IBHRE CEPS-A Certification Exam — Study Set 2026/2027
IBHRE CERTIFIED ELECTROPHYSIOLOGY SPECIALIST–ADULT (CEPS-A) EXAM STUDY
SET
2026/2027 | 175 Questions | 7 Sections | Physician-Level Exam Prep
International Board of Heart Rhythm Examiners
Instructions: Select the best answer for each question. Each question includes the correct answer (green
bold) and a detailed rationale (italic). Covers all CEPS-A exam domains including advanced EP, arrhythmia
management, mapping, ablation, devices, SCD risk stratification, and inherited arrhythmias.
SECTION I: Advanced Cardiac Electrophysiology (Q1–30)
1. Which ion channel is primarily responsible for Phase 4 spontaneous depolarization
(pacemaker potential) in SA node cells?
A. Rapid delayed rectifier potassium current (IKr)
B. Hyperpolarization-activated cyclic nucleotide-gated channel (If/funny current)
C. Transient outward potassium current (Ito)
D. Sodium-calcium exchanger (NCX) current alone
Correct Answer: B. Hyperpolarization-activated cyclic nucleotide-gated channel (If/funny
current)
Rationale: The funny current (If) is carried by hyperpolarization-activated cyclic nucleotide-gated (HCN)
channels activated at approximately -60 mV and contributes to slow diastolic depolarization in SA node
pacemaker cells. If is a nonselective cation current carrying both Na+ and K+. While IKr decay contributes
to late Phase 4, If is the primary pacemaker current. Ito is responsible for Phase 1 early repolarization in
ventricular myocytes.
2. Delayed afterdepolarizations (DADs) are most closely associated with intracellular calcium
overload from which mechanism?
A. Beta-adrenergic blockade reducing cAMP levels
B. Increased sympathetic tone, digoxin toxicity, or heart failure with elevated intracellular calcium
C. Hyperkalemia causing membrane hyperpolarization
D. Sodium channel blockade with class I antiarrhythmics
Correct Answer: B. Increased sympathetic tone, digoxin toxicity, or heart failure with
elevated intracellular calcium
Rationale: DADs occur during Phase 3 or Phase 4 when intracellular calcium overload triggers
spontaneous calcium release from the sarcoplasmic reticulum via the ryanodine receptor. This activates the
sodium-calcium exchanger (NCX) in the forward mode (3 Na+ in, 1 Ca2+ out), generating a net inward
depolarizing current. DADs are associated with digoxin toxicity, catecholamine excess, and heart failure.
Beta-blockers reduce DADs by lowering intracellular cAMP and calcium.
3. Which type of cardiac gap junction protein is predominantly found in ventricular
myocardium and is critical for impulse propagation?
A. Connexin 40 (Cx40)
B. Connexin 43 (Cx43)
C. Connexin 45 (Cx45)
D. Connexin 50 (Cx50)
Correct Answer: B. Connexin 43 (Cx43)
Rationale: Connexin 43 (Cx43) is the most abundant gap junction protein in ventricular myocardium and
is essential for rapid electrical coupling between ventricular myocytes. Cx43 forms gap junction channels
allowing ions and small molecules to pass between cells, enabling coordinated impulse propagation.
Reduced Cx43 expression or lateralization is observed in heart failure and contributes to slowed conduction
1
, IBHRE CEPS-A Certification Exam — Study Set 2026/2027
and arrhythmia susceptibility. Cx40 is predominant in atrial myocardium and His-Purkinje system. Cx45
is found in AV nodal tissue.
4. The leading circle model of reentry requires which essential condition?
A. A unidirectional block in one limb of a circuit with a functional (reversible) block in the other
B. A permanently anatomically defined circuit with no wavelength mismatch
C. Complete absence of refractory tissue within the reentrant circuit
D. Continuous vagal stimulation throughout the circuit
Correct Answer: A. A unidirectional block in one limb of a circuit with a functional
(reversible) block in the other
Rationale: The leading circle model (Mines, 1914; Allessie, 1977) describes functional reentry that can
occur without a fixed anatomic obstacle. It requires a unidirectional block in one direction and a region of
conduction able to recover excitability (functional block) in the other direction. The wavelength of the
reentrant circuit (conduction velocity x refractory period) must be shorter than the path length. This model
explains reentry in atrial fibrillation and some forms of ventricular tachycardia.
5. Class III antiarrhythmic drugs that selectively block IKr (rapid delayed rectifier potassium
current) are associated with which proarrhythmic risk?
A. Brugada syndrome phenotype
B. Torsades de pointes due to excessive QT prolongation and reverse use-dependence
C. Accelerated junctional rhythm
D. Atrial fibrillation initiation
Correct Answer: B. Torsades de pointes due to excessive QT prolongation and reverse use-
dependence
Rationale: Pure IKr blockers (e.g., sotalol, dofetilide, ibutilide) produce reverse use-dependence: greater
QT prolongation at slower heart rates than at faster rates. This creates heterogeneous repolarization at
slow rates, predisposing to early afterdepolarizations (EADs) and torsades de pointes (TdP). The lack of
IKs blockade means faster rates shorten the QT, while slower rates allow maximal IKr block. This is why
TdP often occurs during pauses or bradycardia.
6. Early afterdepolarizations (EADs) typically occur during which phase(s) of the cardiac
action potential?
A. Phase 0 and Phase 1 only
B. Phase 2 and early Phase 3 (plateau and early repolarization)
C. Phase 4 (diastolic depolarization)
D. Only during complete repolarization at resting membrane potential
Correct Answer: B. Phase 2 and early Phase 3 (plateau and early repolarization)
Rationale: EADs are secondary depolarizations that occur during Phase 2 (plateau) or early Phase 3 of
the action potential. They are favored by conditions that prolong the action potential duration, including
bradycardia, hypokalemia, hypomagnesemia, and drugs that block potassium channels (IKr). EADs are
caused by reactivation of L-type calcium channels (ICa,L) or activation of the sodium-calcium exchange
current (NCX) during the plateau. When an EAD reaches threshold, it can trigger torsades de pointes.
7. Which potassium current is the primary contributor to Phase 1 (early repolarization) in
ventricular myocytes?
A. IK1 (inward rectifier)
B. IKr (rapid delayed rectifier)
C. Ito (transient outward potassium current)
D. IKs (slow delayed rectifier)
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, IBHRE CEPS-A Certification Exam — Study Set 2026/2027
Correct Answer: C. Ito (transient outward potassium current)
Rationale: The transient outward potassium current (Ito) is responsible for Phase 1 of the ventricular
action potential, producing the notch between Phase 0 and Phase 2. Ito density varies across the
ventricular wall, being greatest in epicardium and least in endocardium. This transmural gradient
contributes to the J wave and physiological ST-segment elevation in early repolarization patterns. Ito has
two components: Ito1 (calcium-independent, 4-AP sensitive) and Ito2 (calcium-dependent).
8. The wavelength of a reentrant circuit is defined as the product of which two parameters?
A. Action potential amplitude and conduction velocity
B. Conduction velocity and refractory period
C. Resting membrane potential and action potential duration
D. Heart rate and QT interval
Correct Answer: B. Conduction velocity and refractory period
Rationale: The wavelength (WL) of a reentrant circuit is calculated as conduction velocity (CV) multiplied
by the effective refractory period (ERP): WL = CV x ERP. For reentry to sustain, the path length must be
longer than the wavelength; otherwise, the wavefront would encounter refractory tissue. A short
wavelength (slow conduction + short ERP) favors reentry. Antiarrhythmic drugs that prolong ERP or slow
conduction excessively can prevent reentry by making the wavelength longer than the path length.
9. In the anatomically determined reentry model, which cardiac structure serves as the
central obstacle around which atrial flutter circuits typically revolve?
A. Fossa ovalis
B. Tricuspid valve annulus
C. Mitral valve annulus
D. Coronary sinus os
Correct Answer: B. Tricuspid valve annulus
Rationale: Typical counterclockwise atrial flutter uses the tricuspid valve annulus as the anterior
boundary and the crista terminalis/inferior vena cava as the posterior boundary, creating a
macroreentrant circuit in the right atrium. The cavotricuspid isthmus (between the tricuspid annulus and
the inferior vena cava) is the critical isthmus for this circuit and is the target for ablation. The fossa ovalis,
mitral annulus, and coronary sinus os are important anatomic structures but not the central obstacle in
typical atrial flutter.
10. Which intracellular organelle plays a central role in calcium-induced calcium release
(CICR) during cardiac excitation-contraction coupling?
A. Mitochondria
B. Sarcoplasmic reticulum
C. Lysosome
D. Golgi apparatus
Correct Answer: B. Sarcoplasmic reticulum
Rationale: During cardiac excitation-contraction coupling, a small amount of calcium entering through
L-type calcium channels (ICa,L) during the plateau phase triggers a much larger release of calcium from
the sarcoplasmic reticulum (SR) via ryanodine receptors (RyR2). This process is called calcium-induced
calcium release (CICR). The released calcium binds to troponin C, initiating cross-bridge cycling and
myocardial contraction. SR dysfunction is central to heart failure-related arrhythmias (DADs).
11. The inward rectifier potassium current (IK1) is unique in its conduction properties
because it:
A. Conducts more current during depolarization than at resting potential
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, IBHRE CEPS-A Certification Exam — Study Set 2026/2027
B. Conducts more current at resting membrane potential but conducts less (rectifies) during
depolarization
C. Is only active during the plateau phase
D. Is completely insensitive to extracellular potassium concentration
Correct Answer: B. Conducts more current at resting membrane potential but conducts less
(rectifies) during depolarization
Rationale: IK1 exhibits inward rectification, meaning it passes current more easily in the inward
direction at membrane potentials negative to the potassium reversal potential but conducts less in the
outward direction during depolarization. This property is due to block of the channel pore by intracellular
magnesium and polyamines at depolarized potentials. IK1 is the dominant current at the resting
membrane potential (-90 mV), maintaining it close to the potassium equilibrium potential.
12. Which conditions can cause decreased connexin 43 expression or lateralization in
ventricular myocardium?
A. Chronic heart failure with ventricular remodeling
B. Acute myocardial infarction (within hours)
C. Atrial fibrillation
D. Hypertrophic cardiomyopathy
E. Normal aging in healthy elderly without structural heart disease
Correct Answer: A. Chronic heart failure with ventricular remodeling
Rationale: Decreased Cx43 expression and redistribution (lateralization) are well-documented in chronic
heart failure, contributing to slowed conduction and reentry. In acute MI, ischemia rapidly causes Cx43
dephosphorylation and gap junction uncoupling within minutes. In HCM, disarray of myocyte architecture
includes abnormal Cx43 distribution. AF primarily affects atrial connexins (Cx40) rather than ventricular
Cx43. Normal aging does not cause significant Cx43 lateralization without structural disease.
13. Amiodarone exerts its antiarrhythmic effects through blockade of which ion channels?
A. Potassium channels only (class III)
B. Sodium, potassium, and calcium channels (class I, III, and IV effects)
C. Beta-adrenergic receptors only (class II effect)
D. Sodium channels only (class I effect)
Correct Answer: B. Sodium, potassium, and calcium channels (class I, III, and IV effects)
Rationale: Amiodarone is a multichannel blocker with class I (sodium channel block), class II
(noncompetitive beta-blockade), class III (potassium channel block: IKr, IKs, Ito), and class IV (calcium
channel block) properties. This broad-spectrum activity makes it effective for both supraventricular and
ventricular arrhythmias. Despite its class III effect, amiodarone has a low risk of torsades de pointes
because it also blocks the late sodium current and has beta-blocking properties that reduce EAD formation.
14. The figure-of-eight reentry model differs from the leading circle model in that it requires:
A. No anatomic obstacles and purely functional blocks
B. Two arcs of functional block creating two counter-rotating wavefronts around a common central line
of block
C. A single permanently refractory obstacle
D. Continuous atrial fibrillation with multiple wandering wavelets
Correct Answer: B. Two arcs of functional block creating two counter-rotating wavefronts
around a common central line of block
Rationale: The figure-of-eight reentry model features a central line of functional block with two reentrant
wavefronts circulating in opposite directions around the block, each forming its own circuit. This model is
commonly observed in ventricular tachycardia after myocardial infarction, where islands of scar create
functional block lines. Unlike the leading circle model which requires no anatomic obstacles, the figure-of-
eight model can arise around areas of scar or functional conduction block.
4
IBHRE CERTIFIED ELECTROPHYSIOLOGY SPECIALIST–ADULT (CEPS-A) EXAM STUDY
SET
2026/2027 | 175 Questions | 7 Sections | Physician-Level Exam Prep
International Board of Heart Rhythm Examiners
Instructions: Select the best answer for each question. Each question includes the correct answer (green
bold) and a detailed rationale (italic). Covers all CEPS-A exam domains including advanced EP, arrhythmia
management, mapping, ablation, devices, SCD risk stratification, and inherited arrhythmias.
SECTION I: Advanced Cardiac Electrophysiology (Q1–30)
1. Which ion channel is primarily responsible for Phase 4 spontaneous depolarization
(pacemaker potential) in SA node cells?
A. Rapid delayed rectifier potassium current (IKr)
B. Hyperpolarization-activated cyclic nucleotide-gated channel (If/funny current)
C. Transient outward potassium current (Ito)
D. Sodium-calcium exchanger (NCX) current alone
Correct Answer: B. Hyperpolarization-activated cyclic nucleotide-gated channel (If/funny
current)
Rationale: The funny current (If) is carried by hyperpolarization-activated cyclic nucleotide-gated (HCN)
channels activated at approximately -60 mV and contributes to slow diastolic depolarization in SA node
pacemaker cells. If is a nonselective cation current carrying both Na+ and K+. While IKr decay contributes
to late Phase 4, If is the primary pacemaker current. Ito is responsible for Phase 1 early repolarization in
ventricular myocytes.
2. Delayed afterdepolarizations (DADs) are most closely associated with intracellular calcium
overload from which mechanism?
A. Beta-adrenergic blockade reducing cAMP levels
B. Increased sympathetic tone, digoxin toxicity, or heart failure with elevated intracellular calcium
C. Hyperkalemia causing membrane hyperpolarization
D. Sodium channel blockade with class I antiarrhythmics
Correct Answer: B. Increased sympathetic tone, digoxin toxicity, or heart failure with
elevated intracellular calcium
Rationale: DADs occur during Phase 3 or Phase 4 when intracellular calcium overload triggers
spontaneous calcium release from the sarcoplasmic reticulum via the ryanodine receptor. This activates the
sodium-calcium exchanger (NCX) in the forward mode (3 Na+ in, 1 Ca2+ out), generating a net inward
depolarizing current. DADs are associated with digoxin toxicity, catecholamine excess, and heart failure.
Beta-blockers reduce DADs by lowering intracellular cAMP and calcium.
3. Which type of cardiac gap junction protein is predominantly found in ventricular
myocardium and is critical for impulse propagation?
A. Connexin 40 (Cx40)
B. Connexin 43 (Cx43)
C. Connexin 45 (Cx45)
D. Connexin 50 (Cx50)
Correct Answer: B. Connexin 43 (Cx43)
Rationale: Connexin 43 (Cx43) is the most abundant gap junction protein in ventricular myocardium and
is essential for rapid electrical coupling between ventricular myocytes. Cx43 forms gap junction channels
allowing ions and small molecules to pass between cells, enabling coordinated impulse propagation.
Reduced Cx43 expression or lateralization is observed in heart failure and contributes to slowed conduction
1
, IBHRE CEPS-A Certification Exam — Study Set 2026/2027
and arrhythmia susceptibility. Cx40 is predominant in atrial myocardium and His-Purkinje system. Cx45
is found in AV nodal tissue.
4. The leading circle model of reentry requires which essential condition?
A. A unidirectional block in one limb of a circuit with a functional (reversible) block in the other
B. A permanently anatomically defined circuit with no wavelength mismatch
C. Complete absence of refractory tissue within the reentrant circuit
D. Continuous vagal stimulation throughout the circuit
Correct Answer: A. A unidirectional block in one limb of a circuit with a functional
(reversible) block in the other
Rationale: The leading circle model (Mines, 1914; Allessie, 1977) describes functional reentry that can
occur without a fixed anatomic obstacle. It requires a unidirectional block in one direction and a region of
conduction able to recover excitability (functional block) in the other direction. The wavelength of the
reentrant circuit (conduction velocity x refractory period) must be shorter than the path length. This model
explains reentry in atrial fibrillation and some forms of ventricular tachycardia.
5. Class III antiarrhythmic drugs that selectively block IKr (rapid delayed rectifier potassium
current) are associated with which proarrhythmic risk?
A. Brugada syndrome phenotype
B. Torsades de pointes due to excessive QT prolongation and reverse use-dependence
C. Accelerated junctional rhythm
D. Atrial fibrillation initiation
Correct Answer: B. Torsades de pointes due to excessive QT prolongation and reverse use-
dependence
Rationale: Pure IKr blockers (e.g., sotalol, dofetilide, ibutilide) produce reverse use-dependence: greater
QT prolongation at slower heart rates than at faster rates. This creates heterogeneous repolarization at
slow rates, predisposing to early afterdepolarizations (EADs) and torsades de pointes (TdP). The lack of
IKs blockade means faster rates shorten the QT, while slower rates allow maximal IKr block. This is why
TdP often occurs during pauses or bradycardia.
6. Early afterdepolarizations (EADs) typically occur during which phase(s) of the cardiac
action potential?
A. Phase 0 and Phase 1 only
B. Phase 2 and early Phase 3 (plateau and early repolarization)
C. Phase 4 (diastolic depolarization)
D. Only during complete repolarization at resting membrane potential
Correct Answer: B. Phase 2 and early Phase 3 (plateau and early repolarization)
Rationale: EADs are secondary depolarizations that occur during Phase 2 (plateau) or early Phase 3 of
the action potential. They are favored by conditions that prolong the action potential duration, including
bradycardia, hypokalemia, hypomagnesemia, and drugs that block potassium channels (IKr). EADs are
caused by reactivation of L-type calcium channels (ICa,L) or activation of the sodium-calcium exchange
current (NCX) during the plateau. When an EAD reaches threshold, it can trigger torsades de pointes.
7. Which potassium current is the primary contributor to Phase 1 (early repolarization) in
ventricular myocytes?
A. IK1 (inward rectifier)
B. IKr (rapid delayed rectifier)
C. Ito (transient outward potassium current)
D. IKs (slow delayed rectifier)
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, IBHRE CEPS-A Certification Exam — Study Set 2026/2027
Correct Answer: C. Ito (transient outward potassium current)
Rationale: The transient outward potassium current (Ito) is responsible for Phase 1 of the ventricular
action potential, producing the notch between Phase 0 and Phase 2. Ito density varies across the
ventricular wall, being greatest in epicardium and least in endocardium. This transmural gradient
contributes to the J wave and physiological ST-segment elevation in early repolarization patterns. Ito has
two components: Ito1 (calcium-independent, 4-AP sensitive) and Ito2 (calcium-dependent).
8. The wavelength of a reentrant circuit is defined as the product of which two parameters?
A. Action potential amplitude and conduction velocity
B. Conduction velocity and refractory period
C. Resting membrane potential and action potential duration
D. Heart rate and QT interval
Correct Answer: B. Conduction velocity and refractory period
Rationale: The wavelength (WL) of a reentrant circuit is calculated as conduction velocity (CV) multiplied
by the effective refractory period (ERP): WL = CV x ERP. For reentry to sustain, the path length must be
longer than the wavelength; otherwise, the wavefront would encounter refractory tissue. A short
wavelength (slow conduction + short ERP) favors reentry. Antiarrhythmic drugs that prolong ERP or slow
conduction excessively can prevent reentry by making the wavelength longer than the path length.
9. In the anatomically determined reentry model, which cardiac structure serves as the
central obstacle around which atrial flutter circuits typically revolve?
A. Fossa ovalis
B. Tricuspid valve annulus
C. Mitral valve annulus
D. Coronary sinus os
Correct Answer: B. Tricuspid valve annulus
Rationale: Typical counterclockwise atrial flutter uses the tricuspid valve annulus as the anterior
boundary and the crista terminalis/inferior vena cava as the posterior boundary, creating a
macroreentrant circuit in the right atrium. The cavotricuspid isthmus (between the tricuspid annulus and
the inferior vena cava) is the critical isthmus for this circuit and is the target for ablation. The fossa ovalis,
mitral annulus, and coronary sinus os are important anatomic structures but not the central obstacle in
typical atrial flutter.
10. Which intracellular organelle plays a central role in calcium-induced calcium release
(CICR) during cardiac excitation-contraction coupling?
A. Mitochondria
B. Sarcoplasmic reticulum
C. Lysosome
D. Golgi apparatus
Correct Answer: B. Sarcoplasmic reticulum
Rationale: During cardiac excitation-contraction coupling, a small amount of calcium entering through
L-type calcium channels (ICa,L) during the plateau phase triggers a much larger release of calcium from
the sarcoplasmic reticulum (SR) via ryanodine receptors (RyR2). This process is called calcium-induced
calcium release (CICR). The released calcium binds to troponin C, initiating cross-bridge cycling and
myocardial contraction. SR dysfunction is central to heart failure-related arrhythmias (DADs).
11. The inward rectifier potassium current (IK1) is unique in its conduction properties
because it:
A. Conducts more current during depolarization than at resting potential
3
, IBHRE CEPS-A Certification Exam — Study Set 2026/2027
B. Conducts more current at resting membrane potential but conducts less (rectifies) during
depolarization
C. Is only active during the plateau phase
D. Is completely insensitive to extracellular potassium concentration
Correct Answer: B. Conducts more current at resting membrane potential but conducts less
(rectifies) during depolarization
Rationale: IK1 exhibits inward rectification, meaning it passes current more easily in the inward
direction at membrane potentials negative to the potassium reversal potential but conducts less in the
outward direction during depolarization. This property is due to block of the channel pore by intracellular
magnesium and polyamines at depolarized potentials. IK1 is the dominant current at the resting
membrane potential (-90 mV), maintaining it close to the potassium equilibrium potential.
12. Which conditions can cause decreased connexin 43 expression or lateralization in
ventricular myocardium?
A. Chronic heart failure with ventricular remodeling
B. Acute myocardial infarction (within hours)
C. Atrial fibrillation
D. Hypertrophic cardiomyopathy
E. Normal aging in healthy elderly without structural heart disease
Correct Answer: A. Chronic heart failure with ventricular remodeling
Rationale: Decreased Cx43 expression and redistribution (lateralization) are well-documented in chronic
heart failure, contributing to slowed conduction and reentry. In acute MI, ischemia rapidly causes Cx43
dephosphorylation and gap junction uncoupling within minutes. In HCM, disarray of myocyte architecture
includes abnormal Cx43 distribution. AF primarily affects atrial connexins (Cx40) rather than ventricular
Cx43. Normal aging does not cause significant Cx43 lateralization without structural disease.
13. Amiodarone exerts its antiarrhythmic effects through blockade of which ion channels?
A. Potassium channels only (class III)
B. Sodium, potassium, and calcium channels (class I, III, and IV effects)
C. Beta-adrenergic receptors only (class II effect)
D. Sodium channels only (class I effect)
Correct Answer: B. Sodium, potassium, and calcium channels (class I, III, and IV effects)
Rationale: Amiodarone is a multichannel blocker with class I (sodium channel block), class II
(noncompetitive beta-blockade), class III (potassium channel block: IKr, IKs, Ito), and class IV (calcium
channel block) properties. This broad-spectrum activity makes it effective for both supraventricular and
ventricular arrhythmias. Despite its class III effect, amiodarone has a low risk of torsades de pointes
because it also blocks the late sodium current and has beta-blocking properties that reduce EAD formation.
14. The figure-of-eight reentry model differs from the leading circle model in that it requires:
A. No anatomic obstacles and purely functional blocks
B. Two arcs of functional block creating two counter-rotating wavefronts around a common central line
of block
C. A single permanently refractory obstacle
D. Continuous atrial fibrillation with multiple wandering wavelets
Correct Answer: B. Two arcs of functional block creating two counter-rotating wavefronts
around a common central line of block
Rationale: The figure-of-eight reentry model features a central line of functional block with two reentrant
wavefronts circulating in opposite directions around the block, each forming its own circuit. This model is
commonly observed in ventricular tachycardia after myocardial infarction, where islands of scar create
functional block lines. Unlike the leading circle model which requires no anatomic obstacles, the figure-of-
eight model can arise around areas of scar or functional conduction block.
4
