QCM : Cardiac Electrical Physiology and Arrhythmias — 10 questions

Questions et réponses du QCM

1. What is the conduction pathway in the heart?

The physical anatomical route of the electrical wiring within the heart tissue.
The pathway through which blood flows during cardiac contraction.
The sequence of electrical activation that ensures coordinated contraction of the heart muscle.
The sequence of mechanical events leading to heart muscle contraction.

The sequence of electrical activation that ensures coordinated contraction of the heart muscle.

Explication

The conduction pathway is the sequence of electrical activation in the heart that ensures coordinated contraction, starting from the SA node and passing through atria, AV node, bundle of His, bundle branches, and Purkinje fibers.

2. Which structure acts as the heart's natural pacemaker and initiates electrical impulses?

Atrial Conduction System
SA Node
AV Node
Purkinje Fibers

SA Node

Explication

The SA Node, or sinoatrial node, is the primary pacemaker of the heart, setting the rhythm by initiating electrical impulses. The other options play roles in conduction but do not originate the impulse.

3. During which ionic movement does Phase 0 of the cardiac action potential primarily occur?

Efflux of potassium ions through delayed rectifier channels
Efflux of chloride ions through chloride channels
Influx of calcium ions through L-type calcium channels
Influx of sodium ions through fast sodium channels

Influx of sodium ions through fast sodium channels

Explication

Phase 0 of the cardiac action potential is characterized by a rapid influx of sodium ions through fast sodium channels, leading to depolarisation. This is the primary ionic event during this phase, making it the correct answer. The other options refer to ionic movements that occur during different phases: calcium influx during Phase 2 (plateau), potassium efflux during Phase 3 (repolarisation), and chloride channels are not the main contributors to Phase 0.

4. What is the primary function of the AV node in cardiac conduction?

Fire electrical impulses rapidly to ventricles
Delay conduction to allow atrial contraction
Generate pacemaker activity
Distribute impulses to the Purkinje fibers

Delay conduction to allow atrial contraction

Explication

The AV node delays the electrical impulses from the atria to the ventricles, ensuring atrial contraction occurs prior to ventricular contraction for efficient cardiac function.

5. What is the primary role of refractory periods in cardiac electrophysiology?

To initiate action potentials in cardiac cells
To coordinate atrial and ventricular contractions
To prevent re-entry circuits and abnormal rhythms
To generate the heart's pacemaker activity

To prevent re-entry circuits and abnormal rhythms

Explication

Refractory periods serve to prevent re-entry circuits and abnormal rhythms by ensuring that cardiac cells cannot be re-excited immediately after depolarisation, thus maintaining a coordinated and rhythmic heartbeat.

6. Which phase of the cardiac action potential is characterized by rapid Na⁺ influx?

Phase 0: Depolarisation
Phase 2: Plateau
Phase 3: Repolarisation
Phase 4: Resting potential

Phase 0: Depolarisation

Explication

Phase 0 involves rapid Na⁺ entry through fast sodium channels, causing rapid depolarisation of the cardiac cell membrane.

7. How do the conduction speeds vary across the cardiac conduction pathway?

Slow in the His-Purkinje system and fast in the atria
Fast in atria and ventricles, slow in AV node
Slow in atria, very slow in AV node, very fast in His-Purkinje system
Constant throughout the pathway

Slow in atria, very slow in AV node, very fast in His-Purkinje system

Explication

The conduction speed is slow in the atria, very slow at the AV node to allow filling, and very fast in the His-Purkinje system for synchronised ventricular contraction.

8. What is the significance of the AV delay in cardiac conduction?

Prevents atrial contraction
Allows ventricles to fill after atrial contraction
Initiates ventricular depolarisation
Speeds up overall conduction velocity

Allows ventricles to fill after atrial contraction

Explication

The AV delay permits the atria to contract and empty blood into the ventricles before the ventricles contract, optimizing cardiac efficiency.

9. Which ion movement sustains the plateau phase during the cardiac action potential?

Na⁺ influx
K⁺ efflux
Ca²⁺ influx
Cl⁻ influx

Ca²⁺ influx

Explication

The plateau phase is mainly maintained by the influx of Ca²⁺ via L-type calcium channels, balancing K⁺ efflux and prolonging depolarisation.

10. Which structure rapidly distributes impulses throughout the ventricles, causing synchronized contraction?

SA Node
Bundle of His
Purkinje fibers
Atrial myocardium

Purkinje fibers

Explication

Purkinje fibers form a network that rapidly conducts electrical impulses, ensuring the ventricles contract in a coordinated manner for effective pumping.

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Refractory periods — purpose?

Prevent premature contractions and re-entry arrhythmias.

Conduction pathway order?

SA node, atria, AV node, bundle of His, bundle branches, Purkinje fibers, ventricles.

Conduction pathway — sequence?

SA node → atria → AV node → Bundle of His → bundle branches → Purkinje fibers.

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