IBHRE - International Board of Heart Rhythm Examiners Electrophysiology Principles Questions and Answers

Question 1

Which of the following conditions is essential for the initiation and maintenance of a re-entrant tachyarrhythmia?

Accepted Answer

A region of unidirectional conduction block.

Answer

Homogeneous conduction velocity throughout the myocardium.

Answer

A long refractory period relative to the conduction time around the circuit.

Answer

Enhanced automaticity in a focal group of cells.

Question 2

A 65-year-old patient is undergoing an electrophysiology study. Programmed electrical stimulation reveals that a premature impulse delivered during the last two-thirds of the T-wave on the surface ECG is able to initiate a ventricular tachyarrhythmia. This premature impulse most likely fell during which period of the ventricular action potential?

Accepted Answer

Relative Refractory Period (RRP)

Answer

Effective Refractory Period (ERP)

Answer

Absolute Refractory Period (ARP)

Answer

Supranormal Period

Question 3

The spontaneous Phase 4 depolarization characteristic of pacemaker cells in the sinoatrial (SA) node is primarily mediated by which ionic current?

Accepted Answer

Inward 'funny' current (If)

Answer

Inward fast sodium current (INa)

Answer

Inward L-type calcium current (ICa-L)

Answer

Outward potassium current (IKr)

Question 4

Anisotropy in cardiac tissue refers to the property where conduction velocity is dependent on the direction of wavefront propagation relative to the myocardial fiber orientation. In healthy ventricular tissue, conduction velocity is typically:

Accepted Answer

Fastest in the direction longitudinal (parallel) to the fiber orientation.

Answer

Fastest in the direction transverse (perpendicular) to the fiber orientation.

Answer

Equal in all directions, demonstrating isotropic conduction.

Answer

Slowest at the epicardial surface compared to the endocardium.

Question 5

During which phase of the ventricular myocyte action potential is the cell membrane absolutely refractory, meaning it cannot be depolarized to generate another action potential regardless of stimulus strength?

Accepted Answer

Phase 0, Phase 1, Phase 2, and the initial part of Phase 3

Answer

Phase 4

Answer

Phase 0, Phase 1, and the early part of Phase 2

Answer

The latter half of Phase 3

Question 6

A patient with a history of myocardial infarction develops a stable monomorphic ventricular tachycardia. The underlying mechanism is most likely a re-entrant circuit that has formed around the infarct scar. Which electrophysiologic property of the scar border zone is critical for sustaining this arrhythmia?

Accepted Answer

A zone of slow conduction

Answer

Enhanced automaticity

Answer

A shortened effective refractory period

Answer

Absence of anisotropic conduction