THE MERCK MANUAL: The Merck Manual of Diagnosis and Therapymultimedia

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  • Cardiovascular Examination
  • Split 2nd Heart Sound in Left Bundle Branch Block

    Sound is that of paradoxical splitting, ie, S1-P2-A2 at rest (“out”) and S1-S2 with inspiration (“in”). Left bundle branch block delays aortic valve closure, so that split is audible at rest; inspiration decreases intrathoracic pressure, drawing more blood into the right ventricle and postponing pulmonic valve closure until it is superimposed on A2 and splitting becomes inaudible.

    Recording provided by Jules Constant, MD.