Arrhythmia Recognition, Anatomy, and Physiology Flashcards

The cardiac action potential plateau phase (Phase 2) is maintained primarily by which ion current?

Answer: Slow inward calcium current (ICa-L)

Phase 2 of the ventricular action potential is sustained by the slow inward L-type calcium current, which balances potassium efflux and maintains the membrane potential near zero for an extended period.

Which ECG finding is expected during the absolute refractory period of the cardiac cycle?

Answer: No cardiac stimulus can produce a new action potential — corresponds to the QRS complex through early T wave

During the absolute refractory period (QRS through mid-T wave), cardiac cells are completely depolarized and cannot respond to any stimulus regardless of its strength.

Which ion primarily responsible for Phase 3 (rapid repolarization) of the ventricular action potential?

Answer: Potassium efflux through IKr and IKs channels

Phase 3 rapid repolarization is driven by potassium efflux through the delayed rectifier potassium channels (IKr and IKs), restoring the negative resting membrane potential.

Automaticity in pacemaker cells is generated by which mechanism?

Answer: Spontaneous slow diastolic depolarization (Phase 4) driven by the If funny current

Pacemaker cell automaticity results from Phase 4 spontaneous diastolic depolarization — a slow inward current (If, the funny current) that progressively depolarizes the cell toward threshold during diastole.

A reentrant arrhythmia requires which three conditions to be established and maintained?

Answer: A closed circuit pathway, unidirectional block in one limb, and slow conduction in the other limb allowing recovery

Reentry requires an anatomical or functional circuit with two pathways, unidirectional block in one pathway (impulse cannot go forward but can conduct backward), and slow enough conduction in the alternate pathway that the blocked pathway recovers and can be re-excited.

The atrioventricular node (AV node) is located in which part of the heart?

Answer: Posteroinferior right atrium at the junction with the interventricular septum (Koch's triangle)

The AV node lies in the posteroinferior right atrium, within Koch's triangle — bounded by the tricuspid annulus, tendon of Todaro, and the coronary sinus ostium.