Page 1 of 181
Relias Dysrhythmia Basic A & B all exams
bundle
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
Rationale: The sinoatrial (SA) node, located in the right atrium, is
the heart's natural pacemaker. It normally discharges at 60–100
beats per minute. The AV node (A) delays impulses; Purkinje
fibers (D) are the terminal conduction pathway.
2. At what rate does the SA node normally fire in a resting
adult?
,Page 2 of 181
A. 20–40 beats per minute
B. 40–60 beats per minute
C. 60–100 beats per minute
D. 100–150 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.
3. Which component of the ECG represents ventricular
depolarization?
A. P wave
B. PR interval
C. QRS complex
D. T wave
,Page 3 of 181
Rationale: The QRS complex represents rapid depolarization of
the ventricles, which triggers ventricular contraction. The P wave
(A) represents atrial depolarization. The T wave (D) represents
ventricular repolarization.
4. A nurse is calculating a patient's heart rate from a rhythm strip
recorded at the standard speed of 25 mm/sec. Between two R
waves, there are 4 large boxes. What is the heart rate?
A. 50 beats per minute
B. 75 beats per minute
C. 100 beats per minute
D. 150 beats per minute
Rationale: Standard ECG paper speed is 25 mm/sec. Each
large box (5 mm) = 0.20 sec. The 300 method: HR = 300 ÷
number of large boxes between R waves. Here, 300 ÷ 4 = 75
bpm.
, Page 4 of 181
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
Rationale: At standard speed (25 mm/sec), each small box =
0.04 sec (40 ms). Each large box (5 small boxes) = 0.20 sec. The
PR interval is normally 0.12–0.20 sec (3–5 small boxes).
6. A patient's ECG shows a heart rate of 120 bpm with a
regular rhythm and P waves before each QRS. What is this
rhythm?
Relias Dysrhythmia Basic A & B all exams
bundle
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
Rationale: The sinoatrial (SA) node, located in the right atrium, is
the heart's natural pacemaker. It normally discharges at 60–100
beats per minute. The AV node (A) delays impulses; Purkinje
fibers (D) are the terminal conduction pathway.
2. At what rate does the SA node normally fire in a resting
adult?
,Page 2 of 181
A. 20–40 beats per minute
B. 40–60 beats per minute
C. 60–100 beats per minute
D. 100–150 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.
3. Which component of the ECG represents ventricular
depolarization?
A. P wave
B. PR interval
C. QRS complex
D. T wave
,Page 3 of 181
Rationale: The QRS complex represents rapid depolarization of
the ventricles, which triggers ventricular contraction. The P wave
(A) represents atrial depolarization. The T wave (D) represents
ventricular repolarization.
4. A nurse is calculating a patient's heart rate from a rhythm strip
recorded at the standard speed of 25 mm/sec. Between two R
waves, there are 4 large boxes. What is the heart rate?
A. 50 beats per minute
B. 75 beats per minute
C. 100 beats per minute
D. 150 beats per minute
Rationale: Standard ECG paper speed is 25 mm/sec. Each
large box (5 mm) = 0.20 sec. The 300 method: HR = 300 ÷
number of large boxes between R waves. Here, 300 ÷ 4 = 75
bpm.
, Page 4 of 181
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
Rationale: At standard speed (25 mm/sec), each small box =
0.04 sec (40 ms). Each large box (5 small boxes) = 0.20 sec. The
PR interval is normally 0.12–0.20 sec (3–5 small boxes).
6. A patient's ECG shows a heart rate of 120 bpm with a
regular rhythm and P waves before each QRS. What is this
rhythm?
