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RCES practice questions

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Question 1Cardiac Anatomy, Physiology, and Electrophysiology

At which anatomical site is the sinoatrial node located?

  1. At the inferior right atrium near the coronary sinus ostium
  2. Along the left atrial roof near the pulmonary vein orifices
  3. Within the membranous interventricular septum beneath the aorta
  4. At the SVC-right atrial junction near the sulcus terminalis Correct answer.

Explanation

The sinoatrial node is a spindle-shaped cluster of specialized pacemaker cells lying subepicardially at the junction of the superior vena cava and the right atrium, alongside the sulcus terminalis. Its steep phase 4 slope makes it the dominant pacemaker of the heart. Its nodal artery arises from the right coronary artery in roughly 60% of individuals and from the left circumflex in the remainder.

Question 2Cardiac Anatomy, Physiology, and Electrophysiology

Where is the atrioventricular node normally located?

  1. Within the triangle of Koch in the right atrium Correct answer.
  2. Within the right ventricle along the moderator band
  3. In the left atrium near the left superior pulmonary vein orifice
  4. At the fossa ovalis within the interatrial septum

Explanation

The atrioventricular node sits in the inferior-posterior right atrium at the apex of the triangle of Koch, immediately anterior and superior to the coronary sinus ostium. It forms the only normal electrical bridge between the atria and ventricles. Its blood supply is the atrioventricular nodal artery, usually a branch of the right coronary artery.

Question 3Cardiac Anatomy, Physiology, and Electrophysiology

The bundle of His passes through which structure as it travels from the atria toward the ventricles?

  1. The annulus of the mitral valve along the left fibrous trigone
  2. The valve of the inferior vena cava (Eustachian valve)
  3. The membranous portion of the interatrial septum alone
  4. The central fibrous body of the cardiac skeleton Correct answer.

Explanation

The His bundle continues from the atrioventricular node through the central fibrous body, the collagenous skeleton that electrically insulates atria from ventricles. It is the only normal route across this insulating barrier before it bifurcates into the bundle branches. The proximal His bundle is supplied by the atrioventricular nodal artery.

Question 4Cardiac Anatomy, Physiology, and Electrophysiology

What is the typical resting membrane potential of a ventricular working myocyte?

  1. -70 mV
  2. -120 mV
  3. -50 mV
  4. -90 mV Correct answer.

Explanation

A ventricular working myocyte typically rests near -90 mV, primarily because of high resting potassium permeability. This differs from the less negative, unstable diastolic potential of pacemaker tissue.

Question 5Cardiac Anatomy, Physiology, and Electrophysiology

Phase 0 of the action potential in ventricular myocardium is produced by which current?

  1. A slow inward calcium current through L-type channels
  2. An outward potassium current through delayed rectifier channels
  3. A rapid inward sodium current through voltage-gated channels Correct answer.
  4. An inward funny current through HCN channels

Explanation

Fast-response tissue such as atrial and ventricular myocardium and Purkinje fibers depolarizes through rapid opening of voltage-gated sodium channels, giving a steep upstroke and fast conduction. Nodal cells lack this fast current and instead depolarize slowly through calcium channels. The sodium current is also the reason refractoriness parallels sodium channel recovery.

Question 6Cardiac Anatomy, Physiology, and Electrophysiology

The phase 2 plateau of the ventricular action potential is maintained chiefly by which balance of currents?

  1. Rapid potassium efflux through Kir2.1 channels alone
  2. Balanced L-type calcium influx and potassium efflux Correct answer.
  3. Sodium-calcium exchange current acting alone
  4. Outward chloride conductance exceeding the inward sodium current

Explanation

During phase 2, inward L-type calcium current is closely matched by outward potassium currents, producing a plateau near 0 mV. This plateau prolongs the ventricular action potential and contributes to the long effective refractory period that protects against reentry.

Question 7Cardiac Anatomy, Physiology, and Electrophysiology

What is the principal function of Bachmann's bundle?

