Hi Marc,
The meaning of a single LOINC term is based on the 5 or 6 major Parts (Component, Property, Timing, System, Scale, +/- Method).
When comparing 80234-8 and 8583-7, you will see that the first one has a Method of cardiac catheterization, while the second is methodless, meaning that it represents Right atrial A-wave amplitude as measured by any method. The first code is more specific.
https://loinc.org/80234-8/:
A wave amplitude:Pres:Pt:Heart.atrium.right:Qn:Cardiac catheterization
https://loinc.org/8583-7:
A wave amplitude:Pres:Pt:Heart.atrium.right:Qn:
Thanks,
Swapna