SCST-D1 SCST Diploma in ECG Interpretation
Exam Questions And Correct Answers (Verified
Answers) Plus Explanation 2026 Q&A | Instant
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Question 1:
Which component of the ECG represents atrial depolarization?
A) PR interval
B) QRS complex
C) T wave
D) P wave
Correct Answer: D
Explanation: The P wave reflects atrial depolarization, as the electrical impulse spreads
from the SA node across the atria. The PR interval includes AV nodal delay, the QRS
represents ventricular depolarization, and the T wave represents ventricular
repolarization .
Question 2:
What is the normal duration of the PR interval?
A) 80–120 ms
B) 120–200 ms
C) 200–240 ms
D) 240–300 ms
Correct Answer: B
*Explanation: A normal PR interval measures 120–200 ms (3–5 small boxes). Shorter
intervals suggest pre-excitation syndromes (e.g., WPW), while longer intervals indicate
first-degree AV block .*
,Question 3:
Normal QRS duration in adults should be:
A) <80 ms
B) <100 ms
C) <120 ms
D) <140 ms
Correct Answer: C
Explanation: Normal QRS duration is less than 120 ms (≤0.11–0.12 s, or 3 small boxes). A
QRS ≥120 ms indicates a bundle branch block or intraventricular conduction delay .
Question 4:
The T wave represents:
A) Atrial depolarization
B) Ventricular depolarization
C) Atrial repolarization
D) Ventricular repolarization
Correct Answer: D
Explanation: The T wave represents ventricular repolarization. Atrial repolarization is
normally hidden within the QRS complex .
Question 5:
Which ECG lead is most commonly used for continuous rhythm monitoring in clinical
practice?
A) Lead I
B) Lead II
C) Lead III
D) aVR
Correct Answer: B
Explanation: Lead II is preferred for rhythm monitoring because its axis aligns well with the
heart's electrical axis, producing clear, upright P waves and QRS complexes .
,Question 6:
Which lead set primarily views the inferior wall of the heart?
A) V1–V3
B) I and aVL
C) II, III, aVF
D) V4–V6
Correct Answer: C
Explanation: Leads II, III, and aVF view the inferior wall of the heart. They typically reflect
the territory supplied by the right coronary artery .
Question 7:
Which ECG change is characteristic of hyperkalemia?
A) ST depression
B) Prominent U waves
C) Tall, peaked T waves
D) Prolonged QT interval
Correct Answer: C
Explanation: Hyperkalemia classically produces tall, "tented" or peaked T waves. As
potassium levels rise further, QRS widening and loss of P waves occur .
Question 8:
The normal QRS axis in the frontal plane lies between:
A) 0° and +90°
B) –30° and +90°
C) –90° and 0°
D) +90° and +180°
Correct Answer: B
*Explanation: The normal QRS axis ranges from –30° to +90°. Left axis deviation occurs
beyond –30°, and right axis deviation occurs beyond +90° .*
, Question 9:
Heart rate calculation: If the R-R interval measures 0.8 seconds, what is the heart rate?
A) 60 bpm
B) 70 bpm
C) 75 bpm
D) 80 bpm
Correct Answer: C
*Explanation: Heart rate = 60 ÷ R-R interval (in seconds). 60 ÷ 0.8 = 75 bpm .*
Question 10:
A regular, narrow-complex tachycardia at ~150 bpm with sudden onset and no visible P
waves is most likely:
A) Sinus tachycardia
B) Atrial fibrillation
C) Ventricular tachycardia
D) Supraventricular tachycardia (AVNRT/AVRT)
Correct Answer: D
*Explanation: AV nodal reentrant tachycardia (AVNRT) or AV reentrant tachycardia
(AVRT) typically presents as a regular narrow-complex tachycardia, often around 150
bpm, with sudden onset and P waves hidden within the QRS .*
Question 11:
The "sawtooth" pattern of flutter waves is most characteristic of:
A) Atrial fibrillation
B) Atrial flutter
C) Multifocal atrial tachycardia
D) Sinus arrhythmia
Correct Answer: B
Explanation: Atrial flutter produces a classic "sawtooth" or "picket fence" pattern of flutter
waves, best seen in leads II, III, and aVF .
