PRACTICE EXAMINATION
ECG Waveforms, Segments, and
Intervals Examination
Measurement, Interpretation, and Clinical Application
50 original multiple-choice questions
29 original ECG tracings • Calculations and detailed rationales for every question
P waves, PR interval, QRS complex, ST segment, T and U waves, QT/QTc, and RR
intervals
Name: ______________________________ Date: ________________ Score: ________ / 50
Educational disclaimer
This is an original educational practice examination. It does not reproduce proprietary or confidential examination
questions.
, ECG Waveforms, Segments, and Intervals Examination
Examination Instructions
This examination contains 50 original multiple-choice questions on ECG waveforms, segments, and
intervals, including measurement, calculation, and clinical interpretation. Each question has four choices
(A–D) and one best answer.
• Unless a question states otherwise, assume an adult patient, a paper speed of 25 mm/s, and a
calibration of 10 mm/mV. At 25 mm/s, use the grid to convert boxes into seconds.
• Some tracings are enlarged for measurement. The grid on every figure still shows the standard
small boxes (0.04 second horizontally and 0.1 mV vertically). Lettered arrows appear only when
a question asks you to identify or measure a specific point.
• The correct answer and a detailed rationale, with calculations where applicable, follow each
question. To test yourself, cover the lines below the answer choices until you have decided on
your answer.
• ECG findings must be interpreted together with the patient’s symptoms, history, medications,
laboratory values, and vital signs.
Categories covered
No. Category Questions
1 Category A: ECG Fundamentals and Electrical Activity 1–5
2 Category B: P Waves 6–10
3 Category C: PR Interval 11–15
4 Category D: QRS Complex 16–20
5 Category E: ST Segment 21–25
6 Category F: T Waves and U Waves 26–30
7 Category G: QT Interval and QTc 31–35
8 Category H: RR and Other Time Intervals 36–40
9 Category I: Measurement Skills and Calculation Problems 41–45
10 Category J: Integrated ECG Interpretation and Clinical Applications 46–50
1
, ECG Waveforms, Segments, and Intervals Examination
Category A: ECG Fundamentals and Electrical Activity
Question 1. An ECG is recorded at standard calibration. The R wave in Lead II measures 12 mm from the
baseline to its peak. What is its amplitude?
A. 0.12 mV
B. 0.6 mV
C. 1.0 mV
D. 1.2 mV
Correct Answer: D. 1.2 mV.
Rationale: Standard calibration is 10 mm/mV, so each millimeter of vertical height represents 0.1 mV.
The amplitude is 12 mm ÷ 10 mm/mV = 1.2 mV. A value of 0.12 mV results from a decimal error, and
0.6 mV would result from assuming 20 mm/mV. Voltage should always be interpreted with the
calibration marker in view, because a different gain setting changes the height of every waveform.
Question 2. ECG Figure 1 was recorded with a nonstandard gain. The 1-mV calibration pulse at the left is
5 mm tall, and the R waves are 6 mm tall. What is the true R-wave amplitude?
ECG Figure 1. Lead II tracing with a 1-mV calibration pulse at the left; enlarged for measurement (each small box is 0.04 second
horizontally).
A. 0.6 mV
B. 1.2 mV
C. 0.83 mV
D. 3.0 mV
Correct Answer: B. 1.2 mV.
Rationale: The calibration pulse shows that 1 mV produces a deflection of 5 mm on this tracing, so the
gain is 5 mm/mV. The R wave is 6 mm tall, so its amplitude is 6 mm ÷ 5 mm/mV = 1.2 mV. The value
0.6 mV comes from wrongly assuming the standard 10 mm/mV, 0.83 mV comes from inverting the
ratio, and 3.0 mV has no valid basis. Checking calibration prevents underestimating or overestimating
voltage-based findings.
2
, ECG Waveforms, Segments, and Intervals Examination
Question 3. Mechanical contraction of the ventricles (systole) begins shortly after which electrical
event?
A. Ventricular depolarization, shown by the QRS complex
B. Atrial depolarization, shown by the P wave
C. The peak of the T wave
D. The U wave
Correct Answer: A. Ventricular depolarization, shown by the QRS complex.
