EKG/ECG Interpretation – Rhythms & Abnormalities Practice Exam Updated 2026 🩺 |
Complete Study Guide with Verified Questions and Detailed Rationales Covering Normal
Sinus Rhythm, Arrhythmias (Atrial Fibrillation, Atrial Flutter, SVT, Ventricular Tachycardia,
Ventricular Fibrillation), Heart Blocks (First, Second, Third Degree), ST Elevation and
Depression, Ischemia and Infarction Patterns, Axis Deviation, ECG Waveform Analysis (P,
QRS, T Waves), Rate and Rhythm Calculation, Electrolyte Imbalances, and Scenario-Based
Questions for ECG Interpretation and Cardiac Monitoring Exam Success
Question 1: What is the normal heart rate range for sinus rhythm in adults?
A. 40-60 beats per minute
B. 60-100 beats per minute
C. 100-120 beats per minute
D. 120-160 beats per minute
CORRECT ANSWER: B. 60-100 beats per minute
RATIONALE:Normal sinus rhythm in adults is defined by a heart rate between 60-100
beats per minute, regular rhythm, upright P waves in lead II preceding each QRS
complex, consistent PR interval of 120-200 ms, and narrow QRS complexes less than
120 ms. Rates outside this range indicate sinus bradycardia or tachycardia.
Question 2: Which ECG finding is most characteristic of atrial fibrillation?
A. Sawtooth flutter waves at 300 bpm
B. Absent P waves with irregularly irregular R-R intervals
C. Wide QRS complexes with AV dissociation
D. Prolonged PR interval greater than 200 ms
CORRECT ANSWER: B. Absent P waves with irregularly irregular R-R intervals
RATIONALE:Atrial fibrillation is characterized by the absence of distinct P waves due to
chaotic atrial depolarization, replaced by fibrillatory waves, and an irregularly irregular
ventricular response due to variable AV nodal conduction. This distinguishes it from
atrial flutter (sawtooth waves) and other arrhythmias.
Question 3: A patient presents with a heart rate of 45 bpm, regular rhythm, and
normal P waves preceding each QRS complex. What is the most likely diagnosis?
A. Junctional rhythm
B. Sinus bradycardia
C. First-degree heart block
D. Atrial flutter with 4:1 block
CORRECT ANSWER: B. Sinus bradycardia
RATIONALE:Sinus bradycardia is defined as a sinus rhythm with a rate less than 60
bpm. The presence of normal P waves preceding each QRS complex with consistent PR
interval confirms sinus node origin. Junctional rhythms typically lack preceding P waves
or have inverted P waves in lead II.
Question 4: Which interval on the ECG represents ventricular depolarization?
,A. PR interval
B. QT interval
C. QRS complex
D. ST segment
CORRECT ANSWER: C. QRS complex
RATIONALE:The QRS complex represents ventricular depolarization and normally lasts
80-120 ms. The PR interval represents atrial depolarization and AV nodal conduction
time. The QT interval represents total ventricular electrical activity (depolarization and
repolarization). The ST segment represents the early phase of ventricular repolarization.
Question 5: What ECG finding is diagnostic of third-degree (complete) heart block?
A. Progressive PR interval prolongation until a dropped QRS
B. Constant PR interval with intermittent non-conducted P waves
C. Complete AV dissociation with atrial rate faster than ventricular rate
D. PR interval greater than 200 ms with all P waves conducted
CORRECT ANSWER: C. Complete AV dissociation with atrial rate faster than
ventricular rate
RATIONALE:Third-degree heart block is characterized by complete failure of AV
conduction, resulting in independent atrial and ventricular rhythms (AV dissociation).
The atrial rate exceeds the ventricular escape rate, which may be junctional (40-60
bpm) or ventricular (20-40 bpm) depending on the escape pacemaker location.
Question 6: Which lead is most sensitive for detecting inferior wall myocardial
infarction?
A. Lead I
B. Lead aVL
C. Lead II
D. Lead V1
CORRECT ANSWER: C. Lead II
RATIONALE:Inferior wall MI is best detected in leads II, III, and aVF, which view the
inferior cardiac surface. Lead II is particularly sensitive due to its orientation. ST
elevation in these leads with reciprocal changes in lateral leads suggests acute inferior
MI. Lead V1 views the septum, while I and aVL view the lateral wall.
