USMLE Step 2 Quiz
Practice Cardiac Arrhythmias And Conduction Disorders in USMLE Step 2 with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.
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A 28-year-old woman presents to the emergency department with a 2-hour history of sudden-onset palpitations and lightheadedness. She has no significant past medical history. Her temperature is 37.0°C (98.6°F), blood pressure is 115/75 mm Hg, pulse is 170/min and regular, and respirations are 18/min. The physical examination is unremarkable. An ECG reveals a regular, narrow-complex tachycardia with no discernible P waves.
What is the most likely diagnosis?
This quiz focuses on Cardiac Arrhythmias And Conduction Disorders, giving you a quick way to practice the rules, question types, and explanations that matter most for USMLE Step 2.
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A 28-year-old woman presents to the emergency department with a 2-hour history of sudden-onset palpitations and lightheadedness. She has no significant past medical history. Her temperature is 37.0°C (98.6°F), blood pressure is 115/75 mm Hg, pulse is 170/min and regular, and respirations are 18/min. The physical examination is unremarkable. An ECG reveals a regular, narrow-complex tachycardia with no discernible P waves.
What is the most likely diagnosis?
Explanation: The patient's presentation of sudden-onset palpitations with a regular, narrow-complex tachycardia at a rate of 170/min and absent P waves is classic for atrioventricular nodal reentrant tachycardia (AVNRT), a type of supraventricular tachycardia. Atrial fibrillation would be irregularly irregular. Ventricular tachycardia would typically show a wide QRS complex. Sinus tachycardia is a physiologic response and would have visible P waves preceding each QRS complex.
A 24-year-old graduate student presents to the urgent care clinic with palpitations that started abruptly one hour ago. She feels anxious but is not experiencing chest pain, dyspnea, or syncope. Her blood pressure is 120/80 mm Hg and her heart rate is 160/min. An ECG shows a regular, narrow-complex tachycardia. She is alert and oriented.
Which of the following is the most appropriate initial step in management?
Explanation: This hemodynamically stable patient presents with a supraventricular tachycardia (SVT), most likely AVNRT. The initial management for stable SVT should be vagal maneuvers, such as carotid sinus massage or the Valsalva maneuver. If these are unsuccessful, intravenous adenosine is the next step. Diltiazem is a second-line pharmacologic agent. Synchronized cardioversion is reserved for hemodynamically unstable patients.
A 72-year-old man with a history of ischemic cardiomyopathy is admitted to the telemetry unit. He develops a sustained episode of monomorphic ventricular tachycardia at a rate of 140/min. His blood pressure remains stable at 115/80 mm Hg, and he denies chest pain or shortness of breath. He is conversing comfortably with the nurse.
Which of the following is the most appropriate initial pharmacologic treatment?
Explanation: For a hemodynamically stable patient with monomorphic ventricular tachycardia, the first-line treatment is an intravenous antiarrhythmic agent. Amiodarone is a preferred agent according to ACLS guidelines. Procainamide or sotalol are also options. Adenosine is used for diagnosing and treating supraventricular tachycardia, not VT. Magnesium sulfate is the treatment of choice for torsades de pointes (polymorphic VT). Verapamil (a calcium channel blocker) is contraindicated in wide-complex tachycardias of unknown origin as it can cause hemodynamic collapse if the rhythm is VT.
A 76-year-old woman is diagnosed with new-onset, nonvalvular atrial fibrillation during a routine clinic visit. She has a history of hypertension, for which she takes lisinopril, and type 2 diabetes mellitus, managed with metformin. Her CHA2DS2-VASc score is calculated. She currently has no symptoms.
Which of the following is the most appropriate long-term therapy to reduce her risk of thromboembolic events?
Explanation: This patient's CHA2DS2-VASc score is 4 (Age ≥75=2 points, Hypertension=1 point, Diabetes=1 point). A score of 2 or greater in men or 3 or greater in women is a clear indication for long-term oral anticoagulation. Direct oral anticoagulants (e.g., apixaban, rivaroxaban) or warfarin are recommended over antiplatelet agents like aspirin or clopidogrel, which are less effective for stroke prevention in atrial fibrillation. No therapy would leave her at significant risk for stroke.
A 58-year-old man had a large anterior wall myocardial infarction four months ago. He has completed cardiac rehabilitation and is on optimal medical therapy including an ACE inhibitor, beta-blocker, and statin. A follow-up echocardiogram reveals a left ventricular ejection fraction of 28%. He has NYHA class II heart failure symptoms.
