Page 1 of 145
SCST Diploma in ECG Interpretation
practice : 200 Practice Questions and
Answers with Rationales
Q1. The sinoatrial (SA) node is normally located in which
chamber of the heart?
A) Right ventricle
B) Left atrium
C) Right atrium (at the junction of the superior vena cava)
D) Interventricular septum
Answer: C
Rationale: The SA node is located in the right atrium, near the
opening of the superior vena cava. It is the heart's natural
pacemaker, generating electrical impulses at a rate of 60–100
beats per minute .
,Page 2 of 145
Q2. The normal intrinsic firing rate of the atrioventricular (AV)
node is approximately:
A) 20–40 bpm
B) 40–60 bpm
C) 60–100 bpm
D) 100–140 bpm
Answer: B
Rationale: The AV node has an intrinsic firing rate of 40–60
bpm. If the SA node fails, the AV node can act as a backup
pacemaker .
Q3. Which lead is considered the "reference" or "ground" lead
in standard 12-lead ECG placement?
A) RA (right arm)
B) LA (left arm)
C) RL (right leg)
D) LL (left leg)
,Page 3 of 145
Answer: C
Rationale: The right leg (RL) lead serves as the
ground/reference electrode. The other limb leads provide the
bipolar and unipolar measurements .
Q4. Lead II records the electrical activity between which two
points?
A) Right arm (+) and left arm (–)
B) Right arm (–) and left leg (+)
C) Left arm (–) and right leg (+)
D) Left arm (+) and left leg (–)
Answer: B
Rationale: Lead II is a bipolar limb lead with the negative
electrode on the right arm and the positive electrode on the left
leg. It provides the largest P wave and is often used for rhythm
monitoring.
, Page 4 of 145
Q5. The normal PR interval duration is:
A) 0.04–0.10 seconds
B) 0.12–0.20 seconds (3–5 small squares)
C) 0.20–0.30 seconds
D) 0.30–0.40 seconds
Answer: B
Rationale: The normal PR interval measures 0.12–0.20 seconds
(3–5 small squares at standard 25 mm/s paper speed). It
represents the time from atrial depolarization onset to ventricular
depolarization onset .
Q6. The normal QRS duration is:
A) < 0.08 seconds (< 2 small squares)
B) 0.08–0.12 seconds (2–3 small squares)
C) 0.12–0.16 seconds
D) 0.16–0.20 seconds
SCST Diploma in ECG Interpretation
practice : 200 Practice Questions and
Answers with Rationales
Q1. The sinoatrial (SA) node is normally located in which
chamber of the heart?
A) Right ventricle
B) Left atrium
C) Right atrium (at the junction of the superior vena cava)
D) Interventricular septum
Answer: C
Rationale: The SA node is located in the right atrium, near the
opening of the superior vena cava. It is the heart's natural
pacemaker, generating electrical impulses at a rate of 60–100
beats per minute .
,Page 2 of 145
Q2. The normal intrinsic firing rate of the atrioventricular (AV)
node is approximately:
A) 20–40 bpm
B) 40–60 bpm
C) 60–100 bpm
D) 100–140 bpm
Answer: B
Rationale: The AV node has an intrinsic firing rate of 40–60
bpm. If the SA node fails, the AV node can act as a backup
pacemaker .
Q3. Which lead is considered the "reference" or "ground" lead
in standard 12-lead ECG placement?
A) RA (right arm)
B) LA (left arm)
C) RL (right leg)
D) LL (left leg)
,Page 3 of 145
Answer: C
Rationale: The right leg (RL) lead serves as the
ground/reference electrode. The other limb leads provide the
bipolar and unipolar measurements .
Q4. Lead II records the electrical activity between which two
points?
A) Right arm (+) and left arm (–)
B) Right arm (–) and left leg (+)
C) Left arm (–) and right leg (+)
D) Left arm (+) and left leg (–)
Answer: B
Rationale: Lead II is a bipolar limb lead with the negative
electrode on the right arm and the positive electrode on the left
leg. It provides the largest P wave and is often used for rhythm
monitoring.
, Page 4 of 145
Q5. The normal PR interval duration is:
A) 0.04–0.10 seconds
B) 0.12–0.20 seconds (3–5 small squares)
C) 0.20–0.30 seconds
D) 0.30–0.40 seconds
Answer: B
Rationale: The normal PR interval measures 0.12–0.20 seconds
(3–5 small squares at standard 25 mm/s paper speed). It
represents the time from atrial depolarization onset to ventricular
depolarization onset .
Q6. The normal QRS duration is:
A) < 0.08 seconds (< 2 small squares)
B) 0.08–0.12 seconds (2–3 small squares)
C) 0.12–0.16 seconds
D) 0.16–0.20 seconds
