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ABIM Clinical EP study materials
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ABIM Clinical EP practice questions

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Question 1Patient care and procedural skills

A 68-year-old man with symptomatic sinus bradycardia and recurrent syncope is scheduled for permanent pacemaker implantation. Which periprocedural antibiotic regimen is recommended to reduce pocket infection risk?

  1. Vancomycin given only if the patient develops fever after implantation
  2. No antibiotic prophylaxis, because device infections are rare
  3. A 7-day postoperative course of oral amoxicillin-clavulanate
  4. A single preoperative dose of cefazolin administered within 1 hour before incision Correct answer.

Explanation

Current guidelines recommend a single dose of an anti-staphylococcal antibiotic such as cefazolin given within 1 hour before incision to achieve adequate tissue levels at the time of pocket creation. Prolonged postoperative courses and fever-triggered dosing are not supported and promote resistance.

Question 2Patient care and procedural skills

During femoral venous access for an electrophysiology study, which maneuver most reliably reduces the risk of inadvertent arterial puncture?

  1. Using ultrasound guidance to visualize the femoral vein relative to the artery Correct answer.
  2. Aiming the needle entry point medial to the femoral artery pulsation
  3. Entering the vein at the level of the inguinal ligament
  4. Advancing the needle at a 60-degree angle to the skin

Explanation

Real-time ultrasound guidance allows direct visualization of the femoral vein and its relationship to the artery, reducing arterial puncture and other access complications. Landmark techniques alone are less reliable, particularly in obese or hypotensive patients.

Question 3Patient care and procedural skills

A patient undergoing catheter ablation for atrial fibrillation is receiving uninterrupted warfarin. Which parameter best guides intraprocedural anticoagulation during left atrial access?

  1. Activated partial thromboplastin time checked at case end
  2. International normalized ratio measured hourly during the case
  3. Platelet count measured after transseptal puncture
  4. Activated clotting time maintained above a target threshold Correct answer.

Explanation

During left atrial procedures, heparin is titrated to a target activated clotting time (commonly 300-350 seconds) to prevent thrombus formation on catheters and sheaths. INR reflects baseline warfarin effect but does not measure the heparin effect achieved during the case.

Question 4Patient care and procedural skills

A patient develops sudden hypotension and tachycardia minutes after femoral sheath removal with manual compression. The groin is swollen and tender. What is the most appropriate immediate step?

  1. Administer intravenous fluids and hold pressure while assessing for retroperitoneal bleeding Correct answer.
  2. Start a therapeutic heparin infusion
  3. Discharge the patient after 30 minutes of observation if vital signs stabilize
  4. Obtain an outpatient ultrasound the following week

Explanation

Acute hypotension with a swollen groin after sheath removal suggests access-site bleeding, possibly retroperitoneal. Immediate resuscitation with fluids, continued compression, and urgent imaging or surgical evaluation are indicated.

Question 5Patient care and procedural skills

Which finding on a 12-lead ECG most strongly supports a diagnosis of typical atrioventricular nodal reentrant tachycardia?

  1. Alternating bundle branch block during tachycardia
  2. A delta wave during sinus rhythm
  3. Retrograde P waves buried within or just after the QRS complex Correct answer.
  4. P waves clearly preceding each QRS with a long PR interval

Explanation

In typical AVNRT, atrial and ventricular activation occur nearly simultaneously, so retrograde P waves are often buried in or just after the QRS. A delta wave suggests pre-excitation, and alternating bundle branch block suggests another mechanism.

Question 6Patient care and procedural skills

A patient with a permanent pacemaker is scheduled for an MRI. Which factor most determines whether the device can be safely scanned?

  1. The presence of a temporary pacing wire
  2. Whether the device is MRI-conditional and programmed per manufacturer protocol Correct answer.
  3. The patient's underlying rhythm at the time of scanning
  4. The size of the generator pocket

Explanation

MRI safety depends on whether the system is MRI-conditional and whether it is programmed and monitored according to manufacturer specifications. Non-conditional devices require individualized risk-benefit assessment.

