EKG/ECG Interpretation Rhythms & Abnormalities Practice
Questions & Answers Study Guide Updated 2026 🫀 | 250+
Verified Questions with Detailed Rationales | ECG Waveforms
(P QRS T), Cardiac Conduction System, Normal Sinus Rhythm
Identification, Dysrhythmias (Atrial Fibrillation, Atrial Flutter,
Ventricular Tachycardia, Ventricular Fibrillation), Heart Blocks
(First Second Third Degree), Rate and Rhythm Calculation
Methods, 12-Lead ECG Basics, Axis Determination, Ischemia
and Infarction Patterns, ACLS Correlation | Complete Exam
Prep Resource for Cardiac Monitoring and Certification
Success
Question 1: Which EKG lead is best for visualizing P waves to assess atrial activity?
A. Lead II
B. Lead V1
C. Lead aVR
D. Lead III
CORRECT ANSWER: A. Lead II
Rationale: Lead II is oriented parallel to the normal direction of atrial depolarization,
making it the optimal lead for visualizing P waves. This positioning allows for clear
assessment of P wave morphology, duration, and consistency, which are critical for
diagnosing atrial arrhythmias and conduction abnormalities.
Question 2: A patient presents with a regular rhythm at 45 bpm, narrow QRS
complexes, and no visible P waves. What is the most likely rhythm?
A. Sinus bradycardia
B. Junctional escape rhythm
C. Third-degree heart block
D. Atrial fibrillation with slow ventricular response
CORRECT ANSWER: B. Junctional escape rhythm
Rationale: Junctional escape rhythms typically present with a rate of 40-60 bpm, narrow
QRS complexes (unless bundle branch block is present), and absent or inverted P
waves that may appear before, during, or after the QRS. The absence of visible P waves
with a regular narrow-complex bradycardia strongly suggests a junctional origin rather
than sinus bradycardia, which would show upright P waves in lead II.
Question 3: What is the normal duration of the PR interval in adults?
A. 0.04-0.08 seconds
B. 0.12-0.20 seconds
C. 0.20-0.24 seconds
D. 0.24-0.30 seconds
,CORRECT ANSWER: B. 0.12-0.20 seconds
Rationale: The PR interval represents the time from the onset of atrial depolarization to
the onset of ventricular depolarization, reflecting conduction through the AV node. In
adults, the normal range is 0.12-0.20 seconds (3-5 small boxes on standard EKG paper).
Values outside this range may indicate AV conduction abnormalities such as first-
degree heart block (prolonged) or pre-excitation syndromes (shortened).
Question 4: Which finding is characteristic of atrial flutter on a 12-lead EKG?
A. Irregularly irregular rhythm with no discernible P waves
B. Sawtooth-shaped flutter waves at 250-350 bpm
C. Wide QRS complexes with AV dissociation
D. Progressive prolongation of PR interval until a dropped beat
CORRECT ANSWER: B. Sawtooth-shaped flutter waves at 250-350 bpm
Rationale: Atrial flutter is characterized by regular, sawtooth-shaped atrial waves (F
waves) typically occurring at 250-350 bpm, most prominently visible in leads II, III, aVF,
and V1. The ventricular response depends on the AV conduction ratio (e.g., 2:1, 3:1,
4:1), which determines the regularity and rate of the QRS complexes.
Question 5: In a patient with suspected acute inferior wall myocardial infarction,
which leads would show ST-segment elevation?
A. V1-V4
B. I, aVL, V5-V6
C. II, III, aVF
D. V7-V9
CORRECT ANSWER: C. II, III, aVF
Rationale: The inferior wall of the left ventricle is supplied by the right coronary artery (in
most individuals) and is best visualized by leads II, III, and aVF. ST-segment elevation in
these leads indicates acute injury to the inferior myocardium. Reciprocal ST depression
may be seen in leads I and aVL.
Question 6: What EKG finding is most specific for hyperkalemia?
A. Prolonged QT interval
B. Peaked, narrow-based T waves
C. U waves
D. ST-segment depression
CORRECT ANSWER: B. Peaked, narrow-based T waves
Rationale: Hyperkalemia causes progressive EKG changes starting with tall, peaked,
narrow-based T waves (often described as "tented" T waves), particularly in precordial
leads. As potassium levels rise further, additional findings include PR prolongation, QRS
,widening, loss of P waves, and eventually a sine wave pattern. Peaked T waves are the
earliest and most specific EKG manifestation of hyperkalemia.
