We shall now further evaluate our patient's auscultation at the upper left sternal edge. There is a normal S1 followed by a systolic ejection murmur. The murmur begins after S1 and builds rapidly to a peak, it then gradually decreases in intensity ending in S2. Note that S2 is single and of normal intensity, suggesting an inaudible pulmonary component, as may occur with some forms of severe right ventricular outflow tract obstruction resulting in abnormally low pulmonary artery pressure. [Sounds]
Graphic
By viewing a graphic image and simultaneously listening, we can further appreciate these auscultatory events. The second heart sound remains both single and of normal intensity throughout the respiratory cycle. The pulmonary component, illustrated by the dotted line, is delayed but not audible, because of its low intensity.
Differential diagnosis
Differential diagnosis of a single second heart sound at the upper left sternal edge includes both simultaneous occurrence of the two components and inability to hear one of the two components because it is either absent or too soft to hear.
Simultaneous A2 and P2
Simultaneous occurrence of the aortic and pulmonic heart sounds with no detectable respiratory variation may result from delay of the aortic component, as in aortic stenosis. In this case, normal inspiratory delay of the pulmonic component is too short to result in audible splitting. Conversely, the pulmonic component may occur earlier than normal and may not delay significantly with inspiration. This can happen with pulmonary hypertension. In either case, the combined, audible single second sound is significantly louder than normal.