Sinus Rhythm Interpretation Flashcards

Sinoatrial (SA) exit block type II is distinguished from sinus arrest by which feature?

Answer: SA exit block produces pauses that are exact multiples of the basic P-P cycle length

In sinoatrial exit block type II, the SA node fires normally but the impulse fails to exit to the atria — the resulting pause is an exact multiple (2x, 3x) of the basic P-P interval, confirming the SA node was still cycling.

Sinus node dysfunction presenting with alternating bradycardia and tachycardia (typically AFib with rapid ventricular response alternating with sinus pauses) is called what syndrome?

Answer: Sick sinus syndrome (bradycardia-tachycardia syndrome)

Bradycardia-tachycardia syndrome is a subset of sick sinus syndrome where atrial tachyarrhythmias (often AFib) alternate with periods of profound sinus bradycardia or sinus pauses.

Which physiological mechanism causes increased sinus rate during exercise?

Answer: Sympathetic nervous system activation releasing norepinephrine which increases SA node automaticity

Exercise activates the sympathetic nervous system, releasing catecholamines (norepinephrine, epinephrine) that bind beta-1 adrenergic receptors on SA node cells, increasing the rate of spontaneous diastolic depolarization and thus heart rate.

Which respiratory pattern produces the most pronounced sinus arrhythmia?

Answer: Slow, deep breathing

Slow, deep breathing produces the most pronounced sinus arrhythmia because larger tidal volumes create greater changes in intrathoracic pressure and more significant vagal modulation with each respiratory cycle.

A patient's ECG shows a P wave in every beat, upright in lead II, with a constant PR interval of 220 ms and a rate of 72 bpm. What is the correct interpretation?

Answer: Normal sinus rhythm with first-degree AV block

Rate is 72 bpm (normal sinus range), P waves are upright in II (sinus origin), and PR interval is 220 ms — above the 200 ms upper limit — indicating first-degree AV block superimposed on otherwise normal sinus rhythm.

Hyperthyroidism most commonly affects sinus rhythm by causing which finding?

Answer: Sinus tachycardia or atrial fibrillation

Excess thyroid hormone increases adrenergic sensitivity and cardiac automaticity, most commonly producing sinus tachycardia and, in severe cases, atrial fibrillation.