Week 4: Pharmacologic Modification of Action Potentials

Question 1

What is the primary target of Class I Na⁺ channel blockers?

Answer 1

Voltage-gated fast Na⁺ channels (Phase 0) in myocytes

Question 2

What is the mechanism of action for Class I Na⁺ channel blockers?

Answer 2

↓ Na⁺ influx → ↓ upstroke velocity (Phase 0) → ↓ conduction velocity

Question 3

What are the clinical uses of Class I Na⁺ channel blockers?

Answer 3

Used for atrial and/or ventricular arrhythmias

Question 4

List the drugs included in Class Ia Na⁺ channel blockers.

Answer 4

• Quinidine
• Procainamide
• Disopyramide

Question 5

What is the effect of Class Ia Na⁺ channel blockers on action potential duration?

Answer 5

↑ AP duration, ↑ ERP (Effective Refractory Period)

Question 6

What risk is associated with Class Ia Na⁺ channel blockers?

Answer 6

Can prolong QT → risk of torsades

Question 7

List the drugs included in Class Ib Na⁺ channel blockers.

Answer 7

• Lidocaine
• Mexiletine
• Tocainide

Question 8

What is the primary effect of Class Ib Na⁺ channel blockers on action potential duration?

Answer 8

↓ AP duration, ↓ ERP

Question 9

Class Ib Na⁺ channel blockers are best for which condition?

Answer 9

Post-MI ventricular arrhythmias; minimal atrial effect

Question 10

List the drugs included in Class Ic Na⁺ channel blockers.

Answer 10

• Flecainide
• Propafenone

Question 11

What is a significant contraindication for Class Ic Na⁺ channel blockers?

Answer 11

Contraindicated in structural heart disease (CAST trial)

Question 12

What is the mechanism of action for Class II beta-blockers?

Answer 12

↓ cAMP → ↓ If current and Ca²⁺ current

Question 13

List some examples of Class II beta-blockers.

Answer 13

• Metoprolol
• Esmolol
• Atenolol
• Propranolol
• Carvedilol

Question 14

What is the clinical use of Class II beta-blockers?

Answer 14

First-line in rate control for AF; reduces arrhythmia post-MI

Question 15

What is the primary target of Class III K⁺ channel blockers?

Answer 15

Delayed rectifier K⁺ channels (I_Kr, I_Ks)

Question 16

List some examples of Class III K⁺ channel blockers.

Answer 16

• Amiodarone
• Dofetilide
• Sotalol
• Ibutilide
• Dronedarone

Question 17

What effect do Class III K⁺ channel blockers have on action potential duration?

Answer 17

↑ AP duration, ↑ ERP

Question 18

What is a significant risk associated with Class III K⁺ channel blockers?

Answer 18

Risk of torsades (especially with dofetilide, sotalol)

Question 19

What is the primary target of Class IV Ca²⁺ channel blockers?

Answer 19

L-type Ca²⁺ channels (SA and AV nodes)

Question 20

List some examples of Class IV Ca²⁺ channel blockers.

Answer 20

• Verapamil
• Diltiazem

Question 21

What is the clinical use of Class IV Ca²⁺ channel blockers?

Answer 21

AV nodal arrhythmias (e.g., SVT); avoid in heart failure

Question 22

What is the mechanism of action of adenosine?

Answer 22

Activates A1 receptors → opens K⁺ channels, ↓ cAMP

Question 23

What is the clinical use of adenosine?

Answer 23

Used in acute SVT termination

Question 24

What is the mechanism of action of digoxin?

Answer 24

Inhibits Na⁺/K⁺ ATPase → ↑ intracellular Ca²⁺; vagomimetic at AV node

Question 25

What is the clinical use of digoxin?

Answer 25

Useful in AF with heart failure; risk of toxicity (esp. with hypokalemia)

Question 26

What is the primary use of magnesium sulfate in cardiac conditions?

Answer 26

First-line for torsades de pointes, even with normal Mg²⁺

Question 27

What mechanism is disrupted during ischemia?

Answer 27

Disrupts ion gradients, causes membrane depolarization

Question 28

Which class of drugs is favored in ischemia?

Answer 28

Class Ib drugs which target depolarized tissue

Question 29

What is the risk associated with Long QT Syndromes?

Answer 29

Prolonged repolarization (Phase 3) → predisposes to early afterdepolarizations (EADs) and torsades

Question 30

What should be avoided in Long QT Syndromes?

Answer 30

Avoid Class Ia, III; treat with MgSO₄, pacing

Question 31

What condition results from SA/AV nodal dysfunction?

Answer 31

Bradyarrhythmias → ↓ HR or AV block

Question 32

What may worsen bradyarrhythmias?

Answer 32

May worsen with β-blockers, CCBs, digoxin; treat with atropine or pacing

Question 33

What mechanisms are involved in tachyarrhythmias?

Answer 33

EADs, DADs, reentry circuits → rapid firing

Question 34

What classes of drugs are used for reentry tachyarrhythmias?

Answer 34

* Class II * Class III

Question 35

What is the action of adenosine in the context of tachyarrhythmias?

Answer 35

Adenosine for SVT