CVS Drugs acting on the cvs

Question 1

What are the different types of arrhythmias?

Answer 1

Bradycardia
Tachycardia (ventricular or supraventricular)
Atrial flutter
Atrial and ventricular fibrillation

Question 2

What are the causes of arrhythmias?

Answer 2

• ectopic pacemaker activity (damaged area of myocardium can become depolarised)
• afterdepolarisations (triggered following an AP, more likely if IC [Ca2+] high or AP prolonged)
• Re-entry loop (depolarisation goes round in a loop)

Question 3

What is the effect of local anaesthetics and give an example

Answer 3

Lidocaine (used following MI)
Blocks Na+ channels in the open or inactivated state only (termed “use dependent”)
Rapidly dissociated in time for the next AP (therefore has no effect on normal cardiac tissue at it has dissociated before affecting the next AP however in tachycardic myocardium it regulates APs)

Question 4

What is the effect of beta blockers and give an example

Answer 4

Propanolol, atenolol
Block sympathetic action by preventing NA binding to B1 receptors on heart
Decrease slope of pacemaker potentials

-used to prevent ventricular arrhythmias following MI, reduces O2 demand and slow conduction at AV node

Question 5

What is the effect of drugs that block K+ channels and give an example?

Answer 5

Prolong the AP by preventing the efflux of K+ (doesn’t repolarise)
This lengthens the absolute refractory period so prevents another AP too soon however in reality can cause arrhythmias so not used

Exception - amiodarone (has other actions as well)

Question 6

What is the effect of drugs that block Ca2+ channels and give an example?

Answer 6

Verapamil

• decreases slope of action potential at SA
• decreases AV node conduction
• decreases force (negative inotropy)

Question 7

What is the use of adenosine pharmacologically?

Answer 7

Acts on adenosine receptors at the AV node

• enhances K+ conductance which hyperpolarises cells
• anti-arrhythmic by blocking conduction v. briefly

Question 8

Define heart failure?

What are the features?

Answer 8

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

• reduced force of contraction, cardiac output, tissue perfusion and oedema

Question 9

What drugs are used to treat heart failure?

Answer 9

There are 2 approaches to treating heart failure -

1. Increasing cardiac output: (usually not best)
   - cardiac glycosides, improves symptoms but not long term outcome, digoxin blocks Na-K ATPase so Na accumulates in cell, then there is reduced gradient so less calcium expelled by sodium calcium exchanger so increased force of contraction
   - B agonists eg dobutamine, acts on B1
2. Reducing the work load of the heart
   - reducing afterload (reducing TPR)
   - reducing preload (reducing venous return)

ACE INHIBITORS prevent conversion of angiotensin 1 to 2. Angiotensin 2 increases Na+ and water reabsorption in kidneys so higher blood volume, and is a powerful vasoconstrictor so increases TPR

Beta blockers

Question 10

How is angina treated?

Answer 10

Reducing work load of the heart - beta blockers, calcium channel antagonists, organic nitrates (dilates VEINS)

Improving blood supply to the heart - calcium channel antagonists, organic nitrates (minor effect by acting on collateral arteries)

Organic nitrates eg glyceryl trinitrate release NO which is a powerful vasodilator. It increases cGMP which lowers calcium conc which relaxes vascular smooth muscle

Question 11

What conditions increase the risk of thrombus formation?

Answer 11

Atrial fibrillation (stagnant blood)
Acute MI
Mechanical prosthetic heart valves

Question 12

Give some examples of anti-thrombotic drugs

Answer 12

Anticoagulants

• warfarin used long term
• heparin (given IV) used short term and inhibits thrombin

Antiplatelet drugs
- aspirin given following MI or high risk of MI

Question 13

What values constitute hypertension?

Answer 13

Over 140/90 is mild hypertension

Question 14

Give the equation for pressure and explain how this relates to hypertension

Answer 14

Pressure = flow x resistance

Hypertension is therefore due to blood volume or TPR

Question 15

What drugs are used in the treatment of hypertension?

Answer 15

Diuretics to decrease blood volume
ACE inhibitors to decrease Na+ and water retention and decrease TPR
Beta blockers would work in theory but not used solely for hypertension
Ca2+ channels to vasodilate smooth muscle
a1 agonist - vasodilation

Question 16

Define inotropic drug

Answer 16

Drugs that decrease the force of contraction