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IBHRE CEPS practice questions

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Question 1Cardiac Electrophysiology

During implantation of a dual-chamber pacemaker, the ventricular lead is positioned at the right ventricular apex. Which conduction interval is measured from the local ventricular electrogram to the earliest consistent atrial signal during retrograde conduction testing?

  1. HV interval
  2. Retrograde VA conduction time Correct answer.
  3. Antegrade AV interval
  4. Sinus node recovery time

Explanation

Retrograde VA conduction time is measured from the ventricular electrogram to the resulting atrial electrogram during ventricular pacing or a premature ventricular extrastimulus. It defines whether intact retrograde conduction exists and informs pacemaker mode selection to avoid pacemaker-mediated tachycardia.

Question 2Cardiac Electrophysiology

A 12-lead ECG shows a regular narrow-complex tachycardia at 190 bpm with no visible P waves. Which acute intervention is the most appropriate first step in a hemodynamically stable patient?

  1. Emergent pericardiocentesis
  2. Vagal maneuvers followed by intravenous adenosine if unsuccessful Correct answer.
  3. Intravenous amiodarone bolus
  4. Immediate synchronized cardioversion at 100 J

Explanation

For a stable patient with a regular narrow-complex tachycardia, vagal maneuvers and then adenosine are the standard first-line measures to terminate AV nodal-dependent reentry or to unmask the atrial mechanism. Synchronized cardioversion is reserved for instability or failure of pharmacologic measures.

Question 3Cardiac Electrophysiology

In the standard electrophysiology laboratory, which intracardiac signal is recorded from the His bundle catheter and used to measure the HV interval?

  1. A sharp, high-frequency deflection between the atrial and ventricular electrograms Correct answer.
  2. A fragmented ventricular electrogram after the surface QRS
  3. A continuous sinusoidal signal during atrial pacing
  4. A broad low-frequency atrial deflection preceding the surface P wave

Explanation

The His bundle electrogram appears as a sharp, high-frequency deflection occurring between the local atrial and ventricular electrograms. The HV interval is measured from the onset of this His deflection to the earliest ventricular activation.

Question 4Cardiac Electrophysiology

Which finding on a surface ECG most strongly suggests that a wide-complex tachycardia is ventricular in origin?

  1. A preceding P wave with a short PR interval before every QRS
  2. Rate of 150 bpm
  3. Presence of AV dissociation during the tachycardia Correct answer.
  4. QRS duration of 120 ms

Explanation

AV dissociation during a wide-complex tachycardia is a highly specific marker of ventricular tachycardia because the atria and ventricles are controlled independently. Its absence does not exclude VT, but its presence strongly supports it.

Question 5Cardiac Electrophysiology

A patient with a dual-chamber pacemaker programmed DDD at 60 bpm develops a rapid paced rhythm at the upper rate limit. Interrogation shows retrograde P waves sensed after each paced ventricular beat. Which mechanism best explains this?

  1. Crosstalk inhibition of the ventricular channel
  2. Runaway pacemaker due to battery depletion
  3. Pacemaker-mediated tachycardia Correct answer.
  4. Atrial undersensing of sinus P waves

Explanation

Pacemaker-mediated tachycardia occurs when a paced or intrinsic ventricular beat conducts retrogradely to the atrium, is sensed by the atrial lead, and triggers a paced ventricular beat, creating a reentrant loop limited by the upper tracking rate. Reprogramming to DDI or increasing PVARP interrupts the circuit.

Question 6Cardiac Electrophysiology

During programmed ventricular stimulation, a premature extrastimulus is delivered with progressively shorter coupling intervals. Which response demonstrates that the ventricular myocardium has reached refractoriness?

  1. The extrastimulus resets the sinus node
  2. The extrastimulus produces a fusion beat
  3. The extrastimulus captures with a progressively longer latency
  4. The extrastimulus fails to capture at all Correct answer.

Explanation

Failure to capture with a ventricular extrastimulus at short coupling intervals indicates that the stimulus falls within the effective refractory period of the ventricular myocardium. This defines the local ventricular refractory period at that pacing site.

