Relias Dysrhythmia Basic A – Relias
Learning – 2026/2027 Academic Year –
Verified Q&A
SECTION I: ECG FOUNDATIONS & MEASUREMENTS
Questions 1–15
Question 1
The electrical impulse normally originates from which structure of the heart?
A) AV node
B) Bundle of His
C) SA node
D) Purkinje fibers
Correct Answer: C) SA node
Rationale: The sinoatrial (SA) node, located in the right atrium near the superior
vena cava, is the heart's natural pacemaker. It normally discharges at 60–100
beats per minute. The AV node delays the impulse to allow ventricular filling; the
Bundle of His and Purkinje fibers are part of the conduction pathway that
distributes the impulse to the ventricles.
Question 2
At what rate does the SA node normally fire in a resting adult?
A) 20–40 beats per minute
B) 40–60 beats per minute
C) 60–100 beats per minute
D) 100–150 beats per minute
Correct Answer: C) 60–100 beats per minute
,Rationale: The SA node is the primary pacemaker with an intrinsic firing rate of
60–100 bpm. The AV junction has a backup rate of 40–60 bpm, and the Purkinje
fibers have an intrinsic rate of 20–40 bpm.
Question 3
Which component of the ECG represents ventricular depolarization?
A) P wave
B) PR interval
C) QRS complex
D) T wave
Correct Answer: C) QRS complex
Rationale: The QRS complex represents the electrical impulse traveling through
the ventricles, causing them to contract (ventricular depolarization). The P wave
represents atrial depolarization, and the T wave represents ventricular
repolarization.
Question 4
On standard ECG paper, what is the standard speed?
A) 15 mm/second
B) 25 mm/second
C) 50 mm/second
D) 100 mm/second
Correct Answer: B) 25 mm/second
Rationale: The standard ECG paper speed is 25 mm per second. At this speed,
each small box (1 mm) represents 0.04 seconds, and each large box (5 mm)
represents 0.20 seconds.
Question 5
On standard ECG paper, 1 small box (1 mm) represents how many seconds?
,A) 0.04 seconds
B) 0.10 seconds
C) 0.20 seconds
D) 0.50 seconds
Correct Answer: A) 0.04 seconds
Rationale: At standard speed (25 mm/sec), each small box equals 0.04 seconds
(40 ms). Each large box (5 small boxes) equals 0.20 seconds. The PR interval is
normally 0.12–0.20 seconds, which is 3–5 small boxes.
Question 6
A normal PR interval should measure:
A) 0.04–0.08 seconds
B) 0.08–0.12 seconds
C) 0.12–0.20 seconds
D) 0.20–0.30 seconds
Correct Answer: C) 0.12–0.20 seconds
Rationale: The normal PR interval ranges from 0.12 to 0.20 seconds (3–5 small
boxes). It represents the time from the onset of atrial depolarization to the onset
of ventricular depolarization (AV conduction time).
Question 7
A normal QRS duration should measure:
A) Less than 0.04 seconds
B) Less than 0.08 seconds
C) Less than 0.12 seconds
D) Less than 0.20 seconds
Correct Answer: C) Less than 0.12 seconds
, Rationale: A normal QRS duration is less than 0.12 seconds (< 3 small boxes). A
QRS duration ≥ 0.12 seconds indicates a bundle branch block or ventricular origin
of the rhythm.
Question 8
What does the T wave represent?
A) Atrial depolarization
B) Ventricular depolarization
C) Ventricular repolarization
D) AV nodal conduction delay
Correct Answer: C) Ventricular repolarization
Rationale: The T wave represents ventricular repolarization—the recovery of the
ventricles after contraction. It is normally upright in leads with a positive QRS
complex. Abnormal T waves may indicate ischemia, electrolyte imbalances, or
other cardiac pathology.
Question 9
Which of the following is the correct order of electrical conduction through the
heart?
A) AV node → SA node → Bundle of His → Purkinje fibers
B) SA node → AV node → Bundle of His → Purkinje fibers
C) SA node → Bundle of His → AV node → Purkinje fibers
D) Purkinje fibers → Bundle of His → AV node → SA node
Correct Answer: B) SA node → AV node → Bundle of His → Purkinje fibers
Rationale: The correct sequence of cardiac conduction is: SA node (pacemaker) →
internodal pathways → AV node (delay) → Bundle of His → bundle branches →
Purkinje fibers → ventricular myocardium.
