‘Lone’ atrial fibrillation: Hunting for the underlying causes and links

Update about atrial fibrillation genetics

PURPOSE OF REVIEW

Atrial fibrillation is an important cause of morbidity in the aging population. The mechanisms responsible for the triggering and maintenance of the chaotic atrial rhythm are still poorly understood. In this review, we will focus on the genetic aspects of atrial fibrillation, to understand causality, with special emphasis on recent studies published in the field.

RECENT FINDINGS

Diseases such as hypertension, valvular heart disease, and heart failure may induce atrial fibrillation, which increases the risk of stroke and sudden cardiac death. Clinical studies published in these last two decades have provided evidence that genetics play a key role in atrial fibrillation. Thus, a family history of the disease has been identified in up to 30% of clinically diagnosed patients. In those genotyped families, most carry rare genetic variants in genes associated with ionic channels, calcium handling protein, or predisposing to fibrosis, conduction system disease, and inflammatory processes.

SUMMARY

Currently, atrial fibrillation is the most common sustained arrhythmia in clinical practice. The pathophysiological mechanisms of atrial fibrillation are complex. A better understanding of the molecular basis will help improve both current risk stratification and clinical management.

Genetic basis of atrial fibrillation

Atrial fibrillation is the most common sustained arrhythmia and remains as one of main challenges in current clinical practice. The disease may be induced secondary to other diseases such as hypertension, valvular heart disease, and heart failure, conferring an increased risk of stroke and sudden death. Epidemiological studies have provided evidence that genetic factors play an important role and up to 30% of clinically diagnosed patients may have a family history of atrial fibrillation. To date, several rare variants have been identified in a wide range of genes associated with ionic channels, calcium handling protein, fibrosis, conduction and inflammation. Important advances in clinical, genetic and molecular basis have been performed over the last decade, improving diagnosis and treatment. However, the genetics of atrial fibrillation is complex and pathophysiological data remains still unraveling. A better understanding of the genetic basis will induce accurate risk stratification and personalized clinical treatment. In this review, we have focused on current genetics basis of atrial fibrillation.

Diabetes mellitus and atrial remodeling: mechanisms and potential upstream therapies

Atrial fibrillation (AF) is the most common cardiac arrhythmia in clinical practice, and its prevalence has increasing substantially over the last decades. Recent data suggest that there is an increased risk of AF among the patients with diabetes mellitus (DM). However, the potential molecular mechanisms regarding DM-related AF and diabetic atrial remodeling are not fully understood. In this comprehensive review, we would like to summarize the potential relationship between diabetes and atrial remodeling, including structural, electrical, and autonomic remodeling. Also, some upstream therapies, such as thiazolidinediones, probucol, ACEI/ARBs, may play an important role in the prevention and treatment of AF. Therefore, large prospective randomized, controlled trials and further experimental studies should be challengingly continued.

Lone atrial fibrillation in the young - perhaps not so "lone"?

OBJECTIVE

To determine if pediatric patients with a history of lone atrial fibrillation (AF) have other forms of supraventricular tachycardia (SVT) that may potentially trigger AF.

STUDY DESIGN

A multicenter review of patients with lone AF who underwent electrophysiology (EP) study from 2006-2011 was performed.

INCLUSION CRITERIA

age ≤21 years, normal ventricular function, structurally normal heart, history of AF, and EP study and/or ablation performed.

EXCLUSION CRITERIA

congenital heart disease or cardiomyopathy. Patient demographics, findings at EP study and follow-up data were recorded.

RESULTS

Eighteen patients met inclusion criteria. The mean age was 17.9 ± 2.2 years, weight was 82 ± 21 kg, body mass index was 27 ± 6, and 15 (83%) were males. Eleven (61%) were overweight or obese. Seven (39%) had inducible SVT during EP study: 5 atrioventricular nodal re-entry tachycardia (71%) and 2 concealed accessory pathways with inducible atrioventricular re-entry tachycardia (29%). All 7 patients with inducible SVT underwent radiofrequency ablation. There were no complications during EP study and/or ablation for all 18 patients. The mean follow-up was 1.7 ± 1.5 years and there were no recurrences in the 7 patients who underwent ablation. There were 2 recurrences of AF in patients with no other form of SVT during EP study.

CONCLUSIONS

Inducible SVT was found in 39% of pediatric patients undergoing EP study for lone AF. EP study should be considered for pediatric patients presenting with lone AF.

Atrial fibrillation, physical activity and endurance training

INTRODUCTION

Clinical practice and the results of some studies may indicate that physical exercise in the form of endurance training may influence the development of atrial fibrillation (AF). The aim of this paper is to evaluate the scientific background for the hypothesis that there is a connection between physical activity and AF.

MATERIAL AND METHOD

This paper is a review article based on searches in PubMed on specific topics, limited to the period 1995 through March 2011. We found 17 original articles and three relatively recent reviews. Each was read by at least two of the authors and then discussed. Seven of the original articles were excluded for methodological reasons, and we therefore discuss the other ten.

RESULTS

We found support for the hypothesis that systematic high intensity endurance training such as running can increase the risk of AF, whereas the studies provide no evidence that less intensive physical exercise such as walking increases the risk. Several of the studies have methodological weaknesses.

INTERPRETATION

Important questions remain unanswered. There is a need for more studies that can shed light on the connection between training intensity, total volume of intensive endurance training, age-related changes and AF. Studies that include women are also needed.

Clinically unrecognized mitral regurgitation is prevalent in lone atrial fibrillation

AIM

To investigate the prevalence of clinically unrecognized mitral regurgitation (MR) in lone atrial fibrillation (AF).

METHODS

We studied the prevalence and severity of MR by transesophageal echocardiography (TEE) in patients with "lone" AF as compared to a matched cohort of patients in normal sinus rhythm (NSR) undergoing TEE for other indications besides recognized valvular heart disease.

RESULTS

A total of 157 subjects (57 in the AF group and 100 in the NSR group) with structurally normal cardiac valves were included in the study. In the AF group, moderate MR or more was noted in 66% of the patients, mild MR in 18%, trace or no MR in 16%. In the control group, moderate MR was noted in 6% of patients, mild MR 31%, trace or no MR in 63 % of patients. Moderate MR or greater was significantly more prevalent in the AF group compared to the NSR group (66% vs 6%, P < 0.0001).

CONCLUSION

Clinically unrecognized moderate MR is prevalent in "lone" AF -either as an etiologic factor leading to "lone" AF or developing after onset of AF.

Androgens and atrial fibrillation: friends or foes?

Atrial fibrillation (AF) is the most common sustained arrhythmia encountered in clinical practice. The prevalence of AF increases with age, and this age-specific prevalence is higher in men than in women. However, the mechanisms of aging-induced AF have not been fully elucidated, and this may be related to decline of testosterone with advancing age. On the other hand, anabolic steroid abuse may precipitate the occurrence of AF. Until now, the possible relationship between androgens and AF was not comprehensively reviewed. We intend to review some recent evidence on this issue and propose some potential mechanisms.