  1. Filtering impulses within the atrioventricular node
  2. Rapid conduction from the His bundle to both ventricles
  3. Delaying conduction between the atria and ventricles
  4. Preferential interatrial conduction from right to left Correct answer.

Explanation

Bachmann's bundle is a broad muscular band in the anterior atrial wall that carries the sinus impulse preferentially from the right to the left atrium. This rapid interatrial route allows near-simultaneous activation of both atria. Conduction delay along this route produces an interatrial block pattern on the surface ECG.

Question 8Cardiac Anatomy, Physiology, and Electrophysiology

In most individuals, the atrioventricular node receives its blood supply from which artery?

  1. The left anterior descending artery
  2. The left main coronary artery
  3. The left circumflex artery
  4. The right coronary artery Correct answer.

Explanation

The atrioventricular nodal artery arises from the right coronary artery in roughly 85-90% of hearts, with the left circumflex supplying it in the remainder. This is why inferior myocardial infarction, which usually involves the right coronary artery, so often produces atrioventricular block.

Question 9Cardiac Anatomy, Physiology, and Electrophysiology

Which three structures form the boundaries of the triangle of Koch?

  1. Coronary sinus ostium, tendon of Todaro, and tricuspid annulus Correct answer.
  2. The aortic annulus, the membranous septum, and the bundle of His
  3. The fossa ovalis, the mitral annulus, and the pulmonary vein orifices
  4. The crista terminalis, the Eustachian ridge, and the IVC

Explanation

The triangle of Koch is bounded posteriorly by the tendon of Todaro, anteriorly by the tricuspid annulus, and inferiorly by the coronary sinus ostium. The atrioventricular node sits at its apex and the slow pathway runs along its inferior aspect. These landmarks guide slow pathway ablation for atrioventricular nodal reentrant tachycardia.

Question 10Cardiac Anatomy, Physiology, and Electrophysiology

Where is the fast pathway of the atrioventricular node typically located?

  1. Anteriorly near the apex of Koch's triangle Correct answer.
  2. Within the left atrium along the mitral annulus
  3. Posteriorly near the coronary sinus ostium
  4. In the His bundle distal to the central fibrous body

Explanation

The fast pathway enters the atrioventricular node anteriorly and superiorly near the apex of the triangle of Koch. It conducts quickly but has a relatively long refractory period and is strongly influenced by vagal tone. This contrasts with the posteriorly situated slow pathway.

Question 11Cardiac Anatomy, Physiology, and Electrophysiology

The slow pathway of the atrioventricular node is characteristically located where?

  1. Along the anterior limbus of the fossa ovalis
  2. Within the tendon of Todaro
  3. At the right ventricular apex
  4. Posteriorly near the coronary sinus ostium Correct answer.

Explanation

The slow pathway runs posteriorly and inferiorly within the triangle of Koch, between the coronary sinus ostium and the tricuspid annulus. It conducts slowly but recovers quickly, giving it a short refractory period that allows it to sustain AV nodal reentrant tachycardia. It is the target for anatomic or electrogram-guided ablation near the coronary sinus ostium.

Question 12Cardiac Anatomy, Physiology, and Electrophysiology

An accessory pathway that connects atrial myocardium directly to ventricular myocardium and produces a delta wave is known as which of the following?

  1. A bundle of Kent producing a delta wave Correct answer.
  2. A Mahaim fiber inserting into the right bundle branch
  3. A James fiber inserting into the His bundle
  4. A Bachmann bundle joining the right and left atria

Explanation

The bundle of Kent is an atrioventricular accessory connection that bypasses the atrioventricular node and inserts directly into ventricular myocardium. Because the ventricular insertion is activated early, the surface ECG shows a short PR interval and a slurred initial QRS upstroke, the delta wave. This substrate underlies Wolff-Parkinson-White syndrome.

Question 13Cardiac Anatomy, Physiology, and Electrophysiology

Spontaneous depolarization of sinus node cells during phase 4 is driven primarily by which currents?

