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Flashcards in arrythmia stuff Deck (21):
1

RWD syndrome mutation

1. in the slow cardiac K+ channel IKs (LQT1),
2. the rapid cardiac K+ channel IKr (LQT2)
3. the cardiac Na+ channel INa (LQT3).

2

JLNS mutations are

homozygous carriers of mutations in IKs (LQT1)

3

JLNS symptoms

congenital deafness, (homozygous)

while the heterozygous carriers are asymptomatic

4

the result of reducing the number of K+ channels expressed in the myocyte plasma membrane is?

reduces the size of the K+ current (IKr + IKs) that helps terminate the plateau phase of the fast response and return the membrane to resting potential during diastole.

aka. prolonged plateau

5

effect of LQT1 mutant slow K+ channels

reduced current amplitude

6

effect of LQT3 mutant na+ channels

incomplete activation

7

brugada syndrome mutations

1. More than 30 different mutations in the cardiac Na+ channel have been linked to Brugada,
2. with many of these reducing peak inward Na+ current that drives action potential upstroke in ventricular myocytes.

8

triggered afterdepolarizations: triggered by

action potentials

9

Fast response phase 2 is prolonged by

1. ↑ inward current
(incomplete Na+ channel inactivation in LQT3) or by

2. ↓ outward current
(↓ K+ current in LQT1, LQT2).

10

Ca2+ entry during the prolonged QT interval triggers

1. EADs
(via Ca2+ channel reactivation) or

2. DADs
(via NCX-dependent depolarization).

11

↑ sympathetic tone (startle) ↑ likelihood of

triggered afterdepolarizations because Ca2+ influx is enhanced by β-adrenergic receptor activity.

12

heart failure increases the

frequency of occurrence of triggered afterdepolarizations (even without LQT mutations).

13

Amiodarone is a class

III drug that has, important for its utility, class I action too.

14

• Class I drugs slow

upstroke

15

• Class Ib drugs show

pure class I action: slow upstroke, decreased AP duration

16

• Class Ia & Class Ic drugs delay

delay phase 3 onset via K+ channel block

17

Na+ channel block leads to

1. decreased phase 0 upstroke, which leads to
2. decreased conduction velocity, which leads to
3. decreased re entry

18

All class I:

↓ conduction velocity & ↑refractory period, thereby ↓re-entry

19

The more frequently a channel is used (activated), the greater the chance that

it will become blocked by the drug.

20

2. Compared to less active cardiac tissue, over-active cardiac tissue:

“uses” (activates) Na+ channels more, so Na+ channels in over-active tissue will more likely be blocked.

21

Tissue in which a larger fraction of Na+ channels is blocked will conduct___.

more slowly