Question 7Cardiac Electrophysiology

In a patient with a left bundle branch block and a left ventricular ejection fraction of 30%, which ECG feature predicts a favorable response to cardiac resynchronization therapy?

  1. QRS duration of 160 ms with LBBB morphology Correct answer.
  2. Narrow QRS of 100 ms
  3. QRS duration of 130 ms with right bundle branch block
  4. Atrial fibrillation with slow ventricular response

Explanation

A wide QRS with typical left bundle branch block morphology reflects mechanical dyssynchrony that biventricular pacing can correct, and greater QRS width is associated with better response. LBBB with QRS at least 150 ms is the strongest predictor of benefit.

Question 8Cardiac Electrophysiology

Which intracardiac finding during electrophysiology study confirms a diagnosis of typical atrioventricular nodal reentrant tachycardia?

  1. Earliest ventricular activation at the right ventricular apex
  2. Earliest atrial activation at the His bundle region during tachycardia Correct answer.
  3. A fixed HV interval that lengthens with atrial pacing
  4. Earliest atrial activation at the lateral tricuspid annulus

Explanation

In typical AVNRT the reentry circuit uses the slow and fast AV nodal pathways, so atrial activation during tachycardia is earliest at the septal region near the His bundle. This concentric activation pattern distinguishes it from AVRT via an accessory pathway.

Question 9Cardiac Electrophysiology

A patient with an implantable cardioverter-defibrillator receives an inappropriate shock. Stored electrograms show a rapid atrial rate with irregular ventricular response and no ventricular arrhythmia. Which programming change most directly reduces the risk of recurrent inappropriate therapy?

  1. Shortening the detection interval to 12 of 16 beats
  2. Increasing the ventricular tachycardia detection rate and adding SVT discrimination criteria Correct answer.
  3. Increasing ventricular pacing output
  4. Lowering the ventricular fibrillation detection threshold

Explanation

Inappropriate shocks from atrial tachyarrhythmias are reduced by SVT discrimination algorithms and by raising detection rates so that rapid atrial rates with irregular ventricular response are not classified as VT. These measures preserve detection of true ventricular arrhythmias.

Question 10Cardiac Electrophysiology

Which statement about the effective refractory period of the atrioventricular node is correct?

  1. It shortens as the preceding cycle length shortens
  2. It is independent of autonomic tone
  3. It is shorter than the atrial effective refractory period in all patients
  4. It lengthens as the preceding cycle length shortens Correct answer.

Explanation

The AV node exhibits decremental conduction, so its effective refractory period lengthens when the preceding cycle length shortens. This property underlies rate-dependent AV block and the filtering function of the node during atrial fibrillation.

Question 11Cardiac Electrophysiology

A 12-lead ECG shows a delta wave with a short PR interval and a QRS duration of 140 ms. Which risk stratification finding raises concern for sudden cardiac death in a patient with Wolff-Parkinson-White pattern?

  1. Presence of a delta wave during sinus rhythm
  2. Inducible AV reentrant tachycardia at electrophysiology study
  3. Shortest pre-excited RR interval of 220 ms during atrial fibrillation Correct answer.
  4. History of palpitations

Explanation

A shortest pre-excited RR interval of 250 ms or less during atrial fibrillation indicates rapid antegrade conduction over the accessory pathway, which permits very fast ventricular rates and risk of degeneration to ventricular fibrillation. This finding supports accessory pathway ablation.

Question 12Cardiac Electrophysiology

Which catheter ablation energy source creates lesions primarily through resistive heating of tissue adjacent to the electrode tip?

  1. Radiofrequency ablation Correct answer.
  2. Pulsed field ablation
  3. Laser balloon ablation
  4. Cryoablation

Explanation

Radiofrequency ablation delivers alternating current that causes resistive heating of tissue within a few millimeters of the electrode, producing thermal coagulation necrosis. Cryoablation and pulsed field ablation use freezing and electroporation, respectively, rather than resistive heating.

