A 19-year old woman presents to the clinic for a yearly physical examination. Her past medical history is unremarkable, and she does not take any medications. On physical examination, an S2 split is heard while auscultating over the pulmonic valve. The first sound in the split is louder than the second. The split persists on inspiration and expiration. The duration of the split is the same on both inspiration and expiration.
Which of the following is the most likely cause of this patient’s physical exam findings?
B) Atrial septal defect
An atrial septal defect (ASD) creates a path for blood to flow from the high pressure left atrium to the lower pressure right atrium. During expiration, the reduction in pressure in the right atrium allows more blood to flow through the ASD, causing a delay in the closure of the pulmonic valve and leading to a fixed splitting of the S2 sound.
Answer choice A: Aortic stenosis,is incorrect. Aortic stenosis would delay the closing of the aortic valve, causing a paradoxical split. In the vignette, auscultation of the pulmonic valve revealed that A2 was still before P2.
Answer choice C; Hypertrophic obstructive cardiomyopathy (HOCM), is incorrect. HOCM also would delay the closing of the aortic valve, causing a paradoxical split. In the vignette, auscultation of the pulmonic valve revealed that A2 was still before P2.
Answer choice D: Mitral regurgitation, is incorrect. Mitral regurgitation would cause a widened S2 split as a result of early closure of the aortic valve. In the vignette, auscultation revealed the same length of splitting on inspiration and expiration.
Answer choice E: Right bundle branch block (RBBB), is incorrect. RBBB would cause a widened S2 split as a result of a delay in pulmonic valve closure. In the vignette, auscultation of the pulmonic valve revealed the same length of splitting on inspiration and expiration.
Key Learning Point
A fixed splitting of the S2 heart sound is indicative of atrial septal defect.
