arrythmia stuff

Question 1

RWD syndrome mutation

Answer 1

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

Question 2

JLNS mutations are

Answer 2

homozygous carriers of mutations in IKs (LQT1)

Question 3

JLNS symptoms

Answer 3

congenital deafness, (homozygous)

while the heterozygous carriers are asymptomatic

Question 4

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

Answer 4

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

Question 5

effect of LQT1 mutant slow K+ channels

Answer 5

reduced current amplitude

Question 6

effect of LQT3 mutant na+ channels

Answer 6

incomplete activation

Question 7

brugada syndrome mutations

Answer 7

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.

Question 8

triggered afterdepolarizations: triggered by

Answer 8

action potentials

Question 9

Fast response phase 2 is prolonged by

Answer 9

1. ↑ inward current
   (incomplete Na+ channel inactivation in LQT3) or by
2. ↓ outward current
   (↓ K+ current in LQT1, LQT2).

Question 10

Ca2+ entry during the prolonged QT interval triggers

Answer 10

1. EADs
   (via Ca2+ channel reactivation) or
2. DADs
   (via NCX-dependent depolarization).

Question 11

↑ sympathetic tone (startle) ↑ likelihood of

Answer 11

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

Question 12

heart failure increases the

Answer 12

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

Question 13

Amiodarone is a class

Answer 13

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

Question 14

• Class I drugs slow

Answer 14

upstroke

Question 15

• Class Ib drugs show

Answer 15

pure class I action: slow upstroke, decreased AP duration

Question 16

• Class Ia & Class Ic drugs delay

Answer 16

delay phase 3 onset via K+ channel block

Question 17

Na+ channel block leads to

Answer 17

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

Question 18

All class I:

Answer 18

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

Question 19

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

Answer 19

it will become blocked by the drug.

Question 20

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

Answer 20

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

Question 21

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

Answer 21

more slowly