CVS - Arrrhythmia Drugs

Question 1

What possible effects can drugs have on the CVS?

Answer 1

They can alter:

1) rate and rhythm of heart
2) force of myocardial contraction
3) peripheral resistance and blood flow
4) blood volume

Question 2

Give some causes of tachycardia

Answer 2

• ectopic pacemaker activity
• afterdepolarisations
• atrial flutter/fibrillation
• re-entry loop

Question 3

Give some causes of bradycardia

Answer 3

• sinus bradycardia (may be due to sick sinus syndrome or drugs)
• conduction block

Question 4

What is delayed after-depolarisation?

Answer 4

Extra depolarisation which occurs after the main depolarisation. Usually due to high intracellular Ca2+

Question 5

What are early after-depolarisations?

Answer 5

Extra depolarisations which occur at the end of the plateau phase of depolarisation. More likely to occur when action potential is prolonged, so there is a prolonged QT interval

Question 6

How can a unidirectional block of conduction due to myocardial damage lead to an arrhythmia forming?

Answer 6

The impulse cannot travel down through the affected area, so the equivalent impulse from the other side of the heart (as there are two mirrored impulses) spreads upwards through the area, setting up a ‘circus’ of depolarisation

Question 7

What can be caused by multiple re-entrant circuits in the atria?

Answer 7

Atrial fibrillation

Question 8

How does lidocaine work?

Answer 8

It blocks voltage-dependent Na+ channels

Question 9

Why does lidocaine have little effect on normal cardiac tissue?

Answer 9

It preferentially blocks open/inactive Na+ channels, which are most present in damaged depolarised tissue

Question 10

Why would lidocaine be given (CVS causes)?

Answer 10

Sometimes used following MI if someone has ventricular tachycardia

Question 11

How do beta blockers work?

Answer 11

They block sympathetic action at the B1 adrenoceptors in the heart, which slows conduction at the AV node and decreases the slope of the pacemaker potential

Question 12

Why would beta blockers be used?

Answer 12

• prevent supraventricular tachycardias because they slow the conduction at AV node
• used after MI
• they reduce O2 demand, so they can be used to reduce myocardial ischaemia following MI

Question 13

What is the effect of drugs that block K+ channels?

Answer 13

They lengthen the absolute refractory period, which can have pro-arrhythmic effects

Question 14

Give an example of a drug which blocks K+ channels

Answer 14

Amiodarone

Question 15

What is the effect of drugs which block Ca2+ channels?

Answer 15

• decrease slope of action potential at SA node
• decrease AV node contraction
• decrease force of contraction

Question 16

What is adenosine?

Answer 16

Substance which is produced endogenously, which acts on alpha-1 receptors at the AV node. It enhances K+ conductance and is an antiarrhythmic

Question 17

How can drugs be used to treat heart failure?

Answer 17

Can give:

• positive inotropes to increase cardiac output (not routine)
• drugs which reduce afterload and preload

Question 18

How do cardiac glycosides work?

Answer 18

• inhibit Na+Ka+ATPase, so [Na+] in the cell rises
• this means the Na+Ca2+ exchanger doesn’t work as well, as it relies on the sodium gradient
• [Ca2+] rises and it is stored in the sarcoplasmic reticulum
• more Ca2+ available, so increased force of contraction

They also cause increased vagaries activity, slowing the heart rate

Question 19

When would beta-adrenoceptor agonists be used?

Answer 19

They act on beta-1 receptors and are used in cardiogenic shock or acute but reversible heart failure

Question 20

How do ACE-inhibitors work?

Answer 20

They reduce the workload of the heart by inhibiting the action of angiotensin converting enzyme. This reduces vasoconstriction and blood volume

Question 21

Why are ACE inhibitors particularly useful in heart failure?

Answer 21

They decrease both afterload and preload of the heart

Question 22

How do organic nitrates work?

Answer 22

NO2- is reduced to nitric oxide, which is a powerful vasodilator. They lower the intracellular [Ca2+], causing relaxation of vascular smooth muscle

Question 23

How does nitric oxide help angina?

Answer 23

• causes VENOdilation which lowers preload and reduces work load of heart
• acts on coronary collateral arteries to improve O2 delivery to ischaemic myocardium

Question 24

True or false - NO works on arterioles?

Answer 24

It doesn’t!

Question 25

Which heart conditions carry a higher risk of thrombus formation?

Answer 25

Atrial fibrillation, acute myocardial infarction, mechanical prosthetic heart valves

Question 26

Give some examples of antithrombotic drugs

Answer 26

• anticoagulants (heparin, fractionated heparin, warfarin, oral thrombin inhibitors)
• antiplatelet drugs (aspirin)

Question 27

How does warfarin work?

Answer 27

Antagonises the action of vitamin K

Question 28

How does heparin work?

Answer 28

Inhibits thrombin