A 28-year-old professional endurance athlete comes to the office after his team physician detected a heart murmur. The patient has no symptoms and has no exercise limitations. Medical history is nonsignificant. Blood pressure is 110/66 mm Hg and pulse is 54/min. Physical examination shows a soft systolic murmur best heard at the left second intercostal space in the supine position. The murmur disappears when the patient is upright but reappears after brief exercise. Which of the following cardiovascular adaptations best explains this patient's finding?

Question

A 28-year-old professional endurance athlete comes to the office after his team physician detected a heart murmur.  The patient has no symptoms and has no exercise limitations.  Medical history is nonsignificant.  Blood pressure is 110/66 mm Hg and pulse is 54/min.  Physical examination shows a soft systolic murmur best heard at the left second intercostal space in the supine position.  The murmur disappears when the patient is upright but reappears after brief exercise.  Which of the following cardiovascular adaptations best explains this patient's finding?

Quizplus · Accepted Answer

11ec160b_3ca0_43ba_9249_e5ee974c02e6_MD0001_00 This professional athlete most likely has the cardiovascular adaptations of athlete's heart. The soft systolic murmur likely represents a pulmonic flow murmur, a common finding due to the high stroke volume that develops with intensive endurance training. The adaptations of athlete's heart differ depending on whether intensive endurance training (eg, long-distance running) or resistance training (eg, heavy weightlifting) is pursued. With endurance training, systemic vascular resistance (SVR) is reduced (due to vasodilation in skeletal muscle) and blood volume is increased, leading to increased left ventricular (LV) volume load. To compensate, LV eccentric hypertrophy (ie, LV wall lengthening) develops, which increases LV cavity size to increase diastolic filling capacity and facilitate increased stroke volume and cardiac output. Right ventricular (RV) cavity enlargement also takes place to increase diastolic filling and accommodate the increase in cardiac output; because the right ventricle and left ventricle are arranged in series and contract at the same rate, RV stroke volume must increase to match LV stroke volume and prevent backup of blood flow. An increase in stroke volume is maintained at rest and allows for adequate cardiac output at low resting heart rate (eg, <55/min). The anterior location of the pulmonic valve and slightly smaller valve area compared to the aortic valve often create a pulmonic flow murmur due to the high stroke volume. The murmur is best heard at the left second intercostal space in the supine position and may disappear when venous return is decreased with standing. (Choice A) Pulmonary vascular capacitance is increased with endurance training, allowing the pulmonary circulation to accommodate high flow while minimizing the afterload on the right ventricle. (Choice B) Baseline vagal tone is increased with endurance training, facilitating low resting heart rate. (Choices D and E) Intensive resistance training increases SVR during exercise (due to vascular compression by vigorously contracting muscles), which increases LV pressure load and leads to mild concentric hypertrophy (ie, LV wall thickening). Unlike pathologic concentric LV hypertrophy, the LV cavity remains normal in size and diastolic function is maintained. LV stroke volume and ejection fraction remain normal or are slightly increased, and the right ventricle is unaffected. A flow murmur is not expected. Educational objective: Intensive endurance training causes cavity enlargement of both the left ventricle and right ventricle to facilitate an increase in stroke volume and cardiac output. The high stroke volume may cause a pulmonic valve flow murmur. __________ References: Athlete's heart. (http://www.ncbi.nlm.nih.gov/pubmed/14617564)

A 28-Year-Old Professional Endurance Athlete Comes to the Office After