Cardio: Class I Antiarrhythmics

Question 1

What is the name of the cardiac action potential’s initial upslope?

Answer 1

Phase 0

Question 2

The class I drugs target the _________. What effect does this have on the cardiac action potential?

Answer 2

Open sodium channels (think of the singer clutching the jar of peanut butter that is OPEN) This decreases the slope of the action potential (think of him leaning the microphone over, decreasing the slope of the cord’s wave), this ultimately slows the action potential through the cardiac tissue.

Question 3

The class I anti-arrhythmics have _______ dependence.

Answer 3

use (because they only bind to open Na channels)

Question 4

The nodal upstroke relies on __________, and so is not affected by class I anti-arrhythmics.

Answer 4

calcium

Question 5

Where do the class I anti-arrhythmics act?

Answer 5

On the His-Purkinje system (think of the neon lights on the HP system, not the SA or AV)

Question 6

What ECG finding might you see in someone taking class I anti-arrhythmics?

Answer 6

A widened QRS (think of the wide QRS-shaped crack in the neon sign) because the His-Purkinje fibers have been slowed and the ventricles take longer to depolarize

Question 7

The three class IA drugs are ________________.

Answer 7

quinidine, procainamide, and disopyramide

Question 8

IA can treat ______________.

Answer 8

supraventricular and ventricular arrhythmias

Question 9

Specifically, IA drugs can treat ______________.

Answer 9

Wolff-Parkinson-White syndrome

Question 10

What are the side effects of quinidine?

Answer 10

Cinchonism (tinnitus – tin plates –headache, and dizziness) and thrombocytopenia (broken plates)

Question 11

The IA drugs also ________________.

Answer 11

block potassium channels (just like the prom queen tossing back the banana curtains), thus prolonging the depolarization of the ventricles

Question 12

Long-term use of procainamide can cause ______________.

Answer 12

lupus (think of the PROm king’s wolf)

Question 13

Do not give disopyramide to those with heart failure! Why?

Answer 13

Because at high doses it has a negative inotropic effect

Question 14

All IA drugs can cause ___________.

Answer 14

torsades (think of the banner twisting across the ground floor)

Question 15

Why does prolonged QT interval cause torsades?

Answer 15

Because the voltage-sensitive sodium channels can fire again

Question 16

Any drug that blocks __________ can cause torsades.

Answer 16

potassium channels (because it prolongs the QT interval)

Question 17

Class IB drugs have what effect?

Answer 17

They have the lowest affinity for sodium channels of the class I drugs, so they don’t cause torsades or prolonged QT. Also, they don’t block potassium channels as much (think of Libby closing the potassium curtain), and thus speed up the action potential –shortening its duration. (think of Libby shutting the potassium blinds quickly).

Question 18

What antiseizure medication has antiarrhythmic effects?

Answer 18

Phenytoin (it is a class IB drug –think of the friendly towing truck outside Libby’s window)

Question 19

IB drugs target ___________ tissue.

Answer 19

ischemic/damaged (B = Broken) As such, they’re great for treating ischemia-induced arrhythmias.

Question 20

Which antiarrhythmics can cause neurologic effects?

Answer 20

IB (think of Libby and her boyfriend’s hats –the hat “he got on their first date” that looks like a brain) IB can cause paresthesias or slurred speech.

Question 21

What are the IC drugs?

Answer 21

Propafenone (PuRPle PHONE on the 3rd floor) and flecainide (FLaKes cereal)

Question 22

Which antiarrhythmics do not bind to potassium channels?

Answer 22

The IC. (Think of the untouched curtain on the 3rd floor.) As such, they do not prolong the action potential.

Question 23

IC drugs are great at treating _____________.

Answer 23

atrial fibrillation (at least, the rhythmic aspect of it; other drugs are used to slow the rate) Think of the static, irregularly irregular rhythm on the TV and the guy zapping the channel to a more regular rate.

Question 24

Why should IC drugs not be used in someone with structural defects?

Answer 24

Because they tightly bind sodium channels and thus have the strongest effect on the phase 0 upslope