An electrocardiogram (ECG) is a test that records the heart's electrical activity using skin electrodes. It shows rate and rhythm and helps detect ischemia, infarction, chamber enlargement, conduction blocks, electrolyte effects, and drug influences. A standard 12-lead ECG views the heart from multiple angles at rest or during stress. It is quick, noninvasive, and guides diagnosis, triage, monitoring, and decisions about further testing. Results are interpreted in clinical context by clinicians. Please note that the questions require knowledge and not all questions are the same difficulty level. Ready for my ECG questions?

The main purpose of the electrocardiogram is to:
A) Measure lung volumes during exercise
B) Record the heart’s electrical activity at the body surface
C) Estimate cardiac output by thermodilution
D) Visualize coronary arteries directly

​

The P wave on a standard electrocardiogram represents:
A) Ventricular depolarization
B) Atrial depolarization
C) Ventricular repolarization
D) Atrial repolarization

​

A normal P–R interval (from the beginning of P to the beginning of QRS) is approximately:
A) 60 to 100 milliseconds
B) 120 to 200 milliseconds
C) 220 to 300 milliseconds
D) 320 to 400 milliseconds

​

A normal QRS complex duration is:
A) Less than 80 milliseconds
B) Less than 120 milliseconds
C) 140 to 160 milliseconds
D) Greater than 200 milliseconds

​

The corrected Q–T interval is clinically important because prolonged Q–T increases risk of:
A) Atrial flutter
B) Atrioventricular nodal reentry
C) Torsades de pointes
D) Sinus bradycardia

​

In two or more contiguous leads, new ST segment elevation most often suggests:
A) Hyperkalemia
B) Acute transmural myocardial injury
C) Normal early repolarization in all people
D) Lead misplacement every time

​

T wave inversion in anatomically contiguous leads most often indicates:
A) Ventricular paced rhythm
B) Myocardial ischemia or reperfusion change
C) Artifact
D) Normal finding in all adults

​

Leads V1 and V2 primarily view which region of the heart?
A) Inferior wall
B) High lateral wall
C) Septal region
D) Posterior wall exclusively

​

Which set of leads is considered inferior?
A) I, aVL
B) V1, V2
C) II, III, aVF
D) V5, V6

​

Which leads are classically lateral?
A) II, III, aVF
B) V1, V2
C) I, aVL, V5, V6
D) aVR only

​

Which precordial leads are primarily anterior?
A) V3 and V4
B) V1 and V2
C) V5 and V6
D) aVR and aVL

​

Correct chest placement for lead V1 is at the:
A) Second intercostal space, right sternal border
B) Fourth intercostal space, right sternal border
C) Fifth intercostal space, midclavicular line
D) Fifth intercostal space, anterior axillary line

​

A normal frontal plane QRS axis in adults is approximately:
A) −90° to −30°
B) −30° to +90°
C) +90° to +180°
D) −180° to −90°

​

Left axis deviation is commonly associated with:
A) Left anterior fascicular block
B) Right ventricular hypertrophy
C) Lateral myocardial infarction exclusively
D) Hypercalcemia

​

Right axis deviation may be caused by:
A) Left ventricular hypertrophy
B) Right ventricular hypertrophy
C) Hyperthyroidism only
D) Low potassium

​

Right bundle branch block typically shows:
A) Broad notched R waves in I and V6
B) rsR′ pattern in V1 with a wide S wave in I and V6
C) Small R in V1 and tall R in V6 with narrow QRS
D) Diffuse low voltage only

​

Left bundle branch block typically shows:
A) Predominant S in V6
B) Broad, often notched R in I and V6 with deep S in V1
C) Narrow QRS
D) Tall R in V1

​

Atrial fibrillation is characterized on electrocardiogram by:
A) Regular rhythm at 300 beats per minute with sawtooth waves
B) Irregularly irregular ventricular rhythm with no distinct P waves
C) Regular narrow-complex tachycardia with visible P before every QRS
D) Wide-complex rhythm with fusion beats

​

Atrial flutter typically shows:
A) Sawtooth flutter waves at about 300 per minute with a regular conduction pattern
B) Chaotic baseline with no atrial activity
C) Wide-complex irregular rhythm
D) Only ST segment depression