Question 13Cardiac Electrophysiology

A patient with symptomatic sinus bradycardia and chronotropic incompetence is being evaluated for a pacemaker. Which sensor mode best addresses rate response during exertion when atrial tracking is not possible?

  1. VVIR with an activity sensor Correct answer.
  2. DDD with mode switching
  3. DDI at 60 bpm
  4. VVI at 60 bpm

Explanation

VVIR provides rate-responsive ventricular pacing driven by a sensor when atrial tracking is unavailable, improving heart rate during exertion. Mode switching and DDI address atrial tachyarrhythmias but do not provide rate response.

Question 14Cardiac Electrophysiology

Which finding on a signal-averaged ECG is associated with an increased risk of ventricular arrhythmias in patients after myocardial infarction?

  1. Presence of late potentials Correct answer.
  2. Absence of any low-amplitude terminal signal
  3. Increased high-frequency noise
  4. Shortened filtered QRS duration

Explanation

Late potentials are low-amplitude, high-frequency signals at the end of the QRS that reflect slow conduction through scarred myocardium, creating a substrate for reentrant ventricular arrhythmias. Their presence correlates with increased arrhythmic risk after infarction.

Question 15Cardiac Electrophysiology

During atrial fibrillation, which electrophysiologic change in the atria promotes maintenance of the arrhythmia?

  1. Reduction in atrial fibrosis
  2. Lengthening of the atrial effective refractory period
  3. Shortening of the atrial effective refractory period with increased dispersion Correct answer.
  4. Increased AV nodal conduction velocity

Explanation

Rapid atrial rates shorten the atrial effective refractory period and increase dispersion of refractoriness, which favors multiple reentrant wavelets and sustains fibrillation. This electrical remodeling makes early restoration of sinus rhythm more likely to succeed.

Question 16Cardiac Electrophysiology

A patient with a biventricular pacemaker and chronic atrial fibrillation has an irregular ventricular response with intermittent loss of biventricular capture. Which strategy best ensures consistent biventricular pacing?

  1. Perform AV nodal ablation with ventricular pacing at a stable rate Correct answer.
  2. Program a higher atrial sensitivity
  3. Reduce the ventricular pacing output
  4. Switch to AAI pacing

Explanation

When atrial fibrillation produces irregular, rapid ventricular rates, AV nodal ablation followed by rate-controlled biventricular pacing ensures consistent capture and resynchronization. This approach is used when rate control or biventricular capture cannot be achieved otherwise.

Question 17Cardiac Electrophysiology

Which mechanism best explains why verapamil can terminate idiopathic left ventricular fascicular tachycardia?

  1. Blockade of sodium channels in the ventricular myocardium
  2. Shortening of the ventricular effective refractory period
  3. Enhancement of sympathetic tone
  4. Blockade of L-type calcium channels in the reentrant Purkinje network Correct answer.

Explanation

Fascicular VT involves reentry using Purkinje tissue in which calcium channel-dependent slow conduction is critical, so calcium channel blockade can terminate it. This distinguishes it from most other ventricular tachycardias, which respond poorly to verapamil.

Question 18Cardiac Electrophysiology

During catheter ablation of typical atrial flutter, which anatomic target is the standard ablation line?

  1. Crista terminalis
  2. Cavotricuspid isthmus Correct answer.
  3. Mitral isthmus
  4. Coronary sinus ostium

Explanation

Typical atrial flutter is a macroreentrant circuit around the tricuspid annulus that depends on the cavotricuspid isthmus. Creating a line of block across this isthmus terminates and prevents the arrhythmia.

Question 19Cardiac Electrophysiology

Which property of the atrioventricular node allows it to limit the ventricular rate during atrial fibrillation?

  1. Anisotropic conduction in the His bundle
  2. Short effective refractory period at fast rates
  3. Enhanced automaticity
  4. Decremental conduction with rate-dependent refractoriness Correct answer.

Explanation

The AV node conducts with decremental properties, meaning conduction slows progressively at shorter cycle lengths. Combined with rate-dependent refractoriness, this filters rapid atrial impulses and prevents dangerous ventricular rates during atrial fibrillation.

