I have a situation where a patient came into the ASC, was okay’d for surgery, prepped, moved to the OR, was given anesthesia, but then had an unexpected allergic reaction to the anesthesia before the procedure got started. The surgeon nixed the procedure, obviously, and documented the reaction ("mild arrhythmia") in the op note. They moved the patient to a recovery suite for monitoring, but no treatment was necessary. I know I need to code for the original DX and the arrhythmia (plus the toxic effects, etc). Am I correct that the original DX should be sequenced first given that no treatment was needed for the allergic reaction?