​

A regular narrow-complex tachycardia most consistent with reentry above the ventricles is called:
A) Ventricular tachycardia
B) Atrioventricular nodal reentry supraventricular tachycardia
C) Idioventricular rhythm
D) Torsades de pointes

​

Features that favor ventricular tachycardia over supraventricular tachycardia with aberrancy include:
A) Narrow QRS and visible P before every QRS
B) Atrioventricular dissociation, capture or fusion beats, very wide QRS
C) Perfectly normal axis
D) Consistent preceding P waves

​

Torsades de pointes is most often associated with:
A) Short corrected Q–T interval
B) Prolonged corrected Q–T interval
C) Tall peaked T waves from high potassium
D) Hypercalcemia

​

Asystole appears on electrocardiogram as:
A) Wide irregular complexes without a pulse
B) A straight or nearly flat line without organized electrical activity
C) A regular narrow-complex tachycardia
D) Sawtooth waves

​

Ventricular fibrillation appears as:
A) Regular narrow complexes at high rate
B) Organized atrial waves with dropped beats
C) Chaotic irregular waves with no identifiable QRS complexes
D) Sinus rhythm with premature beats

​

First-degree atrioventricular block is defined by:
A) Progressive P–R prolongation with a dropped beat
B) P–R interval greater than 200 milliseconds with all P waves conducted
C) Some P waves not followed by QRS with constant P–R intervals
D) No relationship between P and QRS

​

Second-degree atrioventricular block, Mobitz type I (Wenckebach), shows:
A) Fixed P–R intervals and dropped QRS complexes
B) Progressive P–R lengthening until a beat is dropped
C) No association between P and QRS
D) Very short P–R interval

​

Second-degree atrioventricular block, Mobitz type II, shows:
A) Progressive P–R prolongation
B) Constant P–R intervals with intermittent non-conducted P waves
C) No P waves present
D) Ventricular fibrillation

​

Third-degree (complete) atrioventricular block is characterized by:
A) Variable P–R intervals with dropped beats
B) Complete atrioventricular dissociation between P waves and QRS complexes
C) Short P–R interval with delta waves
D) Narrow-complex tachycardia

​

Hyperkalemia classically produces on electrocardiogram:
A) Tall peaked T waves and progressive QRS widening
B) Prominent U waves
C) Short Q–T interval with widened P waves
D) Atrial flutter

​

Hypokalemia often produces:
A) Tall peaked T waves
B) Flattened T waves and prominent U waves
C) Marked QRS widening only
D) Delta waves

​

Hypercalcemia typically causes:
A) Prolonged Q–T interval
B) Shortened Q–T interval
C) Widened QRS
D) Tall peaked T waves

​

Hypocalcemia typically causes:
A) Shortened Q–T interval
B) Prolonged Q–T interval
C) Tall peaked T waves
D) Delta waves

​

The “scooped” ST segment with downsloping depression is characteristic of:
A) Severe hypothermia alone
B) Digoxin effect
C) Hyperkalemia
D) Pericarditis

​

Diffuse ST segment elevation with PR segment depression across many leads suggests:
A) Localized transmural infarction
B) Acute pericarditis
C) Right bundle branch block
D) Hyperkalemia

​

Electrocardiogram signs sometimes seen with acute pulmonary embolism include:
A) Left bundle branch block in all cases
B) Sinus tachycardia and right heart strain patterns (for example T wave inversion in V1–V3)
C) Universal ST elevation
D) Atrial flutter every time

​

In suspected right ventricular infarction with inferior changes, an additional useful lead is:
A) V3 left
B) V4 right (V4R)
C) aVR
D) aVL

​

Inferior wall myocardial infarction produces the most prominent changes in:
A) I and aVL
B) V1 and V2
C) II, III, and aVF
D) V5 and V6

​

A pathologic Q wave is generally defined as:
A) Any small initial negative deflection
B) Wider than 40 milliseconds and at least one quarter the height of the following R in that lead
C) Always present in healthy athletes
D) A tall positive deflection

