Anti-Arrhythmic Drugs

Question 1

List the classes of anti-arrhythmic drugs.

Answer 1

(I) Na voltage channel blockers; (II) ß-adrenergic receptor blockers; (III) drugs that prolong phase 2 and delay repolarization; and (IV) calcium-channel blockers

Question 2

Describe how class I anti-arrhythmic drugs prevent re-entry.

Answer 2

Class I drugs block sodium channels, thereby slowing the phase 0 upstroke and hence slowing conduction and delaying repolarization; lengthened repolarization

Question 3

Describe the function of class II drugs.

Answer 3

Class II drugs block the ß-adrenergic receptors, which lowers the heart rate in SA and AV nodal cells.

Question 4

Class I drugs primarily work on ___________.

Answer 4

fast-contracting myocytes

Question 5

Class Ib drugs only affect _________.

Answer 5

sodium channels, thus they shorten action potential duration

Question 6

Class Ia and Ic drugs also affect __________.

Answer 6

potassium channels, so phase 2 is lengthened

Question 7

Class Ib drugs do not ___________.

Answer 7

prolong phase 2, but they do lengthen action potential duration

Question 8

The three main class Ia blockers are __________.

Answer 8

quinidine, procainamide, and disopyramide

Question 9

The three main class Ib blockers are ___________.

Answer 9

lidocaine, phenytoin, and mexiletine

Question 10

Of the class I drugs, _____ have the most powerful effect on prolonging the refractory period.

Answer 10

Ic (such as propafenone and felcainide)

Question 11

Describe the “use-dependent” blocking effects of class I drugs.

Answer 11

Sodium channels are only blocked by class I drugs when they are open, so drugs tend to affect cells whose sodium channels are hyperactive; this effect is important both for myocytes that are firing too quickly and for pain receptors.

Question 12

Blocking sodium channels prolongs the refractory period because many class I drugs ____________.

Answer 12

have a higher affinity for the inactive state of the channel, thus blocking the channels well into the next cycle and decrease the availability of channels to open upon the next depolarization

Question 13

Class I drugs are great at treating re-entrant arrhythmias because they ____________.

Answer 13

slow conduction velocity (which results in a dampened current that passes through the bloc) and lengthen the refractory period

Question 14

ß-blockers are used to treat arrhythmias that result from ___________.

Answer 14

AV node re-entry, because ß-blockers preferentially lengthen the refractory period in AV and SA myocytes

Question 15

ß-blockers make it harder for myocytes to depolarize because they ________; they also lengthen phase 2 by __________.

Answer 15

inactivate I(funny) channels; dampen the CaL and Ikr/Iks response

Question 16

Most, but not all, class III drugs block ________.

Answer 16

Ikr

Question 17

Class IV drugs also lengthen phase 2, but they do so by ___________.

Answer 17

blocking CaL channels, which slows the phase 0 upstroke and decreases the extent of depolarization; with a decreased depolarization peak, fewer Ik channels open and phase 2 is prolonged

Question 18

Adenosine is an ___________; it works by ____________.

Answer 18

unclassified antiarrhythmic drug; binding to a GPCR that inhibits adenylate cyclase (and thus works like a ß-blocker) and then activates a subunit which then activates potassium channels

Question 19

The fibrillations which are manageable with meds are ________.

Answer 19

atrial, most of which arises from re-entry; all other are better treated with ICDs

Question 20

What’s the most important class III drug?

Answer 20

Amiodarone

Question 21

_______ and ________ are pure potassium-channel blockers/

Answer 21

Ibutilide and dofetilide

Question 22

The antiarrhythmic with the shortest half-life is __________.

Answer 22

adenosine