A 40-year-old man is brought to the emergency department due to sudden onset palpitation and chest discomfort. He has no prior medical conditions and takes no mediations. Chest examination reveals no murmurs and the lungs are clear on auscultation. ECG reveals a heart rate of 126/min with an irregularly irregular rhythm, narrow QRS complexes, and no organized P waves. Which of the following physiologic factors most likely determines the ventricular contraction rate in this patient?

Question

A 40-year-old man is brought to the emergency department due to sudden onset palpitation and chest discomfort. He has no prior medical conditions and takes no mediations. Chest examination reveals no murmurs and the lungs are clear on auscultation. ECG reveals a heart rate of 126/min with an irregularly irregular rhythm, narrow QRS complexes, and no organized P waves.  Which of the following physiologic factors most likely determines the ventricular contraction rate in this patient?

Quizplus · Accepted Answer

Eductional Objective: The atrioventricular node refractory period regulates the number of atrial impulses that reach the ventricles and determines the ventricular contraction rate in conditions where the atria undergo rapid depolarization. Ventricular response in atrial fibrillation is dependent on the transmission rate of abnormal atrial impulses through the atrioventricular (AV) node. Each time the AV node is excited, it enters a refractory period during which additional atrial impulses cannot be transmitted to the ventricles; consequently, the majority of atrial impulses never reach the ventricles

A 40-Year-Old Man Is Brought to the Emergency Department Due