Question 7: Which rhythm demonstrates a "grouped beating" pattern with
progressive PR prolongation followed by a dropped QRS complex?
A. Second-degree AV block, Type II (Mobitz II)
B. Second-degree AV block, Type I (Wenckebach)
C. Third-degree AV block
D. Sinus arrhythmia
CORRECT ANSWER: B. Second-degree AV block, Type I (Wenckebach)
Rationale: Mobitz Type I (Wenckebach) AV block is characterized by progressive
prolongation of the PR interval until a P wave is not conducted and a QRS complex is
dropped. This creates a "grouped beating" pattern. The RR interval shortens before the
dropped beat, and the pause containing the dropped beat is less than twice the
preceding RR interval.
Question 8: What is the hallmark EKG feature of ventricular tachycardia?
A. Narrow QRS complexes at rate >100 bpm
B. AV dissociation with capture or fusion beats
C. Regular P waves at rate >100 bpm
D. PR interval variability with constant QRS
CORRECT ANSWER: B. AV dissociation with capture or fusion beats
Rationale: Ventricular tachycardia is characterized by wide QRS complexes (>0.12
seconds) at a rate typically >100 bpm. AV dissociation (independent atrial and
ventricular activity) is present in approximately 50% of cases and is highly specific for
VT. Capture beats (normal QRS following a P wave) or fusion beats (hybrid QRS
morphology) further support the diagnosis of VT over supraventricular tachycardia with
aberrancy.
Question 9: Which EKG change is associated with hypocalcemia?
A. Shortened QT interval
B. Prolonged ST segment with normal T wave
C. Prominent U waves
D. Flattened T waves
CORRECT ANSWER: B. Prolonged ST segment with normal T wave
Rationale: Hypocalcemia prolongs the QT interval primarily by lengthening the ST
segment, while the T wave duration remains relatively unchanged. This differs from
hypokalemia, which causes prominent U waves and T wave flattening. The prolonged QT
interval in hypocalcemia increases the risk of torsades de pointes.
, Question 10: In left bundle branch block, which lead typically shows a broad,
notched R wave without Q waves?
A. V1
B. V6
C. aVR
D. III
CORRECT ANSWER: B. V6
Rationale: Left bundle branch block (LBBB) produces characteristic changes in lateral
leads (I, aVL, V5-V6), including broad, monophasic, notched or slurred R waves without
Q waves. In contrast, V1-V3 typically show wide, deep S waves or QS complexes. The
QRS duration is ≥0.12 seconds, and there is often discordant ST-T wave changes (ST
depression and T wave inversion in leads with dominant R waves).
Question 11: What is the expected heart rate range for an accelerated
idioventricular rhythm?
A. 20-40 bpm
B. 40-100 bpm
C. 100-150 bpm
D. 150-250 bpm
CORRECT ANSWER: B. 40-100 bpm
Rationale: Accelerated idioventricular rhythm (AIVR) is a ventricular rhythm with a rate
typically between 40-100 bpm, faster than a ventricular escape rhythm but slower than
ventricular tachycardia. It often occurs in the setting of acute myocardial infarction,
reperfusion, or digoxin toxicity. AIVR is usually benign and does not require treatment
unless it causes hemodynamic instability.
Question 12: Which EKG finding suggests right atrial enlargement?
A. P wave duration >0.12 seconds in lead II
B. P wave amplitude >2.5 mm in lead II
C. Biphasic P wave in V1 with prominent negative terminal component
D. Notched P wave in lead II
CORRECT ANSWER: B. P wave amplitude >2.5 mm in lead II
Rationale: Right atrial enlargement (P pulmonale) is characterized by tall, peaked P
waves with amplitude >2.5 mm (0.25 mV) in lead II and/or >1.5 mm in lead V1. This
reflects increased right atrial depolarization forces. Left atrial enlargement, in contrast,
produces broad, notched P waves in lead II and a prominent negative terminal
deflection in V1.
Question 13: What is the primary EKG criterion for diagnosing left ventricular
hypertrophy using the Sokolov-Lyon voltage criteria?
