Let us focus on the heart sounds at the upper left sternal edge and listen together using the diaphragm of the stethoscope while we observe respiration. [Cut-away]
We learned a tremendous amount of information by focusing and tuning in on the heart sounds at the upper left sternal edge, particularly the behavior of the second heart sound. The second heart sounds were widely split. What do we think when we hear wide splitting of the second heart sound? such things as right bundle branch block with slower activation of the right ventricle and, therefore, some delay in pulmonary closure. And, if it is not an electrical delay, could it be a mechanical delay, such as it might be seen on the right side with pulmonary stenosis or a shunt lesion. But in our case, it was not only disely split, it was fixed split, and that is characteristic of an atrial septal defect.
Heart sounds oscilloscope
By viewing an oscilloscopic image and simultaneously listening, we can further appreciate these auscultatory events.
Fixed splitting
The two components of the second heart sound are widely split. They are also fixed, meaning that respiration does not alter the splitting interval. Fixed splitting of the second heart sound typically occurs in patients with an atrial septal defect, because high volume flow into the pulmonary arterial bed maximizes pulmonary arterial compliance, negating the usual effect of respiration. Before one can confirm that there is fixed splitting of the second heart sound, auscultation should be performed with the patient sitting and standing. In the absence of an atrial septal defect, these maneuvers decrease venous return and tend to bring the two components of the second heart sound closer together.
Wide persistent splitting
Wide inspiratory splitting of the second heart sound with persistent expiratory splitting may be confused with fixed splitting. It typically occurs when pulmonary closure is delayed. This could be due to an electrical delay, as with right bundle branch block or a mechanical delay, as with pulmonary stenosis. An additional cause relates to an inspiratory increase in pulmonary vascular capacitance that allows the pulmonary arteries to receive a greater volume of blood during inspiration, resulting in an inertial delay of the pulmonary second sound. Normal children and young adults may have persistence of expiratory splitting when supine, but this typically disappears when they sit or stand.