ECG ECG Troubleshooting 3 — Questions and Answers
Question 1: An ECG shows a rate of 150 bpm with narrow QRS complexes and no visible P waves. Which arrhythmia should be considered first?
- Ventricular tachycardia
- Atrial flutter with 2:1 conduction (Correct answer)
- Junctional tachycardia
- Sinus tachycardia
Correct answer: Atrial flutter with 2:1 conduction
Atrial flutter at a typical atrial rate of 300 bpm with 2:1 AV conduction produces a ventricular rate of approximately 150 bpm; flutter waves may be hidden in the QRS or T wave.
Question 2: When a patient's ECG shows motion artifact making interpretation difficult, what is the FIRST action the ECG technician should take?
- Reapply all electrodes with fresh conductive gel
- Ask the patient to relax and lie still, then repeat the recording (Correct answer)
- Increase filter settings to eliminate noise
- Immediately notify the physician of uninterpretable tracing
Correct answer: Ask the patient to relax and lie still, then repeat the recording
Patient movement is the most common cause of artifact, and instructing the patient to remain still and relaxed should be the first step before any equipment adjustments.
Question 3: Which finding on a 12-lead ECG is most suggestive of left ventricular hypertrophy (LVH)?
- S wave in V1 plus R wave in V5 or V6 exceeding 35 mm (Correct answer)
- R wave in aVR greater than 8 mm
- QRS duration greater than 120 ms
- PR interval greater than 200 ms
Correct answer: S wave in V1 plus R wave in V5 or V6 exceeding 35 mm
The Sokolow-Lyon criterion (SV1 + RV5 or RV6 ≥ 35 mm) is a widely used ECG voltage criterion for diagnosing LVH.
Question 4: A 60-year-old male presents with chest pain. The ECG shows ST depression in leads V1-V3. Which condition should be ruled out first?
- Anterior STEMI
- Posterior MI (reciprocal changes) (Correct answer)
- Right bundle branch block
- Digitalis effect
Correct answer: Posterior MI (reciprocal changes)
ST depression in V1-V3 may represent reciprocal changes of a posterior MI; posterior leads (V7-V9) should be obtained to look for ST elevation confirming posterior STEMI.
Question 5: An ECG shows a short PR interval of 100 ms, a delta wave, and a wide QRS. What is the diagnosis?
- First-degree AV block with aberrant conduction
- Wolff-Parkinson-White (WPW) syndrome (Correct answer)
- Accelerated junctional rhythm
- Left bundle branch block
Correct answer: Wolff-Parkinson-White (WPW) syndrome
WPW syndrome is characterized by a short PR interval, slurred upstroke (delta wave) of the QRS, and widened QRS due to ventricular pre-excitation via an accessory pathway.
Question 6: Which electrode placement error causes leads V1 and V2 to appear reversed on an ECG?
- Placing V1 at the 2nd intercostal space instead of the 4th (Correct answer)
- Swapping the V1 and V2 electrode positions
- Using right-sided precordial placement
- Placing V1 on the left sternal border
Correct answer: Placing V1 at the 2nd intercostal space instead of the 4th
Placing V1 too high (2nd intercostal space instead of 4th) produces rS or QS morphology in V1 and V2, mimicking anteroseptal infarction or lead reversal.
Question 7: What is the likely interpretation when an ECG shows varying QRS morphologies with no identifiable P waves and an irregularly irregular rhythm at 90 bpm?
- Multifocal atrial tachycardia
- Atrial fibrillation with aberrant conduction (Correct answer)
- Ventricular tachycardia
- Accelerated idioventricular rhythm
Correct answer: Atrial fibrillation with aberrant conduction
Atrial fibrillation with aberrant conduction (rate-related bundle branch block) produces irregularly irregular rhythm with varying QRS morphology and absent P waves.
ECG ECG Troubleshooting 3
An ECG shows a rate of 150 bpm with narrow QRS complexes and no visible P waves.
Which arrhythmia should be considered first?