USMLE Step 3 - Question 7

An 18 year old male with no significant past medical history presents to his primary care physician for a routine physical examination. He has no physical complaints. His blood pressure is 115/85, heart rate 80, respirations 12, and he is afebrile. His physical examination reveals normal lung sounds, a V/VI holosystolic murmur with a thrill at the left lower sternal border and no change in intensity with inspiration, no gallops or extra heart sounds, and normal jugular venous pressures. His ECG and laboratory studies are normal. What is his most likely diagnosis?

A. Mitral regurgitation

B. Atrial septal defect

C. Tricuspid regurgitation

D. Ventricular septal defect

There are only 3 causes of holosystolic murmurs: mitral regurgitation, tricuspid regurgitation, and a ventricular septal defect. A small ventricular septal defect is quite benign and can cause a very loud holosystolic murmur with a thrill. Think of a putting your thumb over water coming out of a hose causing it to spray at high velocity (causing turbulence and a loud murmur) versus not putting your thumb over the hose (causing little turbulence and a soft murmur). Due to the loud murmur, a small VSD is frequently mistaken for significant pathology. VSD closure is indicated for patients with symptoms or with a shunt fraction (aka Qp/Qs or ratio of flow through the pulmonic valve to that through the aortic valve) of 1.5:1 or greater.

In a patient with mitral regurgitation you would expect to hear a click of mitral valve prolapse present or for there to be a history of other heart disease which may cause mitral regurgitation (such as a previous inferior wall myocardial infarction). The murmur is typically located at the cardiac apex and not the left lower sternal border. Symptoms of congestive heart failure may also be present.

While the murmur of tricuspid regurgitation is heard best at the left lower sternal border similar to a VSD, it should get louder with inspiration (Carvallo's sign). Also, tricuspid regurgitation would result in significant "V waves" in the jugular venous pulsation due to backward flow from the right ventricle into the jugular vein with each heart beat. Finally, it would be very rare for isolated tricuspid regurgitation to occur in a young otherwise healthy person.

The murmur of a patent ductus arteriosus is a continuous "machinary" murmur last is in both systole and diastole (since the systolic and diastolic pressure in the aorta is always higher than the systolic and diastolic pressure in the pulmonary artery causing continuous flow).