ECG ECG in Clinical Practice 3 — Questions and Answers
Question 1: Which lead configuration would produce a completely flat line (asystole appearance) if a limb lead becomes disconnected?
- The affected lead traces flat while others remain (Correct answer)
- All leads go flat simultaneously
- Only the chest leads are affected
- The ECG stops printing entirely
Correct answer: The affected lead traces flat while others remain
A disconnected limb lead causes a flat trace in the specific lead using that electrode, not true asystole.
Question 2: A regular narrow-complex tachycardia at 150 bpm with no visible P waves most likely represents what?
- Supraventricular tachycardia (Correct answer)
- Ventricular tachycardia
- Sinus bradycardia
- First-degree AV block
Correct answer: Supraventricular tachycardia
A regular narrow-complex tachycardia around 150 bpm is typically supraventricular tachycardia.
Question 3: What does the PR interval represent on an ECG?
- Time from atrial depolarization to ventricular depolarization (Correct answer)
- Time for ventricular repolarization
- Duration of the QRS complex
- Time for atrial repolarization only
Correct answer: Time from atrial depolarization to ventricular depolarization
The PR interval measures conduction from the atria through the AV node to the ventricles.
Question 4: Which artifact appears as consistent, fine, fast oscillations often caused by 60 Hz electrical sources?
- AC electrical interference (Correct answer)
- Wandering baseline
- Muscle tremor artifact
- Somatic tremor
Correct answer: AC electrical interference
Uniform fast oscillations are typically AC interference from nearby electrical equipment.
Question 5: A normal QRS complex duration should be less than which value?
- 0.12 seconds (Correct answer)
- 0.20 seconds
- 0.40 seconds
- 0.06 seconds
Correct answer: 0.12 seconds
A normal QRS complex is less than 0.12 seconds (three small boxes).
Question 6: If the limb leads on the right and left arms are reversed, what change is commonly seen?
- Lead I becomes inverted (Correct answer)
- V1 becomes inverted
- The QRS widens abnormally
- The heart rate doubles
Correct answer: Lead I becomes inverted
Right/left arm lead reversal typically inverts lead I and can mimic pathology.
Question 7: Which of the following patients requires modified electrode placement using a right-sided ECG?
- Suspected right ventricular infarction (Correct answer)
- Suspected pericarditis
- Atrial fibrillation
- Sinus tachycardia
Correct answer: Suspected right ventricular infarction
Right-sided leads (e.g., V4R) are used to assess suspected right ventricular infarction.
ECG ECG in Clinical Practice 3
Which lead configuration would produce a completely flat line (asystole appearance) if a limb lead becomes disconnected?