​

Electrical alternans (beat-to-beat QRS amplitude variation) is most classically associated with:
A) Hypercalcemia
B) Pericardial tamponade
C) Left bundle branch block
D) Hypokalemia

​

A functioning ventricular pacemaker often shows:
A) No evidence on the tracing
B) Small vertical pacer spikes before each QRS complex
C) Only ST depression
D) Tall P waves

​

The “300–150–100–75–60–50” method for rate requires:
A) Measuring ten seconds only
B) Regular rhythm and large box counting between R waves
C) Counting P waves
D) Using a calculator

​

Using the small-box method for heart rate, rate equals:
A) 1500 divided by the number of small squares between R waves
B) 300 divided by the number of small squares
C) 10 times the number of complexes in one second
D) 60 divided by large squares

​

A common source of electrocardiogram artifact that can mimic atrial activity is:
A) Paper speed
B) Skeletal muscle tremor or shivering
C) Very high blood pressure
D) Low body temperature only

​

Right and left arm lead reversal most often produces:
A) Inverted lead I with unexpected positive aVR
B) Tall R in V1
C) ST elevation in all leads
D) Atrial flutter

​

In normal sinus rhythm, lead aVR typically shows:
A) Positive P, QRS, and T waves
B) Predominantly negative complexes
C) Flat line
D) Only pacer spikes

​

A simple quadrant method for axis uses:
A) Only precordial leads
B) The polarity of QRS in leads I and aVF
C) The size of the P wave in V1
D) The ST segment in V5

​

Sinus bradycardia is defined as:
A) Heart rate less than 100 beats per minute
B) Heart rate less than 60 beats per minute with sinus P before each QRS
C) Heart rate greater than 120 beats per minute
D) No P waves present

​

Sinus tachycardia is defined as:
A) Heart rate greater than 100 beats per minute with normal P before each QRS
B) Narrow complex without P waves
C) Wide complex with fusion beats
D) No electrical activity

​

Respiratory sinus arrhythmia refers to:
A) Tachycardia during exhalation only
B) Normal variation in sinus rate with breathing
C) Atrial fibrillation
D) Ventricular bigeminy

​

A junctional rhythm typically shows:
A) Tall P waves before each QRS
B) Absent or inverted P waves with narrow QRS and rate 40–60
C) Wide QRS with fusion beats
D) Sawtooth flutter waves

​

A premature atrial complex is recognized by:
A) An early, wide bizarre QRS
B) An early P wave of different shape followed by a normal or narrow QRS
C) No preceding P wave
D) Prolonged Q–T interval

​

A premature ventricular complex is recognized by:
A) Early narrow QRS with normal P
B) Early wide bizarre QRS not preceded by a normal P and followed by a compensatory pause
C) Late narrow QRS
D) Only T wave inversion

​

Bigeminy refers to:
A) Two P waves for every QRS
B) A repeating pattern of one premature beat followed by one normal beat
C) Alternating bundle branch block
D) Two QRS complexes fused into one

​

The Wolff–Parkinson–White pattern includes:
A) Very long P–R interval
B) Short P–R interval, slurred upstroke of QRS (delta wave), and wide QRS
C) Tall U waves
D) Negative P waves in all leads

​

Criteria often used for acute ST segment elevation myocardial infarction include new ST elevation of at least:
A) 0.25 millimeters in any lead
B) 1 millimeter in limb leads or 2 millimeters in precordial leads in two contiguous leads
C) 5 millimeters everywhere
D) 10 millimeters in aVR

​

Non-ST elevation myocardial infarction is more commonly associated with:
A) Diffuse ST elevation
B) ST depression and/or T wave inversion in contiguous leads
C) Ventricular fibrillation only
D) Normal electrocardiogram in all cases

​

A common voltage criterion for left ventricular hypertrophy (Sokolow–Lyon) is:
A) R in V6 plus S in V1 less than 10 millimeters
B) S in V1 plus R in V5 or V6 greater than 35 millimeters
C) R in aVL less than 7 millimeters
D) S in V2 greater than 10 millimeters

​

Right ventricular hypertrophy on electrocardiogram often shows:
A) Right axis deviation with R/S ratio greater than 1 in V1
B) Left axis deviation with tall R in V6
C) Very prolonged Q–T interval only
D) Diffuse low voltage

​

Left atrial enlargement is suggested by:
A) Peaked P waves in lead II
B) Broad, notched P in lead II and a biphasic negative terminal P in V1
C) Narrow P waves everywhere
D) Absence of P waves

​

Right atrial enlargement is suggested by:
A) Very small P waves
B) Tall peaked P waves in inferior leads (>2.5 millimeters)
C) Negative P in V1
D) Absent P waves

​

True or false: The QRS complex represents ventricular depolarization.