  1. The inward rectifier current (IK1)
  2. The funny current (If) with T-type calcium current Correct answer.
  3. Rapid sodium current through Nav1.5 channels
  4. Delayed rectifier potassium current (IKr)

Explanation

Phase 4 depolarization in sinus nodal cells depends on the funny current carried by HCN channels, together with T-type calcium current and declining outward potassium conductance. The steepness of this slope determines the intrinsic firing rate. Beta-adrenergic stimulation steepens the slope and accelerates the rate.

Question 14Cardiac Anatomy, Physiology, and Electrophysiology

What effect does vagal stimulation have on the atrioventricular node?

  1. Slower conduction and longer refractoriness Correct answer.
  2. Increased slope of phase 0 in nodal cells
  3. Shortening of the AV nodal refractory period
  4. Increased intracellular cAMP in nodal cells

Explanation

Acetylcholine released by vagal fibers acts on M2 receptors, lowers intracellular cAMP, and opens acetylcholine-sensitive potassium channels. The result is slower phase 4 depolarization in the sinus node and slower conduction with prolonged refractoriness in the atrioventricular node.

Question 15Cardiac Anatomy, Physiology, and Electrophysiology

Sympathetic stimulation speeds atrioventricular nodal conduction primarily through which mechanism?

  1. Raising cAMP and enhancing the inward calcium current Correct answer.
  2. Reducing the inward L-type calcium current during phase 2
  3. Flattening the phase 4 slope in sinus node cells
  4. Opening acetylcholine-sensitive potassium channels in nodal cells

Explanation

Norepinephrine acting on beta-1 receptors increases intracellular cAMP, which enhances the L-type calcium current and steepens phase 4 depolarization. The resulting effects are faster atrioventricular nodal conduction, shorter nodal refractoriness, and a higher sinus rate.

Question 16Cardiac Anatomy, Physiology, and Electrophysiology

The effective refractory period of ventricular myocardium is best defined as which of the following?

  1. The time needed for an impulse to reach the Purkinje fibers
  2. The time during which a stronger-than-normal stimulus elicits a response
  3. The period when no stimulus, however strong, evokes a response Correct answer.
  4. The interval between two consecutive spontaneous cardiac beats

Explanation

The effective refractory period is the interval during which no stimulus of any strength produces a propagated action potential, ending when enough sodium channels have recovered. The relative refractory period follows and does permit propagation if the stimulus is suprathreshold. These properties determine vulnerability to reentry.

Question 17Cardiac Anatomy, Physiology, and Electrophysiology

The cavotricuspid isthmus lies between which two structures?

  1. The inferior vena cava and the tricuspid annulus Correct answer.
  2. The coronary sinus and the mitral annulus
  3. The superior vena cava and the crista terminalis ridge
  4. The fossa ovalis and the aortic annulus

Explanation

The cavotricuspid isthmus is the band of right atrial myocardium between the inferior vena cava and the tricuspid annulus. It forms a critical slow-conducting limb of the reentrant circuit of typical atrial flutter. Creating a line of block across this isthmus terminates and prevents typical flutter.

Question 18Cardiac Anatomy, Physiology, and Electrophysiology

Which description best characterizes the crista terminalis?

  1. A muscular ridge separating smooth right atrium from the appendage Correct answer.
  2. The ridge overlying the coronary sinus ostium
  3. A remnant of the foramen ovale within the interatrial septum
  4. A fibrous band that electrically separates ventricles from the atria

Explanation

The crista terminalis is a prominent muscular ridge running from the superior to the inferior vena cava that divides the smooth-walled sinus venarum from the trabeculated right atrial appendage. The sinoatrial node lies at its anterosuperior end, and the ridge is a frequent origin of focal atrial tachycardia.

Question 19Cardiac Anatomy, Physiology, and Electrophysiology

The tendon of Todaro is best described as which of the following?

