A mechanism of a cardiac murmur with respiratory variation in a patient with straight back syndrome

Abstract A 20-year-old male without any symptoms was referred for heart murmur on a medical examination. A thrill was palpable at the upper left sternal border. His cardiac murmur showed respiratory variation. The systolic murmur was louder (Levine grade IV/VI) during expiration and diminished during inspiration (Levine grade I/VI). He was thin and had a narrow thoracic cage in the anteroposterior direction due to straight back syndrome (SBS). An echocardiogram and a right ventriculogram showed changes in the diameter of the right ventricular outflow tract (RVOT) on respiration. During expiration, the RVOT was compressed and narrow, while it was expanded during inspiration. Cardiac catheterization demonstrated a 10-mmHg of pressure gradient across the RVOT during expiration but no pressure gradient during inspiration. Thus, respiratory compression to the RVOT by a narrow thoracic cage due to SBS was the cause of the cardiac murmur with respiratory alterations. Our case highlights the importance of physical examination, including an inspection of the patient’s physique.