​

True or false: A small U wave can be normal, but a prominent U wave often suggests low potassium.

​

True or false: The ST segment is normally elevated in most leads at rest.

​

True or false: Atrial flutter always produces an irregular ventricular rhythm.

​

True or false: Atrial fibrillation increases the risk of clot formation and stroke.

​

True or false: Ventricular fibrillation requires immediate defibrillation.

​

True or false: Sinus rhythm implies an upright P in leads I and II with each P followed by a QRS at a consistent P–R interval.

​

True or false: Left bundle branch block can mask or mimic acute anterior ST elevation, complicating diagnosis.

​

True or false: PR segment depression is a supportive electrocardiogram sign of acute pericarditis.

​

True or false: Corrected Q–T accounts for heart rate to better estimate repolarization duration.

​

True or false: Right axis deviation is commonly seen in chronic lung disease and right ventricular hypertrophy.

​

True or false: Hyperkalemia is classically associated with tall peaked T waves.

​

True or false: Asystole is a shockable rhythm that should be defibrillated immediately.

​

True or false: Pacemaker failure to capture appears as pacing spikes without subsequent P waves or QRS complexes.

​

True or false: Inferior myocardial infarction produces changes mainly in leads II, III, and aVF.

​

True or false: Electrical axis cannot be determined from precordial leads alone using the quadrant method.

​

True or false: Lead II records the potential of the left leg relative to the right arm.

​

True or false: Lead aVR is usually predominantly positive during normal sinus rhythm.

​

True or false: Using the 300 rule to calculate rate assumes a regular rhythm.

​

Fill in the blank: The P wave represents ____________________________ depolarization.

​

Fill in the blank: The normal P–R interval is ____________________________ to ____________________________ milliseconds.

​

Fill in the blank: The isoelectric segment between ventricular depolarization and repolarization is called the ____________________________ segment.

​

Fill in the blank: Lead V4 is placed at the ____________________________ intercostal space at the ____________________________ line.

Fill in the blank: A widened QRS complex is greater than ____________________________ milliseconds.

Fill in the blank: With the small-box method, heart rate equals 1500 divided by the number of ____________________________ between R waves.

Fill in the blank: Pathologic Q waves are ____________________________ seconds or more in duration and at least ____________________________ of the following R wave amplitude in that lead.

Fill in the blank: A common voltage criterion for left ventricular hypertrophy is S in V1 plus R in V5 or V6 greater than ____________________________ millimeters.

Fill in the blank: In atrial fibrillation the ventricular rhythm is described as ____________________________.

Fill in the blank: The corrected Q–T interval adjusts the Q–T for the ____________________________ rate.

Short answer: Describe how to calculate heart rate using the “300 rule,” and give an example.

​

Short answer: Explain why left bundle branch block complicates diagnosis of acute anterior myocardial infarction on the electrocardiogram.

​

Short answer: State two electrocardiogram features that favor ventricular tachycardia over supraventricular tachycardia with aberrancy.

​

Short answer: Give two electrocardiogram findings that support acute pericarditis.

​

Short answer: Describe the standard limb lead electrode positions for a 12-lead electrocardiogram.

​

Short answer: What does “contiguous leads” mean when interpreting ST segment changes?

​

Short answer: Name one common cause of electrocardiogram artifact and one way to reduce it.

​

Short answer: Briefly describe the typical electrocardiographic evolution after a transmural myocardial infarction.

​

Short answer: What distinguishes first-degree from second-degree atrioventricular block?

​

Short answer: When should right-sided precordial leads be obtained, and what can they reveal during inferior infarction?