –> so slow down depolarisation (phase 0)….and so the cardiac AP and AP conduction

There are 3 different types

1a (Disopyramide) –> Intermediate dissociation rate

Also block K+ channels, so prolong the QT interval (phase 3)

1b (Lidocaine) –> Fast dissociation rate

1c (Flecanide)–> Slow dissociation rate

Question 13

How do Beta-Blockers (Class II) work?

Answer 13

Block B1-adrenoceptors

Slow conduction of at the AV node

Question 14

How do class III drugs, like amiodarone, work?

Answer 14

Block voltage-activated K+ channels, preventing repolarisation in phase 3

So they prolong the duration of the cardiac AP and the QT interval –> Increasing the refractory period….so slowing the HR

Also blocks Na+, Ca2+ channels

Decreases expression of B1-adrenoceptors

A modest A-adrenergic receptor antagonist

Question 15

What Beta-Blocker is also a Class III drug?

Answer 15

Sotalol

Question 16

What is Sick Sinus Syndrome?

And what is the solution?

Answer 16

A group of heart rhythm disorders due to the misfunction of the SAN

• Sinus pause
• Sinus arrest (pause for over 3 seconds)
• Bradycardia-Tachycardia syndrome

Solution = Implantable transcutaneous pacemaker (TCP)

Question 17

What’s The AV Block?

Answer 17

There are 3 degrees….

1st –> Slowed AV conduction

2nd –> Missed beats to the venticles

Split into Mobitz 1 (progressive prolongation of PR intervals) and Mobitz 2 (no pattern)

3rd –> Complete block, so no conduction to the ventricles

Question 18

What type of tachyarrhythmia is Atrial Fibrillation (AF)?

Answer 18

Supraventricular tachycardia (SVT)

Question 19

What are the 2 different mechanisms of tachyarrhythmias?

Answer 19

Automaticity –> Enhanced (sympathetic overactivity) or Abnormal (ectopic pacemaker)

Triggered –> Re-entry…..Early-after-depolarisation (EAD)…..Delayed after-depolarisation (DAD)

Question 20

What is caused by Atrioventricular Nodal Re-entrant Tachycardia (AVNRT)?

Answer 20

Paroxysmal SVT

Question 21

How does Ventricular Tachycardia (micro re-entry) occur?

Answer 21

Similar to AVNRT (re-entry), but occurs in the ventricular myocardium and Purkinje fibres

Question 22

What is Wolff-Parkinson-White Syndrome?

Answer 22

Macro re-entry

Atrioventricular Reciprocating Tachycardia (AVRT), which is where there is re-entry via accessory pathways

Question 23

What are the factors that can promote EAD (early after-depolarisations) and DAD (delayed after-depolarisations)

Answer 23

Question 24

What’s the difference between AF and an Atrial Flutter?

Answer 24

AF –> Fast irregulaly irregular heartbeat

Atrial Flutter –> Fast regular heartbeat