Question 7Patient care and procedural skills

During radiofrequency ablation near the cavotricuspid isthmus, which structure is at greatest risk of injury if the catheter is positioned too close to the coronary sinus ostium?

  1. The pulmonary artery
  2. The left phrenic nerve
  3. The esophagus
  4. The right coronary artery Correct answer.

Explanation

The right coronary artery courses near the cavotricuspid isthmus and can be injured during ablation in that region. Careful imaging and limiting energy near the ostium reduce this risk.

Question 8Patient care and procedural skills

Which patient is most appropriate for catheter ablation as first-line therapy for symptomatic paroxysmal supraventricular tachycardia?

  1. A patient with severe aortic stenosis awaiting valve replacement
  2. A patient with recurrent symptomatic AVNRT despite beta-blocker therapy Correct answer.
  3. A patient with permanent atrial fibrillation and a mechanical mitral valve
  4. A patient with asymptomatic pre-excitation on a routine ECG

Explanation

Catheter ablation is a reasonable first-line or early option for symptomatic recurrent AVNRT, with high success and low risk. Asymptomatic pre-excitation and complex structural disease require individualized assessment.

Question 9Patient care and procedural skills

A patient with a dual-chamber pacemaker reports palpitations. Interrogation shows rapid atrial pacing at the upper rate limit with paced ventricular complexes. Which pacemaker behavior best explains this?

  1. Lead insulation failure
  2. Loss of capture in the atrium
  3. Pacemaker-mediated tachycardia from retrograde VA conduction Correct answer.
  4. Battery depletion

Explanation

Pacemaker-mediated tachycardia occurs when retrograde conduction to the atrium is sensed and triggers ventricular pacing, resulting in a reentrant circuit at the upper rate limit. Reprogramming or magnet application can interrupt it.

Question 10Patient care and procedural skills

A patient with a single-chamber ventricular pacemaker develops an irregular narrow-complex tachycardia. Which feature on the ECG most suggests that the tachycardia is atrial in origin rather than ventricular?

  1. Pacing spikes preceding each QRS complex
  2. Wide QRS complexes with left bundle branch morphology
  3. Regular ventricular rate at the programmed lower rate
  4. Narrow QRS complexes with P waves dissociated from ventricular pacing spikes Correct answer.

Explanation

Narrow QRS complexes indicate supraventricular activation, and P waves independent of pacing artifacts suggest atrial tachycardia with underlying conduction. Wide complexes or paced complexes would point toward ventricular or pacing-related mechanisms.

Question 11Patient care and procedural skills

During an electrophysiology study, programmed atrial extrastimulation produces a sudden increase in AH interval with a jump of greater than 50 ms before initiation of tachycardia. What does this finding indicate?

  1. Conduction over an accessory pathway
  2. Sinoatrial node suppression
  3. Decremental conduction in the slow AV nodal pathway consistent with AVNRT Correct answer.
  4. Ventricular tachycardia induction

Explanation

A sudden jump in AH interval reflects a shift from fast to slow AV nodal pathway conduction, the substrate for typical AVNRT. Accessory pathway conduction would not produce this characteristic AH jump.

Question 12Patient care and procedural skills

A patient with an implantable cardioverter-defibrillator has multiple shocks in one day without preceding symptoms. Interrogation shows appropriate detection of ventricular fibrillation. Which initial step is most appropriate?

  1. Disable the defibrillator to prevent further shocks
  2. Evaluate for reversible triggers and consider antiarrhythmic therapy or ablation Correct answer.
  3. Increase the detection rate to a very high threshold
  4. Perform elective generator replacement

Explanation

Appropriate shocks for VF require evaluation for ischemia, electrolyte abnormalities, and heart failure, followed by antiarrhythmic therapy or catheter ablation. Disabling therapy or replacing the generator does not address the arrhythmia.

