In the Milrinone topic in DynaMed, you can look at the Cautions and Adverse Effects section and see a summary of a prospective cohort study of 232 patients having elective cardiac surgery (Milrinone Use Is Associated With Postoperative Atrial Fibrillation After Cardiac Surgery.  Circulation 2008 Oct 14;118(16):1619.)  The exposure was whether or not the patients received milrinone.  Milrinone used for patients with postbypass LVEF <30%, with evidence of right ventricular dysfunction, or with pulmonary hypertension.
28.9% of patients developed atrial fibrillation.  Rate of developing atrial fibrillation was 58.2% in milrinone group v. 26.1% in the no milrinone  group.

PubMed
Full list of systematic reviews can be seen here: systematic[sb] AND (milrinone OR cardiotonic agents OR inotropic drugs) AND cardiac surgery AND adverse effects

There is a systematic review on the topic (Gillies M, et al.  Bench-to-bedside review: Inotropic drug therapy after adult cardiac surgery — a systematic literature review.  Crit Care. 2005 Jun;9(3):266-79. Epub 2004 Dec 16.), but the authors found no studies reporting “data relating to the effect of milrinone on major clinical outcomes or survival in cardiac surgery patients.”   The RCTs included in the review only reported data for a short period of time (up to 24 hours), one of the trials (Doolan, 1997) reported findings of atrial fibrillation.  The rate in milrinone use was very low (5%),  but the study only reported data collected for 4 hours after surgery.

Reviewed 4/14/14  AA