Question 20Cardiac Electrophysiology

A patient with hypertrophic cardiomyopathy and a high-risk profile is being considered for an implantable cardioverter-defibrillator. Which finding is a recognized major risk marker for sudden cardiac death in this population?

  1. Maximum left ventricular wall thickness of 32 mm Correct answer.
  2. Left ventricular ejection fraction of 65%
  3. Absence of left ventricular outflow tract obstruction
  4. Normal ambulatory Holter monitoring

Explanation

Extreme left ventricular hypertrophy, generally defined as maximal wall thickness of 30 mm or more, is a recognized major risk factor for sudden cardiac death in hypertrophic cardiomyopathy and supports ICD consideration. Other risk markers include prior cardiac arrest, family history, and nonsustained VT.

Question 21Cardiac Electrophysiology

Which statement about the QT interval and torsades de pointes is correct?

  1. Shortening the QT interval increases the risk of torsades de pointes
  2. A prolonged QT interval predisposes to early afterdepolarizations and polymorphic ventricular tachycardia Correct answer.
  3. Torsades de pointes occurs only with a normal QT interval
  4. Torsades de pointes is typically terminated by vagal maneuvers

Explanation

QT prolongation permits reactivation of calcium or sodium channels during repolarization, generating early afterdepolarizations that can trigger torsades de pointes. Management includes correcting electrolyte abnormalities, stopping offending drugs, and magnesium administration.

Question 22Cardiac Electrophysiology

A 68-year-old with prior myocardial infarction and an ejection fraction of 30% has nonsustained ventricular tachycardia on Holter monitoring. Which test is most useful to determine whether an ICD is indicated?

  1. Electrophysiology study with programmed ventricular stimulation Correct answer.
  2. Signal-averaged ECG
  3. Cardiac magnetic resonance imaging
  4. Exercise treadmill testing

Explanation

In patients with ischemic cardiomyopathy, reduced ejection fraction, and nonsustained VT, an electrophysiology study can determine whether sustained ventricular arrhythmia is inducible. Inducibility identifies those who benefit from an ICD.

Question 23Cardiac Electrophysiology

Which characteristic of the accessory pathway determines the degree of pre-excitation seen on the surface ECG in Wolff-Parkinson-White syndrome?

  1. Antegrade conduction velocity and refractory period of the pathway Correct answer.
  2. Autonomic tone of the His bundle
  3. Length of the AV node
  4. Retrograde conduction velocity of the pathway

Explanation

The amount of ventricular pre-excitation depends on how quickly the accessory pathway conducts antegradely relative to the AV node. A fast-conducting pathway with a short refractory period produces a larger delta wave and greater risk of rapid pre-excited conduction.

Question 24Cardiac Electrophysiology

Which finding during an electrophysiology study confirms that a line of ablation has produced bidirectional conduction block across the cavotricuspid isthmus?

  1. Continuous fractionated electrograms at the isthmus
  2. Split, widely separated double potentials along the ablation line with a change in activation sequence Correct answer.
  3. Tachycardia termination alone
  4. Shortening of the flutter cycle length

Explanation

Bidirectional isthmus block is confirmed by widely split double potentials along the ablation line and reversal of the atrial activation sequence when pacing from either side of the line. Termination of flutter alone does not prove durable block.

Question 25Cardiac Electrophysiology

Which mechanism is responsible for the therapeutic effect of cardiac resynchronization therapy in patients with left bundle branch block?

  1. Suppression of ventricular ectopy
  2. Increased atrial contractility
  3. Restoration of coordinated left ventricular activation by pre-exciting the lateral wall Correct answer.
  4. Reduction of myocardial fibrosis

Explanation

In left bundle branch block, the lateral left ventricular wall activates late, producing dyssynchrony and inefficient contraction. Biventricular pacing pre-excites the lateral wall to restore coordinated activation and improve hemodynamics.

Question 26Cardiac Electrophysiology

Which phase of the cardiac action potential in ventricular myocytes is primarily responsible for the plateau and is generated by the influx of calcium through L-type channels?