In addition to his current medications, which of the following is indicated to reduce his risk of sudden cardiac death?
Explanation: An implantable cardioverter-defibrillator (ICD) is indicated for primary prevention of sudden cardiac death in patients with ischemic cardiomyopathy, an LVEF ≤35%, and NYHA class II or III symptoms, provided they are at least 40 days post-MI and are on optimal medical therapy. A pacemaker is for bradyarrhythmias. Prophylactic amiodarone has not been shown to improve survival in this population and has significant side effects. Bypass grafting is for revascularization and would have been considered earlier if appropriate.
A 65-year-old man undergoes a routine pre-operative ECG. The tracing shows a regular rhythm at 70/min. The PR interval progressively increases with each beat until a P wave appears that is not followed by a QRS complex. This pattern then repeats.
Which of the following is the most likely diagnosis?
Explanation: The ECG finding of progressive PR interval prolongation followed by a non-conducted P wave ('dropped beat') is the classic description of second-degree AV block, Mobitz type I (also known as Wenckebach phenomenon). First-degree AV block involves a constantly prolonged PR interval with no dropped beats. Mobitz type II involves dropped beats without preceding PR prolongation. Third-degree AV block involves complete dissociation between P waves and QRS complexes.
A 55-year-old woman with a history of alcoholism and poor nutrition is admitted for syncope. Her initial ECG shows a prolonged QT interval. While on the telemetry monitor, she develops an episode of tachycardia where the QRS complexes appear to twist around the isoelectric baseline. She becomes unresponsive and pulseless.
In addition to defibrillation and CPR, which of the following is the most appropriate immediate pharmacologic treatment?
Explanation: The patient has developed torsades de pointes (TdP), a polymorphic ventricular tachycardia occurring in the setting of a prolonged QT interval. Her alcoholism and malnutrition put her at risk for electrolyte abnormalities like hypomagnesemia and hypokalemia, common causes of QT prolongation. The first-line treatment for TdP (both stable and unstable) is intravenous magnesium sulfate, which helps stabilize the cardiac membrane. Amiodarone can further prolong the QT interval and should be avoided. Calcium is for hyperkalemia, and bicarbonate is for specific toxicities or acidosis.
A 68-year-old man with hypertension and dyslipidemia is found to have atrial flutter with a 2:1 block and a ventricular rate of 150/min. He is hemodynamically stable. His cardiologist is planning an outpatient catheter ablation.
Which of the following best describes the approach to stroke prevention in this patient?
Explanation: Atrial flutter carries a similar thromboembolic risk to atrial fibrillation. Therefore, the management of stroke prevention is identical. The decision to initiate anticoagulation should be based on the CHA2DS2-VASc score, regardless of whether the arrhythmia is atrial flutter or atrial fibrillation. The ventricular rate and future plans for ablation do not change the need for risk stratification and appropriate anticoagulation.
An 88-year-old woman is brought to the emergency department after a syncopal episode. Her ECG shows a ventricular rate of 40/min and an atrial rate of 90/min. There is no consistent relationship between the P waves and the QRS complexes. The QRS complexes are narrow.
What is the most likely diagnosis?
Explanation: The ECG findings describe complete atrioventricular (AV) dissociation, where the atria (P waves at 90/min) and ventricles (QRS complexes at 40/min) are beating independently. This is the definition of third-degree, or complete, AV block. The narrow QRS indicates the escape rhythm is originating from the AV junction. Mobitz II would show some relationship between P waves and QRS complexes (e.g., 2:1 or 3:1 block). Sick sinus syndrome can cause bradycardia but not necessarily complete AV dissociation.
An 80-year-old man with a history of aortic stenosis presents to the emergency department with dizziness and confusion. His blood pressure is 75/45 mm Hg and his heart rate is 35/min. An ECG shows third-degree AV block. He is lethargic and slow to respond.
What is the most appropriate immediate next step in management?
Explanation: This patient has symptomatic, high-degree AV block causing hemodynamic instability (hypotension, altered mental status). The immediate priority is to increase the heart rate and restore cardiac output. Transcutaneous pacing is the fastest and most reliable method to achieve this in an unstable patient. Atropine is unlikely to be effective for a high-degree (infranodal) block and should not delay more definitive therapy. While a permanent pacemaker will be needed, it is not the immediate intervention. Vasopressors like dopamine can be used as a bridge but pacing is the primary treatment.