Question 13Patient care and procedural skills

A patient requires temporary pacing after transcatheter aortic valve replacement and develops pacing spikes without capture. Which action is most appropriate next?

  1. Change to a fixed-rate mode without repositioning
  2. Reduce output to preserve battery
  3. Increase output and reposition the lead under fluoroscopic guidance Correct answer.
  4. Administer atropine and observe

Explanation

Loss of capture indicates lead malposition or inadequate contact. Increasing output and repositioning the lead under imaging is the appropriate step before considering other interventions.

Question 14Patient care and procedural skills

A patient with atrial flutter undergoes cavotricuspid isthmus ablation. Bidirectional isthmus block is confirmed. What is the expected long-term outcome?

  1. Need for continued anticoagulation only if flutter recurs
  2. High likelihood of freedom from recurrent typical atrial flutter Correct answer.
  3. Complete elimination of all atrial fibrillation risk
  4. Requirement for repeat ablation in most patients

Explanation

Achieving bidirectional isthmus block provides durable freedom from typical atrial flutter in most patients. It does not eliminate the risk of atrial fibrillation or alter stroke risk stratification.

Question 15Patient care and procedural skills

Which patient is at highest risk of torsades de pointes during initiation of a class III antiarrhythmic?

  1. A patient with a normal QT and normal electrolytes
  2. A patient with hypertension and left ventricular hypertrophy
  3. A patient with hypokalemia and a prolonged baseline QT interval Correct answer.
  4. A patient with paroxysmal atrial fibrillation and normal renal function

Explanation

Hypokalemia and baseline QT prolongation increase the risk of drug-induced torsades de pointes. Electrolytes and QT must be corrected and monitored during initiation of QT-prolonging agents.

Question 16Patient care and procedural skills

A patient with a subcutaneous ICD reports a shock while showering. Device interrogation shows noise and inappropriate detection. What is the most likely cause?

  1. Lead fracture of a transvenous lead
  2. Battery depletion
  3. Electromagnetic interference from a household source Correct answer.
  4. Atrial fibrillation with rapid ventricular response

Explanation

The subcutaneous ICD is more susceptible to electromagnetic interference and myopotential noise, which can be misinterpreted as arrhythmia. Avoiding known sources and appropriate programming reduce inappropriate shocks.

Question 17Patient care and procedural skills

A patient with a biventricular pacemaker for heart failure has worsening symptoms. ECG shows a wide QRS with a left bundle branch block pattern despite biventricular pacing. What is the most appropriate next step?

  1. Replace the generator
  2. Discontinue all heart failure medications
  3. Interrogate the device and optimize AV and VV timing Correct answer.
  4. Immediately refer for heart transplantation

Explanation

Loss of effective cardiac resynchronization may result from suboptimal AV or interventricular timing, lead issues, or remodeling. Device interrogation and optimization should precede more drastic measures.

Question 18Patient care and procedural skills

During an EP study, a catheter in the His position records a His bundle potential. Which interval is measured from the onset of the surface P wave to the onset of the His potential?

  1. QT interval
  2. AH interval Correct answer.
  3. HV interval
  4. PR segment

Explanation

The AH interval is measured from the earliest atrial activation to the His potential and reflects AV nodal conduction. The HV interval measures His to ventricular activation.

Question 19Patient care and procedural skills

A patient with recurrent vasovagal syncope has failed lifestyle measures and pharmacotherapy. Which finding during tilt-table testing best predicts benefit from permanent pacing?

  1. Isolated systolic blood pressure decline without bradycardia
  2. Normal tilt-table response
  3. Prolonged asystole during the vasovagal response Correct answer.
  4. Early heart rate acceleration before syncope

Explanation

Cardioinhibitory responses with significant bradycardia or asystole are most likely to benefit from pacing. Vasodepressor responses without bradycardia do not respond well to pacing.