  1. Phase 0
  2. Phase 2 Correct answer.
  3. Phase 4
  4. Phase 1

Explanation

Phase 2 is the plateau phase, during which slow inward calcium current through L-type channels balances outward potassium currents, prolonging the action potential and refractoriness. Phase 0 is the rapid sodium-dependent upstroke, and phase 4 is the resting or diastolic depolarization phase.

Question 27Cardiac Electrophysiology

On the surface ECG, which interval best reflects the time from the onset of atrial depolarization to the onset of ventricular depolarization?

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

Explanation

The PR interval measures from the beginning of the P wave to the beginning of the QRS complex, encompassing atrial activation and conduction through the atrioventricular node and His-Purkinje system. The QT interval reflects total ventricular depolarization and repolarization.

Question 28Cardiac Electrophysiology

Which intracardiac recording site is used to measure the His bundle electrogram and the HV interval during an electrophysiology study?

  1. Coronary sinus ostium
  2. Right ventricular apex
  3. High right atrium
  4. His bundle region Correct answer.

Explanation

A catheter positioned at the His bundle region records the His deflection, allowing measurement of the AH and HV intervals. The HV interval reflects conduction from the His bundle through the Purkinje system to ventricular myocardium.

Question 29Cardiac Electrophysiology

In the standard electrophysiology laboratory, which pacing maneuver is used to assess the antegrade effective refractory period of the atrioventricular node?

  1. Programmed atrial extrastimuli with decremental coupling intervals Correct answer.
  2. Ventricular burst pacing at 200 ms cycle length
  3. Burst atrial pacing at 300 ms cycle length
  4. Programmed ventricular extrastimuli with a fixed coupling interval

Explanation

The antegrade AV nodal effective refractory period is determined by delivering atrial extrastimuli at progressively shorter coupling intervals after a drive train until the extrastimulus fails to conduct to the His bundle. This defines the longest coupling interval that does not produce a His response.

Question 30Cardiac Electrophysiology

Which waveform on an intracardiac electrogram represents local ventricular myocardial activation during sinus rhythm?

  1. A continuous fractionated signal throughout diastole
  2. A low-frequency deflection occurring after the surface T wave
  3. A small, high-frequency deflection preceding the surface P wave
  4. A sharp, high-amplitude deflection coinciding with the surface QRS complex Correct answer.

Explanation

The local ventricular electrogram is a sharp, high-amplitude deflection that aligns temporally with the surface QRS complex because it records depolarization of the local myocardium. Atrial electrograms precede the surface P wave and are typically lower amplitude and higher frequency in the atrium.

Question 31Cardiac Electrophysiology

Which finding on the surface ECG is characteristic of typical counterclockwise atrial flutter?

  1. Chaotic, irregular fibrillatory waves
  2. Sawtooth flutter waves that are negative in the inferior leads Correct answer.
  3. Positive flutter waves in leads II, III, and aVF
  4. A flat baseline with discrete P waves at 150 beats per minute

Explanation

Typical counterclockwise atrial flutter produces negative sawtooth flutter waves in the inferior leads (II, III, aVF) and positive waves in V1 because the reentrant circuit travels up the interatrial septum and down the lateral right atrial wall. The flutter rate is typically near 300 beats per minute.

Question 32Cardiac Electrophysiology

Which structure is the target for slow pathway modification in catheter ablation of atrioventricular nodal reentrant tachycardia?

  1. The anterolateral mitral annulus
  2. The left posterior fascicle
  3. The cavotricuspid isthmus
  4. The inferoposterior region of the triangle of Koch near the coronary sinus ostium Correct answer.

Explanation

Slow pathway ablation is performed in the inferoposterior portion of the triangle of Koch, near the coronary sinus ostium, where the slow pathway is located. This region is anatomically distinct from the compact AV node, reducing the risk of complete heart block.

Question 33Cardiac Electrophysiology

Which parameter on a routine 12-lead ECG is most directly prolonged by hypokalemia?