Question 7: A QRS duration of 140 ms with an rSR' pattern in V1 and wide S wave in
V6 suggests which conduction abnormality?
A. Left bundle branch block
B. Right bundle branch block
C. Left anterior fascicular block
D. Bifascicular block
,CORRECT ANSWER: B. Right bundle branch block
RATIONALE:Right bundle branch block is characterized by QRS duration ≥120 ms, rSR'
pattern (M-shaped) in V1-V2, and wide slurred S wave in lateral leads (I, V5-V6). Left
bundle branch block shows broad monophasic R waves in lateral leads and deep S
waves in V1. Fascicular blocks typically have narrow QRS complexes.
Question 8: Which electrolyte abnormality is most commonly associated with
peaked, tented T waves on ECG?
A. Hypokalemia
B. Hyperkalemia
C. Hypocalcemia
D. Hypernatremia
CORRECT ANSWER: B. Hyperkalemia
RATIONALE:Hyperkalemia causes progressive ECG changes starting with tall, peaked,
symmetric T waves due to accelerated repolarization. As potassium rises further, PR
prolongation, QRS widening, and eventually sine wave pattern may occur. Hypokalemia
causes flattened T waves and prominent U waves.
Question 9: What is the hallmark ECG feature of Wolff-Parkinson-White syndrome?
A. Short PR interval with delta wave
B. Prolonged QT interval
C. ST segment elevation in multiple leads
D. Inverted T waves in precordial leads
CORRECT ANSWER: A. Short PR interval with delta wave
RATIONALE:WPW syndrome results from an accessory pathway (bundle of Kent)
causing pre-excitation. This manifests as a short PR interval (<120 ms) and a slurred
upstroke of the QRS called a delta wave. The QRS is typically widened. This predisposes
to reentrant tachycardias.
Question 10: Which rhythm is characterized by a heart rate of 150 bpm with regular
sawtooth flutter waves best seen in leads II, III, and aVF?
A. Atrial fibrillation
B. Atrial flutter
C. Multifocal atrial tachycardia
D. Sinus tachycardia
CORRECT ANSWER: B. Atrial flutter
RATIONALE:Atrial flutter typically presents with atrial rates of 250-350 bpm and
characteristic sawtooth flutter waves, most prominent in inferior leads. With 2:1 AV
conduction, the ventricular rate is often around 150 bpm. The regularity and flutter wave
morphology distinguish it from atrial fibrillation.
, Question 11: What is the normal duration of the PR interval in adults?
A. 80-120 ms
B. 120-200 ms
C. 200-240 ms
D. 240-300 ms
CORRECT ANSWER: B. 120-200 ms
RATIONALE:The normal PR interval ranges from 120-200 ms (3-5 small boxes). It
represents the time from onset of atrial depolarization to onset of ventricular
depolarization, including AV nodal conduction delay. PR interval >200 ms indicates first-
degree AV block.
Question 12: Which finding on ECG suggests left ventricular hypertrophy?
A. R wave in V1 + S wave in V5 > 10 mm
B. S wave in V1 + R wave in V5 > 35 mm
C. R wave in aVL < 5 mm
D. QRS duration < 80 ms
CORRECT ANSWER: B. S wave in V1 + R wave in V5 > 35 mm
RATIONALE:Sokolov-Lyon criteria for LVH include S wave in V1 plus R wave in V5 or V6
exceeding 35 mm. Other criteria include R wave in aVL > 11 mm or Cornell criteria. LVH
may also show ST-T changes (strain pattern) with asymmetric T wave inversion.
Question 13: A patient has a regular narrow-complex tachycardia at 180 bpm with
no visible P waves. What is the most likely diagnosis?
A. Sinus tachycardia
B. Atrial fibrillation
C. AV nodal reentrant tachycardia
D. Ventricular tachycardia
CORRECT ANSWER: C. AV nodal reentrant tachycardia
RATIONALE:AVNRT typically presents as a regular narrow-complex tachycardia at 150-
250 bpm. P waves are often buried within the QRS complex or appear as pseudo-r' in V1
or pseudo-S in inferior leads, making them difficult to identify. This distinguishes it from
sinus tachycardia where P waves are visible and precede QRS.
Question 14: Which ECG change is most specific for acute myocardial infarction?