Rationale: Electrical activation precedes mechanical contraction. Ventricular depolarization (the QRS
complex) triggers the excitation–contraction process, so ventricular systole begins shortly after the
QRS onset. The P wave precedes atrial contraction, the T wave reflects ventricular repolarization as
the ventricles relax, and the U wave occurs after the T wave. The ECG does not directly show whether
contraction is effective, so a patient’s pulse and blood pressure must still be assessed.
Question 4. A tracing is recorded at 50 mm/s instead of 25 mm/s. The PR interval spans 8 small boxes.
What is the true PR interval?
A. 0.08 second
B. 0.16 second
C. 0.32 second
D. 0.64 second
Correct Answer: B. 0.16 second.
Rationale: At 50 mm/s, each 1-mm small box represents 0.02 second (half of the 0.04 second at 25
mm/s). Eight small boxes therefore represent 8 × 0.02 = 0.16 second, which is within the normal range
of 0.12–0.20 second. Assuming the standard 25 mm/s would give 8 × 0.04 = 0.32 second and a false
diagnosis of a prolonged PR interval. The recorded paper speed must always be confirmed before
measuring intervals.
Question 5. Why is Lead II commonly used for continuous rhythm monitoring?
A. Its axis is roughly parallel to normal atrial and ventricular depolarization, so P waves and QRS
complexes are usually upright and easy to see.
B. It is the only lead that records the heart’s electrical activity.
C. It shows ST-segment changes in every wall of the heart.
D. It completely eliminates artifact.
Correct Answer: A. Its axis is roughly parallel to normal atrial and ventricular depolarization, so P
waves and QRS complexes are usually upright and easy to see.
Rationale: In most patients the overall direction of normal atrial and ventricular depolarization points
toward the left leg, which is the positive axis of Lead II. As a result, P waves are clear and upright and
QRS complexes are well defined, which makes rhythm analysis easier. Lead II does not record all
electrical activity, it does not reliably show ischemia in all walls, and it can still show artifact. A 12-
lead ECG is needed to evaluate ST segments and regional changes.
3
ECG Waveforms, Segments, and
Intervals Examination
Measurement, Interpretation, and Clinical Application
50 original multiple-choice questions
29 original ECG tracings • Calculations and detailed rationales for every question
P waves, PR interval, QRS complex, ST segment, T and U waves, QT/QTc, and RR
intervals
Name: ______________________________ Date: ________________ Score: ________ / 50
Educational disclaimer
This is an original educational practice examination. It does not reproduce proprietary or confidential examination
questions.
, ECG Waveforms, Segments, and Intervals Examination
Examination Instructions
This examination contains 50 original multiple-choice questions on ECG waveforms, segments, and
intervals, including measurement, calculation, and clinical interpretation. Each question has four choices
(A–D) and one best answer.
• Unless a question states otherwise, assume an adult patient, a paper speed of 25 mm/s, and a
calibration of 10 mm/mV. At 25 mm/s, use the grid to convert boxes into seconds.
• Some tracings are enlarged for measurement. The grid on every figure still shows the standard
small boxes (0.04 second horizontally and 0.1 mV vertically). Lettered arrows appear only when
a question asks you to identify or measure a specific point.
• The correct answer and a detailed rationale, with calculations where applicable, follow each
question. To test yourself, cover the lines below the answer choices until you have decided on
your answer.
• ECG findings must be interpreted together with the patient’s symptoms, history, medications,
laboratory values, and vital signs.
Categories covered
No. Category Questions
1 Category A: ECG Fundamentals and Electrical Activity 1–5
2 Category B: P Waves 6–10
3 Category C: PR Interval 11–15
4 Category D: QRS Complex 16–20
5 Category E: ST Segment 21–25
6 Category F: T Waves and U Waves 26–30
7 Category G: QT Interval and QTc 31–35
8 Category H: RR and Other Time Intervals 36–40
9 Category I: Measurement Skills and Calculation Problems 41–45
10 Category J: Integrated ECG Interpretation and Clinical Applications 46–50
1
, ECG Waveforms, Segments, and Intervals Examination
Category A: ECG Fundamentals and Electrical Activity
Question 1. An ECG is recorded at standard calibration. The R wave in Lead II measures 12 mm from the
baseline to its peak. What is its amplitude?
