16 Intro to Cardiac Electrophysiology

Question 1

inward rectifier K currents work better at what membrane potential

Answer 1

more negative Vm

Question 2

effective refractory period

Answer 2

too many Na channels still inactive for AP

inward current would be too small to spread to neighbors

Question 3

are mostly depolarized by Ca2+ current rather than Na+ current

Answer 3

nodal cells(SA, AV)

Question 4

describe adenosine/acetylcholine effects on nodal cells

Answer 4

• *act on M2 receptors **
• decreases cAMP, pacemaker(funny) current initiates at more negative/later potentials
• decreased PKA activity means less Ca current

act on IKAdo/IKACh directly

• increase K efflux making APs take longer

Question 5

describe NE modulation of nodal cells

Answer 5

• *increases cAMP**
• makes pacemaker current initiate sooner during repolarization
• indirectly activates Ca channels via PKA prodution

Question 6

pacemaker current

Answer 6

Na and K; Na predominates allowing eventual threshold/AP generation

Question 7

strategies for interrupting arrhythmias

Answer 7

increase threshold(decrease Na current)

extend refractory period(increase AP duration, decrease K current)

Question 8

EAD vs DAD

Answer 8

EAD appear during normal repolarization prior to complete repolarization

• most common in prolonged QT

DAD occur after max hyperpolarization

• occur with high intracellular calcium(digitalis)

Question 9

blocking of hERG channels is associated with what pathology?

Answer 9

long QT syndrome

hERG channels are K channels; less K current means longer time to repolarize