  1. QRS duration
  2. PR interval
  3. P wave amplitude
  4. QT interval Correct answer.

Explanation

Hypokalemia delays ventricular repolarization, prolonging the QT interval and predisposing to torsades de pointes. It may also produce U waves and ST depression, but the QT prolongation is the key repolarization marker.

Question 34Cardiac Electrophysiology

A 55-year-old with recurrent paroxysmal supraventricular tachycardia undergoes an electrophysiology study. During ventricular pacing, the earliest retrograde atrial activation is recorded at the coronary sinus ostium, and atrial activation is eccentric (earliest in the lateral coronary sinus). Which mechanism is most consistent with these findings?

  1. Atrioventricular reentrant tachycardia using a posteroseptal pathway
  2. Atrial tachycardia originating near the sinus node
  3. A left-sided accessory pathway Correct answer.
  4. Typical atrioventricular nodal reentrant tachycardia

Explanation

Eccentric retrograde atrial activation with the earliest site in the lateral coronary sinus indicates retrograde conduction over a left-sided accessory pathway. Concentric activation with the earliest site at the septum would favor AVNRT or a septal pathway.

Question 35Cardiac Electrophysiology

During an electrophysiology study, ventricular pacing at a cycle length of 400 ms is performed, and the stimulus-to-atrial interval progressively lengthens until retrograde conduction block occurs. This phenomenon is best described by which property?

  1. Decremental conduction in the atrioventricular node Correct answer.
  2. Physiologic refractoriness of the His-Purkinje system
  3. Enhanced conduction over an accessory pathway
  4. Anisotropic conduction in ventricular myocardium

Explanation

Progressive lengthening of conduction time with faster pacing rates reflects decremental conduction, a characteristic of the AV node due to its slow, calcium-dependent upstroke. Accessory pathways generally conduct non-decrementally and would not show this progressive prolongation.

Question 36Cardiac Electrophysiology

A patient with a dual-chamber pacemaker has a programmed paced AV delay of 200 ms. Which timing parameter determines the total atrial-to-ventricular pacing interval when atrial pacing is delivered?

  1. The post-ventricular atrial refractory period
  2. The ventricular blanking period
  3. The sensed AV delay only
  4. The paced AV delay, which includes the atrial pacing latency Correct answer.

Explanation

When the atrium is paced, the pacemaker uses the paced AV delay, which is typically programmed slightly longer than the sensed AV delay to account for atrial pacing latency and the time for atrial depolarization to reach the AV node. The sensed AV delay applies when intrinsic atrial activity is detected.

Question 37Cardiac Electrophysiology

Which mechanism is primarily responsible for the antiarrhythmic effect of beta-blockers in preventing sudden cardiac death in patients with heart failure?

  1. Direct blockade of the rapid delayed rectifier potassium current
  2. Reduction of sympathetic tone with attenuation of triggered activity and ischemia-related arrhythmias Correct answer.
  3. Prolongation of the QRS duration to slow conduction
  4. Selective inhibition of the L-type calcium channel in the Purkinje system

Explanation

Beta-blockers reduce sympathetic stimulation, which attenuates triggered activity, reduces ischemia, and stabilizes repolarization, thereby lowering the risk of ventricular arrhythmias and sudden death. They do not primarily act by blocking potassium channels or prolonging QRS duration.

Question 38Cardiac Electrophysiology

A patient with a single-chamber ventricular pacemaker has a programmed lower rate of 60 beats per minute and hysteresis of 10 beats per minute. What is the resulting hysteresis escape rate?

  1. 70 beats per minute
  2. 80 beats per minute
  3. 50 beats per minute Correct answer.
  4. 60 beats per minute

Explanation

Hysteresis lowers the pacing rate below the programmed lower rate to allow intrinsic conduction to emerge. A lower rate of 60 beats per minute with 10 beats per minute of hysteresis produces an escape rate of 50 beats per minute.

Question 39Cardiac Electrophysiology

During catheter ablation of typical atrioventricular nodal reentrant tachycardia, which finding indicates that the slow pathway has been successfully modified?