A 45-year-old woman collapses at home and is successfully resuscitated by paramedics from ventricular fibrillation. An urgent coronary angiogram reveals no significant coronary artery disease. An echocardiogram shows a normal left ventricular ejection fraction. Her electrolyte levels are normal and a toxicology screen is negative.
Which of the following is the most appropriate long-term management to prevent a recurrence?
Explanation: This patient survived a cardiac arrest due to ventricular fibrillation not associated with a transient or reversible cause (like an acute MI or electrolyte disturbance). This constitutes a clear indication for secondary prevention of sudden cardiac death. An implantable cardioverter-defibrillator (ICD) is the standard of care and has been proven to improve survival in these patients. While antiarrhythmic drugs like amiodarone may be used as adjunctive therapy, they are not a substitute for an ICD. A pacemaker would not treat a tachyarrhythmia.
A 22-year-old man presents for evaluation of intermittent episodes of rapid heartbeat. A 12-lead ECG performed while he is asymptomatic shows a sinus rhythm with a PR interval of 100 ms and a slurred upstroke of the QRS complex.
These ECG findings are most characteristic of which underlying condition?
Explanation: The combination of a short PR interval (<120 ms) and a slurred upstroke of the QRS complex, known as a 'delta wave,' is the pathognomonic ECG finding for Wolff-Parkinson-White (WPW) syndrome. This pattern is caused by pre-excitation of the ventricles via an accessory pathway that bypasses the AV node. Brugada syndrome has a characteristic coved ST-segment elevation in V1-V2. Long QT syndrome is defined by a prolonged QT interval. Hypertrophic cardiomyopathy may show signs of left ventricular hypertrophy but not a short PR and delta wave.
A 70-year-old man is referred to a cardiologist after an ECG during a health screening revealed an abnormality. The patient is completely asymptomatic and physically active. The ECG shows a regular rhythm with occasional dropped QRS complexes. When conduction occurs, the PR interval is constant at 200 ms. When QRS complexes are dropped, there is no change in the PR interval of the surrounding conducted beats. The heart rate is 60/min.
What is the most appropriate next step in management?
Explanation: The ECG describes second-degree AV block, Mobitz type II, characterized by intermittent non-conducted P waves with a constant PR interval in the conducted beats (no gradual PR prolongation before the dropped beat). Mobitz type II block is considered high-risk because it occurs below the AV node (infranodal) and can unpredictably progress to complete heart block and asystole. Therefore, a permanent pacemaker is indicated, even in asymptomatic patients. Reassurance is inappropriate due to the high risk of progression. Atropine is not a long-term solution. Stress testing is not indicated and could be dangerous.
A 35-year-old man with a known history of Wolff-Parkinson-White (WPW) syndrome presents to the emergency department with palpitations. His blood pressure is 110/70 mm Hg. The ECG shows an irregularly irregular, wide-complex tachycardia with a rate of 220/min.
Which of the following medications should be avoided in this patient?
Explanation: This patient has atrial fibrillation with rapid conduction down an accessory pathway, a life-threatening arrhythmia in WPW syndrome. Administering AV nodal blocking agents (such as adenosine, beta-blockers, calcium channel blockers, or digoxin) is contraindicated because blocking the normal AV pathway can lead to preferential and extremely rapid conduction down the accessory pathway, potentially degenerating into ventricular fibrillation. The treatment of choice for a stable patient is an antiarrhythmic like procainamide or ibutilide. If the patient were unstable, synchronized cardioversion would be appropriate.
A 55-year-old high school teacher with new-onset atrial fibrillation was started on metoprolol for rate control. Her ventricular rate is now 80-90/min at rest. However, she continues to experience significant palpitations and shortness of breath with minimal exertion, which interferes with her ability to work. Her echocardiogram is normal.
What is the most appropriate next step in her management?
Explanation: This patient remains highly symptomatic from her atrial fibrillation despite adequate rate control. In such cases, especially in a younger, active individual, a rhythm-control strategy is indicated to improve symptoms and quality of life. Options for rhythm control include antiarrhythmic medications (e.g., flecainide, amiodarone) or catheter ablation. Simply increasing the beta-blocker or adding digoxin would further control the rate but is unlikely to resolve symptoms that are due to the loss of sinus rhythm itself. Reassurance is inappropriate given her functional impairment.
