Pathophysiology of Dysrhythmias + Classification of Antiarrhythmics 1 Flashcards
What do ions move down?
Electrochemical gradient
How is intracellular Na+, K+ + Ca2+ maintained?
Active transport
What is the charge of the inside of the cell?
Negative
What exchanges Na+?
Na+/K+-ATPase exchange pump
3:2
What exchanges Ca2+?
Na+/Ca2+ exchanger
1:3
What does the Ca2+=ATPase exchanger pump do?
Transports one Ca2+ out BUT with no exchange
What are inward currents?
Depolarising
= movement of positive charge into cell or negative out of the cell
What are outward currents?
Repolarising
= positive charge out cell or negative into the cell
What are the 3 conformational states of voltage-gated ion channels?
Closes
Open
Inactive
What are the 2 type of action potentials in the heart?
Heart muscle
Pacemaker
What happens in the cardiac ventricular AP?
Na+ influx
K+ channels open = K+ efflux
Influx of Va2+ through L-type channels
Ca2+ + Na+ channels close
K+ remain open to return + maintain -90mv
What is a ventricular cell ion channel connected by?
Gap junctions
= current flows to depolarise
What happens first to INa?
Inactivates rapidly
Whilst ICa sustained for longer
What is the depolarising action of ICa offset by?
Successive activation of outward K+ currents = plateau phase
What happens when Ikr + IKs are activated?
Repolarisation follows
What happens in Phase 0?
Rapid depolarisation
= opening of Na+ channels
-70mv
What happens in Phase 1?
Initial Repolarisation
= K+ moving out + Cl- moving in
What happens in Phase 2?
Plateau phase
= L-type calcium channels open
= balance between inward Ca2+ + outward K+
What happens in Phase 3?
Repolarisation
L-type Ca2+ channels close
Rectifier K+ remains open
What do pacemaker cells cause?
Adjacent cardiac muscle cells to reach threshold voltage
= initiating cardiomyocyte AP
What does it mean that pacemaker cells have an unstable membrane potential?
Generates AP spontaneously
Describe the refractory period
No electrical impulse will activate AP
Membrane NOT repolarised
Na+ channels not recovered from inactivated state
What does a relative refractory period require?
Large stimulus to initiate AP
What does a supernormal period require?
Threshold lower than typically required to generate AP
How does the refractory period last?
200 msec = one cardiac contraction
