AF Electrophysiology & ECG Interpretation 1 — Questions and Answers
Question 1: What is the characteristic ECG finding that distinguishes atrial fibrillation from normal sinus rhythm?
- Peaked T waves with prolonged QT interval
- Absence of distinct P waves with an irregularly irregular ventricular rhythm (Correct answer)
- Regular sawtooth baseline waves at 300 bpm
- Wide QRS complexes with left bundle branch block pattern
Correct answer: Absence of distinct P waves with an irregularly irregular ventricular rhythm
AF is characterized by absent organized P waves replaced by chaotic fibrillatory waves and an irregularly irregular ventricular rhythm.
Question 2: What is the typical atrial rate during atrial fibrillation?
- 60–100 impulses per minute
- 250–350 impulses per minute
- 350–600 impulses per minute (Correct answer)
- 150–250 impulses per minute
Correct answer: 350–600 impulses per minute
In AF, the atria fire chaotically at 350–600 impulses per minute, far exceeding any organized atrial rhythm.
Question 3: In atrial fibrillation, the RR intervals on the ECG are best described as:
- Fixed at 0.60 seconds
- Regularly irregular with group beating
- Irregularly irregular with no repeating pattern (Correct answer)
- Regular with rare ectopic beats
Correct answer: Irregularly irregular with no repeating pattern
The hallmark of AF is irregularly irregular RR intervals, meaning there is no consistent repeating pattern to ventricular activation.
Question 4: Which ECG lead is most useful for identifying fibrillatory (f) waves in atrial fibrillation?
- Lead I
- Lead V1 (Correct answer)
- Lead aVR
- Lead V5
Correct answer: Lead V1
Lead V1, positioned closest to the right atrium, best displays fibrillatory waves because it directly captures atrial electrical activity.
Question 5: In uncomplicated atrial fibrillation, the QRS complex width is typically:
- Greater than 0.12 seconds (wide)
- Between 0.08–0.12 seconds (narrow) (Correct answer)
- Absent due to ventricular standstill
- Exactly 0.20 seconds
Correct answer: Between 0.08–0.12 seconds (narrow)
Without an aberrant conduction pathway or bundle branch block, ventricular depolarization follows normal pathways in AF, producing a narrow QRS.
Question 6: How is atrial flutter differentiated from atrial fibrillation on ECG?
- Atrial flutter has an irregularly irregular ventricular response
- Atrial flutter shows organized sawtooth waves at 250–350 bpm (Correct answer)
- Atrial fibrillation has a regular ventricular rate of 150 bpm
- Atrial flutter has no visible atrial activity on ECG
Correct answer: Atrial flutter shows organized sawtooth waves at 250–350 bpm
Atrial flutter produces organized, regular sawtooth flutter waves at 250–350 bpm, in contrast to the chaotic, disorganized fibrillatory waves of AF.
Question 7: The PR interval in a patient with atrial fibrillation:
- Is consistently prolonged at 0.24 seconds
- Is shortened due to enhanced AV conduction
- Cannot be measured because distinct P waves are absent (Correct answer)
- Remains fixed at 0.20 seconds throughout
Correct answer: Cannot be measured because distinct P waves are absent
Because AF produces no identifiable P waves, the PR interval — which requires a measurable P wave — cannot be determined.
AF Electrophysiology & ECG Interpretation 1
What is the characteristic ECG finding that distinguishes atrial fibrillation from normal sinus rhythm?