DC Dysrhythmia Pathophysiology & Electrophysiology 2 — Questions and Answers
Question 1: Which arrhythmia mechanism involves an impulse reentering previously depolarized tissue through an alternative pathway?
- Triggered activity from afterdepolarizations
- Reentry via a circular conduction circuit (Correct answer)
- Enhanced automaticity of an ectopic focus
- Abnormal phase 4 depolarization
Correct answer: Reentry via a circular conduction circuit
Reentry occurs when an impulse reenters depolarized tissue through an alternative pathway before full repolarization, creating a self-sustaining circular electrical circuit responsible for many tachyarrhythmias.
Question 2: Why is the peak of the T wave considered the 'vulnerable period' of the cardiac cycle?
- The AV node is completely refractory during this time
- Ventricular repolarization is inhomogeneous, making the heart susceptible to VF induction (Correct answer)
- All ventricular cells are simultaneously depolarized
- Ischemia is most likely to manifest during this phase
Correct answer: Ventricular repolarization is inhomogeneous, making the heart susceptible to VF induction
During the T wave peak, ventricular repolarization is uneven across myocardial cells, creating dispersion of refractoriness that makes the heart highly susceptible to R-on-T phenomenon triggering VF.
Question 3: Which ion is primarily responsible for the rapid depolarization phase (phase 0) of the ventricular action potential?
- Potassium (K+) efflux
- Calcium (Ca2+) influx
- Sodium (Na+) influx (Correct answer)
- Chloride (Cl-) influx
Correct answer: Sodium (Na+) influx
Phase 0 (rapid depolarization) of the ventricular action potential is driven by the rapid influx of sodium ions through fast voltage-gated sodium channels, producing the steep upstroke.
Question 4: Which arrhythmia most directly results from enhanced automaticity in an ectopic focus?
- Atrial flutter sustained by macroreentry
- Premature ventricular contractions originating from an irritable focus (Correct answer)
- Second-degree AV block from structural disease
- Sinus bradycardia induced by vagal stimulation
Correct answer: Premature ventricular contractions originating from an irritable focus
Enhanced automaticity occurs when ectopic foci outside the SA node develop an abnormally accelerated spontaneous depolarization rate, generating premature beats or sustained tachyarrhythmias.
Question 5: What is the primary electrophysiologic mechanism underlying Wolff-Parkinson-White (WPW) syndrome tachycardia?
- Enhanced SA node automaticity
- Triggered activity from early afterdepolarizations
- Reentry using an accessory pathway (Bundle of Kent) (Correct answer)
- Abnormal slow pathway conduction within the AV node
Correct answer: Reentry using an accessory pathway (Bundle of Kent)
WPW tachycardia is caused by reentrant conduction using an accessory pathway (Bundle of Kent) that bypasses the AV node, creating an atrioventricular circuit capable of sustaining rapid tachycardia.
Question 6: Which electrophysiologic property describes the inability of cardiac cells to respond to a new stimulus immediately after depolarization?
- Automaticity
- Conductivity
- Refractoriness (Correct answer)
- Excitability
Correct answer: Refractoriness
Refractoriness is the post-depolarization period during which cardiac cells cannot respond (absolute refractory period) or require a stronger-than-normal stimulus to respond (relative refractory period).
DC Dysrhythmia Pathophysiology & Electrophysiology 2
Which arrhythmia mechanism involves an impulse reentering previously depolarized tissue through an alternative pathway?