Exam Questions And Correct Answers (Verified
Answers) Plus Explanation 2026 Q&A | Instant
Download Pdf.
Question 1:
Which component of the ECG represents atrial depolarization?
A) PR interval
B) QRS complex
C) T wave
D) P wave
Correct Answer: D
Explanation: The P wave reflects atrial depolarization, as the electrical impulse spreads
from the SA node across the atria. The PR interval includes AV nodal delay, the QRS
represents ventricular depolarization, and the T wave represents ventricular
repolarization .
Question 2:
What is the normal duration of the PR interval?
A) 80–120 ms
B) 120–200 ms
C) 200–240 ms
D) 240–300 ms
Correct Answer: B
*Explanation: A normal PR interval measures 120–200 ms (3–5 small boxes). Shorter
intervals suggest pre-excitation syndromes (e.g., WPW), while longer intervals indicate
first-degree AV block .*
,Question 3:
Normal QRS duration in adults should be:
A) <80 ms
B) <100 ms
C) <120 ms
D) <140 ms
Correct Answer: C
Explanation: Normal QRS duration is less than 120 ms (≤0.11–0.12 s, or 3 small boxes). A
QRS ≥120 ms indicates a bundle branch block or intraventricular conduction delay .
Question 4:
The T wave represents:
A) Atrial depolarization
B) Ventricular depolarization
C) Atrial repolarization
D) Ventricular repolarization
Correct Answer: D
Explanation: The T wave represents ventricular repolarization. Atrial repolarization is
normally hidden within the QRS complex .
Question 5:
Which ECG lead is most commonly used for continuous rhythm monitoring in clinical
practice?
A) Lead I
B) Lead II
C) Lead III
D) aVR
Correct Answer: B
Explanation: Lead II is preferred for rhythm monitoring because its axis aligns well with the
heart's electrical axis, producing clear, upright P waves and QRS complexes .
,Question 6:
Which lead set primarily views the inferior wall of the heart?
A) V1–V3
B) I and aVL
C) II, III, aVF
D) V4–V6
Correct Answer: C
Explanation: Leads II, III, and aVF view the inferior wall of the heart. They typically reflect
the territory supplied by the right coronary artery .
Question 7:
Which ECG change is characteristic of hyperkalemia?
A) ST depression
B) Prominent U waves
C) Tall, peaked T waves
D) Prolonged QT interval
Correct Answer: C
Explanation: Hyperkalemia classically produces tall, "tented" or peaked T waves. As
potassium levels rise further, QRS widening and loss of P waves occur .
Question 8:
The normal QRS axis in the frontal plane lies between:
A) 0° and +90°
B) –30° and +90°
C) –90° and 0°
D) +90° and +180°
Correct Answer: B
*Explanation: The normal QRS axis ranges from –30° to +90°. Left axis deviation occurs
beyond –30°, and right axis deviation occurs beyond +90° .*
, Question 9:
Heart rate calculation: If the R-R interval measures 0.8 seconds, what is the heart rate?
A) 60 bpm
B) 70 bpm
C) 75 bpm
D) 80 bpm
Correct Answer: C
*Explanation: Heart rate = 60 ÷ R-R interval (in seconds). 60 ÷ 0.8 = 75 bpm .*
Question 10:
A regular, narrow-complex tachycardia at ~150 bpm with sudden onset and no visible P
waves is most likely:
A) Sinus tachycardia
B) Atrial fibrillation
C) Ventricular tachycardia
D) Supraventricular tachycardia (AVNRT/AVRT)
Correct Answer: D
*Explanation: AV nodal reentrant tachycardia (AVNRT) or AV reentrant tachycardia
(AVRT) typically presents as a regular narrow-complex tachycardia, often around 150
bpm, with sudden onset and P waves hidden within the QRS .*
Question 11:
The "sawtooth" pattern of flutter waves is most characteristic of:
A) Atrial fibrillation
B) Atrial flutter
C) Multifocal atrial tachycardia
D) Sinus arrhythmia
Correct Answer: B
Explanation: Atrial flutter produces a classic "sawtooth" or "picket fence" pattern of flutter
waves, best seen in leads II, III, and aVF .
