Cardiac Action Potential and Antiarrhythmics

Questions and Answers

What is Pacemaker Action Potential?

Name the channels or receptors blocked by the major classes of antiarrhythmics.

Sodium channels (Class I), Beta receptors (Class II), Potassium channels (Class III), Calcium channels (Class IV)

Which class of antiarrhythmics are used for rate control and which are used for rhythm control?

Rate control: Class II and IV; Rhythm control: Class I and III

Which two classes of antiarrhythmics can cause QT prolongation?

Class IA and Class III Signup and view all the answers

Match the feature with the Class 1 Antiarrhythmic:

Increase length of AP = 1A No change on length of AP = 1C Shorten length of AP = 1B Fast rate of dissociation with sodium channels = 1B Slow rate of dissociation with sodium channels = 1C Intermediate rate of dissociation with sodium channels = 1A Neurologic side effects = 1B Can be used for both SVTs and VTs = 1A Preferentially used to treat VTs post MI = 1B Proarrhythmic and contraindicated post MI = 1C Especially used in WPW and reentrant tachycardias = 1A Used in Afib = 1A or 1C Signup and view all the answers

Rank the Class 1 Antiarrhythmics based on their affinity towards the fast sodium channel.

C > A > B Signup and view all the answers

Which Class 1 Antiarrhythmics affect phase 3 of the action potential?

Class 1A and Class 1B Signup and view all the answers

Describe the changes on the ECG seen in Class 1 Antiarrhythmics.

Prolongation of QRS and QT intervals. Signup and view all the answers

Match the feature with the Class 1A Antiarrhythmic:

Anticholinergic actions = Disopyramide > Quinidine Greatest negative inotropic effect = Disopyramide (CI in HF) Drug induced SLE = Procainamide Thrombocytopenia = Quinidine Agranulocytosis = Procainamide Increased QT interval = All 3 Metabolized by acetylation = Procainamide Cinchonism = Quinidine Signup and view all the answers

A 57-year-old man is being treated for an atrial arrhythmia. Which antiarrhythmic drug is he most likely taking? A. Metoprolol B. Disopyramide C. Dronedarone D. Sotalol

Disopyramide Signup and view all the answers

Which of the following requires a check-up for symptoms of sore throat, bleeding gums, or general fatigue? A. Lidocaine B. Procainamide C. Sotalol D. Potassium ions E. Quinidine

Procainamide Signup and view all the answers

Study Notes

Cardiac Action Potential and Antiarrhythmics

Pacemaker Action Potential: Key mechanism driving rhythmic heart activity, generated in the sinoatrial node.
Major Classes of Antiarrhythmics:
- Class I: Sodium channel blockers
- Class II: Beta blockers
- Class III: Potassium channel blockers
- Class IV: Calcium channel blockers
- Mnemonic: Some Block Potassium Channels
Rate vs. Rhythm Control:
- Rate control: Class II (beta blockers) and Class IV (calcium channel blockers), affecting nodal action potentials.
- Rhythm control: Class I (sodium channel blockers) and Class III (potassium channel blockers), affecting cardiac myocyte action potentials.
QT Prolongation:
- Classes causing QT prolongation: Class IA and Class III
- Increased effective refractory period (ERP) can help treat reentrant tachycardias.
- Prolonged QT interval risks Torsades de Pointes.

Class I Antiarrhythmics Features

Increase in AP Length: Class IA
No Change in AP Length: Class IC
Shorten AP Length: Class IB
Dissociation Rates:
- Fast: Class IB
- Intermediate: Class IA
- Slow: Class IC
Neurologic Side Effects: Primarily associated with Class IB (ex: stimulation or depression).
Indications:
- Class IA: Both supraventricular tachycardias (SVTs) and ventricular tachycardias (VTs).
- Class IB: Preferentially for VTs post-myocardial infarction.
- Class IC: Contraindicated post-MI due to proarrhythmic potential.
- Class IA: Effective in Wolff-Parkinson-White (WPW) syndrome and reentrant tachycardias.
- Class IA or IC: Used for Atrial fibrillation (Afib).
Affinities Towards Sodium Channels:
- Classes ranked by binding affinity: Class IC > Class IA > Class IB (Mnemonic: CAB).
- Class IC causes significant phase 0 depolarization inhibition; Class IB has minimal inhibition.
Phase 3 Action Potential Effects:
- Class IA blocks potassium channels, increasing ERP and AP duration.
- Class IB decreases duration of phase 3 repolarization, leading to shorter AP duration.

ECG Changes with Class I Antiarrhythmics

Phase 0 Depolarization: Represented by QRS complex; prolonged due to sodium channel blockade.
Phase 3 Repolarization: Associated with QT interval changes; influenced by specific class actions.
Prolongation Effects:
- Class IA: Prolongs QT due to potassium channel blockade.
- Class IB: Decreases QT duration due to reduced phase 3 repolarization duration.

Class 1A Antiarrhythmic Features

Anticholinergic Actions: More prominent with Disopyramide than Quinidine.
Negative Inotropic Effect: Greatest with Disopyramide; avoided in patients with heart failure.
Adverse Effects:
- Drug-induced lupus erythematosus: Associated with Procainamide.
- Thrombocytopenia: Seen with Quinidine.
- Agranulocytosis: Risk with Procainamide.
- Increased QT interval: All Class 1A agents have this effect.
Metabolism: Procainamide is metabolized by acetylation.
Cinchonism: Associated with Quinidine.

Patient Scenarios with Antiarrhythmics

Dry mouth, blurred vision, urinary hesitancy: Likely caused by Disopyramide, indicative of anticholinergic side effects.
Sore throat, bleeding gums, fatigue: Symptom check-up essential for patients on Procainamide due to the risk of agranulocytosis.

Description

Test your knowledge on cardiac action potentials and the major classes of antiarrhythmic drugs. This quiz covers definitions, key channels involved, and important mnemonics to aid memorization. Ideal for students in pharmacology and cardiology courses.