Overview
M1 and T1 are the mitral and tricuspid components of S1. Normal separation is brief; the RBBB example delays T1 and widens it. S1 is not given the prominent respiratory variation of S2.
Normal S2 separates on inspiration and narrows on expiration. RBBB or pulmonary stenosis can widen it; a large ASD gives relatively fixed splitting. Delayed left-sided closure in LBBB, RV pacing or sufficiently severe LV outflow obstruction can reverse the order to P2 then A2.
The selected ECG conduction variant is used. Hover or touch the sound strip for the components, interval and explanation. End inspiration and end expiration compare the same teaching beat. Numerical intervals are illustrative, and findings are not universal. Controlled ventilation retains reference splitting.