  1. A tendinous insertion of the mitral valve chordae into the left ventricular wall
  2. The membranous portion of the interventricular septum
  3. A conduction band connecting the SA node directly to the AV node
  4. A fibrous strand from the central fibrous body to the Eustachian ridge Correct answer.

Explanation

The tendon of Todaro is a fibrous strand running from the central fibrous body toward the Eustachian ridge, forming the posterior boundary of the triangle of Koch. It serves as a fluoroscopic and electroanatomic landmark for locating the atrioventricular node and slow pathway. It is fibrous tissue and does not itself conduct impulses.

Question 20Cardiac Anatomy, Physiology, and Electrophysiology

Which statement best describes conduction through the atrioventricular node?

  1. It is faster than conduction through the Purkinje system
  2. It conducts with equal decrement in both directions
  3. It is unaffected by changes in autonomic tone
  4. It is decremental, slowing with earlier or faster input Correct answer.

Explanation

Atrioventricular nodal conduction is decremental, meaning that progressively earlier or faster atrial inputs conduct more slowly because the upstroke depends on slowly recovering calcium channels. This property underlies Wenckebach periodicity at fast atrial rates. It also limits the ventricular rate during atrial fibrillation and flutter.

Question 21Cardiac Anatomy, Physiology, and Electrophysiology

Which connexin isoform predominates at gap junctions between ventricular working myocytes?

  1. Connexin 43 Correct answer.
  2. Connexin 40
  3. Connexin 45
  4. Connexin 37

Explanation

Connexin 43 is the dominant gap junction protein of ventricular working myocardium and is concentrated at intercalated discs. Connexin 40 predominates in atrial and His-Purkinje tissue, while connexin 45 is characteristic of nodal tissue. The non-uniform distribution of these channels contributes to anisotropic conduction.

Question 22Cardiac Anatomy, Physiology, and Electrophysiology

Concealed conduction is best described as which of the following?

  1. Complete block of an impulse within the His-Purkinje system
  2. Partial penetration of the AV node that alters refractoriness Correct answer.
  3. Conduction over an accessory pathway during normal sinus rhythm
  4. Delay in conduction produced by antiarrhythmic drug therapy

Explanation

Concealed conduction occurs when an impulse enters the atrioventricular node or His-Purkinje system far enough to change the tissue's refractoriness but never emerges to activate the ventricles. Its presence is inferred indirectly, for example from a prolonged PR interval after an interpolated premature ventricular complex. It explains several otherwise puzzling patterns of block and facilitation.

Question 23Cardiac Anatomy, Physiology, and Electrophysiology

Supernormal conduction refers to which phenomenon?

  1. Improved conduction of a weak stimulus late in repolarization Correct answer.
  2. Conduction velocity exceeding that of the Purkinje system during exercise
  3. Increased conduction velocity following a long pause
  4. Propagation of an impulse during the absolute refractory period

Explanation

Supernormal conduction is paradoxical propagation of a weak, otherwise subthreshold stimulus late in repolarization or early diastole, when enough sodium channels have recovered and threshold is transiently lowered. It can explain unexpected conduction of late premature beats that would ordinarily be blocked. It must be distinguished from enhanced conduction after simple recovery from refractoriness.

Question 24Cardiac Anatomy, Physiology, and Electrophysiology

A wide QRS complex with right bundle branch block morphology occurring after a long-short cycle sequence most likely represents which of the following?

  1. Ashman phenomenon from aberrant ventricular conduction Correct answer.
  2. A premature ventricular complex from the left ventricle
  3. Rate-dependent bundle branch block occurring at slow rates
  4. Antidromic conduction over a left-sided accessory pathway

Explanation

Ashman phenomenon is aberrant ventricular conduction triggered by a long-short cycle sequence: the long cycle lengthens refractoriness, so the early beat arrives while a bundle branch, usually the right, is still refractory. The result is a wide QRS with right bundle branch block morphology that is not a premature ventricular complex. It is a normal physiologic response to changing cycle length.

