1. Why will a stenotic RV outflow tract or valve cause a delay of the P2?
ANS: In PS, RV pressure rises to a much higher level than does pulmonary artery pressure. Thus it takes an extra-long time for the RV pressure to drop to the closing pressure of the pulmonary artery valve. Also, RV pressure will have to fall farther below the pulmonary artery pressure before it can move the rigid valve into the closed position. Furthermore, if there is poststenotic dilatation, the increased pulmonary capacitance plus the poor elastic recoil will increase the delay in P2.
Note: A long systolic murmur that continues into or through the A2 along the left sternal border can obscure the widely split S2. You can easily tell if the murmur is obscuring an A2 by exploring the split S2 away from the maximal murmur area.
At the apex, the easily recorded A2 may be heard despite the murmur, which is much softer in that area.
2. How can the A2—P2 interval tell you the probable RV pressure in PS?
ANS: In general, the more severe the obstruction and the higher the RV pressure, the longer the A2-P2 interval.
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