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Profound Cardiac Autonomic Derangement together with altered Ventricular Repolarization pave the Way to Postoperative Atrial Fibrillation
Jurij M. Kališnik, MD, PhD1, Eva Hrovat, MD1, Alenka Hrastovec, MD1, Viktor Avbelj, PhD2, Borut Geršak, MD, PhD1.
1University Medical Center, Ljubljana, Slovenia, 2Josef Stefan Institute, Ljubljana, Slovenia.

OBJECTIVE: Postoperative atrial fibrillation (AF) represents the most frequent complication after heart surgery using cardiopulmonary bypass (CPB) increasing mortality, morbidity and cost. Despite efforts to identify mechanisms and preventive measures, the results remain suboptimal. It has been shown, that cardiac autonomic derangement plays a significant role in genesis of AF and that it might also be promoted by altered repolarization. Thus, the aim of our study was to determine the levels of cardiac autonomic modulation and repolarization properties in patients that develop AF after heart operations as opposed to those that remain in sinus rhythm.
METHODS: 90 consecutive patients scheduled for cardiac surgery with CPB were enrolled in our study prospectively. 9 did not meet inclusion criteria, 2 died in postoperative course, so 79 represented the final sample. High-resolution 20-minute ECG recordings were obtained one day before surgery to determine P, PR, QT and corrected QT (QTc) intervals as well as linear (Time and Frequency domain) and nonlinear HRV parameters (Fractal Dimension, Detrended Fluctuation Analysis (DFA) and Multifractality). QTc interval was calculated using Bazett's and Hodges correction formula. Statistical analyses were performed with Student t test, p value <0,05 was considered significant.
RESULTS: 29 patients developed AF after operation (AF group) and 50 did not (nonAF group). The two groups were similar regarding demographics, surgery type, preoperative and operative characteristics, except for older patients in AF group (74,0 ± 7,7 vs. 69,8 ± 9,4 yrs; p=0,04). QT and QTc intervals (Bazett's and Hodges correction) were longer in AF group (442,00 ± 44,13 vs. 422,26 ± 28,17 ms; p=0,02, 454,90 ± 49,65 vs. 438,07 ± 28,46 ms; p=0,06 and 448,64 ± 42,77 vs. 430,87 ± 23,51 ms; p=0,02, respectively). Among nonlinear parameters DFA parameter α2 was lower in AF group (0,81 ± 0,21 vs. 0,91 ± 0,20; p=0,03).
CONCLUSIONS: Patients, who developed AF after cardiac surgery with CPB, were found to have severe cardiac autonomic derangement already preoperatively. Our study identifies additional marker α2 to differentiate AF from nonAF group. We demonstrate for the first time that prolonged QT and QTc intervals are associated with increased risk for postoperative AF.

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