Antiarrhythmics Flashcards
Electric potential
Amount of work needed to move a unit of positive charge a fixed distance
Action potential
Change in membrane potential associated with the passage of an impulse along the cardiac syncytium
Explain how cardiac myocytes are connected
Portions of the cell membrane contain intercalated disks which have gap junctions
The junctions form channels between cells and allow depolarizing current to flow from one cell to the next
What do we call the transmission of action potentials that allows for coordinated contraction?
Electric coupling
Duration of cardiac action potential
0.2 seconds
Amplitude of cardiac action potential
100 mV
-80 to +20
3 types of channels involved in cardiac cell action potentials
Fast sodium channels
Voltage gated potassium channels
Slowwwww calcium channels
Phase 0
Depolarization- Na fast channels open
Potential raises to threshold (-70) due to influx through gap junctions (na+ca)
That opens the fast channels and raises potential to +20
Phase 1
Early Repolarization- voltage gated potassium
K efflux
Phase 2
Plateau- calcium channels open
Slow Ca influx- activates muscle contraction
Plateau created by balance of influx (Ca) and efflux (K)
Phase 3
Rapid (late) repolarization- continued K efflux
Calcium channels close, K channels close at end of this phase
Phase 4
Resting potential
-90mV
Maintained by non-voltage K channels (leak)
What is different about pacemaker cells?
Slow phase 4 depolarization
Only have phases 0,3,4
What is the basis for automaticity?
Phase four slow depolarization
How do we classify antiarrhythmics?
Singh-Vaughan-Williams SVW
Based on electrophysiology
What drugs do not fall into the SVW classification?
Adenosine
Digoxin
Class I SVW
Membrane stabilizing agents
Block Na channels
Delay phase 0 depolarization
Class II SVW
Beta blockers
Decrease SA and AV activity
Decrease conduction
Decrease automaticity
Class III SVW
Block potassium channels
Prolongs repolarization and refractory period
Class IV SVW
Block Ca channels
Slower phase 0 of nodal action potential (slows conduction in AV and SA nodes)
Normal automaticity arrhythmias
- sinus tach, ventricular tach
regular rhythms with shortened phase 4 depolarization
treat with beta blockers
Abnormal automaticity rhythms
Ectopic atrial tachycardia
Irregular, spontaneous impulse formation from partially depolarized cells
Treatment-calcium channel blockers
(Triggered arrhythmias)
Early after-depolarization arrhythmias
Tornadoes de pointes
Caused by drugs that delay repolarization-long QT
Results in new action potential before myocyte has fully repolarized
Treatment: beta blockers or calcium channel blockers
(Triggered arrhythmias)
Delayed after-depolarization
Digitalis toxicity
Action too early in phase 4
Typically caused by rise in calcium
Treatment: calcium channel blockers
Reentrant Circuit Arrhythmias
Atrial flutter, SVT, VT
Occur when an area of the heart contains a region of slowed ion conduction
-normal conduction cannot go unidirectional but goes in a circle
Micro- one chamber macro- multiple
SVT-adenosine
Monomorphic VT- class Ia
Fibrillation arrhythmias
Multiple microreentrant circuits in one chamber
AF: class Ia or III drugs
VF: amiodarone
What is Amiodarone?
Class III Potassium channel blocker
Prolongs action potential and increases refractory period
What is Diltiazam
Class IV calcium channel blocker
Slows AV nodal conduction
Can cause VF in WPW
WPW- what is it
Accessory pathway that bypasses AV node allowing for rapid conduction between atria and ventricles
This results in classic delta wave and short PR interval
