MAYO EKG COMPETENCY VERIFIED EXAM SOLUTIONS - COMPREHENSIVE
QUESTIONS AND WELL-EXPLAINED ANSWERS - CURRENT VERSION GRADED
A+ (2026/2027)
1. What is the normal duration of the PR interval?
A) 0.06–0.10 seconds
B) 0.12–0.20 seconds
C) 0.22–0.30 seconds
D) 0.30–0.40 seconds
✓ Answer: B) 0.12–0.20 seconds
Explanation: The normal PR interval is 0.12–0.20 seconds (3–5 small
squares). A PR interval >0.20 seconds suggests first-degree AV block.
2. What does the QRS complex represent?
A) Atrial depolarization
B) Ventricular repolarization
C) Ventricular depolarization
D) SA node firing
✓ Answer: C) Ventricular depolarization
Explanation: The QRS complex represents ventricular depolarization — the
electrical activation that triggers ventricular contraction.
3. What is the normal QRS duration?
A) < 0.06 seconds
B) 0.06–0.10 seconds
C) 0.12–0.20 seconds
D) 0.20–0.30 seconds
✓ Answer: B) 0.06–0.10 seconds
Explanation: Normal QRS duration is 0.06–0.10 seconds. A QRS ≥ 0.12
seconds indicates a bundle branch block or ventricular conduction delay.
4. What does the T wave represent?
A) Atrial depolarization
B) Atrial repolarization
C) Ventricular depolarization
, D) Ventricular repolarization
✓ Answer: D) Ventricular repolarization
Explanation: The T wave represents ventricular repolarization — the
recovery of the ventricles in preparation for the next beat.
5. At standard EKG paper speed, one large square represents how many
seconds?
A) 0.04 seconds
B) 0.10 seconds
C) 0.20 seconds
D) 0.40 seconds
✓ Answer: C) 0.20 seconds
Explanation: At 25 mm/sec standard speed, one large square (5 small
squares) = 0.20 seconds. One small square = 0.04 seconds.
6. What is the normal heart rate range?
A) 40–60 bpm
B) 60–100 bpm
C) 100–120 bpm
D) 50–90 bpm
✓ Answer: B) 60–100 bpm
Explanation: Normal sinus rhythm has a heart rate of 60–100 bpm. Below 60
is bradycardia; above 100 is tachycardia.
7. Which lead provides the best view of inferior myocardial injury?
A) Leads I, aVL
B) Leads V1–V2
C) Leads II, III, aVF
D) Leads V4–V6
✓ Answer: C) Leads II, III, aVF
Explanation: Leads II, III, and aVF are the inferior leads and reflect the
inferior wall of the left ventricle, supplied by the RCA.
8. What does the P wave represent?
A) Ventricular depolarization
B) Atrial depolarization
C) SA node recovery
D) AV node conduction
✓ Answer: B) Atrial depolarization
Explanation: The P wave represents atrial depolarization — the spread of the
electrical impulse through both atria.
,9. In the standard 12-lead EKG, how many chest leads are there?
A) 3
B) 4
C) 6
D) 9
✓ Answer: C) 6
Explanation: There are 6 precordial (chest) leads: V1, V2, V3, V4, V5, and
V6. These are unipolar leads placed on the chest wall.
10. What is the normal QTc interval for men?
A) < 430 ms
B) < 450 ms
C) < 460 ms
D) < 480 ms
✓ Answer: B) < 450 ms
Explanation: The corrected QT interval (QTc) is considered normal when <
450 ms in men and < 460 ms in women. Prolonged QTc increases risk of
Torsades de Pointes.
11. Which formula is most commonly used to calculate QTc?
A) Bazett formula
B) Brugada formula
C) Wolff formula
D) Parkinson formula
✓ Answer: A) Bazett formula
Explanation: The Bazett formula (QTc = QT / √RR) is the most widely used,
though it can overcorrect at high or low heart rates.
