arrhythmias Flashcards
how many phases are in the action potential of a purkinje cell
5
What happens during phase 0 in the action potential of a purkinje cell
- opening of the sodium channels, rapid depolarization, inactivation of the sodium channels
what happens during phase 1 of action potential of purkinje fibers
– rapid partial repolarization due to the inactivation of fast sodium channels and increased K+ channel permeability.
what happens during phase 2 of action potential of purkinje fibers
plateau phase, Ca2+ (main effector, L-type) and some Na+ (aka: “window” or late current) channels are open
what happens during phase 3 of action potential of purkinje fibers
repolarization, Ca2+ channels inactivated, K+ channels open, Na+ channels turning to rested state
what happens during phase 4 of action potential of purkinje fibers
– resting membrane potential
Effective Refractory Period (ERP)
- ERP is the shortest interval at which a premature stimulus results in a propagated response. The ERP usually includes phase 0, 1, 2 and most of 3.
- it is due to the availability of resting Na+ channels
What phases are present in action potential of SA node cell
- 0, 3, 4
What is happening during phase 0 in SA node cell action potential
- opening of the Ca2+ channels (T-type depolarize early, but are not responsible for action potential, but L-type channels are) causing a slow depolarization.
What is happening during phase 3 in SA node cell action potential
repolarization, Ca2+ channels inactivated, K+ channels open
what is happening during phase 4 in SA node action potential
- resting membrane potential never static like in the Purkinje cell, rather a spontaneous depolarization occurs because of a slow Na+ current (If, or “funny” current), at a more depolarized potential, T- and L-type Ca 2+ channels also open and cause phase 0
is there ever a static resting potential in the SA node
resting membrane potential never static like in the Purkinje cell, rather a spontaneous depolarization occurs because of a slow Na+ current (If, or “funny” current),
The fraction of Na+ channels available for opening in a purkinje fiber in response to a stimulus is determined by
the membrane potential immediately preceding the stimulus.
Action Potential Duration (APD)
Action potential duration is the time interval between the point of depolarization and repolarization. Normally, the ERP and APD are closely linked with the ERP being roughly 85% of APD.
what are the basic causes of cardiac arrhythmias
- disturbances in impulse formation
- disturbances in impulse conduction
- both
SA node reaches threshold at what potential
-40 mV
SA node is at resting membrane potential at what value
-65 mV
List the 4 factors that determine rate of pacemaker cells
- maximum diastolic potential
- slope of phase 4 depolarization
- threshold potential
- duration of action potential
list the two causes of simple block disturbance of impulse conduction
- AV nodal block
- bundle branch block
list the two causes of reentry mechanism disturbance of impulse conduction
*major mechanism
- obstacle to homogenous condution
- unidirectional block at some point
- condution time along the circuit is long enough to find excitable tissues
Explain what happens in normal electircal impulse condution
- two impulses meet and extinguish eachother due to trying to activate cells in the effective refractory period
- all electrical activity stops and allows for resetting of the channels
explain what occurs during unidirectional block and reentry
- the impulse traveling through the unidirectional block is extinguished in the anterograde direction
- the conduction pathway can now re-enter in the retrograde direction and will cause a reentry arrhythmia circuit
Remember the Gaussian distribution of patient responses! Antiarrhythmic agents can precipitate what
lethal arrhythmias
- at higher doses, antiarrhythmic agents can depress conduction in normal tissues and produce drug induced arrhthymias
list the drugs in class 1A of sodium channel blockers
- Quinidine (Quinora)
- Procainamide (Pronestyl)