Questions & Answers Study Guide Updated 2026 🫀 | 250+
Verified Questions with Detailed Rationales | ECG Waveforms
(P QRS T), Cardiac Conduction System, Normal Sinus Rhythm
Identification, Dysrhythmias (Atrial Fibrillation, Atrial Flutter,
Ventricular Tachycardia, Ventricular Fibrillation), Heart Blocks
(First Second Third Degree), Rate and Rhythm Calculation
Methods, 12-Lead ECG Basics, Axis Determination, Ischemia
and Infarction Patterns, ACLS Correlation | Complete Exam
Prep Resource for Cardiac Monitoring and Certification
Success
Question 1: Which EKG lead is best for visualizing P waves to assess atrial activity?
A. Lead II
B. Lead V1
C. Lead aVR
D. Lead III
CORRECT ANSWER: A. Lead II
Rationale: Lead II is oriented parallel to the normal direction of atrial depolarization,
making it the optimal lead for visualizing P waves. This positioning allows for clear
assessment of P wave morphology, duration, and consistency, which are critical for
diagnosing atrial arrhythmias and conduction abnormalities.
Question 2: A patient presents with a regular rhythm at 45 bpm, narrow QRS
complexes, and no visible P waves. What is the most likely rhythm?
A. Sinus bradycardia
B. Junctional escape rhythm
C. Third-degree heart block
D. Atrial fibrillation with slow ventricular response
CORRECT ANSWER: B. Junctional escape rhythm
Rationale: Junctional escape rhythms typically present with a rate of 40-60 bpm, narrow
QRS complexes (unless bundle branch block is present), and absent or inverted P
waves that may appear before, during, or after the QRS. The absence of visible P waves
with a regular narrow-complex bradycardia strongly suggests a junctional origin rather
than sinus bradycardia, which would show upright P waves in lead II.
Question 3: What is the normal duration of the PR interval in adults?
A. 0.04-0.08 seconds
B. 0.12-0.20 seconds
C. 0.20-0.24 seconds
D. 0.24-0.30 seconds
,CORRECT ANSWER: B. 0.12-0.20 seconds
Rationale: The PR interval represents the time from the onset of atrial depolarization to
the onset of ventricular depolarization, reflecting conduction through the AV node. In
adults, the normal range is 0.12-0.20 seconds (3-5 small boxes on standard EKG paper).
Values outside this range may indicate AV conduction abnormalities such as first-
degree heart block (prolonged) or pre-excitation syndromes (shortened).
Question 4: Which finding is characteristic of atrial flutter on a 12-lead EKG?
A. Irregularly irregular rhythm with no discernible P waves
B. Sawtooth-shaped flutter waves at 250-350 bpm
C. Wide QRS complexes with AV dissociation
D. Progressive prolongation of PR interval until a dropped beat
CORRECT ANSWER: B. Sawtooth-shaped flutter waves at 250-350 bpm
Rationale: Atrial flutter is characterized by regular, sawtooth-shaped atrial waves (F
waves) typically occurring at 250-350 bpm, most prominently visible in leads II, III, aVF,
and V1. The ventricular response depends on the AV conduction ratio (e.g., 2:1, 3:1,
4:1), which determines the regularity and rate of the QRS complexes.
Question 5: In a patient with suspected acute inferior wall myocardial infarction,
which leads would show ST-segment elevation?
A. V1-V4
B. I, aVL, V5-V6
C. II, III, aVF
D. V7-V9
CORRECT ANSWER: C. II, III, aVF
Rationale: The inferior wall of the left ventricle is supplied by the right coronary artery (in
most individuals) and is best visualized by leads II, III, and aVF. ST-segment elevation in
these leads indicates acute injury to the inferior myocardium. Reciprocal ST depression
may be seen in leads I and aVL.
Question 6: What EKG finding is most specific for hyperkalemia?
A. Prolonged QT interval
B. Peaked, narrow-based T waves
C. U waves
D. ST-segment depression
CORRECT ANSWER: B. Peaked, narrow-based T waves
Rationale: Hyperkalemia causes progressive EKG changes starting with tall, peaked,
narrow-based T waves (often described as "tented" T waves), particularly in precordial
leads. As potassium levels rise further, additional findings include PR prolongation, QRS
,widening, loss of P waves, and eventually a sine wave pattern. Peaked T waves are the
earliest and most specific EKG manifestation of hyperkalemia.