Question 20Patient care and procedural skills

A patient with long QT syndrome and recurrent syncope despite beta-blockade is being considered for device therapy. Which option is most appropriate?

  1. Implantable cardioverter-defibrillator combined with continued beta-blockade Correct answer.
  2. Permanent pacemaker alone
  3. No device therapy
  4. Class IC antiarrhythmic therapy

Explanation

For high-risk long QT syndrome with syncope despite beta-blockade, an ICD plus continued beta-blockade reduces sudden death risk. Pacing alone does not reliably prevent torsades.

Question 21Patient care and procedural skills

A patient with hypertrophic cardiomyopathy and a recent syncope is evaluated for sudden death risk. Which factor most strongly supports ICD implantation?

  1. Preserved exercise tolerance
  2. A family history of sudden cardiac death at a young age Correct answer.
  3. Mild left ventricular hypertrophy
  4. Normal ambulatory ECG monitoring

Explanation

A family history of sudden cardiac death, especially at a young age, is a major risk marker in hypertrophic cardiomyopathy and supports ICD placement. Mild hypertrophy or preserved exercise tolerance is less concerning.

Question 22Patient care and procedural skills

A patient with an ICD and recurrent ventricular tachycardia receives multiple shocks. Which intervention most directly reduces future shocks by addressing the arrhythmia substrate?

  1. Reducing the detection rate
  2. Catheter ablation of the ventricular tachycardia Correct answer.
  3. Adding a second ICD lead
  4. Increasing the shock energy

Explanation

Catheter ablation targets the reentrant circuit responsible for ventricular tachycardia and reduces recurrent arrhythmia and shocks. Programming changes and device modifications do not treat the underlying substrate.

Question 23Patient care and procedural skills

During mapping of a premature ventricular complex with a right bundle branch block morphology and inferior axis, which location is most consistent with the origin?

  1. Left ventricular lateral wall
  2. Right ventricular apex
  3. Right atrial appendage
  4. Left ventricular outflow tract Correct answer.

Explanation

A right bundle branch block morphology with an inferior axis suggests an origin in the left ventricular outflow tract or aortic cusps. Apical and lateral origins produce different axis and morphology patterns.

Question 24Patient care and procedural skills

A patient with a left bundle branch area pacing lead develops intermittent loss of capture with a change in QRS morphology. What is the most likely explanation?

  1. Battery end-of-life
  2. Atrial undersensing
  3. Programming to VVI mode
  4. Lead displacement or loss of conduction system capture Correct answer.

Explanation

Intermittent loss of capture with changing QRS morphology suggests lead displacement or loss of capture of the conduction system. Device interrogation, imaging, and possible lead revision are indicated.

Question 25Patient care and procedural skills

A patient with a history of atrial fibrillation and a CHA2DS2-VASc score of 3 undergoes successful catheter ablation and remains in sinus rhythm. How should anticoagulation be managed?

  1. Stop anticoagulation immediately after the procedure
  2. Continue long-term oral anticoagulation based on stroke risk score Correct answer.
  3. Stop anticoagulation after 3 months regardless of risk
  4. Use aspirin alone indefinitely

Explanation

Anticoagulation after ablation is guided by the patient's thromboembolic risk, not by rhythm outcome. Patients with elevated CHA2DS2-VASc scores should generally continue long-term anticoagulation.

Question 26Patient care and procedural skills

A 68-year-old man with symptomatic sinus node dysfunction is scheduled for implantation of a permanent pacemaker. He has no history of atrial fibrillation or high-grade atrioventricular block. Which pacing mode is most appropriate to preserve physiological ventricular activation and reduce the risk of pacemaker syndrome?

  1. DDD Correct answer.
  2. AAI
  3. VDD
  4. VVI

Explanation

Dual-chamber pacing (DDD) maintains atrioventricular synchrony and allows ventricular pacing only when needed, which reduces the risk of pacemaker syndrome compared with single-chamber ventricular pacing. It is preferred in patients with sinus node dysfunction who have intact AV conduction.

