An 18-year-old man is evaluated for a murmur detected during a college sports physical examination. He reports no symptoms and has no history of cardiac disease. He takes no medications.
On physical examination, vital signs are normal. He has a normal central venous pressure, waveform, precordial palpation, and S1. A continuous murmur is heard beneath the left clavicle that envelops the S2. The remainder of the examination is unremarkable.
Which of the following is the most likely cause of this patient's murmur?
A. Bicuspid aortic valve with aortic regurgitation
B. Patent ductus arteriosus
C. Pulmonary regurgitation
D. Ventricular septal defect
MKSAP Answer and Critique
The correct answer is B. Patent ductus arteriosus. This content is available to MKSAP 18 subscribers as Question 12 in the Cardiovascular Medicine section. More information about MKSAP is available online.
This patient has a patent ductus arteriosus (PDA). A continuous murmur heard beneath the left clavicle that envelops the S2 is typical of a PDA; it is often described as a “machinery” murmur. A tiny PDA is generally asymptomatic with an inaudible murmur. Patients with a small PDA may have an audible murmur but no other cardiovascular features. Patients with a moderate-sized PDA may have bounding pulses, a wide pulse pressure, left heart enlargement and dysfunction, and clinical heart failure. A large PDA may present with pulmonary hypertension and shunt reversal (Eisenmenger syndrome) in adults.
Aortic regurgitation due to a bicuspid aortic valve causes a diastolic murmur, most commonly heard along the left sternal border. A brief systolic murmur is also commonly heard at the second right intercostal space, from increased flow across the bicuspid aortic valve. A systolic ejection click is often heard in patients with bicuspid aortic valve, but a continuous murmur that envelops the S2 is not expected.
Pulmonary regurgitation occurs most commonly after balloon or surgical intervention for congenital pulmonary stenosis. It is characterized by a diastolic murmur heard along the left sternal border that increases with inspiration; a systolic ejection murmur is also commonly heard from increased flow across the pulmonary valve. Although the pulmonary component of S2 may be reduced or absent in patients with pulmonary regurgitation, separation between systole and diastole is distinct, and the aortic component should be audible.
A small ventricular septal defect (VSD) presents with a loud holosystolic murmur located at the left sternal border that may obliterate the S2; a palpable thrill is often present. The pressure gradient between the ventricles determines the murmur quality and duration. A diastolic component of the murmur is not expected. Small VSDs do not cause left heart enlargement or pulmonary hypertension. Progressive pulmonary hypertension results in shortening of the murmur.
- Patients with a small patent ductus arteriosus may present with a continuous murmur beneath the left clavicle that envelops the S2 but no other cardiovascular features.