Drugs

Question 1

What are the basic classes of anti-arrhythmic drugs

Answer 1

I - drugs that block voltage-sensitive sodium channels

II - antagonists of B-adrenoreceptors

III - drugs that block potassium channels

IV - drugs that block calcium channels

Question 2

Name some class I drugs

Answer 2

Lidocaine

Question 3

Describe liocaines use and how it works

Answer 3

Sometimes used following an MI - only if signs of ventricular tachycardia. Areas of damaged myocardium may be depolarised and fire automatically, drug suppresses this

Blocks voltage gated Na channels in open or inactive state (preferentially blocks damaged depolarised tissue)

Blocks during depolarisation but dissociates in time for next AP so can help to prevent premature depolarisation while allowing normal depolarisation to take place

Question 4

Name some Class II drugs

Answer 4

Propranolol

Atenolol

Question 5

How do class II drugs function and when are they used

Answer 5

Block sympathetic action (B1 adrenoreceptors in heart)

They decrease slope of pacemaker potential and slow AV node conduction by blocking L type Ca channels

Can prevent supraventricular tachycardia

Used following myocardial infarction - MI often increases sympathtic activity so B-blockers used to reduce chance of arrhythmias occuring due to this

To reduce oxygen demand by making the heart have to work less hard

Question 6

Describe the action of class III drugs

Answer 6

Prolong the action potential mainly by blocking K channels, lengthening absolute refractory period

Not generally used as can also be pro-arrhythmic

Question 7

What class III drug is used, what for and why

Answer 7

Amiodarone

Treat tachycardia associated with Wolff-Parkinson-White syndrome

Also effective in suppressing ventricular arrhythmias post MI

The drug blocks Na, Ca and K channels so can be used

Question 8

Name some class IV drugs

Answer 8

Verapamil

Ditiazem

Question 9

What do class IV drugs act to do

Answer 9

Decrease slope of action potential at SA node

Decrease AV nodal conduction

Cause negative inotropy

Question 10

What is adenosine and what can it be used for

Answer 10

It is a nucleoside, it is produced endogenously at physiological levels

Acts on A1 receptors at AV node to enhance K conductance causing hyperpolarisation of the cells

This can be used to suppress conduction at the AV node and is used to terminate re-entrant SVT

Question 11

What other dugs act on the CVS

Answer 11

ACE inhibitors and AngII receptor blockers

Diuretics

Ca channel antagonists

Positive inotropes

Alpha adrenoreceptor blocker and beta blocker

Antithrombotic drugs

Question 12

Name an ACE inhibitor and describe how they work and what they are used in

Answer 12

Perindopril

Inhibit action of angtiotensin converting enzyme

Treatment of hypertension and heart failure

Question 13

What is heart failure

Answer 13

Chronic failure of the heart to provide sufficient output to meet the body’s requirements

Can cause peripheral and pulmonary oedema

Question 14

What changes do ACE inhibitors cause in the body

Answer 14

Decrease vasomotor tone (decrease BP), reducing afterload

Decrease fluid retention (decrease blood volume), reducing preload

Question 15

Why are angiotensin II receptor blockers (ARBs) used and what are they used for

Answer 15

Used to treat hypertension and heart failure in patients who cannot tolerate ACEi

Question 16

What are diuretics used for and how do they achieve this

Answer 16

Used in treatment of heart failure and hypertension

They reduce fluid volume which decreases BP and volume, reducing the preload and afterload

Question 17

What are dihydropyridine blockers and how do they work

Answer 17

Ca channel blockers that act on vascular smooth muscle

They reduce Ca influx causing a relaxation of blood vessels

This decreases peripheral resistance and arterial BP which reduces afterload and workload of the heart

Question 18

What are Ca channel blockers used to treat

Answer 18

Hypertension

Angina

Coronary artery spasm

SVTs

Question 19

What are the types of postivie inotropes and what do positive inotropes do

Answer 19

Increase contractility and cardiac output

Types: cardiac glycosides, B-adrenergic agonists

Question 20

How do cardiac glycosides work

Answer 20

They block Na/K ATPase

This increases intracellular Na, so Na-Ca exchanger activity decreases leading to a rise in intracellular Ca

More Ca in the cell means a greater force of contraction

Also cause increased vagal activity which slows AV conduction and slows heart rate

Question 21

When are cardiac glycosides used

Answer 21

Heart failure

e.g. arrhythmia such as AF

Question 22

How do B-adrenoreceptors agonists work and what are they used for

Answer 22

They are selective B1-adrenoreceptors which stimulate receptors at the SA node, AV node and on ventricular myocytes (dobutamine)

Used in cardiogenic shock and acute but reversible heart failure

Question 23

What are organic nitrates used for

Answer 23

Used to treat angina

They undergo reaction and reduction to NO which is released from endothelial cells to cause vasodilation, especially in veins

This then lowers preload and so reduces the workload on the heart, lowering oxygen demand

Question 24

How does NO cause vasodilation

Answer 24

NO activates guanylate cyclase

This acts to increase cGMP

This lower intracellular [Ca]

This relaxes vascular smooth muscle

Question 25

What types of drugs are used in treating angina and what do they do

Answer 25

Reduce workload of the heart

• Organic nitrates
• B-adrenoreceptor blockers
• Ca channel antagonists

Improve blood supply to the heart

• Ca channel antagonists
• Organic nitrates (minor effect)

Question 26

What heart conditions carry an increased risk of thrombus formation

Answer 26

Atrial fibrillation

Acute MI

Mechanical prosthetic heart valves

Question 27

What types of antithrombotic drugs are used

Answer 27

Anticoagulants

Drugs that prevent venous thromboembolism

Antiplatelet drugs