Question 25Cardiac Anatomy, Physiology, and Electrophysiology

Which feature of the pulmonary vein ostia is most relevant to the initiation of atrial fibrillation?

  1. Dense parasympathetic innervation without myocardium
  2. Abundant fibrous tissue producing slow conduction
  3. Absence of gap junctions within the vessel wall
  4. Myocardial sleeve tissue with automatic and triggered activity Correct answer.

Explanation

Extensions of atrial myocardium onto the pulmonary veins, called myocardial sleeves, exhibit automaticity and triggered activity that generate the ectopic beats initiating atrial fibrillation. Because these sleeves are largely confined to the vein ostia and antra, pulmonary vein isolation is the cornerstone of ablation for atrial fibrillation. Sleeve length and arrhythmogenicity vary between veins and between patients.

Question 26Cardiac Anatomy, Physiology, and Electrophysiology

During phase 0 of the ventricular myocyte action potential, the principal inward current is carried by which ion?

  1. Chloride
  2. Calcium
  3. Potassium
  4. Sodium Correct answer.

Explanation

Phase 0 of the ventricular action potential is generated by rapid opening of voltage-gated sodium channels, producing a large inward sodium current. This fast upstroke is responsible for rapid depolarization and fast conduction in working myocardium. Calcium entry dominates the later plateau phase, while potassium currents drive repolarization.

Question 27Cardiac Anatomy, Physiology, and Electrophysiology

In the normal heart, which structure conducts the electrical impulse most rapidly?

  1. Atrioventricular node
  2. Sinoatrial node
  3. Ventricular working myocardium
  4. Purkinje fibers Correct answer.

Explanation

Purkinje fibers have the highest conduction velocity in the heart because of their large diameter and rich gap junction coupling. This allows rapid activation of the ventricular myocardium. The atrioventricular and sinoatrial nodes conduct slowly, which helps create physiologic delay and automaticity.

Question 28Cardiac Anatomy, Physiology, and Electrophysiology

An increase in ventricular end-diastolic volume within the physiologic range raises stroke volume primarily through which mechanism?

  1. Greater myofilament calcium sensitivity from stretch Correct answer.
  2. A fall in afterload caused by reflex peripheral vasodilation
  3. Prolongation of the action potential plateau through reduced potassium efflux
  4. A rise in heart rate driven by sympathetic nerve activity

Explanation

The Frank-Starling relationship describes how increased preload stretches cardiac myocytes and enhances force generation. Stretch increases myofilament calcium sensitivity and optimizes cross-bridge formation, so stroke volume rises. Afterload, heart rate, and action potential duration are separate determinants of cardiac performance.

Question 29Cardiac Anatomy, Physiology, and Electrophysiology

On the surface ECG, which interval most directly reflects the time required for conduction from the atria to the ventricles?

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

Explanation

The PR interval begins with atrial depolarization and ends at the start of ventricular depolarization, so it includes conduction through the atrioventricular node and His-Purkinje system. The QRS duration reflects ventricular depolarization, the QT interval reflects ventricular depolarization and repolarization, and the RR interval reflects cycle length.

Question 30Cardiac Anatomy, Physiology, and Electrophysiology

A patient with severe hyperkalemia develops slowing of ventricular conduction. Which change best explains this effect?

  1. Increased gap junction conductance between myocytes
  2. Shortening of phase 3 repolarization
  3. A less negative resting membrane potential Correct answer.
  4. Enhanced phase 4 automaticity in Purkinje fibers

Explanation

Hyperkalemia reduces the potassium gradient across the membrane, making the resting membrane potential less negative. This partially inactivates voltage-gated sodium channels and reduces the phase 0 upstroke, slowing conduction. Changes in gap junctions or automaticity do not explain the conduction slowing caused by elevated extracellular potassium.

