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Selective downregulation of mitochondrial electron transport chain activity and increased oxidative stress in human atrial fibrillation. Am J Physiol Heart Circ Physiol 311: H54 -H63, 2016. First published May 6, 2016 doi:10.1152/ajpheart.00699.2015Mitochondria are critical for maintaining normal cardiac function, and a deficit in mitochondrial energetics can lead to the development of the substrate that promotes atrial fibrillation (AF) and its progression. However, the link between mitochondrial dysfunction and AF in humans is still not fully defined. The aim of this study was to elucidate differences in the functional activity of mitochondrial oxidative phosphorylation (OXPHOS) complexes and oxidative stress in right atrial tissue from patients without (non-AF) and with AF (AF) who were undergoing open-heart surgery and were not significantly different for age, sex, major comorbidities, and medications. The overall functional activity of the electron transport chain (ETC), NADH:O2 oxidoreductase activity, was reduced by 30% in atrial tissue from AF compared with non-AF patients. This was predominantly due to a selective reduction in complex I (0.06 Ϯ 0.007 vs. 0.09 Ϯ 0.006 nmol·min Ϫ1 ·citrate synthase activity Ϫ1 , P ϭ 0.02) and II (0.11 Ϯ 0.012 vs. 0.16 Ϯ 0.012 nmol·min Ϫ1 ·citrate synthase activity Ϫ1 , P ϭ 0.003) functional activity in AF patients. Conversely, complex V activity was significantly increased in AF patients (0.21 Ϯ 0.027 vs. 0.12 Ϯ 0.01 nmol·min Ϫ1 ·citrate synthase activity Ϫ1 , P ϭ 0.005). In addition, AF patients exhibited a higher oxidative stress with increased production of mitochondrial superoxide (73 Ϯ 17 vs. 11 Ϯ 2 arbitrary units, P ϭ 0.03) and 4-hydroxynonenal level (77.64 Ϯ 30.2 vs. 9.83 Ϯ 2.83 ng·mg Ϫ1 protein, P ϭ 0.048). Our findings suggest that AF is associated with selective downregulation of ETC activity and increased oxidative stress that can contribute to the progression of the substrate for AF. atrial fibrillation; humans; mitochondria; electron transport chain complexes; oxidative phosphorylation; oxidative stress; superoxide; 4-hydroxynonenal protein adducts NEW & NOTEWORTHYThe study provides evidence of a selective downregulation of mitochondrial electron transport chain functional activity predominantly affecting complexes I and II and associated increase ATRIAL FIBRILLATION (AF), a rapid irregular rhythm of the atria, is associated with electrical, functional, and structural changes in the atria that promote the substrate for its recurrence and progression (36, 53, 60). The incidence and prevalence of AF increase with advancing age and aging-associated diseases such as hypertension, ischemic heart disease, and heart failure (2, 40) and contribute to increased morbidity, particularly an increased risk for stroke, heart failure, and death (25,52). Although the pathophysiology of AF has been well characterized, the underlying mechanisms that contribute to the progression of AF in human atria have not been fully defined (33,35,57,58,60). Mitochondria, occupying 30% ...

Summary Atrial fibrillation (AF) complicating cardiac surgery continues to be a major problem that increases the postoperative risk of stroke, myocardial infarction, heart failure, costs and long-term survival. The incidence of AF after surgery has not significantly changed over the last two decades, despite improvement in medical and surgical techniques. The mechanism and pathophysiology underlying postoperative AF (PoAF) is incompletely understood and results from a combination of acute and chronic factors, superimposed on an underlying abnormal atrial substrate with increased interstitial fibrosis. Several antiarrhythmic and non-antiarrhythmic medications have been used for the prevention of PoAF, but the effectiveness of these strategies has been limited due to a poor understanding of the basis for the increased susceptibility of the atria to AF in the postoperative setting. In this review, we summarize the pathophysiology underlying the development of PoAF and evidence behind pharmacological approaches used for its prevention in the postoperative setting.

Postoperative atrial fibrillation (PoAF), a common complication of cardiac surgery, contributes significantly to morbidity, mortality, and increasing health care costs. Despite advances in surgical and medical management, the overall incidence of PoAF has not changed significantly, partly due to the limited understanding of mechanisms underlying acute surgery-related factors, such as myocardial injury, inflammation, sympathetic activation, and oxidative stress, which play an important role in the initiation of PoAF, while a preexisting atrial substrate appears to be more important in the maintenance of this dysrhythmia. Thus, in a majority of patients, PoAF becomes a manifestation of an underlying arrhythmogenic substrate that is unmasked following acute surgical stress. As such, the ability to identify which patients have this proarrhythmic substrate and are, therefore, at high risk for developing AF postoperatively, is important for the improved selection for prophylactic interventions, closer monitoring for complications, and establishing the probability of AF in the long term. This review highlights the role of the underlying substrate in promoting PoAF, proposed mechanisms, and the potential role of serum biomarkers to identify patients at risk for PoAF.