What pathology is indicated by reverse splitting of the S2 heart sound during expiration?

Reverse splitting of the S2 heart sound during expiration indicates a specific timing issue with the closure of the aortic and pulmonic valves. Normally, the second heart sound (S2) is composed of two components: the closure of the aortic valve (A2) followed by the closure of the pulmonic valve (P2). During normal respiration, this sound typically splits due to variations in intrathoracic pressure that allow more blood to flow into the right side of the heart during inspiration.

When reverse splitting occurs, it suggests a specific scenario where the aortic valve closes before the pulmonic valve during expiration, which is often a result of conduction abnormalities in the heart, such as those caused by a ventricular pacemaker. A pacemaker bypasses the normal conduction pathways, which can lead to changes in the temporal relationships of heart sounds, especially S2.

This situation is distinct from valvular stenosis, aortic regurgitation, or bradycardia, as those conditions typically exhibit different heart sound characteristics and may not specifically lead to reverse splitting during expiration. Thus, the presence of reverse splitting in this context is most indicative of conduction issues commonly associated with a ventricular pacemaker.