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.
