ECG interpretation Practice Questions

Question 1

An ECG from an 8-year-old male with neurosensory deafness and a family history of sudden cardiac arrest demonstrates QT-interval prolongation. Which of the following is this patient most at risk of developing?

Accepted Answer

Torsades de pointes

Answer

Hypertrophic cardiac myopathy

Answer

Cardiac tamponade

Answer

Essential hypertension

Answer

First degree atrioventricular block

Question 2

A 24-year-old woman comes to the physician for a routine health maintenance examination. She feels well. On questioning, she has had occasional morning dizziness and palpitations during the past year. She is a graduate student. She does not smoke and drinks 1–2 glasses of wine on the weekends. Her vital signs are within normal limits. Physical examination shows an irregular pulse. On auscultation of the chest, S1 and S2 are normal and there are no murmurs. An ECG is shown. Which of the following is the most appropriate next step in management?

Accepted Answer

Reassurance

Answer

Event recorder implantation

Answer

Administration of flecainide

Answer

Administration of metoprolol

Answer

Stress echocardiography

Question 3

A researcher is studying how electrical activity propagates across the heart. In order to do this, he decides to measure the rate at which an action potential moves within various groups of cardiac muscle tissue. In particular, he isolates fibers from areas of the heart with the following characteristics:

A) Dysfunction leads to fixed PR intervals prior to a dropped beat
B) Dysfunction leads to increasing PR intervals prior to a dropped beat
C) Dysfunction leads to tachycardia with a dramatically widened QRS complex
D) Dysfunction leads to tachycardia with a sawtooth pattern on electrocardiogram

Which of the following is the proper order of these tissues from fastest action potential propagation to slowest action potential propagation.

Accepted Answer

A > D > C > B

Answer

B > D > C > A

Answer

D > C > A > B

Answer

B > C > D > A

Answer

A > C > D > B

Question 4

A 72-year-old man comes to the physician because of a 2-month history of intermittent retrosternal chest pain and tightness on exertion. He has type 2 diabetes mellitus, osteoarthritis of the right hip, and hypertension. Current medications include insulin, ibuprofen, enalapril, and hydrochlorothiazide. Vital signs are within normal limits. His troponin level is within the reference range. An ECG at rest shows a right bundle branch block and infrequent premature ventricular contractions. The patient's symptoms are reproduced during adenosine stress testing. Repeat ECG during stress testing shows new ST depression of > 1 mm in leads V2, V3, and V4. Which of the following is the most important underlying mechanism of this patient's ECG changes?

Accepted Answer

Diversion of blood flow from stenotic coronary arteries

Answer

Transient atrioventricular nodal blockade

Answer

Reduced left ventricular preload

Answer

Ruptured cholesterol plaque within a coronary vessel

Answer

Increased myocardial oxygen demand

Question 5

A 55-year-old man comes to the emergency department because of left-sided chest pain and difficulty breathing for the past 30 minutes. His pulse is 88/min. He is pale and anxious. Serum studies show increased cardiac enzymes. An ECG shows ST-elevations in leads I, aVL, and V5-V6. A percutaneous coronary intervention is performed. In order to localize the site of the lesion, the catheter must pass through which of the following structures?

Accepted Answer

Left coronary artery → left circumflex artery

Answer

Right coronary artery → posterior descending artery

Answer

Left coronary artery → left anterior descending artery

Answer

Right coronary artery → right marginal artery

Answer

Left coronary artery → posterior descending artery

Question 6

A 65-year-old woman comes to the physician because of a 3-month history of intermittent palpitations and shortness of breath. Cardiopulmonary examination shows no other abnormalities. An ECG shows an absence of P waves, an oscillating baseline, and irregular RR intervals at a rate of approximately 95 beats per minute. The difference between atrial and ventricular rates in this patient is most likely due to which of the following?

Accepted Answer

Temporary inactivation of Na+ channels in the AV node

Answer

Prolonged influx through voltage-gated Ca2+ channels in the bundle of His

Answer

Transient activation of K+ current in Purkinje fibers

Answer

Inhibition of the Na+/K+-ATPase pump in ventricular cells

Answer

Limited speed of conduction through the left bundle branch

Question 7

In a patient with acute myocardial ischemia, which of the following cardiovascular structures is at greatest risk of damage?

Accepted Answer

Cardiac conduction system

Answer

Pulmonary valve

Answer

Coronary artery

Answer

Cardiac septum

Answer

Temporal artery

Question 8

Cardiac muscle serves many necessary functions, leading to a specific structure that serves these functions. The structure highlighted is an important histology component of cardiac muscle. What would be the outcome if this structure diffusely failed to function?

Accepted Answer

Failure of propagation of the action potential from the conduction system

Answer

Failure of potassium channels to appropriately open to repolarize the cell

Answer

Ineffective excitation-contraction coupling due to insufficient calcium ions

Answer

Inappropriate formation of cardiac valve leaflets

Answer

Outflow tract obstruction

Question 9

A 17-year-old boy comes to the physician for a follow-up examination. Two months ago, he suffered a spinal fracture after a fall from the roof. He feels well. His father has multiple endocrine neoplasia type 1. Vital signs are within normal limits. Examination shows no abnormalities. Laboratory studies show:
Hemoglobin 13.7 g/dL
Serum
Creatinine 0.7 mg/dL
Proteins
Total 7.0 g/dL
Albumin 4.1 g/dL
Calcium 11.4 mg/dL
Phosphorus 5.3 mg/dL
Alkaline phosphatase 100 U/L
Which of the following is the most likely cause of these findings?

Accepted Answer

Immobilization

Answer

Parathyroid adenoma

Answer

Paraneoplastic syndrome

Answer

Sarcoidosis

Answer

Pseudohypercalcemia

Question 10

A 52-year-old man is brought to the emergency department by ambulance after a motor vehicle accident. He was an unrestrained passenger who was ejected from the vehicle. On presentation, he is found to be actively bleeding from numerous wounds. His blood pressure is 76/42 mmHg and pulse is 152/min. Attempts at resuscitation fail, and he dies 25 minutes later. Autopsy shows blood in the peritoneal cavity, and histology of the kidney reveals swelling of the proximal convoluted tubule epithelial cells. Which of the following is most likely the mechanism underlying the renal cell findings?

Accepted Answer

Decreased function of the Na+/K+-ATPase

Answer

Decreased activity of caspase 7

Answer

Increased activity of caspase 9

Answer

Increased function of the Na+/K+-ATPase

Answer

Increased activity of caspase 8

ECG interpretation

Study Resources

Lessons

Questions

Flashcards

Lessons

ECG basics and lead placement

Cardiac axis determination

P wave and atrial depolarization

PR interval significance

QRS complex analysis

ST segment evaluation

T wave and repolarization

QT interval and QTc calculation

Bundle branch blocks

Chamber enlargement patterns

Ischemia and infarction patterns

Common arrhythmia recognition

Electrolyte effects on ECG

Practice Questions

Flashcards

About ECG interpretation for USMLE

Lessons in ECG interpretation

Master ECG interpretation