Question 31Electrophysiology Equipment, Instrumentation, and Basic Principles

The primary purpose of engaging a 60-Hz notch filter on an EP recording channel is to:

  1. Increase the channel's effective sampling rate
  2. Attenuate 50/60-Hz power-line interference Correct answer.
  3. Reduce the amplitude of far-field ventricular signals
  4. Remove low-frequency baseline wander from the tracing

Explanation

A notch filter is a narrow band-reject filter centered on the power-line frequency (50 or 60 Hz); it removes that sinusoidal interference while leaving adjacent frequencies largely intact. Baseline wander is a low-frequency problem addressed by the high-pass filter, and far-field signal content is minimized by electrode choice and spacing rather than by notching.

Question 32Electrophysiology Equipment, Instrumentation, and Basic Principles

Which term describes the opposition to alternating current flow at the electrode–tissue interface that an EP system reports for each catheter electrode?

  1. Capacitance
  2. Inductance
  3. Impedance Correct answer.
  4. Voltage

Explanation

Impedance is the frequency-dependent opposition to current flow, combining resistance and reactance, and is reported in ohms for each electrode or electrode pair. Markedly high impedance suggests poor contact, fracture, or coagulum, while unusually low impedance may indicate a short.

Question 33Electrophysiology Equipment, Instrumentation, and Basic Principles

At a standard sweep speed of 25 mm/s, a distance of 1 mm on the recording corresponds to which time interval?

  1. 100 ms
  2. 10 ms
  3. 40 ms Correct answer.
  4. 20 ms

Explanation

At 25 mm/s, 25 mm of tracing equals one second, so 1 mm equals 1/25 s, or 40 ms. Sweep speed changes only the horizontal scale; calibration markers convert measured distance back into time.

Question 34Electrophysiology Equipment, Instrumentation, and Basic Principles

A differential amplifier's ability to reject a signal that appears identically at both inputs is expressed as the:

  1. Gain-bandwidth product
  2. Common-mode rejection ratio Correct answer.
  3. Input offset voltage
  4. Slew rate

Explanation

A differential amplifier amplifies the difference between its two inputs, so any signal identical at both inputs (such as 60-Hz interference) is rejected as a common-mode signal. The ratio of differential gain to common-mode gain is the common-mode rejection ratio, and a higher value indicates a cleaner recording.

Question 35Electrophysiology Equipment, Instrumentation, and Basic Principles

The patient ground/reference connection in the EP laboratory is intended primarily to:

  1. Provide a low-impedance return path for stray current Correct answer.
  2. Improve signal-to-noise ratio of surface leads
  3. Synchronize recording with fluoroscopy
  4. Allow the stimulator to deliver higher current outputs

Explanation

The ground reference gives leakage and stray current a low-impedance return path so that current flows away from the heart rather than through the myocardium. It is fundamentally a safety feature and does not enhance signal quality or stimulator output.

Question 36Electrophysiology Equipment, Instrumentation, and Basic Principles

Which statement best describes a bipolar intracardiac electrogram?

  1. Requires a notch filter because it is prone to 60-Hz noise
  2. Recorded between two widely separated catheters
  3. Recorded between two adjacent electrodes on the same catheter Correct answer.
  4. Recorded between one electrode and the Wilson central terminal

Explanation

A bipolar electrogram is the potential difference between two closely spaced electrodes, so it preferentially records local depolarization beneath the distal pair and rejects distant activity. Widely spaced or unipolar configurations record much more far-field signal.

Question 37Electrophysiology Equipment, Instrumentation, and Basic Principles

Radiofrequency energy delivered during cardiac ablation typically oscillates at approximately:

  1. 2.45 GHz
  2. 1 kHz
  3. 50 Hz
  4. 500 kHz Correct answer.

Explanation

Clinical RF ablation generators deliver alternating current in the radiofrequency range, generally around 500 kHz (roughly 300–1000 kHz), which heats tissue resistively without directly stimulating myocardium. Frequencies near the power-line range would stimulate the heart rather than produce controlled heating.

