AF Anatomy & Physiology Fundamentals 2 — Questions and Answers
Question 1: Which layer of the heart wall contains the specialized conduction tissue responsible for impulse propagation?
- Epicardium
- Myocardium (Correct answer)
- Endocardium
- Pericardium
Correct answer: Myocardium
The myocardium contains both working cardiomyocytes and the specialized conduction fibers (Purkinje fibers) that propagate electrical impulses.
Question 2: The coronary sinus drains deoxygenated blood from the myocardium into which cardiac chamber?
- Right ventricle
- Left atrium
- Right atrium (Correct answer)
- Left ventricle
Correct answer: Right atrium
The coronary sinus empties deoxygenated blood from the coronary circulation directly into the right atrium.
Question 3: Which autonomic receptor type, when stimulated, slows the heart rate by increasing potassium conductance in SA nodal cells?
- Beta-1 adrenergic
- Alpha-1 adrenergic
- M2 muscarinic (Correct answer)
- M1 muscarinic
Correct answer: M2 muscarinic
M2 muscarinic receptors activate GIRK channels, increasing K+ outflow and hyperpolarizing SA nodal cells to slow the heart rate.
Question 4: The fibrous skeleton of the heart serves what primary function relevant to atrial fibrillation?
- Provides blood supply to the conduction system
- Electrically insulates the atria from the ventricles (Correct answer)
- Anchors the coronary arteries
- Generates the resting membrane potential
Correct answer: Electrically insulates the atria from the ventricles
The fibrous skeleton acts as an electrical barrier, ensuring atrial impulses can only reach the ventricles through the AV node.
Question 5: Stretch of atrial myocytes due to increased filling pressure promotes AF through which mechanism?
- Shortening of atrial effective refractory period (Correct answer)
- Prolongation of PR interval
- Increased AV nodal conduction velocity
- Decreased sympathetic tone
Correct answer: Shortening of atrial effective refractory period
Mechanical stretch activates stretch-sensitive ion channels that shorten the atrial effective refractory period, promoting reentrant circuits.
Question 6: What is the primary pacemaker role of the interatrial septum in atrial fibrillation initiation?
- It acts as a dominant ectopic focus
- It contains preferential conduction tracts (Bachmann's bundle) that can propagate abnormal impulses (Correct answer)
- It prevents electrical conduction between atria
- It generates high-frequency fibrillatory waves
Correct answer: It contains preferential conduction tracts (Bachmann's bundle) that can propagate abnormal impulses
Bachmann's bundle runs through the interatrial septum and serves as the primary interatrial conduction pathway, so abnormal impulses can rapidly spread between atria.
Question 7: Which anatomical feature of the left atrium makes it the most common site of AF-triggering ectopic foci?
- Thick trabeculated walls
- Sleeves of myocardial tissue extending into the pulmonary veins (Correct answer)
- Direct connection to the coronary sinus
- Presence of the fossa ovalis
Correct answer: Sleeves of myocardial tissue extending into the pulmonary veins
Myocardial sleeves extending into the pulmonary veins exhibit automaticity and triggered activity, making them the predominant source of AF-initiating ectopic beats.
AF Anatomy & Physiology Fundamentals 2
Which layer of the heart wall contains the specialized conduction tissue responsible for impulse propagation?