Investigating the micro-RNA and metabolic signature of human postoperative atrial fibrillation

Atrial fibrillation (AF) is the commonest disorder of cardiac rhythm. Following coronary artery surgery approximately 1 in 3 patients will develop de novo post-operative AF (POAF) leading not only to prolonged hospital stay but also to increased morbidity and mortality. The pathophysiology of this arrhythmia is highly complex, and combines factors such as ion channel dysfunction, inflammation, oxidative stress, fibrosis and autonomic dysfunction that through electrical and structural remodelling promote both triggering and maintenance of this arrhythmia. For many years POAF has been regarded as a reactive phenomenon, occurring in response to post surgical inflammatory stressors and electrolyte imbalance. However, it is also possible that in a proportion of patients, prior cardiomyocyte remodelling predisposes to atrial arrhythmogenesis when exposed to surgical stress. Understanding the genomic and metabolic mechanisms that underlie this substrate may not only provide novel diagnostic biomarkers to identify at risk patients, but also isolate previously unrecognised therapeutic targets for prevention and treatment. In this work, a clinical observational study was utilised to obtain microRNA, gene expression and metabolic profiles of patients developing POAF after coronary artery bypass graft (CABG) surgery. Based on these results, a network of genomic and subsequent downstream pathway interactions was established to characterise the atrial substrate of post-operative AF. Furthermore, analysis of pre-operative blood was performed in order to identify novel microRNA that may provide a platform for biomarker development. Finally, the metabolic signature of the atrial myocardium and its relationship with the surrounding epicardial adipose were investigated to complete a comprehensive overview of the central mechanisms thought to underlie POAF pathogenesis. This work demonstrates that prior to surgery and the onset of arrhythmia, several distinct genomic and post-translational characteristics are evident in the both the myocardium and circulating blood of patients going on to develop POAF. Analysis of right atrial biopsies highlights a characteristic microRNA profile associated with POAF, and identifies target genes regulating intracellular signalling pathways, leukocyte recruitment, and ion channel remodelling. Furthermore, selected gene expression analysis demonstrates a de-differentiated phenotype similar to that seen in chronic AF, whilst at the same time establishing that disordered cardiomyocyte calcium handling is apparent at the time of surgery. Finally, analysis of the pre-operative circulating blood serum highlights microRNA selectively upregulated in POAF and establishes the potential for future biomarker development. In summary, the results presented here support the presence of a pre-existing atrial substrate in POAF, suggesting the potential exists for high-risk patients to be identified prior to surgery and the onset of arrhythmia. Furthermore, for the first time a number of similarities have been made apparent between post-operative and chronic AF, implying a common mechanistic spectrum of structural and electrical remodelling. As a consequence, the results presented in this thesis have not only improved our understanding of the complex interplay of factors leading to the pathogenesis of AF, but also provide a platform for both the development of a unique clinical biomarker and the identification of novel therapeutic targets.Open Acces

A proposed role for sepsis in the pathogenesis of myocardial calcification

Myocardial calcification is a rare and life-threatening condition that is a recognised complication of ischaemic heart disease, cardiac surgery, rheumatic fever and myocarditis. It is distinct from coronary artery or valvular calcification, and can be seen in patients with abnormal calcium metabolism1 . Its presence in the context of sepsis is less well recognised and the mechanisms responsible are poorly understood. We review the relevant literature and propose a mechanistic theory for its pathogenesi

Strategies in the Surgical Management of Atrial Fibrillation

Atrial fibrillation (AF) is associated with substantial morbidity, mortality, and economic burden and confers a lifetime risk of up to 25%. Current medical management involves thromboembolism prevention, rate, and rhythm control. An increased understanding of AF pathophysiology has led to enhanced pharmacological and medical therapies; however this is often limited by toxicity, variable symptom control, and inability to modulate the atrial substrate. Surgical AF ablation has been available since the original description of the Cox Maze procedure, either as a standalone or concomitant intervention. Advances in novel energy delivery systems have allowed the development of less technically demanding procedures potentially eliminating the need for median sternotomy and cardiopulmonary bypass. Variations in the definition, duration, and reporting of AF have produced methodological limitations impacting on the validity of interstudy comparisons. Standardization of these parameters may, in future, allow us to further evaluate clinical endpoints and establish the efficacy of these techniques

Antioxidant Vitamins in the Prevention of Atrial Fibrillation: What Is the Evidence?