A. 0.12 mV
B. 0.6 mV
C. 1.0 mV
D. 1.2 mV
Correct Answer: D. 1.2 mV.
Rationale: Standard calibration is 10 mm/mV, so each millimeter of vertical height represents 0.1 mV.
The amplitude is 12 mm ÷ 10 mm/mV = 1.2 mV. A value of 0.12 mV results from a decimal error, and
0.6 mV would result from assuming 20 mm/mV. Voltage should always be interpreted with the
calibration marker in view, because a different gain setting changes the height of every waveform.
Question 2. ECG Figure 1 was recorded with a nonstandard gain. The 1-mV calibration pulse at the left is
5 mm tall, and the R waves are 6 mm tall. What is the true R-wave amplitude?
ECG Figure 1. Lead II tracing with a 1-mV calibration pulse at the left; enlarged for measurement (each small box is 0.04 second
horizontally).
A. 0.6 mV
B. 1.2 mV
C. 0.83 mV
D. 3.0 mV
Correct Answer: B. 1.2 mV.
Rationale: The calibration pulse shows that 1 mV produces a deflection of 5 mm on this tracing, so the
gain is 5 mm/mV. The R wave is 6 mm tall, so its amplitude is 6 mm ÷ 5 mm/mV = 1.2 mV. The value
0.6 mV comes from wrongly assuming the standard 10 mm/mV, 0.83 mV comes from inverting the
ratio, and 3.0 mV has no valid basis. Checking calibration prevents underestimating or overestimating
voltage-based findings.
2
, ECG Waveforms, Segments, and Intervals Examination
Question 3. Mechanical contraction of the ventricles (systole) begins shortly after which electrical
event?
A. Ventricular depolarization, shown by the QRS complex
B. Atrial depolarization, shown by the P wave
C. The peak of the T wave
D. The U wave
Correct Answer: A. Ventricular depolarization, shown by the QRS complex.
Rationale: Electrical activation precedes mechanical contraction. Ventricular depolarization (the QRS
complex) triggers the excitation–contraction process, so ventricular systole begins shortly after the
QRS onset. The P wave precedes atrial contraction, the T wave reflects ventricular repolarization as
the ventricles relax, and the U wave occurs after the T wave. The ECG does not directly show whether
contraction is effective, so a patient’s pulse and blood pressure must still be assessed.
Question 4. A tracing is recorded at 50 mm/s instead of 25 mm/s. The PR interval spans 8 small boxes.
What is the true PR interval?
A. 0.08 second
B. 0.16 second
C. 0.32 second
D. 0.64 second
Correct Answer: B. 0.16 second.
Rationale: At 50 mm/s, each 1-mm small box represents 0.02 second (half of the 0.04 second at 25
mm/s). Eight small boxes therefore represent 8 × 0.02 = 0.16 second, which is within the normal range
of 0.12–0.20 second. Assuming the standard 25 mm/s would give 8 × 0.04 = 0.32 second and a false
diagnosis of a prolonged PR interval. The recorded paper speed must always be confirmed before
measuring intervals.
Question 5. Why is Lead II commonly used for continuous rhythm monitoring?
A. Its axis is roughly parallel to normal atrial and ventricular depolarization, so P waves and QRS
complexes are usually upright and easy to see.
B. It is the only lead that records the heart’s electrical activity.
C. It shows ST-segment changes in every wall of the heart.
D. It completely eliminates artifact.
Correct Answer: A. Its axis is roughly parallel to normal atrial and ventricular depolarization, so P
waves and QRS complexes are usually upright and easy to see.
Rationale: In most patients the overall direction of normal atrial and ventricular depolarization points
toward the left leg, which is the positive axis of Lead II. As a result, P waves are clear and upright and
QRS complexes are well defined, which makes rhythm analysis easier. Lead II does not record all
electrical activity, it does not reliably show ischemia in all walls, and it can still show artifact. A 12-
lead ECG is needed to evaluate ST segments and regional changes.
3
