Drugs On The Circulation (9)

Question 0

What are the main abnormalities that can affect the heart rate or rhythm?

Answer 0

• Bradycardia
• Tachycardia
• Atrial fibrillation
• Ventricular fibrillation
• Atrial flutter

Question 1

What are the main effects drugs can have on the heart?

Answer 1

• Rate and rhythm
• Force of myocardial contraction
• Peripheral resistance and blood flow
• Blood volume

Question 2

What are the three main causes of arrhythmia?

Answer 2

• Ectopic pacemaker activity
• Afterdepolarisations
• Reentry loop

Question 3

What does ectopic pacemaker activity mean?

Answer 3

• Damaged myocardium becomes depolarised and spontaneously active
• Latent pacemaker region activated due to ischaemia
• Dominates over SAN

Question 4

What is meant by a reentry loop?

Answer 4

• Conduction delay
• Conduction is blocked by damaged region
• If there’s incomplete conduction damage excitation can take a longer route through damaged area, mixing signals

Question 5

What is meant by an afterdepolarisation?

Answer 5

• Abnormal depolarisations following AP

Question 6

What are the 4 basic classes of anti-arrhythmic drugs?

Answer 6

• 1) blocks voltage sensitive Na channels
• 2) antagonists of B-adrenoreceptors
• 3) block K channels
• 4) block Ca channels

Question 7

Give an example of a class I anti-arrhythmic drug and what does it do?

Answer 7

• Lidocaine only blocks open/inactive voltage gated Na channels
• Use dependent block
• Used following MI if ventricular tachycardia shown
• Damaged areas of myocardium may be depolarised and fire automatically, lidocaine blocks Na channels to prevent automatic firing and so less tachycardia

Question 8

Give an example of a class II anti-arrhythmic drug and what does it do?

Answer 8

• B blockers
• Blocks sympathetic action to decrease slope of pacemaker potential in SAN
• Prevents ventricular arrhythmias (may be due to increased sympathetic action)
• Reduces O2 demand: reduce myocardial ischaemia
• Slow conduction in AVN can prevent supraventricular tachycardia

Question 9

What do class III anti-arrhythmics do?

Answer 9

• Prolong AP
• Lengthens absolute refractory period
• Prevents another AP occurring too soon

Question 10

What do class IV drugs do?

Answer 10

• Decrease slope of pacemaker AP at SAN
• Decrease AVN conduction
• Decrease force of contraction (can also cause some coronary and peripheral vasodilation)

Question 11

What role does adenosine have as an anti-arrhythmic?

Answer 11

• Enhances K conduction
• Hyperpolarises cells of conducting tissue
• Decreases cAMP levels
• Short lived
• alpha 1 receptors at AVN

Question 12

What are the main features of heart failure?

Answer 12

• Decreased cardiac output
• Decreased force of contraction
• Decreased tissue perfusion
• Oedema

Question 13

What drugs are there to treat heart failure by increasing cardiac output?

Answer 13

• Positive inotropes
• Cardiac glycosides
• B- adrenergic agonists

Question 14

What drugs are there to increase myocardial contractility?

Answer 14

• Cardiac glycosides
• Digoxin to block Na/K ATPase
• B adrenoreceptor agonists

Question 15

What is the action of cardiac glycosides?

Answer 15

• Block Na/K ATPase
• Increase in Na concentration inside the cell lead ps inhibition of NCX
• Increases Ca concentration inside cardiac myocytes: -ve ionotropic effect & increase in contraction force
• Increases vagal activity: slows AV conduction, slows heart rate

Question 16

What do ACE inhibitors do?

Answer 16

• Decrease vasomotor tone- decreasing blood pressure
• Reduce after load of heart
• Decrease fluid retention- decrease blood volume
• Reduce preload and work load of heart

Question 17

Which two drugs are the main alleviators of workload for the heart?

Answer 17

• B blockers

- Diuretics (decreases blood pressure)

Question 18

How is angina treated?

Answer 18

• Reduce the workload of the heart: B blockers, Ca channel antagonists and organic nitrates
• Improve blood supply to heart: organic nitrates and Ca channel antagonists

Question 19

What do the organic nitrates do?

Answer 19

• React with triols (-SH) groups in vascular smooth muscle causes NO2- to be released
• NO2- -> NO (powerful vasodilator)

Question 20

How does NO cause vasodilation?

Answer 20

• NO stimulates guanylate cyclase
• Guanylate cyclase acts as catalyst for GTP -> cGMP
• cGMP -> PKG -> Decreased Ca conc inside the cell -> vasodilation

Question 21

What is the primary action of organic nitrates?

Answer 21

• Lowers preload by venodilation
• Decreases workload of heart
• Heart fills less therefore force of contraction decreases
• Lowers O2 demand

Question 22

What is the secondary action of organic nitrates?

Answer 22

• Acts on coronary arteries to improve O2 delivery to ischaemic myocardium
• Acts on collateral arteries to improve blood supply to all of the heart including ischaemic areas

Question 23

What heart conditions can increase the risk of forming a thrombus?

Answer 23

• Atrial fibrillation
• Acute MI
• Mechanical prosthetic heart valves

Question 24

Give some examples of anticoagulants and what do they do?

Answer 24

• Heparin (IV): - inhibits thrombin
  - short term
• Fractionated heparin (subcutaneous)
• Warfarin (orally): - antagonises action of Vit K
  - long term

Question 25

What is a good example of an anti platelet drug used after an MI?

Answer 25

• Aspirin

Question 26

What are the causes of hypertension?

Answer 26

• Increase in blood volume

- Increased TPR

Question 27

What are the drugs that could be used in the treatment of hypertension?

Answer 27

• Diuretic
• ACE inhibitors
• B blockers
• Ca channel blockers (vasodilation)
• alpha 1 adrenoceptor antagonists (vasodilation)