ECG Clinical Applications 1 — Questions and Answers
Question 1: What is the standard number of leads in a 12-lead ECG?
- 12 leads from 10 electrodes (Correct answer)
- 12 leads from 12 electrodes
- 10 leads from 10 electrodes
- 6 leads from 6 electrodes
Correct answer: 12 leads from 10 electrodes
A 12-lead ECG uses 10 physical electrodes (4 limb, 6 precordial) to generate 12 different electrical views of the heart.
Question 2: Where should the V4 precordial electrode be placed?
- Fifth intercostal space at the midclavicular line (Correct answer)
- Fourth intercostal space right sternal border
- Fifth intercostal space at the anterior axillary line
- Second intercostal space left sternal border
Correct answer: Fifth intercostal space at the midclavicular line
V4 is placed at the fifth intercostal space at the midclavicular line, serving as the reference point for V5 and V6 placement.
Question 3: Why is a baseline ECG important before starting certain medications?
- To detect pre-existing QT prolongation or other abnormalities (Correct answer)
- To determine the patient's blood pressure
- To measure oxygen saturation
- To assess lung function
Correct answer: To detect pre-existing QT prolongation or other abnormalities
A baseline ECG identifies pre-existing cardiac abnormalities (especially QT prolongation) that certain medications could worsen, preventing dangerous drug-induced arrhythmias.
Question 4: What artifact can be caused by patient movement during ECG recording?
- Wandering baseline and muscle tremor artifact (Correct answer)
- ST elevation
- Peaked T waves
- Bundle branch block pattern
Correct answer: Wandering baseline and muscle tremor artifact
Patient movement causes wandering baseline (slow undulation) and muscle tremor artifact (irregular, fine oscillations), which can obscure the true ECG signal.
Question 5: When should a 12-lead ECG be performed for a patient with chest pain?
- Within 10 minutes of arrival (Correct answer)
- After blood work results return
- Only if symptoms persist for 1 hour
- At the next scheduled appointment
Correct answer: Within 10 minutes of arrival
Guidelines recommend obtaining a 12-lead ECG within 10 minutes of arrival for any patient presenting with chest pain to rapidly identify acute myocardial infarction.
Question 6: What does reciprocal change mean on an ECG?
- ST depression in leads opposite to those showing ST elevation (Correct answer)
- Identical changes in all 12 leads
- P waves appearing after QRS complexes
- T wave inversion in limb leads only
Correct answer: ST depression in leads opposite to those showing ST elevation
Reciprocal changes are ST depressions seen in leads opposite to the primary area of ST elevation during acute MI, helping confirm the diagnosis and localize the infarct.
ECG Clinical Applications 1
What is the standard number of leads in a 12-lead ECG?