Question 38Electrophysiology Equipment, Instrumentation, and Basic Principles

A surface ECG channel shows a slowly undulating baseline. Which filter adjustment is most appropriate?

  1. Increase the high-pass setting from 0.05 to 0.5 Hz Correct answer.
  2. Decrease the low-pass setting from 100 to 40 Hz
  3. Engage a 60-Hz notch filter
  4. Increase the gain of the channel

Explanation

Baseline wander is low-frequency drift, so raising the high-pass cutoff removes it. The setting must be chosen carefully, because too high a high-pass cutoff can distort low-frequency components such as the ST segment.

Question 39Electrophysiology Equipment, Instrumentation, and Basic Principles

An intracardiac channel contains signal content up to 300 Hz. What is the minimum sampling rate required to reconstruct it without aliasing?

  1. 600 Hz Correct answer.
  2. 150 Hz
  3. 1200 Hz
  4. 300 Hz

Explanation

The Nyquist theorem requires sampling at more than twice the highest frequency present in the signal, so 2 × 300 Hz = 600 Hz is the minimum. Sampling below this limit produces aliasing, in which high frequencies appear as spurious low frequencies.

Question 40Electrophysiology Equipment, Instrumentation, and Basic Principles

A blanking period is applied to the recording amplifiers immediately after a pacing stimulus in order to:

  1. Delay delivery of subsequent pacing pulses in the drive train
  2. Remove 60-Hz interference from the channel
  3. Prevent artifact from masking the evoked electrogram Correct answer.
  4. Automatically measure the pacing threshold

Explanation

The pacing artifact is far larger than the local electrogram and can saturate the amplifier, hiding the evoked response. Blanking briefly suppresses the input around the stimulus so the evoked depolarization can be seen and measured.

Question 41Electrophysiology Equipment, Instrumentation, and Basic Principles

Bipolar pacing thresholds are generally higher than unipolar thresholds mainly because:

  1. The bipolar circuit has a much greater interelectrode distance
  2. Bipolar stimuli are always delivered at shorter pulse widths
  3. Bipolar current must traverse the myocardium twice
  4. The small ring anode concentrates anodal current density Correct answer.

Explanation

In unipolar pacing the anode is a large skin patch, so anodal current density and polarization are low. In bipolar pacing the small ring electrode acts as the anode, concentrating anodal current density and adding polarization, so more current is needed for capture.

Question 42Electrophysiology Equipment, Instrumentation, and Basic Principles

During RF ablation, impedance suddenly rises from 95 to 250 ohms and delivered current falls. The most likely cause is:

  1. The generator switching to temperature control
  2. A drop in the patient's core temperature
  3. Coagulum formation on the ablation electrode tip Correct answer.
  4. A break in the indifferent patch cable

Explanation

Coagulum forms when heated blood proteins denature on the electrode tip, insulating it and raising impedance while delivered current falls. The generator may then reduce power or abort delivery; the tip is typically withdrawn and cleaned.

Question 43Electrophysiology Equipment, Instrumentation, and Basic Principles

Decreasing the interelectrode spacing of a bipolar recording pair will generally produce:

  1. A narrower, more local signal with less far-field content Correct answer.
  2. A larger far-field contribution to the recorded electrogram
  3. An electrode impedance too high to record reliably
  4. A wider local electrogram with higher amplitude

Explanation

Closely spaced bipolar electrodes sample a small volume of tissue, yielding a sharp, narrow, local electrogram with little far-field contribution. Widening the spacing enlarges the recording field and increases far-field pickup and amplitude.

Question 44Electrophysiology Equipment, Instrumentation, and Basic Principles

Which electroanatomic mapping system calculates catheter position primarily from impedance measured across transthoracic electrical fields applied through skin patches?