  1. Loss of retrograde VA conduction
  2. Prolongation of the HV interval
  3. Elimination of the jump in AH interval with atrial extrastimuli and non-inducibility of tachycardia Correct answer.
  4. Development of complete ventriculoatrial block

Explanation

Successful slow pathway modification is demonstrated by loss of the discontinuous AH jump during atrial extrastimulus testing and by non-inducibility of AVNRT with and without isoproterenol. Retrograde VA conduction and HV interval are not the primary endpoints.

Question 40Cardiac Electrophysiology

A patient with a dual-chamber implantable cardioverter-defibrillator has a ventricular fibrillation detection zone set at 200 beats per minute. Which parameter most directly reduces the risk of inappropriate therapy from a rapidly conducted atrial arrhythmia?

  1. Increasing the lower pacing rate
  2. Programming a longer ventricular fibrillation detection interval
  3. Shortening the post-ventricular atrial refractory period
  4. Enabling a supraventricular tachycardia discrimination algorithm Correct answer.

Explanation

Supraventricular tachycardia discrimination algorithms compare atrial and ventricular timing and morphology to distinguish atrial arrhythmias from ventricular arrhythmias, reducing inappropriate shocks. A longer detection interval delays but does not distinguish the rhythm.

Question 41Cardiac Electrophysiology

Which finding during an electrophysiology study is most consistent with a diagnosis of atrioventricular reentrant tachycardia using a concealed accessory pathway?

  1. Earliest retrograde atrial activation at the lateral mitral annulus with eccentric activation Correct answer.
  2. Earliest retrograde atrial activation at the His bundle during ventricular pacing
  3. A discontinuous AH curve during atrial extrastimuli
  4. A short HV interval during sinus rhythm

Explanation

A concealed accessory pathway conducts only retrogradely, producing eccentric atrial activation during ventricular pacing with the earliest site along the mitral annulus. A short HV interval in sinus rhythm suggests antegrade pre-excitation, which is absent in concealed pathways.

Question 42Cardiac Electrophysiology

A patient with a biventricular pacemaker and chronic atrial fibrillation has a persistently irregular ventricular rate despite device therapy. Which programming strategy best improves ventricular resynchronization in this setting?

  1. Performing atrioventricular junctional ablation to achieve 100% biventricular capture Correct answer.
  2. Increasing the lower rate limit to ensure continuous pacing
  3. Reducing the ventricular pacing output to subthreshold levels
  4. Programming biventricular pacing with a rate-responsive sensor and aggressive AV timing

Explanation

In chronic atrial fibrillation with an irregular ventricular response, AV junctional ablation eliminates irregular intrinsic conduction and allows consistent biventricular pacing, improving resynchronization. Programming alone cannot reliably achieve high biventricular capture when intrinsic conduction is irregular.

Question 43Cardiac Electrophysiology

Which mechanism explains the termination of atrioventricular nodal reentrant tachycardia by vagal maneuvers?

  1. Blockade of the slow pathway by increased vagal tone, interrupting the reentrant circuit Correct answer.
  2. Increased sympathetic tone to the His-Purkinje system
  3. Prolongation of the QRS duration
  4. Direct suppression of atrial automaticity

Explanation

Vagal maneuvers increase parasympathetic tone, slowing conduction and prolonging refractoriness in the AV node, which can interrupt the slow pathway limb of the reentrant circuit. They do not act by suppressing atrial automaticity or altering ventricular conduction.

Question 44Cardiac Electrophysiology

A patient with a history of syncope and a left bundle branch block has an HV interval of 90 ms during electrophysiology study. What does this finding most likely indicate?

  1. Significant disease of the His-Purkinje system Correct answer.
  2. An accessory pathway
  3. Normal His-Purkinje conduction
  4. Isolated first-degree AV block at the AV node

Explanation

A markedly prolonged HV interval (greater than 55 to 70 ms) suggests significant His-Purkinje conduction disease and an increased risk of progression to complete heart block. The AV node is not the site of delay when the AH interval is normal.

