A 20-year-old man is brought to the emergency department 20 minutes after collapsing while playing basketball. There is no personal or family history of serious illness. On arrival, there is no palpable pulse and no respiratory effort is seen. Blood pressure is 125/75 mm Hg and pulse is 55/min. Echocardiography shows interventricular septal hypertrophy and increased left ventricular mass. The patient is started on high-dose beta blocker therapy. On follow-up 2 weeks later, he reports significant improvement in his shortness of breath. Physical examination reveals no murmurs supine or with Valsalva. Which of the following best accounts for improvement of this patient's symptoms?

Question

A 20-year-old man is brought to the emergency department 20 minutes after collapsing while playing basketball. There is no personal or family history of serious illness. On arrival, there is no palpable pulse and no respiratory effort is seen.  Blood pressure is 125/75 mm Hg and pulse is 55/min.  Echocardiography shows interventricular septal hypertrophy and increased left ventricular mass.  The patient is started on high-dose beta blocker therapy.  On follow-up 2 weeks later, he reports significant improvement in his shortness of breath.  Physical examination reveals no murmurs supine or with Valsalva.  Which of the following best accounts for improvement of this patient's symptoms?

Quizplus · Accepted Answer

Eductional Objective: Many patients with hypertrophic cardiomyopathy have exercise intolerance due to left ventricular (LV) outflow tract obstruction.  This outflow obstruction is worsened by decreased LV blood volume.  Beta blockers decrease heart rate and LV contractility to increase LV blood volume, reduce LV outflow tract obstruction, and improve symptoms.

A 20-Year-Old Man Is Brought to the Emergency Department 20