Learning – 2026/2027 Academic Year –
Verified Q&A
SECTION I: ECG FOUNDATIONS & MEASUREMENTS
Questions 1–15
Question 1
The electrical impulse normally originates from which structure of the heart?
A) AV node
B) Bundle of His
C) SA node
D) Purkinje fibers
Correct Answer: C) SA node
Rationale: The sinoatrial (SA) node, located in the right atrium near the superior
vena cava, is the heart's natural pacemaker. It normally discharges at 60–100
beats per minute. The AV node delays the impulse to allow ventricular filling; the
Bundle of His and Purkinje fibers are part of the conduction pathway that
distributes the impulse to the ventricles.
Question 2
At what rate does the SA node normally fire in a resting adult?
A) 20–40 beats per minute
B) 40–60 beats per minute
C) 60–100 beats per minute
D) 100–150 beats per minute
Correct Answer: C) 60–100 beats per minute
,Rationale: The SA node is the primary pacemaker with an intrinsic firing rate of
60–100 bpm. The AV junction has a backup rate of 40–60 bpm, and the Purkinje
fibers have an intrinsic rate of 20–40 bpm.
Question 3
Which component of the ECG represents ventricular depolarization?
A) P wave
B) PR interval
C) QRS complex
D) T wave
Correct Answer: C) QRS complex
Rationale: The QRS complex represents the electrical impulse traveling through
the ventricles, causing them to contract (ventricular depolarization). The P wave
represents atrial depolarization, and the T wave represents ventricular
repolarization.
Question 4
On standard ECG paper, what is the standard speed?
A) 15 mm/second
B) 25 mm/second
C) 50 mm/second
D) 100 mm/second
Correct Answer: B) 25 mm/second
Rationale: The standard ECG paper speed is 25 mm per second. At this speed,
each small box (1 mm) represents 0.04 seconds, and each large box (5 mm)
represents 0.20 seconds.
Question 5
On standard ECG paper, 1 small box (1 mm) represents how many seconds?
,A) 0.04 seconds
B) 0.10 seconds
C) 0.20 seconds
D) 0.50 seconds
Correct Answer: A) 0.04 seconds
Rationale: At standard speed (25 mm/sec), each small box equals 0.04 seconds
(40 ms). Each large box (5 small boxes) equals 0.20 seconds. The PR interval is
normally 0.12–0.20 seconds, which is 3–5 small boxes.
Question 6
A normal PR interval should measure:
A) 0.04–0.08 seconds
B) 0.08–0.12 seconds
C) 0.12–0.20 seconds
D) 0.20–0.30 seconds
Correct Answer: C) 0.12–0.20 seconds
Rationale: The normal PR interval ranges from 0.12 to 0.20 seconds (3–5 small
boxes). It represents the time from the onset of atrial depolarization to the onset
of ventricular depolarization (AV conduction time).
Question 7
A normal QRS duration should measure:
A) Less than 0.04 seconds
B) Less than 0.08 seconds
C) Less than 0.12 seconds
D) Less than 0.20 seconds
Correct Answer: C) Less than 0.12 seconds
, Rationale: A normal QRS duration is less than 0.12 seconds (< 3 small boxes). A
QRS duration ≥ 0.12 seconds indicates a bundle branch block or ventricular origin
of the rhythm.
Question 8
What does the T wave represent?
A) Atrial depolarization
B) Ventricular depolarization
C) Ventricular repolarization
D) AV nodal conduction delay
Correct Answer: C) Ventricular repolarization
Rationale: The T wave represents ventricular repolarization—the recovery of the
ventricles after contraction. It is normally upright in leads with a positive QRS
complex. Abnormal T waves may indicate ischemia, electrolyte imbalances, or
other cardiac pathology.
Question 9
Which of the following is the correct order of electrical conduction through the
heart?
A) AV node → SA node → Bundle of His → Purkinje fibers
B) SA node → AV node → Bundle of His → Purkinje fibers
C) SA node → Bundle of His → AV node → Purkinje fibers
D) Purkinje fibers → Bundle of His → AV node → SA node
Correct Answer: B) SA node → AV node → Bundle of His → Purkinje fibers
Rationale: The correct sequence of cardiac conduction is: SA node (pacemaker) →
internodal pathways → AV node (delay) → Bundle of His → bundle branches →
Purkinje fibers → ventricular myocardium.