Question 7: Which rhythm demonstrates a "grouped beating" pattern with
progressive PR prolongation followed by a dropped QRS complex?
A. Second-degree AV block, Type II (Mobitz II)
B. Second-degree AV block, Type I (Wenckebach)
C. Third-degree AV block
D. Sinus arrhythmia
CORRECT ANSWER: B. Second-degree AV block, Type I (Wenckebach)
Rationale: Mobitz Type I (Wenckebach) AV block is characterized by progressive
prolongation of the PR interval until a P wave is not conducted and a QRS complex is
dropped. This creates a "grouped beating" pattern. The RR interval shortens before the
dropped beat, and the pause containing the dropped beat is less than twice the
preceding RR interval.
Question 8: What is the hallmark EKG feature of ventricular tachycardia?
A. Narrow QRS complexes at rate >100 bpm
B. AV dissociation with capture or fusion beats
C. Regular P waves at rate >100 bpm
D. PR interval variability with constant QRS
CORRECT ANSWER: B. AV dissociation with capture or fusion beats
Rationale: Ventricular tachycardia is characterized by wide QRS complexes (>0.12
seconds) at a rate typically >100 bpm. AV dissociation (independent atrial and
ventricular activity) is present in approximately 50% of cases and is highly specific for
VT. Capture beats (normal QRS following a P wave) or fusion beats (hybrid QRS
morphology) further support the diagnosis of VT over supraventricular tachycardia with
aberrancy.
Question 9: Which EKG change is associated with hypocalcemia?
A. Shortened QT interval
B. Prolonged ST segment with normal T wave
C. Prominent U waves
D. Flattened T waves
CORRECT ANSWER: B. Prolonged ST segment with normal T wave
Rationale: Hypocalcemia prolongs the QT interval primarily by lengthening the ST
segment, while the T wave duration remains relatively unchanged. This differs from
hypokalemia, which causes prominent U waves and T wave flattening. The prolonged QT
interval in hypocalcemia increases the risk of torsades de pointes.
, Question 10: In left bundle branch block, which lead typically shows a broad,
notched R wave without Q waves?
A. V1
B. V6
C. aVR
D. III
CORRECT ANSWER: B. V6
Rationale: Left bundle branch block (LBBB) produces characteristic changes in lateral
leads (I, aVL, V5-V6), including broad, monophasic, notched or slurred R waves without
Q waves. In contrast, V1-V3 typically show wide, deep S waves or QS complexes. The
QRS duration is ≥0.12 seconds, and there is often discordant ST-T wave changes (ST
depression and T wave inversion in leads with dominant R waves).
Question 11: What is the expected heart rate range for an accelerated
idioventricular rhythm?
A. 20-40 bpm
B. 40-100 bpm
C. 100-150 bpm
D. 150-250 bpm
CORRECT ANSWER: B. 40-100 bpm
Rationale: Accelerated idioventricular rhythm (AIVR) is a ventricular rhythm with a rate
typically between 40-100 bpm, faster than a ventricular escape rhythm but slower than
ventricular tachycardia. It often occurs in the setting of acute myocardial infarction,
reperfusion, or digoxin toxicity. AIVR is usually benign and does not require treatment
unless it causes hemodynamic instability.
Question 12: Which EKG finding suggests right atrial enlargement?
A. P wave duration >0.12 seconds in lead II
B. P wave amplitude >2.5 mm in lead II
C. Biphasic P wave in V1 with prominent negative terminal component
D. Notched P wave in lead II
CORRECT ANSWER: B. P wave amplitude >2.5 mm in lead II
Rationale: Right atrial enlargement (P pulmonale) is characterized by tall, peaked P
waves with amplitude >2.5 mm (0.25 mV) in lead II and/or >1.5 mm in lead V1. This
reflects increased right atrial depolarization forces. Left atrial enlargement, in contrast,
produces broad, notched P waves in lead II and a prominent negative terminal
deflection in V1.
Question 13: What is the primary EKG criterion for diagnosing left ventricular
hypertrophy using the Sokolov-Lyon voltage criteria?
