ECG Practical Content and Preparation 3 — Questions and Answers
Question 1: A QRS complex that is wider than 0.12 seconds most likely indicates:
- First-degree AV block
- Accelerated junctional rhythm
- Ventricular conduction abnormality or bundle branch block (Correct answer)
- Sinus tachycardia
Correct answer: Ventricular conduction abnormality or bundle branch block
A QRS duration ≥0.12 seconds indicates delayed intraventricular conduction, typical of bundle branch blocks or ventricular rhythms.
Question 2: Which precordial lead is positioned at the fourth intercostal space, right sternal border?
- V2
- V1 (Correct answer)
- V3R
- V4
Correct answer: V1
V1 is placed at the fourth intercostal space along the right sternal border, directly over the right ventricle.
Question 3: In a patient with atrial fibrillation, which ECG feature is characteristically absent?
- QRS complexes
- T waves
- Distinct P waves (Correct answer)
- R waves
Correct answer: Distinct P waves
Atrial fibrillation produces chaotic atrial activity with no discernible P waves, replaced by irregular fibrillatory baseline.
Question 4: When measuring QT interval, the measurement should end at:
- The peak of the T wave
- The point where the T wave returns to the isoelectric baseline (Correct answer)
- The beginning of the U wave
- The J point
Correct answer: The point where the T wave returns to the isoelectric baseline
The QT interval is measured from the start of the QRS to the point where the T wave returns to baseline, not its peak.
Question 5: Which of the following rhythms would show a 'sawtooth' flutter wave pattern at approximately 300 bpm?
- Atrial fibrillation
- Atrial flutter (Correct answer)
- Multifocal atrial tachycardia
- Junctional tachycardia
Correct answer: Atrial flutter
Atrial flutter produces regular sawtooth flutter waves (F waves) typically at 250–350 bpm, best seen in leads II, III, and aVF.
Question 6: A technician notices 60-Hz electrical interference on the ECG tracing. The most appropriate first step is to:
- Increase the paper speed to 50 mm/sec
- Check and improve electrode-skin contact and grounding (Correct answer)
- Apply a notch filter and re-record
- Reposition the patient to the right lateral decubitus position
Correct answer: Check and improve electrode-skin contact and grounding
60-Hz artifact usually results from poor electrode contact or nearby electrical interference; improving skin prep and contact is the first corrective step.
Question 7: Delta waves on an ECG are associated with which pre-excitation syndrome?
- Brugada syndrome
- Long QT syndrome
- Wolff-Parkinson-White syndrome (Correct answer)
- Lown-Ganong-Levine syndrome
Correct answer: Wolff-Parkinson-White syndrome
Wolff-Parkinson-White syndrome causes delta waves due to early ventricular activation via an accessory pathway (Bundle of Kent).
ECG Practical Content and Preparation 3
A QRS complex that is wider than 0.12 seconds most likely indicates: