IBHRE CCDS Certification Exam — Study Set 2026/2027
IBHRE CCDS CERTIFICATION EXAM STUDY SET
2026/2027 | 200 Questions | 9 Sections | Exam Prep
Instructions: Select the best answer for each question. Each question includes the correct answer and a
detailed rationale. Covers all CCDS exam domains.
SECTION I: Cardiac Anatomy, Physiology & EP Fundamentals (Q1–25)
1. The sinoatrial (SA) node is located in which anatomic structure?
A. Right atrial appendage
B. Superior aspect of the crista terminalis near the SVC-RA junction
C. Coronary sinus os
D. Interventricular septum at the His bundle location
Correct Answer: B. Superior aspect of the crista terminalis near the SVC-RA junction
Rationale: The SA node is located at the superior aspect of the crista terminalis at the junction of the
superior vena cava and the right atrium. It is the primary pacemaker of the heart and is richly innervated
by both sympathetic and parasympathetic fibers. The right atrial appendage (A) is a distinct structure on
the lateral RA. The coronary sinus os (C) drains venous blood from the cardiac veins. The His bundle (D) is
located in the interventricular septum.
2. During which phase of the ventricular action potential does calcium influx through L-type
calcium channels occur?
A. Phase 0
B. Phase 1
C. Phase 2 (plateau)
D. Phase 3 (repolarization)
Correct Answer: C. Phase 2 (plateau)
Rationale: Phase 2 (plateau) of the ventricular action potential is maintained by the balance of inward
calcium current (ICaL) through L-type calcium channels and outward potassium current (IKr). This
plateau phase is critical for excitation-contraction coupling. Phase 0 is rapid depolarization via sodium
channels. Phase 1 is early rapid repolarization via Ito. Phase 3 is final repolarization dominated by
potassium efflux.
3. The effective refractory period (ERP) of a cardiac cell is best defined as:
A. The time during which a stimulus of any strength cannot produce a propagated response
B. The time during which only a strong stimulus can produce a response
C. The time from phase 0 to the end of phase 3
D. The time during which the cell is in a hyperpolarized state
Correct Answer: A. The time during which a stimulus of any strength cannot produce a
propagated response
Rationale: The ERP is defined as the longest coupling interval (S1-S2) at which a premature stimulus fails
to produce a propagated response. During the ERP, the cell is absolutely refractory. Option B describes the
relative refractory period. Option C is incorrect because the ERP is a functional property, not a phase
definition. Option D is incorrect because hyperpolarization is not a component of the ERP definition.
4. Which ECG finding is most characteristic of first-degree AV block?
A. Prolonged PR interval greater than 200 ms with constant PR morphology
B. Intermittent non-conducted P waves with progressive PR prolongation
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, IBHRE CCDS Certification Exam — Study Set 2026/2027
C. P waves with variable PR intervals not related to cycle length
D. Absence of P waves with irregular R-R intervals
Correct Answer: A. Prolonged PR interval greater than 200 ms with constant PR morphology
Rationale: First-degree AV block is characterized by a PR interval exceeding 200 ms (0.20 seconds) with
consistent 1:1 AV conduction and stable PR morphology. Option B describes second-degree AV block type I
(Wenckebach/Mobitz I). Option C describes second-degree AV block type II (Mobitz II) with variable
conduction. Option D describes atrial fibrillation.
5. A 45-year-old patient presents with a wide-complex tachycardia at a rate of 180 bpm. Which
finding would most strongly suggest ventricular tachycardia over supraventricular
tachycardia with aberrant conduction?
A. QRS duration of 140 ms
B. Atrioventricular dissociation on ECG
C. Left bundle branch block morphology
D. Heart rate of 180 bpm
Correct Answer: B. Atrioventricular dissociation on ECG
Rationale: AV dissociation is the most reliable criterion for differentiating VT from SVT with aberrancy.
When atria and ventricles beat independently, with the atrial rate slower than the ventricular rate, VT is
strongly suggested. Brugada criteria also include QRS >140 ms (but this alone is not specific), concordance
in precordial leads, and specific morphologic criteria. LBBB morphology (C) and heart rate of 180 bpm (D)
can occur with both VT and SVT.
6. Third-degree (complete) AV block is characterized by which of the following?
A. Progressive PR interval prolongation until a P wave is non-conducted
B. Intermittent failure of conduction of P waves without PR prolongation
C. Complete absence of AV conduction with independent atrial and ventricular rhythms
D. Prolonged QRS duration with normal PR interval
Correct Answer: C. Complete absence of AV conduction with independent atrial and
ventricular rhythms
Rationale: Third-degree AV block (complete heart block) is characterized by complete failure of AV
conduction, resulting in independent atrial and ventricular rhythms (AV dissociation). The atrial rate is
typically faster than the ventricular escape rhythm. Option A describes Wenckebach (second-degree type I).
Option B describes Mobitz II (second-degree type II). Option D is not an AV block pattern.
7. What is the normal resting membrane potential of a ventricular myocyte?
A. +20 mV to +30 mV
B. 0 mV
C. -60 mV to -70 mV
D. -80 mV to -90 mV
Correct Answer: D. -80 mV to -90 mV
Rationale: The normal resting membrane potential of a ventricular myocyte is approximately -80 to -90
mV, maintained by the Na+/K+ ATPase pump and potassium permeability (IK1). During phase 0, rapid
depolarization brings the membrane potential to approximately +20 to +30 mV (A). Phase 2 plateau is
near 0 mV (B). -60 to -70 mV (C) is near the threshold potential for depolarization.
8. The QT interval on a surface ECG most closely approximates which electrophysiologic
interval?
A. QRS duration plus PR interval
B. Ventricular action potential duration
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, IBHRE CCDS Certification Exam — Study Set 2026/2027
C. SA node recovery time
D. AV nodal conduction time
Correct Answer: B. Ventricular action potential duration
Rationale: The QT interval on the surface ECG approximates the ventricular action potential duration
(ventricular depolarization and repolarization). Prolongation of the QT interval reflects prolonged
ventricular repolarization and is associated with increased risk of torsades de pointes. QTc (Bazett
formula: QT/√RR) corrects for heart rate. The QRS duration represents ventricular depolarization alone,
not repolarization.
9. Which autonomic nervous system effect would increase the heart rate through sympathetic
stimulation of the SA node?
A. Increased acetylcholine release at the SA node
B. Increased norepinephrine release activating beta-1 adrenergic receptors
C. Vagal stimulation increasing potassium conductance
D. Decreased calcium current through the AV node
Correct Answer: B. Increased norepinephrine release activating beta-1 adrenergic receptors
Rationale: Sympathetic stimulation releases norepinephrine, which activates beta-1 adrenergic receptors
in the SA node, increasing the rate of phase 4 depolarization (If current) and accelerating heart rate.
Acetylcholine (A) is parasympathetic and slows heart rate. Vagal stimulation (C) increases potassium
conductance, hyperpolarizing cells. Decreased calcium current (D) is a parasympathetic effect on the AV
node.
10. A patient with atrial fibrillation has an irregularly irregular rhythm with no discernible P
waves. The ventricular rate is controlled at 72 bpm. Which atrial rate is most typical in
untreated atrial fibrillation?
A. 100-150 bpm
B. 250-350 bpm
C. 350-600 bpm
D. 60-100 bpm
Correct Answer: C. 350-600 bpm
Rationale: In atrial fibrillation, the atria depolarize at rates typically between 350 and 600 bpm due to
multiple reentrant wavelets circulating through the atria. AV nodal filtering limits ventricular response.
Atrial flutter (B) typically occurs at 250-350 bpm. Sinus tachycardia (D) occurs at 100-150 bpm. The rapid,
disorganized atrial activity in AF prevents organized atrial contraction.
11. The His-Purkinje system normally conducts impulses at what approximate velocity?
A. 0.01-0.1 m/s
B. 0.5-1.0 m/s
C. 2.0-4.0 m/s
D. 5.0-10.0 m/s
Correct Answer: C. 2.0-4.0 m/s
Rationale: The His-Purkinje system is specialized for rapid conduction at approximately 2-4 m/s,
ensuring near-synchronous ventricular depolarization. Atrial myocardium conducts at approximately 0.5-
1.0 m/s (B). The AV node is the slowest at approximately 0.01-0.1 m/s (A). Values of 5-10 m/s (D) are not
physiological for cardiac tissue.
12. Which of the following best describes the mechanism of typical atrial flutter?
A. Multiple wavelets circulating randomly through the atria
B. A macroreentrant circuit around the tricuspid annulus utilizing the cavotricuspid isthmus
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, IBHRE CCDS Certification Exam — Study Set 2026/2027
C. An automatic focus in the pulmonary veins
D. A microreentrant circuit confined to the sinoatrial node region
Correct Answer: B. A macroreentrant circuit around the tricuspid annulus utilizing the
cavotricuspid isthmus
Rationale: Typical (counterclockwise) atrial flutter is caused by a macroreentrant circuit that circulates
around the tricuspid annulus, utilizing the cavotricuspid isthmus (CTI) as the critical isthmus. The circuit
travels cranially up the interatrial septum, across the atrial roof, and down the right atrial free wall.
Option A describes the mechanism of atrial fibrillation. Option C describes focal atrial tachycardia. Option
D describes sinus node reentry.
13. The normal QRS axis in an adult is oriented in which direction?
A. -30 to -90 degrees
B. -30 to +90 degrees
C. +90 to +180 degrees
D. +180 to -90 degrees
Correct Answer: B. -30 to +90 degrees
Rationale: The normal QRS axis in adults ranges from -30 to +90 degrees. A left axis deviation is -30 to -
90 degrees, often seen with left anterior fascicular block or inferior MI. A right axis deviation is +90 to
+180 degrees, seen with right ventricular hypertrophy or left posterior fascicular block. An extreme axis
deviation (+180 to -90) suggests complex conduction abnormalities.
14. Which of the following is a characteristic ECG finding of left bundle branch block (LBBB)?
A. QRS duration less than 120 ms with rSR' pattern in V1
B. Broad notched or slurred R wave in leads I, aVL, V5-V6 and broad QS in V1-V2
C. Right axis deviation with tall R waves in V1
D. Normal QRS duration with ST depression in lateral leads
Correct Answer: B. Broad notched or slurred R wave in leads I, aVL, V5-V6 and broad QS in
V1-V2
Rationale: LBBB is characterized by QRS duration ≥120 ms (usually >140 ms), a broad notched or
slurred R wave in lateral leads (I, aVL, V5-V6), and broad QS or rS in V1-V2. There is associated ST-T wave
discordance. Option A describes right bundle branch block (rSR' in V1). Option C (right axis deviation with
tall R in V1) suggests RVH or RBBB. Option D is not characteristic of LBBB.
15. Afterdepolarizations that occur during phase 2 or phase 3 of the action potential are
classified as:
A. Delayed afterdepolarizations (DADs)
B. Early afterdepolarizations (EADs)
C. Triggered activity
D. Reentry
Correct Answer: B. Early afterdepolarizations (EADs)
Rationale: Early afterdepolarizations (EADs) occur during phases 2 and 3 of the action potential,
typically when the action potential duration is prolonged (e.g., LQTS). They are triggered by conditions
that slow repolarization. DADs (A) occur during phase 4, after full repolarization, often due to calcium
overload. Both can lead to triggered activity (C), which is the mechanism, not the classification of the
afterdepolarization itself. Reentry (D) is a separate mechanism.
16. The coronary sinus receives venous drainage from which cardiac structure?
A. Right ventricle only
B. Left ventricle only
4
IBHRE CCDS CERTIFICATION EXAM STUDY SET
2026/2027 | 200 Questions | 9 Sections | Exam Prep
Instructions: Select the best answer for each question. Each question includes the correct answer and a
detailed rationale. Covers all CCDS exam domains.
SECTION I: Cardiac Anatomy, Physiology & EP Fundamentals (Q1–25)
1. The sinoatrial (SA) node is located in which anatomic structure?
A. Right atrial appendage
B. Superior aspect of the crista terminalis near the SVC-RA junction
C. Coronary sinus os
D. Interventricular septum at the His bundle location
Correct Answer: B. Superior aspect of the crista terminalis near the SVC-RA junction
Rationale: The SA node is located at the superior aspect of the crista terminalis at the junction of the
superior vena cava and the right atrium. It is the primary pacemaker of the heart and is richly innervated
by both sympathetic and parasympathetic fibers. The right atrial appendage (A) is a distinct structure on
the lateral RA. The coronary sinus os (C) drains venous blood from the cardiac veins. The His bundle (D) is
located in the interventricular septum.
2. During which phase of the ventricular action potential does calcium influx through L-type
calcium channels occur?
A. Phase 0
B. Phase 1
C. Phase 2 (plateau)
D. Phase 3 (repolarization)
Correct Answer: C. Phase 2 (plateau)
Rationale: Phase 2 (plateau) of the ventricular action potential is maintained by the balance of inward
calcium current (ICaL) through L-type calcium channels and outward potassium current (IKr). This
plateau phase is critical for excitation-contraction coupling. Phase 0 is rapid depolarization via sodium
channels. Phase 1 is early rapid repolarization via Ito. Phase 3 is final repolarization dominated by
potassium efflux.
3. The effective refractory period (ERP) of a cardiac cell is best defined as:
A. The time during which a stimulus of any strength cannot produce a propagated response
B. The time during which only a strong stimulus can produce a response
C. The time from phase 0 to the end of phase 3
D. The time during which the cell is in a hyperpolarized state
Correct Answer: A. The time during which a stimulus of any strength cannot produce a
propagated response
Rationale: The ERP is defined as the longest coupling interval (S1-S2) at which a premature stimulus fails
to produce a propagated response. During the ERP, the cell is absolutely refractory. Option B describes the
relative refractory period. Option C is incorrect because the ERP is a functional property, not a phase
definition. Option D is incorrect because hyperpolarization is not a component of the ERP definition.
4. Which ECG finding is most characteristic of first-degree AV block?
A. Prolonged PR interval greater than 200 ms with constant PR morphology
B. Intermittent non-conducted P waves with progressive PR prolongation
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, IBHRE CCDS Certification Exam — Study Set 2026/2027
C. P waves with variable PR intervals not related to cycle length
D. Absence of P waves with irregular R-R intervals
Correct Answer: A. Prolonged PR interval greater than 200 ms with constant PR morphology
Rationale: First-degree AV block is characterized by a PR interval exceeding 200 ms (0.20 seconds) with
consistent 1:1 AV conduction and stable PR morphology. Option B describes second-degree AV block type I
(Wenckebach/Mobitz I). Option C describes second-degree AV block type II (Mobitz II) with variable
conduction. Option D describes atrial fibrillation.
5. A 45-year-old patient presents with a wide-complex tachycardia at a rate of 180 bpm. Which
finding would most strongly suggest ventricular tachycardia over supraventricular
tachycardia with aberrant conduction?
A. QRS duration of 140 ms
B. Atrioventricular dissociation on ECG
C. Left bundle branch block morphology
D. Heart rate of 180 bpm
Correct Answer: B. Atrioventricular dissociation on ECG
Rationale: AV dissociation is the most reliable criterion for differentiating VT from SVT with aberrancy.
When atria and ventricles beat independently, with the atrial rate slower than the ventricular rate, VT is
strongly suggested. Brugada criteria also include QRS >140 ms (but this alone is not specific), concordance
in precordial leads, and specific morphologic criteria. LBBB morphology (C) and heart rate of 180 bpm (D)
can occur with both VT and SVT.
6. Third-degree (complete) AV block is characterized by which of the following?
A. Progressive PR interval prolongation until a P wave is non-conducted
B. Intermittent failure of conduction of P waves without PR prolongation
C. Complete absence of AV conduction with independent atrial and ventricular rhythms
D. Prolonged QRS duration with normal PR interval
Correct Answer: C. Complete absence of AV conduction with independent atrial and
ventricular rhythms
Rationale: Third-degree AV block (complete heart block) is characterized by complete failure of AV
conduction, resulting in independent atrial and ventricular rhythms (AV dissociation). The atrial rate is
typically faster than the ventricular escape rhythm. Option A describes Wenckebach (second-degree type I).
Option B describes Mobitz II (second-degree type II). Option D is not an AV block pattern.
7. What is the normal resting membrane potential of a ventricular myocyte?
A. +20 mV to +30 mV
B. 0 mV
C. -60 mV to -70 mV
D. -80 mV to -90 mV
Correct Answer: D. -80 mV to -90 mV
Rationale: The normal resting membrane potential of a ventricular myocyte is approximately -80 to -90
mV, maintained by the Na+/K+ ATPase pump and potassium permeability (IK1). During phase 0, rapid
depolarization brings the membrane potential to approximately +20 to +30 mV (A). Phase 2 plateau is
near 0 mV (B). -60 to -70 mV (C) is near the threshold potential for depolarization.
8. The QT interval on a surface ECG most closely approximates which electrophysiologic
interval?
A. QRS duration plus PR interval
B. Ventricular action potential duration
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, IBHRE CCDS Certification Exam — Study Set 2026/2027
C. SA node recovery time
D. AV nodal conduction time
Correct Answer: B. Ventricular action potential duration
Rationale: The QT interval on the surface ECG approximates the ventricular action potential duration
(ventricular depolarization and repolarization). Prolongation of the QT interval reflects prolonged
ventricular repolarization and is associated with increased risk of torsades de pointes. QTc (Bazett
formula: QT/√RR) corrects for heart rate. The QRS duration represents ventricular depolarization alone,
not repolarization.
9. Which autonomic nervous system effect would increase the heart rate through sympathetic
stimulation of the SA node?
A. Increased acetylcholine release at the SA node
B. Increased norepinephrine release activating beta-1 adrenergic receptors
C. Vagal stimulation increasing potassium conductance
D. Decreased calcium current through the AV node
Correct Answer: B. Increased norepinephrine release activating beta-1 adrenergic receptors
Rationale: Sympathetic stimulation releases norepinephrine, which activates beta-1 adrenergic receptors
in the SA node, increasing the rate of phase 4 depolarization (If current) and accelerating heart rate.
Acetylcholine (A) is parasympathetic and slows heart rate. Vagal stimulation (C) increases potassium
conductance, hyperpolarizing cells. Decreased calcium current (D) is a parasympathetic effect on the AV
node.
10. A patient with atrial fibrillation has an irregularly irregular rhythm with no discernible P
waves. The ventricular rate is controlled at 72 bpm. Which atrial rate is most typical in
untreated atrial fibrillation?
A. 100-150 bpm
B. 250-350 bpm
C. 350-600 bpm
D. 60-100 bpm
Correct Answer: C. 350-600 bpm
Rationale: In atrial fibrillation, the atria depolarize at rates typically between 350 and 600 bpm due to
multiple reentrant wavelets circulating through the atria. AV nodal filtering limits ventricular response.
Atrial flutter (B) typically occurs at 250-350 bpm. Sinus tachycardia (D) occurs at 100-150 bpm. The rapid,
disorganized atrial activity in AF prevents organized atrial contraction.
11. The His-Purkinje system normally conducts impulses at what approximate velocity?
A. 0.01-0.1 m/s
B. 0.5-1.0 m/s
C. 2.0-4.0 m/s
D. 5.0-10.0 m/s
Correct Answer: C. 2.0-4.0 m/s
Rationale: The His-Purkinje system is specialized for rapid conduction at approximately 2-4 m/s,
ensuring near-synchronous ventricular depolarization. Atrial myocardium conducts at approximately 0.5-
1.0 m/s (B). The AV node is the slowest at approximately 0.01-0.1 m/s (A). Values of 5-10 m/s (D) are not
physiological for cardiac tissue.
12. Which of the following best describes the mechanism of typical atrial flutter?
A. Multiple wavelets circulating randomly through the atria
B. A macroreentrant circuit around the tricuspid annulus utilizing the cavotricuspid isthmus
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, IBHRE CCDS Certification Exam — Study Set 2026/2027
C. An automatic focus in the pulmonary veins
D. A microreentrant circuit confined to the sinoatrial node region
Correct Answer: B. A macroreentrant circuit around the tricuspid annulus utilizing the
cavotricuspid isthmus
Rationale: Typical (counterclockwise) atrial flutter is caused by a macroreentrant circuit that circulates
around the tricuspid annulus, utilizing the cavotricuspid isthmus (CTI) as the critical isthmus. The circuit
travels cranially up the interatrial septum, across the atrial roof, and down the right atrial free wall.
Option A describes the mechanism of atrial fibrillation. Option C describes focal atrial tachycardia. Option
D describes sinus node reentry.
13. The normal QRS axis in an adult is oriented in which direction?
A. -30 to -90 degrees
B. -30 to +90 degrees
C. +90 to +180 degrees
D. +180 to -90 degrees
Correct Answer: B. -30 to +90 degrees
Rationale: The normal QRS axis in adults ranges from -30 to +90 degrees. A left axis deviation is -30 to -
90 degrees, often seen with left anterior fascicular block or inferior MI. A right axis deviation is +90 to
+180 degrees, seen with right ventricular hypertrophy or left posterior fascicular block. An extreme axis
deviation (+180 to -90) suggests complex conduction abnormalities.
14. Which of the following is a characteristic ECG finding of left bundle branch block (LBBB)?
A. QRS duration less than 120 ms with rSR' pattern in V1
B. Broad notched or slurred R wave in leads I, aVL, V5-V6 and broad QS in V1-V2
C. Right axis deviation with tall R waves in V1
D. Normal QRS duration with ST depression in lateral leads
Correct Answer: B. Broad notched or slurred R wave in leads I, aVL, V5-V6 and broad QS in
V1-V2
Rationale: LBBB is characterized by QRS duration ≥120 ms (usually >140 ms), a broad notched or
slurred R wave in lateral leads (I, aVL, V5-V6), and broad QS or rS in V1-V2. There is associated ST-T wave
discordance. Option A describes right bundle branch block (rSR' in V1). Option C (right axis deviation with
tall R in V1) suggests RVH or RBBB. Option D is not characteristic of LBBB.
15. Afterdepolarizations that occur during phase 2 or phase 3 of the action potential are
classified as:
A. Delayed afterdepolarizations (DADs)
B. Early afterdepolarizations (EADs)
C. Triggered activity
D. Reentry
Correct Answer: B. Early afterdepolarizations (EADs)
Rationale: Early afterdepolarizations (EADs) occur during phases 2 and 3 of the action potential,
typically when the action potential duration is prolonged (e.g., LQTS). They are triggered by conditions
that slow repolarization. DADs (A) occur during phase 4, after full repolarization, often due to calcium
overload. Both can lead to triggered activity (C), which is the mechanism, not the classification of the
afterdepolarization itself. Reentry (D) is a separate mechanism.
16. The coronary sinus receives venous drainage from which cardiac structure?
A. Right ventricle only
B. Left ventricle only
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