Question 27Patient care and procedural skills

A 72-year-old woman with a dual-chamber pacemaker presents with fatigue. Interrogation reveals that the paced QRS duration is 180 ms with a left bundle branch block morphology. What is the most likely cause?

  1. Left ventricular lead displacement
  2. Loss of atrial capture
  3. Battery depletion
  4. Right ventricular apical pacing Correct answer.

Explanation

Right ventricular apical pacing produces a left bundle branch block pattern because activation begins in the right ventricle and spreads slowly to the left ventricle. A paced QRS duration >160 ms with LBBB morphology is typical of RV apical pacing.

Question 28Patient care and procedural skills

A 55-year-old man with recurrent symptomatic paroxysmal atrial fibrillation has failed antiarrhythmic drug therapy. He has a normal left ventricular ejection fraction and no significant structural heart disease. Which catheter ablation strategy is most appropriate?

  1. Pulmonary vein isolation Correct answer.
  2. Atrioventricular node ablation and pacemaker implantation
  3. Left atrial appendage ligation
  4. Cavotricuspid isthmus ablation

Explanation

Pulmonary vein isolation is the cornerstone of catheter ablation for paroxysmal atrial fibrillation, as the pulmonary veins are the predominant triggers. It is recommended for symptomatic patients who have failed or are intolerant to antiarrhythmic drugs.

Question 29Patient care and procedural skills

A 60-year-old woman with a dual-chamber pacemaker implanted 2 weeks ago presents with hiccups and rhythmic abdominal twitching synchronous with her heartbeat. Device interrogation shows normal pacing parameters. What is the most likely cause?

  1. Diaphragmatic stimulation from the right ventricular lead Correct answer.
  2. Twiddler's syndrome
  3. Lead perforation
  4. Pacemaker-mediated tachycardia

Explanation

Diaphragmatic stimulation occurs when the pacing lead stimulates the diaphragm or phrenic nerve, causing hiccups or abdominal twitching synchronous with pacing. It can occur with normal pacing parameters and is often due to lead position or high output.

Question 30Patient care and procedural skills

A 70-year-old man with an implantable cardioverter-defibrillator (ICD) for ischemic cardiomyopathy presents with multiple shocks. Interrogation reveals several episodes of rapid ventricular tachycardia that were appropriately detected and treated. He is on amiodarone and a beta-blocker. Which intervention is most likely to reduce future shocks?

  1. Replace the ICD generator
  2. Add sotalol
  3. Catheter ablation of ventricular tachycardia Correct answer.
  4. Increase the ventricular tachycardia detection rate

Explanation

Catheter ablation of ventricular tachycardia reduces recurrent VT and shocks in patients with ischemic cardiomyopathy who have recurrent VT despite antiarrhythmic therapy. It targets the arrhythmogenic substrate and is recommended for patients with recurrent VT.

Question 31Patient care and procedural skills

A 45-year-old woman with symptomatic bradycardia and a normal left ventricular ejection fraction is undergoing pacemaker implantation. The physician aims to achieve physiological pacing by capturing the left bundle branch. Which of the following is a characteristic of left bundle branch area pacing?

  1. A paced QRS with a left bundle branch block pattern in lead V1
  2. A paced QRS with a right bundle branch block pattern in lead V1 Correct answer.
  3. Loss of capture at high output
  4. A short stimulus-to-ventricular activation time in the His bundle

Explanation

Left bundle branch area pacing captures the left bundle branch, leading to rapid activation of the left ventricle and a right bundle branch block pattern in lead V1. This is a marker of successful conduction system pacing.

Question 32Patient care and procedural skills

A 58-year-old man with a history of myocardial infarction and an ejection fraction of 30% is being evaluated for an implantable cardioverter-defibrillator (ICD). He has a history of nonsustained ventricular tachycardia and a life expectancy of more than 1 year. According to current guidelines, which factor is most important in determining his eligibility for a primary prevention ICD?

