SCST-D1 DIPLOMA IN ECG INTERPRETATION – PRACTICE EXAM QUESTIONS AND WELL-EXPLAINED ANSWERS

1. Which component of the ECG represents atrial depolarization?

A. P wave
B. PR interval
C. QRS complex
D. T wave

Answer: A. P wave
Explanation: The P wave reflects atrial depolarization, the initiation of impulse
from the SA node spreading across atria.



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

Answer: B. 120–200 ms
Explanation: A PR interval of 120–200 ms indicates normal AV conduction.
Shorter suggests pre-excitation; longer indicates first-degree AV block.



3. Which ECG change is typical of hyperkalemia?

A. ST depression
B. Tall, peaked T waves
C. U waves
D. QT prolongation

,Answer: B. Tall, peaked T waves
Explanation: Hyperkalemia classically causes tall, tented T waves and
widening of QRS with progression.



4. Which lead best detects right atrial enlargement (RAE)?

A. V2
B. Lead II
C. V5
D. aVL

Answer: B. Lead II
Explanation: Right atrial enlargement is suggested by tall, peaked P waves
(>2.5 mm) best seen in Lead II.



5. What is the heart rate if the R-R interval measures 0.8 seconds?

A. 60 bpm
B. 70 bpm
C. 75 bpm
D. 90 bpm

Answer: C. 75 bpm
Explanation: HR = 60 ÷ R-R interval (in seconds). 60 ÷ 0.8 = 75 bpm.



6. Which arrhythmia is most commonly associated with irregularly
irregular rhythm?

A. Atrial flutter
B. Atrial fibrillation
C. Ventricular tachycardia
D. Junctional tachycardia

Answer: B. Atrial fibrillation
Explanation: Atrial fibrillation shows no distinct P waves and an irregularly
irregular ventricular rhythm.

,7. The ST segment elevation in leads II, III, aVF indicates:

A. Anterior MI
B. Lateral MI
C. Inferior MI
D. Posterior MI

Answer: C. Inferior MI
Explanation: Inferior leads (II, III, aVF) correspond to inferior myocardial wall
supplied by right coronary artery.



8. Which electrolyte abnormality causes prolonged QT interval?

A. Hyperkalemia
B. Hypocalcemia
C. Hypercalcemia
D. Hypermagnesemia

Answer: B. Hypocalcemia
Explanation: Low calcium prolongs QT interval by lengthening repolarization.



9. Which ECG finding is pathognomonic for pericarditis?

A. ST depression in V1–V2
B. Diffuse concave ST elevation with PR depression
C. Peaked T waves
D. Pathological Q waves

Answer: B. Diffuse concave ST elevation with PR depression
Explanation: Pericarditis produces widespread ST elevation and PR segment
depression.



10. In left bundle branch block (LBBB), which lead usually shows a broad,
notched R wave?

A. V1
B. V6
C. aVR
D. III

, Answer: B. V6
Explanation: LBBB causes broad QRS (>120 ms), with notched “M-shaped” R
wave in lateral leads (V5, V6).



11. The U wave is most prominent in which electrolyte abnormality?

A. Hyperkalemia
B. Hypokalemia
C. Hypercalcemia
D. Hyponatremia

Answer: B. Hypokalemia
Explanation: U waves, best seen in V2–V4, are a hallmark of hypokalemia.



12. Which is the normal axis of the QRS complex?

A. –30° to –90°
B. –30° to +90°
C. +90° to +180°
D. –90° to –180°

Answer: B. –30° to +90°
Explanation: Normal axis lies between –30° and +90°. Deviations suggest
conduction or structural abnormalities.



13. Mobitz type I (Wenckebach) AV block is characterized by:

A. Sudden dropped QRS with constant PR
B. Progressive PR lengthening then dropped QRS
C. Wide QRS complexes
D. No relationship between P and QRS

Answer: B. Progressive PR lengthening then dropped QRS
Explanation: Mobitz I is marked by gradual prolongation of PR until one P
wave fails to conduct.