If an abnormal S2 sound on cardiac exam is detected, which of the following findings has the strongest evidence according to McGee (2022)?
The correct answer and explanation is:
Correct Answer: Widely split S2 that varies with inspiration
An abnormal second heart sound (S2) can provide crucial diagnostic clues in cardiac auscultation. According to McGee (2022), the widely split S2 that varies with inspiration has the strongest evidence among findings associated with abnormal S2 sounds. This specific auscultatory feature is most strongly linked to right bundle branch block (RBBB) and pulmonary stenosis, which delay right ventricular systole and therefore delay pulmonary valve closure.
The second heart sound (S2) is composed of two components: the aortic (A2) and pulmonary (P2) valve closures. Under normal conditions, inspiration delays P2 due to increased venous return, while A2 occurs earlier, leading to a physiological split of S2 during inspiration. When this split becomes wider and more pronounced with inspiration, it is described as a “wide and variable” split, which can signify delayed closure of the pulmonary valve.
The evidence for this finding is classified by McGee as having high specificity, especially when the split exceeds 40 milliseconds and clearly widens during inspiration. This makes it a reliable clue for identifying conduction delays or increased resistance in right ventricular outflow. The variability with respiration helps distinguish it from fixed splitting (seen in atrial septal defects) or paradoxical splitting (seen in conditions like left bundle branch block or aortic stenosis).
Importantly, this finding is best heard at the upper left sternal border using the diaphragm of the stethoscope during slow, deep breathing. McGee emphasizes auscultatory features that offer diagnostic utility and categorizes findings based on their likelihood ratios. A widely split S2 that varies with inspiration has one of the higher positive likelihood ratios for cardiac conditions related to right heart delays, reinforcing its clinical value.