Drugs Flashcards
What can CVS drugs alter?
Rate and rhythm of the heart
Force of myocardial contraction
Peripheral resistance and blood flow
Blood volume
What can cardiovascular drugs be used to treat?
Arrhythmias Hypertension Heart failure Angina Risk of thrombus formation
What is atrial flutter?
An abnormal heart rhythm that occurs in the atria. Associated with tachycardia (100bpm)
What does atrial flutter look like on an ECG?
P waves give a ‘sawtooth’ appearance
4 P waves per QRS complex
Ventricular activation is regular
What is atrial fibrillation?
When the atrial muscle fibres contract independently.
What does atrial fibrillation look like on an ECG?
No P waves and irregular baseline
What is ventricular fibrillation?
When the ventricular muscle fibres contract independently.
Ventricular fibrillation on an ECG?
No QRS complex
Completely disorganised
Causes of arrhythmias?
Ectopic pacemaker activity
Afterdepolarisations
Re-entry loop
4 classes of drugs to treat arrhythmias?
Drugs that block voltage-sensitive sodium channels
Antagonists of β-adrenoceptors
Potassium channel blockers
Calcium channel blockers
What does lidocaine do?
A local anaesthetic
Blocks VG Na channel in open or inactive state
Dissociates rapidly in time for next AP
Use-dependent block
Why is lidocaine used following an MI if a patient has ventricular tachycardia?
Myocardium damaged so may be depolarised and fire automatically
More Na channels are open in depolarised tissue and lidocaine blocks these channels. Prevents automatic.
Name a β-blocker
Propanolol or atenolol
How do β-blockers work?
Block sympathetic action by blocking β-1 adrenoreceptors in the heart.
Decrease the slope of pacemaker potential in the SA node.
When are β blockers used?
Following an MI to
- decrease sympathetic activity and therefore prevent ventricular arrhythmias
- reduce oxygen demand and reduce myocardial ischaemia
Prevent supraventricular tachycardias by slowing conduction in AV node
What do K+ channel blockers do?
Lengthen the absolute refractory period
In theory it would prevent another AP from happening too soon, however can be pro-arrhythmic
What does amiodarone do?
K+ channel blocker.
Anti-arrhythmic
Also used to treat tachycardia associated with Wolff-Parkinson-White syndrome
What is Wolff-Parkinson-White syndrome?
Where there is a re-entry loop due to an extra conduction pathway.
Example of a calcium blocker drug?
Verapamil
How do calcium channel blockers work?
Decrease slope of pacemaker action potential in SA node
Decreases AV nodal conduction
Decreases force of contraction
Cause some coronary and peripheral vasodilation
What does adenosine do?
Acts on α1 receptors at AV node
Enhances K conductance, hyperpolarising cells of conducting tissue
Decreases cAMP levels
Anti-arrhythmic
What is heart failure?
Chronic failure of the heart to provide sufficient output to meet the body’s requirements.
Features of heart failure?
Reduced force of contraction
Reduced cardiac output
Reduced tissue perfusion
Oedema
What types of drugs are used in heart failure?
Positive inotropes to increase cardiac output
Drugs which reduce work load of heart by reducing afterload and preload.
What are cardiac glycosides and how do they work?
Drugs which increase inotropy.
Block NaKATPase
Describe action of cardiac glycosides for increasing contractility?
Calcium is extruded by NaCa exchanger, driven by Na moving down conc gradient set up by NaKATPase.
NaKATPase is blocked so there is a rise in intracellular Na.
Decreased activity of Na-Ca exchanger
Increase in intracellular calcium so more calcium in SR.
Increased force of contraction
How do cardiac glycosides decrease heart rate?
Increase vagal activity. Slows AV conduction. Slows heart rate.
How do ACE-inhibitors work?
Inhibit action of angiotensin converting enzyme
Prevent angiotensin I ➡️ angiotensin II
What does angiotensin II do?
Acts on the kidneys to increase Na+ and water reabsorption
Vasoconstrictor
Overall effects of ACE-inhibitors?
Decrease vasomotor tone
Reduce afterload of the heart
Decrease fluid retention
Reduce preload of the heart
Reduce workload of the heart
What is angina due to?
Narrowing of the coronary arteries
How is angina treated?
β-adrenoreceptor blockers
Ca channel antagonists
Organic nitrates
How does nitric oxide cause vasodilation?
NO activates guanylate cyclase
Increases cGMP
Lowers intracellular calcium concentration
Causes relaxation of vascular smooth muscle
How does vasodilation alleviate symptoms of angina?
Venodilation lowers preload
Reduces work load on the heart
Heart fills less therefore contraction is reduced (Starling’s Law)
Lowers oxygen demand
Which heart conditions can increase the risk of thrombosis?
Atrial fibrillation
Acute MI
Mechanical prosthetic heart valves
List the antithrombotic drugs
Heparin
Warfarin
Antiplatelet drugs (aspirin)
What does heparin do?
Inhibits thrombin
Used acutely for short term action
What does warfarin do?
Antagonises action of vitamin K
Used long term
What drugs are used to treat hypertension?
ACE-inhibitors
β-blockers
Ca channel blockers selective for vascular smooth muscle
Diuretics
α1-adrenoreceptor antagonists for vasodilation
What do class I drugs do?
Block voltage-sensitive sodium channels
Action of class II drugs?
Antagonists if β-adrenoreceptors
Class III drugs?
Block potassium channels
Action of class IV drugs?
Block calcium channels