12. What is the normal P wave duration?
A) < 0.06 seconds
B) < 0.10 seconds
C) < 0.12 seconds
D) < 0.16 seconds
✓ Answer: C) < 0.12 seconds
Explanation: A normal P wave duration is less than 0.12 seconds (3 small
squares). A wider P wave suggests left atrial enlargement or an interatrial
block.
13. The electrical axis of the heart in a normal adult is:
A) −90° to 0°
B) 0° to +90°
, C) +90° to +180°
D) −30° to +30°
✓ Answer: B) 0° to +90°
Explanation: The normal QRS axis ranges from 0° to +90°, representing the
dominant direction of ventricular depolarization in adults.
14. Which of the following is characteristic of left axis deviation?
A) Positive QRS in lead I, positive in aVF
B) Negative QRS in lead I, positive in aVF
C) Positive QRS in lead I, negative in aVF
D) Negative in both lead I and aVF
✓ Answer: C) Positive QRS in lead I, negative in aVF
Explanation: Left axis deviation (LAD) is defined by a positive QRS in lead I
and negative QRS in aVF, with axis between −30° and −90°.
15. What rhythm is characterized by a regular rhythm, rate of 60–100, and P
wave before every QRS?
A) Sinus bradycardia
B) Junctional rhythm
C) Normal sinus rhythm
D) Atrial flutter
✓ Answer: C) Normal sinus rhythm
Explanation: Normal sinus rhythm (NSR): rate 60–100, regular, P wave
before each QRS with normal PR interval, narrow QRS unless aberrant
conduction.
16. In a 6-second rhythm strip, if you count 8 QRS complexes, the
ventricular rate is:
A) 60 bpm
B) 70 bpm
C) 80 bpm
D) 90 bpm
✓ Answer: C) 80 bpm
Explanation: Multiply QRS complexes counted in 6 seconds by 10: 8 × 10 =
80 bpm. This is a standard rate calculation method.
17. Lead aVR is a:
A) Bipolar limb lead
B) Unipolar augmented limb lead
C) Precordial lead
D) Bipolar chest lead
QUESTIONS AND WELL-EXPLAINED ANSWERS - CURRENT VERSION GRADED
A+ (2026/2027)
1. What is the normal duration of the PR interval?
A) 0.06–0.10 seconds
B) 0.12–0.20 seconds
C) 0.22–0.30 seconds
D) 0.30–0.40 seconds
✓ Answer: B) 0.12–0.20 seconds
Explanation: The normal PR interval is 0.12–0.20 seconds (3–5 small
squares). A PR interval >0.20 seconds suggests first-degree AV block.
2. What does the QRS complex represent?
A) Atrial depolarization
B) Ventricular repolarization
C) Ventricular depolarization
D) SA node firing
✓ Answer: C) Ventricular depolarization
Explanation: The QRS complex represents ventricular depolarization — the
electrical activation that triggers ventricular contraction.
3. What is the normal QRS duration?
A) < 0.06 seconds
B) 0.06–0.10 seconds
C) 0.12–0.20 seconds
D) 0.20–0.30 seconds
✓ Answer: B) 0.06–0.10 seconds
Explanation: Normal QRS duration is 0.06–0.10 seconds. A QRS ≥ 0.12
seconds indicates a bundle branch block or ventricular conduction delay.
4. What does the T wave represent?
A) Atrial depolarization
B) Atrial repolarization
C) Ventricular depolarization
, D) Ventricular repolarization
✓ Answer: D) Ventricular repolarization
Explanation: The T wave represents ventricular repolarization — the
recovery of the ventricles in preparation for the next beat.
5. At standard EKG paper speed, one large square represents how many
seconds?
A) 0.04 seconds
B) 0.10 seconds
C) 0.20 seconds
D) 0.40 seconds
✓ Answer: C) 0.20 seconds
Explanation: At 25 mm/sec standard speed, one large square (5 small
squares) = 0.20 seconds. One small square = 0.04 seconds.