Question 45Cardiac Electrophysiology

A patient with hypertrophic cardiomyopathy and a high-risk profile is being evaluated for an implantable cardioverter-defibrillator. Which additional finding most strongly supports ICD implantation for primary prevention?

  1. Paroxysmal atrial fibrillation
  2. A resting heart rate of 55 beats per minute
  3. A family history of sudden cardiac death in a first-degree relative Correct answer.
  4. A maximum left ventricular wall thickness of 12 mm

Explanation

A family history of sudden cardiac death in a first-degree relative is a recognized risk marker that supports primary-prevention ICD implantation in hypertrophic cardiomyopathy. Wall thickness of 12 mm is not in the high-risk range, and atrial fibrillation is not a primary sudden-death risk marker.

Question 46Cardiac Electrophysiology

Which statement about the QT interval and torsades de pointes is most accurate?

  1. QT shortening is the primary risk factor for torsades de pointes
  2. Torsades de pointes occurs only with a normal QT interval
  3. QT prolongation increases the risk of early afterdepolarizations and torsades de pointes Correct answer.
  4. The QT interval is independent of heart rate

Explanation

Prolonged repolarization promotes early afterdepolarizations, which can trigger torsades de pointes, particularly in the setting of bradycardia and electrolyte abnormalities. QT shortening is not the primary risk factor, and the QT interval varies with heart rate, requiring correction.

Question 47Cardiac Electrophysiology

A patient with prior myocardial infarction and an ejection fraction of 30% has nonsustained ventricular tachycardia on ambulatory monitoring. According to current evidence, which management strategy is most appropriate?

  1. Coronary artery bypass grafting regardless of coronary anatomy
  2. Implantable cardioverter-defibrillator implantation for primary prevention Correct answer.
  3. No further evaluation because nonsustained ventricular tachycardia is benign after infarction
  4. Empiric antiarrhythmic therapy alone without device therapy

Explanation

In patients with prior myocardial infarction, reduced ejection fraction, and nonsustained ventricular tachycardia, ICD implantation reduces mortality and is recommended for primary prevention. Antiarrhythmic therapy alone does not provide the same mortality benefit.

Question 48Cardiac Electrophysiology

During programmed ventricular stimulation, a premature extrastimulus is delivered with progressively shorter coupling intervals until it fails to capture the ventricle. This defines which parameter?

  1. The ventricular effective refractory period Correct answer.
  2. The retrograde atrial effective refractory period
  3. The Wenckebach cycle length
  4. The AV nodal effective refractory period

Explanation

The ventricular effective refractory period is the longest coupling interval at which a premature stimulus fails to produce a ventricular response. It is measured during programmed ventricular extrastimulus testing with decremental coupling.

Question 49Cardiac Electrophysiology

During an electrophysiology study, a catheter is positioned in the right ventricular apex and burst pacing is performed. Which intracardiac interval is measured from the local ventricular electrogram to the earliest atrial electrogram to assess retrograde ventriculoatrial conduction?

  1. The HV interval
  2. The AH interval
  3. The stimulus-to-atrial interval
  4. The VA interval Correct answer.

Explanation

The VA interval is measured from the onset of the local ventricular electrogram (during ventricular pacing or a PVC) to the earliest atrial activation, and it characterizes the retrograde limb of a tachycardia circuit. It is a standard measurement used to distinguish retrograde conduction pathways, such as septal versus free-wall or accessory pathway conduction.

Question 50Cardiac Electrophysiology

A patient with a dual-chamber pacemaker has a programmed paced AV delay of 180 ms and a sensed AV delay of 120 ms. Which parameter determines whether the atrial channel responds to a sensed P wave versus a paced atrial event?

  1. The mode switch algorithm
  2. The programmed AV delay pairing Correct answer.
  3. The post-ventricular atrial refractory period
  4. The atrial sensitivity setting

Explanation

Dual-chamber pacemakers program separate paced and sensed AV delays because intrinsic atrial conduction differs from paced atrial activation. The device selects the appropriate delay based on whether the atrial event was sensed or paced, which affects ventricular timing and AV synchrony.