Basic EP (HRS)

Question 1

Delayed rectifier currents

Answer 1

I Kur
I Kr
I Ks

Question 2

I K ur

Answer 2

Ultra rapid delayed rectifier current

Encodes by KCNA5 (K v1.5)

Only detected in atrium

May be target in AFib

Question 3

I K r

Answer 3

Rapid delayed rectifier current

Encoded by KCNH2 (HERG)

HERG mutations are common cause of LQTS

***almost all drugs causing TdP are I Kr blockers

Question 4

I K s

Answer 4

Slow delayed rectifier

Encoded by KvLQT1 + minK (KCNQ1+KCNE1)

KCNQ1 mutation causes LQT1

I Ks current increases with adrenergic stimulation. (Current gets bigger with catecholamine stimulation)

Question 5

Pacemaker channels

Answer 5

HCN4 (target of iverbradine)
T type Ca channels
NCX (?)

Mutations in HCN4 –> those pts need ppm early in life.

Question 6

Gap junctions in heart

Answer 6

connexions - Cx43, Cx40, Cx45

Side to side communication is slower than end to end (contributes to property of anisotropy)
-faster to go length wise along muscle fibers.

Question 7

EADs

Answer 7

QT prolonging drugs
Exaggerated by slow rate, low K
Blunted by rapid rates, K, Mg
Mech: net inward plateau current
Rhythm: TdP

Question 8

DADs

Answer 8

Digitalis, catecholamines
Exaggerated by rapid rates
Blunted by CCB
Mech: intracellular Ca overload (eg leaky ryanodine receptor)

Digoxin toxicity; Ischemia

Question 9

Wavelength equation (for excitable gap)

Answer 9

Wavelength
= refractory period x conduction velocity

Increased wavelength –> re-entry extinction

Question 10

Inactivating currents

Answer 10

I to
I Na
I Ca

Question 11

CYP 2C9

Answer 11

Warfarin

Question 12

CYP 2D6

Answer 12

Propafenone
Metoprolol
Carvedilol

Question 13

CYP 3A4/5/7

Answer 13

Terfenidine

CCB