Test Bank For Advances in Antiarrhythmic Drug Therapy, An Issue of Cardiac
Electrophysiology Clinics, 1st Edition
Authors: Ali R. Keramati,Mohammadali Habibi
,Ionic and Cellular Basis of Antiarrhythmic Drug Therapy
and Its Proarrhythmic Risks
Theory-Based Questions
1. Which phase of the ventricular myocyte action potential is primarily
mediated by rapid sodium influx through fast sodium channels?
A. Phase 0
B. Phase 1
C. Phase 2
D. Phase 4
Correct Answer: A. Phase 0
Explanation:
Phase 0 of the ventricular action potential represents rapid depolarization caused by
opening of fast voltage-gated sodium channels, leading to a sudden influx of sodium ions.
This phase determines conduction velocity through ventricular myocardium and the His-
Purkinje system.
Clinical Reasoning:
Class I antiarrhythmic drugs target sodium channels and therefore slow phase 0 upstroke
velocity, reducing conduction velocity and widening the QRS complex.
Why Incorrect Options Are Wrong:
• B: Phase 1 is transient repolarization mediated by transient outward potassium
current.
• C: Phase 2 is the plateau phase mediated mainly by calcium influx through L-type
calcium channels.
• D: Phase 4 represents resting membrane potential in ventricular cells.
ECG/Electrophysiologic Correlation:
Sodium channel blockade slows ventricular conduction and produces QRS widening on
ECG.
,2. Triggered activity caused by delayed afterdepolarizations is most
commonly associated with which intracellular abnormality?
A. Potassium depletion from extracellular fluid
B. Intracellular calcium overload
C. Reduced sodium conductance
D. Decreased sympathetic tone
Correct Answer: B. Intracellular calcium overload
Explanation:
Delayed afterdepolarizations (DADs) occur after completion of repolarization and are
caused by intracellular calcium excess, which activates transient inward currents capable
of triggering premature action potentials.
Clinical Reasoning:
Digoxin toxicity and catecholaminergic states predispose to DAD-mediated arrhythmias.
Why Incorrect Options Are Wrong:
• A: Potassium depletion predisposes more to early afterdepolarizations and QT
prolongation.
• C: Reduced sodium conductance slows conduction but does not directly cause
DADs.
• D: Increased—not decreased—sympathetic tone promotes DADs.
ECG Correlation:
DADs may manifest clinically as ventricular premature beats or bidirectional ventricular
tachycardia.
3. Which Vaughan-Williams class primarily prolongs repolarization by
blocking potassium channels?
A. Class I
B. Class II
, C. Class III
D. Class IV
Correct Answer: C. Class III
Explanation:
Class III antiarrhythmics inhibit potassium efflux during phase 3 repolarization, thereby
prolonging action potential duration and effective refractory period.
Clinical Reasoning:
These drugs are useful in preventing re-entry arrhythmias by increasing refractoriness.
Why Incorrect Options Are Wrong:
• A: Class I drugs primarily block sodium channels.
• B: Class II drugs are beta-blockers.
• D: Class IV drugs block calcium channels.
ECG Correlation:
QT interval prolongation is a hallmark of Class III drugs.
4. The principal mechanism underlying most sustained monomorphic
ventricular tachycardias in structural heart disease is:
A. Enhanced automaticity
B. Re-entry
C. Early afterdepolarizations
D. Sinus node dysfunction
Correct Answer: B. Re-entry
Explanation:
Scar tissue from ischemia or cardiomyopathy creates zones of slow conduction and
unidirectional block, facilitating re-entry circuits.
Clinical Reasoning:
Antiarrhythmics that prolong refractoriness or interrupt conduction may terminate re-
entrant tachycardias.
Electrophysiology Clinics, 1st Edition
Authors: Ali R. Keramati,Mohammadali Habibi
,Ionic and Cellular Basis of Antiarrhythmic Drug Therapy
and Its Proarrhythmic Risks
Theory-Based Questions
1. Which phase of the ventricular myocyte action potential is primarily
mediated by rapid sodium influx through fast sodium channels?
A. Phase 0
B. Phase 1
C. Phase 2
D. Phase 4
Correct Answer: A. Phase 0
Explanation:
Phase 0 of the ventricular action potential represents rapid depolarization caused by
opening of fast voltage-gated sodium channels, leading to a sudden influx of sodium ions.
This phase determines conduction velocity through ventricular myocardium and the His-
Purkinje system.
Clinical Reasoning:
Class I antiarrhythmic drugs target sodium channels and therefore slow phase 0 upstroke
velocity, reducing conduction velocity and widening the QRS complex.
Why Incorrect Options Are Wrong:
• B: Phase 1 is transient repolarization mediated by transient outward potassium
current.
• C: Phase 2 is the plateau phase mediated mainly by calcium influx through L-type
calcium channels.
• D: Phase 4 represents resting membrane potential in ventricular cells.
ECG/Electrophysiologic Correlation:
Sodium channel blockade slows ventricular conduction and produces QRS widening on
ECG.
,2. Triggered activity caused by delayed afterdepolarizations is most
commonly associated with which intracellular abnormality?
A. Potassium depletion from extracellular fluid
B. Intracellular calcium overload
C. Reduced sodium conductance
D. Decreased sympathetic tone
Correct Answer: B. Intracellular calcium overload
Explanation:
Delayed afterdepolarizations (DADs) occur after completion of repolarization and are
caused by intracellular calcium excess, which activates transient inward currents capable
of triggering premature action potentials.
Clinical Reasoning:
Digoxin toxicity and catecholaminergic states predispose to DAD-mediated arrhythmias.
Why Incorrect Options Are Wrong:
• A: Potassium depletion predisposes more to early afterdepolarizations and QT
prolongation.
• C: Reduced sodium conductance slows conduction but does not directly cause
DADs.
• D: Increased—not decreased—sympathetic tone promotes DADs.
ECG Correlation:
DADs may manifest clinically as ventricular premature beats or bidirectional ventricular
tachycardia.
3. Which Vaughan-Williams class primarily prolongs repolarization by
blocking potassium channels?
A. Class I
B. Class II
, C. Class III
D. Class IV
Correct Answer: C. Class III
Explanation:
Class III antiarrhythmics inhibit potassium efflux during phase 3 repolarization, thereby
prolonging action potential duration and effective refractory period.
Clinical Reasoning:
These drugs are useful in preventing re-entry arrhythmias by increasing refractoriness.
Why Incorrect Options Are Wrong:
• A: Class I drugs primarily block sodium channels.
• B: Class II drugs are beta-blockers.
• D: Class IV drugs block calcium channels.
ECG Correlation:
QT interval prolongation is a hallmark of Class III drugs.
4. The principal mechanism underlying most sustained monomorphic
ventricular tachycardias in structural heart disease is:
A. Enhanced automaticity
B. Re-entry
C. Early afterdepolarizations
D. Sinus node dysfunction
Correct Answer: B. Re-entry
Explanation:
Scar tissue from ischemia or cardiomyopathy creates zones of slow conduction and
unidirectional block, facilitating re-entry circuits.
Clinical Reasoning:
Antiarrhythmics that prolong refractoriness or interrupt conduction may terminate re-
entrant tachycardias.