A 67-year-old man with a history of coronary artery disease and a prior myocardial infarction presents with palpitations and dizziness. His blood pressure is 110/70 mm Hg, and his pulse is 150/min. An ECG shows a regular, wide-complex tachycardia with a QRS duration of 160 ms. He is awake and alert.
What is the most likely diagnosis?
Explanation: In an older patient with structural heart disease (prior MI), any wide-complex tachycardia should be considered ventricular tachycardia (VT) until proven otherwise. While SVT with aberrancy is a possibility, VT is far more common and life-threatening in this clinical context. Atrial flutter would typically have a narrow QRS unless there is a pre-existing bundle branch block. Torsades de pointes is a polymorphic VT, which would appear as an irregular rhythm with varying QRS morphology, unlike the regular rhythm described.
An 82-year-old man with a history of hypertension and osteoarthritis is found to have persistent atrial fibrillation. His heart rate is well-controlled at 75/min with metoprolol. He reports mild fatigue but denies palpitations, dyspnea, or chest pain. He leads a sedentary lifestyle. An echocardiogram shows mild left atrial enlargement and normal left ventricular function.
What is the most appropriate long-term management strategy for his arrhythmia?
Explanation: In an elderly, minimally symptomatic patient with persistent atrial fibrillation, a rate-control strategy is generally preferred and has been shown to have non-inferior outcomes compared to a rhythm-control strategy regarding mortality and stroke risk. Rhythm control strategies (e.g., antiarrhythmic drugs like amiodarone, or catheter ablation) are associated with more side effects and are typically reserved for patients who remain symptomatic despite adequate rate control or in younger patients. Digoxin is primarily used for rate control, not rhythm control.
A 68-year-old man with a long history of severe chronic obstructive pulmonary disease (COPD) is admitted for an acute exacerbation. He is receiving nebulized albuterol, ipratropium, and systemic corticosteroids. His telemetry monitor shows a heart rate of 125/min with an irregularly irregular rhythm. A 12-lead ECG reveals a variable heart rate, at least three distinct P-wave morphologies, and varying PR intervals.
What is the most likely arrhythmia?
Explanation: The presence of a tachycardic rhythm (rate >100/min) with at least three different P-wave morphologies, varying PR intervals, and an irregular rhythm is the definition of multifocal atrial tachycardia (MAT). MAT is strongly associated with severe pulmonary disease, such as a COPD exacerbation. While atrial fibrillation is also irregularly irregular, it has no discernible P waves. Atrial flutter would show characteristic 'sawtooth' flutter waves. Sinus tachycardia with PACs would have a dominant, consistent sinus P-wave morphology.
A 78-year-old man with a history of hypertension is brought to the emergency department due to confusion and severe shortness of breath. His temperature is 37.2°C (99.0°F), blood pressure is 80/50 mm Hg, pulse is 165/min and irregularly irregular, and respirations are 28/min. He is diaphoretic and his extremities are cool. An ECG confirms atrial fibrillation with a rapid ventricular response. Lung examination reveals bibasilar crackles.
Which of the following is the most appropriate immediate intervention?
Explanation: The patient is in atrial fibrillation with rapid ventricular response and is hemodynamically unstable, as evidenced by hypotension, signs of shock (cool extremities, diaphoresis), altered mental status (confusion), and acute heart failure (pulmonary edema). The immediate priority is to restore a stable rhythm and improve cardiac output. Therefore, urgent synchronized cardioversion is indicated. Pharmacologic rate or rhythm control (amiodarone, diltiazem) is too slow for an unstable patient. Anticoagulation with heparin is important but is not the immediate life-saving intervention.
An 85-year-old man presents to his primary care physician with several episodes of syncope over the past month. He feels lightheaded before losing consciousness, with no prodromal chest pain or palpitations. His medical history is significant for hypertension. His vital signs are stable. A 12-lead ECG in the office shows sinus bradycardia with a heart rate of 38/min.
Which of the following is the most appropriate long-term treatment for this patient?
Explanation: This patient has symptomatic bradycardia (syncope) directly attributable to his low heart rate (sinus bradycardia). This is a clear indication for a permanent pacemaker to prevent further syncopal episodes and improve his quality of life. Atropine is used for acute, not chronic, management. An ICD is indicated for preventing sudden death from tachyarrhythmias, not for treating bradycardia. Since the cause of his syncope has been identified on the ECG, further monitoring with an event monitor is unnecessary before intervention.