Arrhythmia Recognition, Anatomy, and Physiology Flashcards

Triggered activity as a mechanism of arrhythmia is caused by which electrophysiological phenomenon?

Answer: Afterdepolarizations (early or delayed) that reach threshold and trigger additional action potentials

Triggered activity results from afterdepolarizations — oscillations in membrane potential that occur during (early afterdepolarizations, EADs) or after (delayed afterdepolarizations, DADs) repolarization and can trigger additional action potentials.

The gap junctions in cardiac muscle (intercalated discs) serve which primary electrical function?

Answer: Allowing direct electrical coupling between adjacent cells for rapid propagation of action potentials

Gap junctions (connexins) in intercalated discs create low-resistance electrical connections between cardiac cells, allowing action potentials to propagate rapidly from cell to cell — making the heart function as an electrical syncytium.

Which anatomical structure separates the atrial and ventricular conduction systems, making the AV node the only normal electrical connection between them?

Answer: The fibrous cardiac skeleton (annulus fibrosus)

The fibrous cardiac skeleton electrically insulates the atria from the ventricles, making the AV node and bundle of His the only normal pathway for electrical conduction — accessory pathways in WPW breach this insulation.

The His-Purkinje system conducts at a significantly faster velocity than the AV node. What is the approximate conduction velocity in Purkinje fibers?

Answer: 2-4 m/sec (up to 4 m/sec)

Purkinje fibers conduct action potentials at 2-4 m/sec — among the fastest conduction velocities in the heart — enabling nearly simultaneous activation of both ventricles for synchronous contraction.

In the autonomic nervous system, vagal (parasympathetic) stimulation affects the heart primarily through which neurotransmitter and receptor?

Answer: Acetylcholine acting on M2 muscarinic receptors in the SA and AV nodes

Parasympathetic (vagal) fibers release acetylcholine, which binds M2 muscarinic receptors on SA and AV nodal cells, slowing the heart rate and prolonging AV nodal conduction via potassium channel activation.

Which concept explains why the SA node normally suppresses potential pacemaker activity in the AV node and His-Purkinje system?

Answer: Overdrive suppression — faster pacemakers suppress slower ones by repeatedly resetting their Phase 4 depolarization

Overdrive suppression occurs when a faster pacemaker (SA node) continuously depolarizes slower potential pacemakers before they reach threshold, accumulating intracellular sodium and activating the Na-K ATPase pump, which hyperpolarizes and suppresses their spontaneous activity.