  1. New York Heart Association functional class Correct answer.
  2. Inducibility of ventricular tachycardia during electrophysiology study
  3. History of syncope
  4. Presence of a left bundle branch block

Explanation

For primary prevention ICD in ischemic cardiomyopathy with reduced ejection fraction, NYHA functional class is a key criterion; patients with NYHA class II or III symptoms and EF ≤35% are eligible. NYHA class IV symptoms generally preclude ICD unless they are candidates for CRT.

Question 33Patient care and procedural skills

A 62-year-old woman with a dual-chamber pacemaker programmed DDD 60–120 bpm presents with palpitations. Interrogation shows a paced ventricular rhythm at 120 bpm with retrograde atrial activation and no underlying sinus activity. Which programming change is most effective to prevent recurrence?

  1. Decrease the maximum tracking rate
  2. Shorten the atrioventricular delay
  3. Extend the post-ventricular atrial refractory period Correct answer.
  4. Increase the lower rate limit

Explanation

Pacemaker-mediated tachycardia occurs when retrograde atrial activation is sensed and triggers ventricular pacing. Extending the post-ventricular atrial refractory period prevents sensing of the retrograde P wave, interrupting the reentrant circuit.

Question 34Patient care and procedural skills

A 50-year-old man with a history of atrial fibrillation and a CHA2DS2-VASc score of 3 undergoes successful catheter ablation and remains in sinus rhythm. He is currently on apixaban. What is the most appropriate long-term anticoagulation strategy?

  1. Switch to aspirin
  2. Perform left atrial appendage occlusion and stop anticoagulation
  3. Discontinue anticoagulation after 3 months of sinus rhythm
  4. Continue anticoagulation indefinitely Correct answer.

Explanation

Anticoagulation should be continued indefinitely in patients with a CHA2DS2-VASc score ≥2, regardless of rhythm outcome after ablation, because the stroke risk is driven by the underlying risk factors, not just the rhythm status.

Question 35Medical knowledge

A 24-year-old man with a structurally normal heart and no family history of sudden death has a resting ECG showing a short PR interval with a slurred upstroke of the QRS. He has had palpitations but no documented tachycardia. Which ECG finding defines this pre-excitation pattern?

  1. Epsilon waves in the right precordial leads
  2. A prolonged QT interval with T-wave alternans
  3. A delta wave with a short PR interval Correct answer.
  4. ST-segment elevation with a saddleback morphology

Explanation

Ventricular pre-excitation results from an accessory atrioventricular pathway that bypasses the AV node, producing early ventricular activation (short PR) and a slurred initial QRS upstroke (delta wave). The combination of short PR and delta wave is the defining surface ECG signature.

Question 36Medical knowledge

A 68-year-old woman with palpitations is found to be in a regular narrow-complex tachycardia at 160 bpm. The rhythm terminates abruptly with a bolus of adenosine. Which mechanism best explains the termination?

  1. Direct suppression of automaticity in an ectopic atrial focus
  2. Increased vagal tone causing sinus node acceleration
  3. Transient AV nodal block interrupting a reentrant circuit that requires the AV node Correct answer.
  4. Blockade of delayed rectifier potassium current prolonging refractoriness

Explanation

Adenosine transiently blocks AV nodal conduction. Tachycardias whose circuit requires the AV node (such as AVNRT or AVRT) terminate when that limb of the circuit is interrupted.

Question 37Medical knowledge

Which ECG interval is the principal determinant of the vulnerable period for induction of ventricular fibrillation?

  1. The QT interval Correct answer.
  2. The PR interval
  3. The PP interval
  4. The QRS duration

Explanation

The QT interval reflects the duration of ventricular repolarization. A prolonged QT widens the dispersion of repolarization and the window during which a premature beat can trigger reentry and fibrillation.