A. T wave inversion
B. ST segment elevation
C. Q waves
D. ST segment depression
CORRECT ANSWER: B. ST segment elevation
Complete Study Guide with Verified Questions and Detailed Rationales Covering Normal
Sinus Rhythm, Arrhythmias (Atrial Fibrillation, Atrial Flutter, SVT, Ventricular Tachycardia,
Ventricular Fibrillation), Heart Blocks (First, Second, Third Degree), ST Elevation and
Depression, Ischemia and Infarction Patterns, Axis Deviation, ECG Waveform Analysis (P,
QRS, T Waves), Rate and Rhythm Calculation, Electrolyte Imbalances, and Scenario-Based
Questions for ECG Interpretation and Cardiac Monitoring Exam Success
Question 1: What is the normal heart rate range for sinus rhythm in adults?
A. 40-60 beats per minute
B. 60-100 beats per minute
C. 100-120 beats per minute
D. 120-160 beats per minute
CORRECT ANSWER: B. 60-100 beats per minute
RATIONALE:Normal sinus rhythm in adults is defined by a heart rate between 60-100
beats per minute, regular rhythm, upright P waves in lead II preceding each QRS
complex, consistent PR interval of 120-200 ms, and narrow QRS complexes less than
120 ms. Rates outside this range indicate sinus bradycardia or tachycardia.
Question 2: Which ECG finding is most characteristic of atrial fibrillation?
A. Sawtooth flutter waves at 300 bpm
B. Absent P waves with irregularly irregular R-R intervals
C. Wide QRS complexes with AV dissociation
D. Prolonged PR interval greater than 200 ms
CORRECT ANSWER: B. Absent P waves with irregularly irregular R-R intervals
RATIONALE:Atrial fibrillation is characterized by the absence of distinct P waves due to
chaotic atrial depolarization, replaced by fibrillatory waves, and an irregularly irregular
ventricular response due to variable AV nodal conduction. This distinguishes it from
atrial flutter (sawtooth waves) and other arrhythmias.
Question 3: A patient presents with a heart rate of 45 bpm, regular rhythm, and
normal P waves preceding each QRS complex. What is the most likely diagnosis?
A. Junctional rhythm
B. Sinus bradycardia
C. First-degree heart block
D. Atrial flutter with 4:1 block
CORRECT ANSWER: B. Sinus bradycardia
RATIONALE:Sinus bradycardia is defined as a sinus rhythm with a rate less than 60
bpm. The presence of normal P waves preceding each QRS complex with consistent PR
interval confirms sinus node origin. Junctional rhythms typically lack preceding P waves
or have inverted P waves in lead II.
Question 4: Which interval on the ECG represents ventricular depolarization?
,A. PR interval
B. QT interval
C. QRS complex
D. ST segment
CORRECT ANSWER: C. QRS complex
RATIONALE:The QRS complex represents ventricular depolarization and normally lasts
80-120 ms. The PR interval represents atrial depolarization and AV nodal conduction
time. The QT interval represents total ventricular electrical activity (depolarization and
repolarization). The ST segment represents the early phase of ventricular repolarization.
Question 5: What ECG finding is diagnostic of third-degree (complete) heart block?
A. Progressive PR interval prolongation until a dropped QRS
B. Constant PR interval with intermittent non-conducted P waves
C. Complete AV dissociation with atrial rate faster than ventricular rate
D. PR interval greater than 200 ms with all P waves conducted
CORRECT ANSWER: C. Complete AV dissociation with atrial rate faster than
ventricular rate
RATIONALE:Third-degree heart block is characterized by complete failure of AV
conduction, resulting in independent atrial and ventricular rhythms (AV dissociation).
The atrial rate exceeds the ventricular escape rate, which may be junctional (40-60
bpm) or ventricular (20-40 bpm) depending on the escape pacemaker location.
Question 6: Which lead is most sensitive for detecting inferior wall myocardial
infarction?
A. Lead I
B. Lead aVL
C. Lead II
D. Lead V1
CORRECT ANSWER: C. Lead II
RATIONALE:Inferior wall MI is best detected in leads II, III, and aVF, which view the
inferior cardiac surface. Lead II is particularly sensitive due to its orientation. ST
elevation in these leads with reciprocal changes in lateral leads suggests acute inferior
MI. Lead V1 views the septum, while I and aVL view the lateral wall.
