VARIATIONS OF AUTONOMIC TONE PRECEDING ONSET OF ATRIAL-FIBRILLATION AFTER CORONARY-ARTERY BYPASS-GRAFTING

Assessment of autonomic tone preceding the onset of atrial fibrillatio n (AF) after coronary artery bypass grafting (CABG) with heart rate va riability was examined in 64 patients scheduled for elective CABG (day s 2 to 5), Ninety-six-hour Holter tapes were analyzed in each patient and all events labeled by an experienced technician. The hour precedin g AF was divided into 4 quarters (heart rate variability calculated pe r quarter) and compared with similar time episodes from the group with out AF. Twenty-six of 64 patients (40%) had a total of 35 episodes. On ly increased age (68 +/- 5 vs 62 +/- 9 years) and lower election fract ion (66 +/- 16% vs 73 +/- 8%) were associated with an increased risk f or AF. Before onset, a greater number of atrial premature complexes wa s observed. The standard deviation of all RR intervals (SDNN) showed a n increase in the group with AF in the last 15 minutes (significant vs controls and within the AF group). The low-frequency/high-frequency r atio was significantly lower in patients in the first 30 minutes, foll owed by an increase mainly because the high-frequency spectrum became less important. Thus, initiation of postoperative AF is influenced by autonomic tone variations. A shift in the autonomic balance with a los s of vagal tone and a moderate increase in sympathetic tone are observ ed before the onset of AF compared with those in controls. (C) 1998 by Excerpta Medico, Inc.