Pathophysiology of Dysrhythmias + Classification of Antiarrhythmics 1

Question 1

What do ions move down?

Answer 1

Electrochemical gradient

Question 2

How is intracellular Na+, K+ + Ca2+ maintained?

Answer 2

Active transport

Question 3

What is the charge of the inside of the cell?

Answer 3

Negative

Question 4

What exchanges Na+?

Answer 4

Na+/K+-ATPase exchange pump
3:2

Question 5

What exchanges Ca2+?

Answer 5

Na+/Ca2+ exchanger
1:3

Question 6

What does the Ca2+=ATPase exchanger pump do?

Answer 6

Transports one Ca2+ out BUT with no exchange

Question 7

What are inward currents?

Answer 7

Depolarising
= movement of positive charge into cell or negative out of the cell

Question 8

What are outward currents?

Answer 8

Repolarising
= positive charge out cell or negative into the cell

Question 9

What are the 3 conformational states of voltage-gated ion channels?

Answer 9

Closes
Open
Inactive

Question 10

What are the 2 type of action potentials in the heart?

Answer 10

Heart muscle
Pacemaker

Question 11

What happens in the cardiac ventricular AP?

Answer 11

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

Question 12

What is a ventricular cell ion channel connected by?

Answer 12

Gap junctions
= current flows to depolarise

Question 13

What happens first to INa?

Answer 13

Inactivates rapidly
Whilst ICa sustained for longer

Question 14

What is the depolarising action of ICa offset by?

Answer 14

Successive activation of outward K+ currents = plateau phase

Question 15

What happens when Ikr + IKs are activated?

Answer 15

Repolarisation follows

Question 16

What happens in Phase 0?

Answer 16

Rapid depolarisation
= opening of Na+ channels
-70mv

Question 17

What happens in Phase 1?

Answer 17

Initial Repolarisation
= K+ moving out + Cl- moving in

Question 18

What happens in Phase 2?

Answer 18

Plateau phase
= L-type calcium channels open
= balance between inward Ca2+ + outward K+

Question 19

What happens in Phase 3?

Answer 19

Repolarisation
L-type Ca2+ channels close
Rectifier K+ remains open

Question 20

What do pacemaker cells cause?

Answer 20

Adjacent cardiac muscle cells to reach threshold voltage
= initiating cardiomyocyte AP

Question 21

What does it mean that pacemaker cells have an unstable membrane potential?

Answer 21

Generates AP spontaneously

Question 22

Describe the refractory period

Answer 22

No electrical impulse will activate AP
Membrane NOT repolarised
Na+ channels not recovered from inactivated state

Question 23

What does a relative refractory period require?

Answer 23

Large stimulus to initiate AP

Question 24

What does a supernormal period require?

Answer 24

Threshold lower than typically required to generate AP

Question 25

How does the refractory period last?

Answer 25

200 msec = one cardiac contraction