Atrial fibrillation after coronary artery bypass surgery: association withchanges in G protein levels in mononuclear leukocytes

Atrial fibrillation (AFib) is a frequent complication of coronary artery by pass grafting (CABG). Its cause. however, is unknown. As the adrenergic sys tem is involved in some types of AFib, we hypothesized that a change in gua nine nucleotide-binding protein (G protein) expression plays a role in the development of post-CABG AFib. In 28 patients undergoing CABG surgery, the G(s alpha)/G(i alpha) ratio (st imulatory/inhibitory G protein alpha) at the protein (Western blotting) and mRNA (reverse transcription poly merase chain reaction) levels was measure d before and after surgery. As a suitable test system allowing multiple ana lysis mononuclear leukocytes (MNL) were chosen. The perioperative change of the G(s alpha)/G(i alpha) ratio of protein and mRNA was significantly diff erent in patients who subsequently developed AFib (eight patients) and in p atients who did not (20 patients; P<0.01 and <0.001, respectively). On aver age, the protein G(s alpha)/G(i alpha) ratio decreased from 1.79+/-1.13 (me an+/-SD) to 1.32+/-0.69 in patients without AFib (P=0.1, n.s.) whereas a si gnificant increase from 0.86+/-0.34 to 1.62+/-0.65 (P<0.01) was observed in patients subsequently developing AFib. The mRNA G(s alpha)/G(i alpha) rati o decreased significantly from 0.53+/-0.24 to 0.36+/-0.11 in patients witho ut AFib (P<0.01) whereas a significant increase from 0.31+/-0.14 to 0.47+/- 0.13 was observed in those who subsequently developed AFib (P<0.05). These results indicate that an increase of the G(s alpha)/G(i alpha) ratio in MNL is associated with AFib after CABG surgery and possibly may be used as a pn,gnostic indicator of this complication.