CVS Session 9- Drugs And The CVS

Question 0

What are the three causes of cardiac arrhythmias?

Answer 0

• ectopic pacemaker activity
• after depolarisations
• Re-entry loop

Question 1

What is an arrhythmia and why do they arise?

Answer 1

Abnormalities of the heart rate or rhythm.

They arise due to disturbances in impulse generation and/or conduction.

Question 2

What is ectopic pacemaker activity?

Answer 2

When a damaged area of myocardium becomes depolarised and spontaneously active, latent pacemaker regions are activated due to Ischaemia and dominate over the SA node.

Question 3

What is an after depolarisation?

Answer 3

An abnormal depolarisation following an action potential.

Question 4

What is a re-entry loop caused by?

Answer 4

Conduction problems or accessory pathways

Question 5

What is bradycardia defined as?

Answer 5

Heart rate < 60bpm

Question 6

What is tachycardia defined as?

Answer 6

Heart rate>100bpm

Question 7

What is atrial flutter?

Answer 7

A disturbance in the rhythm of the atria.

Question 8

When may atrial fibrillation or flutter occur?

Answer 8

As a result of conditions which may put extra pressure/ stretch on the atria.

Question 9

What is a major consequence of atrial fibrillation?

Answer 9

Thrombus formation

Question 10

When is a delayed afterdepolarisation most likely to occur?

Answer 10

When the intracellular calcium concentration is high.

Question 11

When is early afterdepolarisation most likely to occur?

Answer 11

When the action potential is prolonged.

Question 12

What does early afterdepolarisation lead to? (2)

Answer 12

Oscillations

A longer QT wave.

Question 13

What is the result of a unidirectional block?

Answer 13

A re-entry loop that means the excitation goes the wrong way through the damaged area-> circus of excitation.

Question 14

What are the 4 classes on anti-arrhythmic drug?

Answer 14

1. Voltage gated sodium channel blockers
2. Beta adrenoreceptor antagonists (beta blockers)
3. Potassium channel blockers
4. Calcium channel blockers

Question 15

What do voltage gated sodium channel blockers do?

Answer 15

They block sodium channels in the open or inactive state.

Question 16

What do beta blockers do?

Answer 16

Block sympathetic activity- beta 1 adrenoreceptors in the heart and therefore decrease pacemaker potential slope and lower heart rate and AV conduction.

Question 17

When are beta blockers used and why?

Answer 17

Following an MI.
Because they reduce sympathetic activity and therefore can prevent ventricular arrhythmias that often arise due to increased sympathetic activity.

Question 18

What do potassium channel blockers do?

Answer 18

Prolong the action potential and therefore the absolute refractory period. This should prevent premature APs.
ACTUALLY PROARRHYTHMIC!

Question 19

What is the exception potassium channel blocker?

Answer 19

Amiodarone

Question 20

What do calcium channel blockers do? (3)

Answer 20

Decrease the SAN pacemaker action potential slope,
AV node conduction
and force of contraction.

Question 21

What is adenosine and what does it do?

Answer 21

An anti-arrhythmic drug that doesn’t fall into one of the classes.
It acts on alpha 1 adrenoreceptors at the AVN and enhance potassium conductance.
Momentarily stops the heart so it can reset into a normal rhythm.

Question 22

What are inotropic drugs?

Answer 22

Drugs that affect the force of contraction of the heart.

Question 23

Define heart failure

Answer 23

A chronic failure of the heart to provide sufficient output to meet the body’s requirements.

Question 24

What are 4 features of heart failure?

Answer 24

• decreased force of contraction
• decreased cardiac output
• decreased tissue perfusion
• oedema.

Question 25

How is oedema caused in heart failure?

Answer 25

The heart has to work harder, therefore pressure rises inside the heart and in veins supplying the heart. This causes capillary pressure to rise such that fluid is forced out and causes oedema.

Question 26

What two classes of treatment are used in heart failure and what are the two types within each class?

Answer 26

• positive inotropes - cardiac glycosides, beta adrenoreceptor agonists
• work loading reducing drugs - ACE inhibitors, beta adrenoreceptor antagonists

Question 27

How do cardiac glycosides increase the force of contraction?

Answer 27

They inhibit sodium potassium pump and therefore cause a rise in intracellular sodium.
This inhibits the activity of the sodium calcium exchanger and therefore causes calcium levels to rise intracellularly.
This is stored in SR. More is available per AP therefore increased force of contraction.

Question 28

How do ACE inhibitors reduce the workload of the heart?

Answer 28

They inhibit the action of angiotensin converting enzyme therefore prevent the conversion of angiotensin one to two.
As angiotensin 2 normally vasoconstricts and increases sodium and water reabsorption- both of these are opposed; lowering bp and blood volume, therefore reducing pre and after load.

Question 29

By does atrial fibrillation have a risk of thrombus formation?

Answer 29

Because it increases stasis of blood.

Question 30

What is angina?

Answer 30

Insufficient oxygen supply/ Ischaemia of the heart that leads to chest pain upon exertion.

Question 31

What do organic nitrates do in the treatment of angina?

Answer 31

Release nitric oxide which is a powerful vasodilator.
This activates guanylate cyclase which converts GTP to cGMP, which causes intracellular calcium levels to fall. -> relaxation of smooth muscle.

Question 32

What is the primary action of organic nitrates?

Answer 32

Venodilation

Question 33

What is the secondary action of organic nitrates?

Answer 33

Dilate collateral arteries