AF Electrophysiology & ECG Interpretation 2 — Questions and Answers
Question 1: What primary electrophysiological mechanism underlies atrial fibrillation?
- Single-focus rapid automaticity in the SA node
- Enhanced automaticity from the AV node
- Multiple reentrant electrical wavelets within the atria (Correct answer)
- Complete block of conduction at the Bundle of His
Correct answer: Multiple reentrant electrical wavelets within the atria
AF is driven primarily by multiple simultaneous reentrant wavelets circulating chaotically through atrial tissue, preventing coordinated atrial contraction.
Question 2: A patient with Wolff-Parkinson-White (WPW) syndrome who develops atrial fibrillation is at risk for which dangerous ECG pattern?
- Regular narrow complex tachycardia at 150 bpm
- Complete AV block with ventricular escape rhythm
- Wide, bizarre QRS complexes due to rapid accessory pathway conduction (Correct answer)
- Sinus bradycardia with prolonged QT interval
Correct answer: Wide, bizarre QRS complexes due to rapid accessory pathway conduction
In WPW with AF, rapid conduction through the accessory pathway bypasses the rate-limiting AV node, producing wide bizarre QRS complexes that can degenerate into ventricular fibrillation.
Question 3: Which finding best distinguishes multifocal atrial tachycardia (MAT) from atrial fibrillation on ECG?
- MAT has wider QRS complexes than AF
- MAT has an irregularly irregular rhythm while AF is regular
- MAT displays at least 3 distinct P wave morphologies with varying PR intervals (Correct answer)
- MAT has a consistently faster ventricular rate than AF
Correct answer: MAT displays at least 3 distinct P wave morphologies with varying PR intervals
MAT is identified by three or more distinct P wave morphologies with varying PR intervals and an isoelectric baseline, distinguishing it from AF's absent P waves.
Question 4: How would you describe the f-waves (fibrillatory waves) characteristic of atrial fibrillation?
- Regular, organized waves at exactly 300 bpm
- Tall, symmetrical peaked waves following each QRS
- Flat, isoelectric baseline between QRS complexes
- Chaotic, irregular undulations varying in amplitude and morphology (Correct answer)
Correct answer: Chaotic, irregular undulations varying in amplitude and morphology
Fibrillatory waves in AF are chaotic, irregular baseline undulations that vary in amplitude and morphology, reflecting disorganized atrial electrical activity.
Question 5: 'Coarse' atrial fibrillation is differentiated from 'fine' atrial fibrillation on ECG by:
- Coarse AF has f-waves greater than 1mm in amplitude (Correct answer)
- Coarse AF has a regular ventricular rhythm
- Fine AF has more visible and organized P waves
- Coarse AF always shows wide QRS complexes
Correct answer: Coarse AF has f-waves greater than 1mm in amplitude
Coarse AF has fibrillatory waves greater than 1mm in amplitude, often associated with chronic conditions or metabolic disturbances, while fine AF has barely perceptible baseline undulations.
Question 6: A patient presents with an irregularly irregular rhythm, no visible P waves, and a ventricular rate of 82 bpm. Which diagnosis is most consistent?
- Sinus arrhythmia
- Atrial fibrillation with controlled ventricular rate (Correct answer)
- Second-degree AV block Mobitz type I
- Junctional tachycardia
Correct answer: Atrial fibrillation with controlled ventricular rate
The combination of absent P waves, irregularly irregular rhythm, and a rate under 100 bpm is consistent with controlled AF, the goal of rate-control therapy.
Question 7: In atrial fibrillation with a coexisting right bundle branch block (RBBB), the ECG will show:
- Normal narrow QRS with irregularly irregular rhythm
- Regular rhythm with wide QRS and RSR' pattern in V1
- Irregularly irregular rhythm with wide QRS showing RBBB morphology (Correct answer)
- Absent QRS complexes with only f-waves visible
Correct answer: Irregularly irregular rhythm with wide QRS showing RBBB morphology
When AF and RBBB coexist, the ECG combines the RBBB's wide QRS (RSR' in V1, wide S in leads I/V6) with AF's characteristic irregularly irregular ventricular rhythm.
AF Electrophysiology & ECG Interpretation 2
What primary electrophysiological mechanism underlies atrial fibrillation?