  1. Biplane fluoroscopy
  2. The CARTO system
  3. The EnSite NavX system Correct answer.
  4. Intracardiac echocardiography

Explanation

The EnSite NavX system applies low-amplitude electrical fields across the thorax through surface patches and computes catheter location from the measured impedance at each electrode. Magnetic-based localization uses field sensors instead, and echocardiography and fluoroscopy are imaging modalities rather than impedance localization methods.

Question 45Electrophysiology Equipment, Instrumentation, and Basic Principles

Cryoablation differs fundamentally from RF ablation in that cryoablation:

  1. Requires an indifferent return patch on the patient
  2. Uses resistive heating to denature proteins
  3. Freezes tissue rather than heating it resistively Correct answer.
  4. Delivers energy at a higher frequency than RF

Explanation

Cryoablation injures tissue by freezing, causing ice crystal formation and cellular damage, and it does not require a dispersive return patch. RF ablation heats tissue resistively and needs an indifferent electrode to complete the circuit.

Question 46Electrophysiology Equipment, Instrumentation, and Basic Principles

Which of the following most directly increases lesion depth during RF ablation?

  1. Increasing the sweep speed of the display
  2. Increasing the low-pass filter setting on the recording channel
  3. Increasing electrode–tissue contact force Correct answer.
  4. Decreasing the ablation electrode surface area

Explanation

Firm, steady electrode–tissue contact improves energy transfer into the myocardium and is among the strongest determinants of lesion depth and volume. Power, duration, tip size, and catheter orientation also contribute to lesion formation.

Question 47Electrophysiology Equipment, Instrumentation, and Basic Principles

Aliasing in a digital EP recording system occurs when:

  1. The sweep speed is changed during acquisition
  2. Signal frequencies exceed half the sampling rate Correct answer.
  3. Electrode impedance exceeds 10,000 ohms
  4. The notch filter is incorrectly set to 50 Hz instead of 60 Hz

Explanation

Aliasing occurs when the input contains frequencies above the Nyquist limit, defined as half the sampling rate; those frequencies are misrepresented as spurious lower frequencies in the recording. It is prevented by an adequate sampling rate and by anti-aliasing filters ahead of the digitizer.

Question 48Electrophysiology Equipment, Instrumentation, and Basic Principles

An interval measured on the EP recording system is 240 ms at 25 mm/s. If the same recording is displayed at 100 mm/s, the measured interval will be:

  1. Altered unpredictably because the sample rate doubles
  2. 60 ms
  3. 960 ms
  4. Unchanged at 240 ms Correct answer.

Explanation

Sweep speed changes only the horizontal display scale; measured intervals are independent of it because the system is time-calibrated. The tracing simply spreads across more paper or screen space without any change in the underlying timing.

Question 49Electrophysiology Equipment, Instrumentation, and Basic Principles

Two RF applications deliver the same power, one through a 4-mm tip electrode and one through an 8-mm tip electrode. Compared with the 4-mm tip, the 8-mm tip will typically produce:

  1. A smaller lesion because current density is higher
  2. An identical lesion because the power is the same
  3. A larger lesion with lower current density at the tip Correct answer.
  4. A lesion of equal depth but greater steam-pop risk

Explanation

A larger tip spreads current over a greater electrode–tissue interface, lowering current density for a given power and allowing more power to be delivered before impedance rises. The result is a larger, often deeper lesion, although larger tips carry a greater risk of complications such as steam pop if power is not titrated. Power alone does not determine lesion size.

Question 50Electrophysiology Equipment, Instrumentation, and Basic Principles

Setting the low-pass filter on an intracardiac channel to an inappropriately low value (for example 40 Hz) will most likely:

  1. Improve the sharpness of rapid local potentials
  2. Accentuate high-frequency fractionated electrogram components
  3. Blunt high-frequency content and broaden the electrogram Correct answer.
  4. Eliminate 60-Hz interference

Explanation

The low-pass filter removes frequencies above its cutoff, so setting it too low strips high-frequency components and smears or broadens sharp local electrograms. Fractionated and high-frequency potentials are especially vulnerable to this distortion.