The 12-Lead ECG

NCLEX-Style Questions on The 12-Lead ECG

Questions 1-10: Basic Concepts of 12-Lead ECG

1. What does the P wave represent on a 12-lead ECG?
o A) Ventricular depolarization
o B) Atrial depolarization
o C) Ventricular repolarization
o D) Atrial repolarization
Answer: B) Atrial depolarization
Rationale: The P wave indicates the electrical activity of atrial depolarization.
2. Which lead is most commonly used to monitor the heart's rhythm?
o A) Lead I
o B) Lead II
o C) Lead III
o D) Lead V1
Answer: B) Lead II
Rationale: Lead II is preferred for monitoring because it provides a clear view of
the P wave and QRS complex.
3. What is the normal duration of the QRS complex?
o A) Less than 0.10 seconds
o B) 0.10 to 0.12 seconds
o C) 0.12 to 0.20 seconds
o D) Greater than 0.20 seconds
Answer: A) Less than 0.10 seconds
Rationale: A normal QRS complex duration is less than 0.10 seconds, indicating
efficient ventricular depolarization.
4. What does the ST segment represent on an ECG?
o A) Atrial repolarization
o B) Ventricular depolarization
o C) Ventricular repolarization
o D) The time between ventricular depolarization and repolarization
Answer: D) The time between ventricular depolarization and repolarization
Rationale: The ST segment represents the period after the QRS complex when the
ventricles are depolarized.
5. Which of the following indicates a myocardial infarction on a 12-lead ECG?
o A) Inverted T waves
o B) Elevated ST segments
o C) Prolonged QT interval
o D) Shortened PR interval
Answer: B) Elevated ST segments
Rationale: Elevated ST segments are indicative of myocardial injury or
infarction.
6. The PR interval should be measured from which point to which point?
o A) From the beginning of the P wave to the beginning of the QRS complex
o B) From the end of the P wave to the end of the QRS complex

, o C) From the beginning of the P wave to the end of the QRS complex
o D) From the end of the P wave to the beginning of the T wave
Answer: A) From the beginning of the P wave to the beginning of the QRS
complex
Rationale: The PR interval is measured from the start of the P wave to the start of
the QRS complex.
7. Which of the following arrhythmias is characterized by a rapid atrial rate of 240-
300 bpm?
o A) Atrial fibrillation
o B) Atrial flutter
o C) Ventricular tachycardia
o D) Premature atrial contractions
Answer: B) Atrial flutter
Rationale: Atrial flutter typically presents with a rapid atrial rate and a
"sawtooth" appearance of the P waves (F-waves).
8. Which lead provides a view of the left lateral wall of the heart?
o A) Lead II
o B) Lead V1
o C) Lead I
o D) Lead V5
Answer: C) Lead I
Rationale: Lead I views the electrical activity from the right arm to the left arm,
reflecting activity from the left lateral wall.
9. A patient’s 12-lead ECG shows a prolonged QT interval. What is the potential risk
associated with this finding?
o A) Atrial fibrillation
o B) Heart block
o C) Torsades de Pointes
o D) Ventricular hypertrophy
Answer: C) Torsades de Pointes
Rationale: A prolonged QT interval increases the risk for Torsades de Pointes, a
type of life-threatening ventricular tachycardia.
10. What is the primary purpose of performing a 12-lead ECG?
o A) To assess the patient’s heart rate
o B) To evaluate cardiac function over time
o C) To identify arrhythmias and myocardial ischemia or infarction
o D) To determine blood pressure levels
Answer: C) To identify arrhythmias and myocardial ischemia or infarction
Rationale: The primary purpose of a 12-lead ECG is to diagnose arrhythmias and
assess for signs of ischemia or infarction.

Questions 11-20: Interpreting the ECG

11. In which condition would you expect to see a "delta wave" on the ECG?
o A) Atrial fibrillation
o B) Wolff-Parkinson-White syndrome