Question 7: A QRS duration of 140 ms with an rSR' pattern in V1 and wide S wave in
V6 suggests which conduction abnormality?
A. Left bundle branch block
B. Right bundle branch block
C. Left anterior fascicular block
D. Bifascicular block
,CORRECT ANSWER: B. Right bundle branch block
RATIONALE:Right bundle branch block is characterized by QRS duration ≥120 ms, rSR'
pattern (M-shaped) in V1-V2, and wide slurred S wave in lateral leads (I, V5-V6). Left
bundle branch block shows broad monophasic R waves in lateral leads and deep S
waves in V1. Fascicular blocks typically have narrow QRS complexes.
Question 8: Which electrolyte abnormality is most commonly associated with
peaked, tented T waves on ECG?
A. Hypokalemia
B. Hyperkalemia
C. Hypocalcemia
D. Hypernatremia
CORRECT ANSWER: B. Hyperkalemia
RATIONALE:Hyperkalemia causes progressive ECG changes starting with tall, peaked,
symmetric T waves due to accelerated repolarization. As potassium rises further, PR
prolongation, QRS widening, and eventually sine wave pattern may occur. Hypokalemia
causes flattened T waves and prominent U waves.
Question 9: What is the hallmark ECG feature of Wolff-Parkinson-White syndrome?
A. Short PR interval with delta wave
B. Prolonged QT interval
C. ST segment elevation in multiple leads
D. Inverted T waves in precordial leads
CORRECT ANSWER: A. Short PR interval with delta wave
RATIONALE:WPW syndrome results from an accessory pathway (bundle of Kent)
causing pre-excitation. This manifests as a short PR interval (<120 ms) and a slurred
upstroke of the QRS called a delta wave. The QRS is typically widened. This predisposes
to reentrant tachycardias.
Question 10: Which rhythm is characterized by a heart rate of 150 bpm with regular
sawtooth flutter waves best seen in leads II, III, and aVF?
A. Atrial fibrillation
B. Atrial flutter
C. Multifocal atrial tachycardia
D. Sinus tachycardia
CORRECT ANSWER: B. Atrial flutter
RATIONALE:Atrial flutter typically presents with atrial rates of 250-350 bpm and
characteristic sawtooth flutter waves, most prominent in inferior leads. With 2:1 AV
conduction, the ventricular rate is often around 150 bpm. The regularity and flutter wave
morphology distinguish it from atrial fibrillation.
, Question 11: What is the normal duration of the PR interval in adults?
A. 80-120 ms
B. 120-200 ms
C. 200-240 ms
D. 240-300 ms
CORRECT ANSWER: B. 120-200 ms
RATIONALE:The normal PR interval ranges from 120-200 ms (3-5 small boxes). It
represents the time from onset of atrial depolarization to onset of ventricular
depolarization, including AV nodal conduction delay. PR interval >200 ms indicates first-
degree AV block.
Question 12: Which finding on ECG suggests left ventricular hypertrophy?
A. R wave in V1 + S wave in V5 > 10 mm
B. S wave in V1 + R wave in V5 > 35 mm
C. R wave in aVL < 5 mm
D. QRS duration < 80 ms
CORRECT ANSWER: B. S wave in V1 + R wave in V5 > 35 mm
RATIONALE:Sokolov-Lyon criteria for LVH include S wave in V1 plus R wave in V5 or V6
exceeding 35 mm. Other criteria include R wave in aVL > 11 mm or Cornell criteria. LVH
may also show ST-T changes (strain pattern) with asymmetric T wave inversion.
Question 13: A patient has a regular narrow-complex tachycardia at 180 bpm with
no visible P waves. What is the most likely diagnosis?
A. Sinus tachycardia
B. Atrial fibrillation
C. AV nodal reentrant tachycardia
D. Ventricular tachycardia
CORRECT ANSWER: C. AV nodal reentrant tachycardia
RATIONALE:AVNRT typically presents as a regular narrow-complex tachycardia at 150-
250 bpm. P waves are often buried within the QRS complex or appear as pseudo-r' in V1
or pseudo-S in inferior leads, making them difficult to identify. This distinguishes it from
sinus tachycardia where P waves are visible and precede QRS.
Question 14: Which ECG change is most specific for acute myocardial infarction?
A. T wave inversion
B. ST segment elevation
C. Q waves
D. ST segment depression
CORRECT ANSWER: B. ST segment elevation
