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SCST-D1 SCST Diploma in ECG Interpretation
practice : 200 Practice Questions and Answers
with Rationales1. Which ECG lead is most
commonly used for continuous rhythm monitoring
during clinical practice?
A) Lead I
B) Lead II
C) Lead III
D) aVR
Answer: B
Rationale: Lead II best aligns with the electrical axis of the heart
(approximately +60 degrees), providing clear visualization of P
waves and QRS complexes. This lead orientation allows optimal
assessment of both atrial and ventricular activity, making it the
standard choice for rhythm monitoring strips.
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Q2. The P wave on a standard ECG represents:
A) Ventricular depolarization
B) Ventricular repolarization
C) Atrial depolarization
D) Atrial repolarization
Answer: C
Rationale: The P wave represents atrial depolarization—the
spread of electrical impulse through the atria. Atrial
repolarization is typically not visible on the ECG as it occurs
during the QRS complex and is obscured by ventricular electrical
activity.
Q3. A normal PR interval should measure between:
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A) <0.08 seconds
B) 0.12–0.20 seconds
C) 0.20–0.28 seconds
D) >0.28 seconds
Answer: B
Rationale: The normal PR interval ranges from 120 to 200
milliseconds (0.12–0.20 seconds). This represents the time from
the onset of atrial depolarization to the onset of ventricular
depolarization, including conduction through the AV node and
His-Purkinje system. Prolongation suggests AV nodal delay.
Q4. The normal duration of the QRS complex is:
A) <0.08 seconds
B) <0.12 seconds
C) 0.12–0.16 seconds
D) >0.20 seconds
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Answer: B
Rationale: A normal QRS duration is less than 120 milliseconds
(0.12 seconds or 3 small boxes). Narrow QRS complexes
indicate normal ventricular depolarization through the His-
Purkinje system. Widening beyond 0.12 seconds suggests a
bundle branch block or ventricular origin.
Q5. A normal P wave should appear:
A) Negative in lead II
B) Peaked with duration >120 ms
C) Rounded and positive in lead II
D) Followed immediately by the T wave
Answer: C
Rationale: Normal atrial depolarization produces a P wave that
is upright (positive) and rounded in lead II, with duration less than
SCST-D1 SCST Diploma in ECG Interpretation
practice : 200 Practice Questions and Answers
with Rationales1. Which ECG lead is most
commonly used for continuous rhythm monitoring
during clinical practice?
A) Lead I
B) Lead II
C) Lead III
D) aVR
Answer: B
Rationale: Lead II best aligns with the electrical axis of the heart
(approximately +60 degrees), providing clear visualization of P
waves and QRS complexes. This lead orientation allows optimal
assessment of both atrial and ventricular activity, making it the
standard choice for rhythm monitoring strips.
,Page 2 of 180
Q2. The P wave on a standard ECG represents:
A) Ventricular depolarization
B) Ventricular repolarization
C) Atrial depolarization
D) Atrial repolarization
Answer: C
Rationale: The P wave represents atrial depolarization—the
spread of electrical impulse through the atria. Atrial
repolarization is typically not visible on the ECG as it occurs
during the QRS complex and is obscured by ventricular electrical
activity.
Q3. A normal PR interval should measure between:
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A) <0.08 seconds
B) 0.12–0.20 seconds
C) 0.20–0.28 seconds
D) >0.28 seconds
Answer: B
Rationale: The normal PR interval ranges from 120 to 200
milliseconds (0.12–0.20 seconds). This represents the time from
the onset of atrial depolarization to the onset of ventricular
depolarization, including conduction through the AV node and
His-Purkinje system. Prolongation suggests AV nodal delay.
Q4. The normal duration of the QRS complex is:
A) <0.08 seconds
B) <0.12 seconds
C) 0.12–0.16 seconds
D) >0.20 seconds
, Page 4 of 180
Answer: B
Rationale: A normal QRS duration is less than 120 milliseconds
(0.12 seconds or 3 small boxes). Narrow QRS complexes
indicate normal ventricular depolarization through the His-
Purkinje system. Widening beyond 0.12 seconds suggests a
bundle branch block or ventricular origin.
Q5. A normal P wave should appear:
A) Negative in lead II
B) Peaked with duration >120 ms
C) Rounded and positive in lead II
D) Followed immediately by the T wave
Answer: C
Rationale: Normal atrial depolarization produces a P wave that
is upright (positive) and rounded in lead II, with duration less than
