AF Anatomy & Physiology Fundamentals 3

Question 1

During atrial fibrillation, the ventricular rate is irregular primarily because of which property of the AV node?

Accepted Answer

Concealed conduction causing variable refractoriness

Answer

Multiple atrial impulses penetrate the AV node to varying depths (concealed conduction), leaving it in varying states of refractoriness and producing an irregular ventricular response.

Question 2

The 'atrial kick' contributes approximately what percentage of ventricular filling under normal sinus rhythm?

Accepted Answer

15–30%

Answer

Active atrial contraction contributes roughly 15–30% of ventricular end-diastolic volume, a contribution lost during AF.

Question 3

Which ion channel is primarily responsible for the plateau (phase 2) of the cardiac action potential in ventricular cardiomyocytes?

Accepted Answer

L-type calcium (Cav1.2)

Answer

L-type calcium channels carry the slow inward Ca²⁺ current that sustains the plateau phase and triggers excitation-contraction coupling.

Question 4

The crista terminalis in the right atrium is clinically significant in AF because it:

Accepted Answer

Represents a zone of anisotropic conduction that can anchor reentrant circuits

Answer

The crista terminalis is a muscular ridge with marked anisotropy (directional conduction differences) that can serve as a line of functional block anchoring atrial flutter and AF circuits.

Question 5

Increased intracellular calcium overload in atrial myocytes during rapid firing can cause spontaneous depolarizations via which mechanism?

Accepted Answer

Delayed afterdepolarizations through NCX forward mode

Answer

Calcium overload causes spontaneous sarcoplasmic reticulum Ca²⁺ release, which is extruded by the Na⁺/Ca²⁺ exchanger (NCX) in forward mode, generating a transient inward current and delayed afterdepolarizations.

(AF) Atrial Fibrillation Certification Practice Test

(AF) Atrial Fibrillation Certification Practice Test

AF Anatomy & Physiology Fundamentals 3