The last three decades have been characterized by an exponential increase in knowledge and advances in the clinical management of atrial fibrillation. The purpose of the study is to provide an overview of the pathogenesis of nonvalvular atrial fibrillation and a comprehensive investigation of the epidemiological data associated with various risk factors for atrial fibrillation. The leading research methods are analysis and synthesis, comparison, observation, induction and deduction, and grouping method. Research has shown that old age, male gender, and European descent are important risk factors for developing atrial fibrillation. Other modifiable risk factors include a sedentary lifestyle, smoking, obesity, diabetes mellitus, obstructive sleep apnea, and high blood pressure predisposing to atrial fibrillation, and each has been shown to induce structural and electrical atrial remodeling. Both heart failure and myocardial infarction increase the risk of developing atrial fibrillation and vice versa creating feedback that increases mortality. The review is a comprehensive study of the epidemiological data linking nonmodifiable and modifiable risk factors for atrial fibrillation, and the pathophysiological data supporting the relationship between each risk factor and the occurrence of atrial fibrillation. This may be necessary for the practice of the treatment of the cardiac system.

Funding Acknowledgements Type of funding sources: None. Background Right ventricular apical (RVA) pacing deleterious effects on left ventricular ejection fraction (LVEF) had been demonstrated. Non-apical pacing, such as right ventricular mid-septal (RVMS) and His Bundle pacing, appear as practical alternatives. Our purpose is to evaluate the effect of alternate sites of right ventricular (RV) pacing on left ventricular (LV) function and hemodynamics in patients with bradyarrhythmias. Methods We observed 118 patients (age 58±27 years, 64% men) with AV block III, who underwent permanent dual chamber pacemaker implantation. To 72 patients RV lead has implanted the middle area of RV septum (RVMS) and 46 patients’ RV lead has been implanted traditionally to the right ventricular apex (RVA). Color tissue velocity imaging was performed to analyze time to peak systolic velocity (Ts) in a 12 segment model of the LV for each pacing site. Measurements included standard deviation of time to peak systolic velocity (SD-Ts) for all segments, the maximal difference in Ts between any 2/6 basal (Ts-B), any 2/6 mid segments (Ts-M) and maximal Ts difference between any 2/12 segments (Ts-12). Stroke volume was estimated using Doppler velocity time integral (TVI) in the left ventricular outflow tract (LVOT). QRS width for each site was recorded. Measurements were observed by transthoracic echocardiography and electrocardiography before and 12 months after implantation. Results Ts-12 was significantly higher with RVA - pacing (107 ms, p=0.003) compared to RVMS - pacing (81 ms) sites. SD-Ts were significantly higher with RVA - pacing (38.5 ms, p=0.01) than RVMS - pacing (28.7 ms). QRS duration was the longest for RVA - pacing (157 ms) while significantly shorter RVMS - pacing (115 ms, p<0.001). LVOT VTI was significantly higher for RVMS - pacing than for RVA (p=0.0014) pacing. Conclusions Right ventricular mid-septal pacing may reduce electro-mechanical dyssynchrony compared to RVA pacing and RVMS – pacing to effect better LV function and hemodynamics than RVA pacing in patients with permanent pacemaker implantation.