Question 38Medical knowledge

A 55-year-old man with nonischemic cardiomyopathy has a left bundle branch block with QRS 160 ms and an ejection fraction of 28% despite optimal medical therapy. He is in sinus rhythm with NYHA class III symptoms. Which therapy has the strongest evidence to reduce mortality in this setting?

  1. Amiodarone
  2. Ranolazine
  3. Digoxin
  4. Cardiac resynchronization therapy Correct answer.

Explanation

Cardiac resynchronization therapy improves survival and symptoms in patients with reduced ejection fraction, sinus rhythm, and a wide QRS with LBBB morphology. The wide LBBB pattern predicts the greatest benefit from resynchronization.

Question 39Medical knowledge

Which medication class is the first-line antiarrhythmic for suppression of recurrent symptomatic paroxysmal atrial fibrillation in a patient without structural heart disease?

  1. Class IC agents such as flecainide Correct answer.
  2. Beta blockers
  3. Class IA agents such as quinidine
  4. Class III agents such as sotalol

Explanation

In patients without structural heart disease, class IC drugs such as flecainide or propafenone are effective first-line options for maintaining sinus rhythm. Beta blockers are more useful for rate control than rhythm control.

Question 40Medical knowledge

A 30-year-old woman has recurrent syncope. ECG shows a PR interval of 90 ms and a delta wave. Which electrophysiologic property of the accessory pathway most strongly influences the risk of rapid conduction during atrial fibrillation?

  1. The anterograde refractory period of the pathway Correct answer.
  2. The presence of dual AV nodal physiology
  3. The retrograde conduction time of the pathway
  4. The number of pathways present

Explanation

A short anterograde refractory period allows the accessory pathway to conduct rapidly during atrial fibrillation, risking very fast ventricular rates and degeneration to ventricular fibrillation. This property is the key determinant of sudden-death risk in pre-excitation.

Question 41Medical knowledge

A 72-year-old man with atrial fibrillation and a CHA2DS2-VASc score of 4 is being started on anticoagulation. He has severe mitral stenosis. Which anticoagulant is appropriate?

  1. Rivaroxaban
  2. Warfarin Correct answer.
  3. Dabigatran
  4. Apixaban

Explanation

Direct oral anticoagulants have not been validated in moderate-to-severe mitral stenosis, so warfarin remains the recommended anticoagulant in this setting. DOACs are also generally avoided in mechanical valves.

Question 42Medical knowledge

A 60-year-old woman has a regular narrow-complex tachycardia. During electrophysiology study, a premature ventricular beat delivered when the His bundle is refractory terminates the tachycardia without a preceding atrial activation. Which mechanism does this demonstrate?

  1. Focal atrial tachycardia
  2. Sinus node reentry
  3. An accessory pathway-mediated orthodromic tachycardia
  4. AV nodal reentry requiring the His-Purkinje system Correct answer.

Explanation

Termination by a His-refractory premature ventricular beat proves that the His-Purkinje system is part of the reentrant circuit, consistent with AVNRT (or AVRT). A focal atrial tachycardia would not be terminated by a beat that cannot conduct retrogradely to the atrium.

Question 43Medical knowledge

Which ECG feature is most characteristic of typical (type 1) atrial flutter?

  1. Sawtooth flutter waves in inferior leads Correct answer.
  2. Chaotic irregular baseline activity
  3. A flat isoelectric baseline between discrete P waves
  4. P waves of varying morphology at 300 bpm

Explanation

Typical atrial flutter produces continuous sawtooth waves best seen in inferior leads, reflecting a macroreentrant circuit around the tricuspid annulus. The atrial rate is typically about 300 bpm with variable AV conduction.

Question 44Medical knowledge

A 45-year-old man with a prior inferior myocardial infarction has recurrent sustained monomorphic ventricular tachycardia. Which substrate is most likely responsible?