6. What is the normal heart rate range?
A) 40–60 bpm
B) 60–100 bpm
C) 100–120 bpm
D) 50–90 bpm
✓ Answer: B) 60–100 bpm
Explanation: Normal sinus rhythm has a heart rate of 60–100 bpm. Below 60
is bradycardia; above 100 is tachycardia.
7. Which lead provides the best view of inferior myocardial injury?
A) Leads I, aVL
B) Leads V1–V2
C) Leads II, III, aVF
D) Leads V4–V6
✓ Answer: C) Leads II, III, aVF
Explanation: Leads II, III, and aVF are the inferior leads and reflect the
inferior wall of the left ventricle, supplied by the RCA.
8. What does the P wave represent?
A) Ventricular depolarization
B) Atrial depolarization
C) SA node recovery
D) AV node conduction
✓ Answer: B) Atrial depolarization
Explanation: The P wave represents atrial depolarization — the spread of the
electrical impulse through both atria.
,9. In the standard 12-lead EKG, how many chest leads are there?
A) 3
B) 4
C) 6
D) 9
✓ Answer: C) 6
Explanation: There are 6 precordial (chest) leads: V1, V2, V3, V4, V5, and
V6. These are unipolar leads placed on the chest wall.
10. What is the normal QTc interval for men?
A) < 430 ms
B) < 450 ms
C) < 460 ms
D) < 480 ms
✓ Answer: B) < 450 ms
Explanation: The corrected QT interval (QTc) is considered normal when <
450 ms in men and < 460 ms in women. Prolonged QTc increases risk of
Torsades de Pointes.
11. Which formula is most commonly used to calculate QTc?
A) Bazett formula
B) Brugada formula
C) Wolff formula
D) Parkinson formula
✓ Answer: A) Bazett formula
Explanation: The Bazett formula (QTc = QT / √RR) is the most widely used,
though it can overcorrect at high or low heart rates.
12. What is the normal P wave duration?
A) < 0.06 seconds
B) < 0.10 seconds
C) < 0.12 seconds
D) < 0.16 seconds
✓ Answer: C) < 0.12 seconds
Explanation: A normal P wave duration is less than 0.12 seconds (3 small
squares). A wider P wave suggests left atrial enlargement or an interatrial
block.
13. The electrical axis of the heart in a normal adult is:
A) −90° to 0°
B) 0° to +90°
, C) +90° to +180°
D) −30° to +30°
✓ Answer: B) 0° to +90°
Explanation: The normal QRS axis ranges from 0° to +90°, representing the
dominant direction of ventricular depolarization in adults.
14. Which of the following is characteristic of left axis deviation?
A) Positive QRS in lead I, positive in aVF
B) Negative QRS in lead I, positive in aVF
C) Positive QRS in lead I, negative in aVF
D) Negative in both lead I and aVF
✓ Answer: C) Positive QRS in lead I, negative in aVF
Explanation: Left axis deviation (LAD) is defined by a positive QRS in lead I
and negative QRS in aVF, with axis between −30° and −90°.
15. What rhythm is characterized by a regular rhythm, rate of 60–100, and P
wave before every QRS?
A) Sinus bradycardia
B) Junctional rhythm
C) Normal sinus rhythm
D) Atrial flutter
✓ Answer: C) Normal sinus rhythm
Explanation: Normal sinus rhythm (NSR): rate 60–100, regular, P wave
before each QRS with normal PR interval, narrow QRS unless aberrant
conduction.
16. In a 6-second rhythm strip, if you count 8 QRS complexes, the
ventricular rate is:
A) 60 bpm
B) 70 bpm
C) 80 bpm
D) 90 bpm
✓ Answer: C) 80 bpm
Explanation: Multiply QRS complexes counted in 6 seconds by 10: 8 × 10 =
80 bpm. This is a standard rate calculation method.
17. Lead aVR is a:
A) Bipolar limb lead
B) Unipolar augmented limb lead
C) Precordial lead
D) Bipolar chest lead
