Atrial Bigeminy is a pretty common arrhythmia in post-CABG or valve replacements, and can often times precipitate into Atrial fibrillation. I've also seen it in quite a few patients in PACU, probably due to some of the hypoxia that they may have due to mildly low resp. rates. Best course of action is to prevent it from becoming something worse, such as Atrial Fib, therefore most of the time I see it in a "cardiac" patient, I'll ask for a dose of IV Lopressor if their pressure is fine, or Digoxin on occasion too.
The great thing about seeing it on a pleth or arterial wave form is that it gives people an idea of what happens to atrial kick and filling pressures when a patient becomes tachycardic.
Here's a strip of it I found online....
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