5.1.1 Cardiac Arrhythmia Drugs Flashcards
What does each part of the ECG represent?
P wave- depolarisation of atria
QRS complex- depolarisation of ventricle
T wave- repolarisation of ventricles
What is an arrhythmia?
Heart condition where there are disturbances in:
- Pacemaker impulse formation
- Contraction impulse conduction
- or a combination of the two
What does an arrhythmia result in?
Rate and/or timing of contraction of heart muscle that may be insufficient to maintain normal CO
Describe the concentration of ions inside and outside of the cell
Na+ higher outside
Ca2+ much higher outside
K+ lower outside
How are ion concentrations maintained?
Ion selective channels
Active pumps
Exchangers
How can ions move into cells?
Passive diffusion
Ligand-gated
Voltage-gated
What happens in the phases of the cardiac action potential?
0- Depolarisation-Na+ enters cells via Na+ gated channels
1- Early repolarisation-transient outflow of K+, Na+ channels inactivate
2-Plateau- Ca2+ into cell via voltage-gated
3-Repolarisation-Ca2+channels inactivate, voltage-gated K+ channels still open K+ leaves the cell
4-Resting membrane potential
What do class 1 drugs do?
Block Na+ channels
Therefore slower upstroke, slows conduction in tissue
Minor effects on AP duration
Only blocks open/inactive Na+ channels to block damaged depolarised tissue
Give examples of Class 1 drugs
Flecainide
Propafenone
What do class 2 drugs do?
Diminish phase 4 depolarisation and automaticity
Slows conduction at AV node, blocking sympathetic action
Give an example of class 2 drugs
Beta blockers e.g. atenolol,metoprolol,bisoprolol,labetalol
-olol suffix
2= second letter in alphabet is B, Beta blocker
What do class 3 drugs do?
Block K+ channels
Increases the length of the plateau phase
Increases refractory period length
Pro-antiarrhythmic as it prolongs QT
Give examples of class 3 drugs
Amiodarone
Dofetilide
Sotalol (beta blocker but also acts on K+ channels)
What do class 4 drugs do?
Calcium channel blockers, decrease inward Ca2+ influx
Decrease the slope of phases 0 and 4 and prolongs phase 2
Decreases AV nodal conduction
Give some examples of class 4 drugs
Verapamil
Diltiazem
Label the image of the slow cardiac action potential
What is the effect of Ca2+ channel blockers on the slow cardiac action potential?
Decreases slope of phase 0, decreasing AV nodal conduction velocity
Increased length of refractory period
What drugs affect automaticity?
B agonist- increases the upstroke, increasing heart rate
Muscarinic agonists, Adenosine- decreases upstroke, slowing heart rate