Atrial fibrillation (AF) is the most common sustained arrhythmia that is associated with significant morbidity and mortality. Current available therapies remain inadequate in symptom control and secondary prevention and are often associated with significant side effects. The mechanisms underlying the pathogenesis of AF are poorly understood, although electrophysiological remodeling has been described as an important initiating step. Recently, increasing evidence implicates oxidative stress and inflammation in the pathogenesis of AF. We searched the literature for evidence to support the use of antioxidant vitamins C and E in the prevention of AF. These vitamins, through their reactive-oxygen-species- (ROS-) scavenging effect, have shown a role in AF prevention in both animal and small clinical studies. The available evidence, however, is currently insufficient to support recommendations for their use in the wider patient population. Larger-scale clinical studies are required to confirm these preliminary results. Research is also required to further the understanding of the processes involved in the pathogenesis of AF and the role of antioxidant therapies to prevent the arrhythmia

A competency framework in cardiothoracic surgery for training and revalidation — an international comparison

The conventional methods of education, certification and recertification in cardiothoracic surgery face a paradigm shift in line with recent innovations in diagnostics and therapeutics. The attributes of a competent clinician entail proficiency in knowledge, communication, teamwork, management, health advocacy, professionalism and technical skills. This article investigates the skills required for a cardiothoracic surgeon to be competent. The relevant practice of certification and recertification across various regions has also been explored. Validated and competency-based curricula should be designed to develop core competencies to successfully integrate them into practice. Challenges to the implementation of such curricula and potential solutions are explored. Patient safety remains the ultimate aim to ensure excellence of both competency and performanc

Aortic stiffness as a marker of cardiac function and myocardial strain in patients undergoing aortic valve replacement

Background: Cardiac function and myocardial strain are affected by cardiac afterload, which is in part due to the stiffness of the aortic wall. In this study, we hypothesize that aortic pulse wave velocity (PWV) as a marker of aortic stiffness correlates with conventional clinical and biochemical markers of cardiac function and perioperative myocardial strain in aortic valve replacement (AVR). Methods: Patients undergoing AVR for aortic stenosis between June 2010 and August 2012 were recruited for inclusion in this study. PWV, NYHA class and left ventricular (LV) function were assessed pre-operatively. PWV was analysed both as a continuous and dichotomous variable according to age-standardized reference values. B-type natriuretic peptide (BNP) was measured pre-operatively, and at 3 h and 18-24 h after cardiopulmonary bypass (CPB). NYHA class, leg edema, and LV function were recorded at follow-up (409 ± 159 days). Results: Fifty-six patients (16 females) with a mean age of 71 ± 8.4 years were included, with 50 (89%) patients completing follow-up. The NYHA class of PWV-norm patients was significantly lower than PWV-high patients both pre- and post-operatively. Multiple logistic regression also highlighted PWV-cut off as an independent predictor of NYHA class pre- and post-operatively (OR 8.3, 95%CI [2.27,33.33] and OR 14.44, 95%CI [1.49,139.31] respectively). No significant relationship was observed between PWV and either LV function or plasma BNP. Conclusion: In patients undergoing AVR for aortic stenosis, PWV is independently related to pre- and post-operative NYHA class but not to LV function or BNP. These findings provisionally support the use of perioperative PWV as a non-invasive marker of clinical functional status, which when used in conjunction with biomarkers of myocardial strain such as BNP, may provide a holistic functional assessment of patients undergoing aortic valve surgery. However, in order for PWV assessment to be translated into clinical practice and utilised as more than simply a research tool, further validation is required in the form of larger prospective studies specifically designed to assess the relationship between PWV and these functional clinical outcomes