  1. Automaticity from the right ventricular outflow tract
  2. Triggered activity from early afterdepolarizations
  3. Enhanced abnormal automaticity of the His bundle
  4. A reentrant circuit through scar in the inferior left ventricle Correct answer.

Explanation

Sustained monomorphic ventricular tachycardia late after infarction is usually due to scar-related reentry. The infarct border zone provides the slow-conducting channels that sustain the circuit.

Question 45Medical knowledge

A patient with long QT syndrome and recurrent torsades de pointes remains symptomatic despite magnesium and beta blockade. Which intervention is most likely to reduce recurrent arrhythmia?

  1. Isoproterenol infusion
  2. Sotalol initiation
  3. Class IA antiarrhythmic therapy
  4. Left cardiac sympathetic denervation Correct answer.

Explanation

Left cardiac sympathetic denervation reduces sympathetic input to the heart and lowers arrhythmia burden in high-risk long QT syndrome when drugs and beta blockade fail. It is particularly useful when an ICD alone is insufficient.

Question 46Medical knowledge

Which finding on an implantable cardioverter-defibrillator interrogation suggests an appropriate shock rather than an inappropriate one?

  1. Episodes preceded by rapid ventricular rates with a morphology matching the clinical VT Correct answer.
  2. Episodes triggered by rapid atrial rates with a narrow QRS
  3. Episodes associated with lead impedance changes
  4. Episodes preceded by sinus tachycardia and a normal ventricular rate

Explanation

An appropriate ICD therapy is delivered for a ventricular tachyarrhythmia. Rapid ventricular rates with a morphology consistent with the patient's clinical VT support an appropriate shock.

Question 47Medical knowledge

A 28-year-old athlete has a resting ECG with a prolonged QT interval. Which additional finding would most raise concern for arrhythmogenic syncope risk?

  1. A short PR interval
  2. T-wave alternans and a history of syncope during exertion Correct answer.
  3. Sinus bradycardia at rest
  4. Left axis deviation

Explanation

T-wave alternans reflects electrical instability, and syncope during exertion in a patient with long QT syndrome indicates a high risk of arrhythmic events. These features identify patients who may warrant more aggressive therapy.

Question 48Medical knowledge

Which mechanism best explains syncope in a patient with hypertrophic cardiomyopathy during exercise?

  1. Atrioventricular block from fibrosis of the conduction system
  2. Primary sinus node dysfunction
  3. Increased vagal tone causing profound bradycardia
  4. Dynamic left ventricular outflow tract obstruction exacerbated by reduced preload Correct answer.

Explanation

In hypertrophic cardiomyopathy, exercise-induced vasodilation and reduced preload can worsen dynamic outflow tract obstruction and impair cardiac output. This hemodynamic mechanism is a common cause of exertional syncope.

Question 49Medical knowledge

A 35-year-old woman has palpitations with a regular narrow-complex tachycardia. During tachycardia, the ECG shows a pseudo-r' in V1 and a pseudo-s in inferior leads. Which diagnosis is most likely?

  1. AV nodal reentrant tachycardia Correct answer.
  2. Sinus tachycardia
  3. Atrioventricular reentrant tachycardia using a concealed pathway
  4. Atrial flutter with 2:1 block

Explanation

Pseudo-r' in V1 and pseudo-s in inferior leads reflect retrograde P waves buried in the terminal QRS, a hallmark of typical AVNRT. These subtle deflections occur because atrial activation is nearly simultaneous with ventricular activation.

Question 50Medical knowledge

Which situation most strongly supports implantation of a permanent pacemaker?

  1. First-degree AV block with PR of 220 ms
  2. Sinus arrhythmia with normal rate
  3. Asymptomatic Mobitz I second-degree AV block during sleep
  4. Symptomatic third-degree AV block Correct answer.

Explanation

Symptomatic third-degree AV block is a class I indication for permanent pacing. Complete heart block carries a risk of syncope and sudden death that pacing mitigates.