Atrial fibrillation pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Anahita Deylamsalehi, M.D.[2]Syed Hassan A. Kazmi BSc, MD [3]

Overview

Numerous triggers such as sympathetic or parasympathetic stimulation, ectopic activity in muscular sleeves, atrial stretch, premature atrial beats and accessory AV (atrio-ventricular) pathways have been responsible in initiation of atrial fibrillation. Younger patients with paroxysmal atrial fibrillation may have ectopic foci of electrical activity in the pulmonary vein. While the pulmonary vein is a common source of these ectopic foci, there may also be foci present in the atrium itself. Unfortunately the reason why the pulmonary vein turns to an arrhythmogenic foci is not fully understood. It seems that structure of the pulmonary vein makes it potential for re-entry formation which can lead to atrial fibrillation. Presence of the aformentioned triggers produce re-enterant wavelets of electrical activity due to shortened effective refractory period (ERP). Furthermore mechanosensitivity of cardiac myocytes is thought to play a pivotal role in initiation of atrial fibrillation. Mechanisms such as altered myocyte stress/strain, catecholamine release secondary to atrial stretch and activation of G-protein coupled pathways have been introduced in the pathogenesis of atrial fibrillation. Dilatation of the atria can be due to structural abnormalities such as hypertension, valvular heart disease and congestive heart failure that can cause a rise in the intra-cardiac pressures. Once dilatation of the atria has occurred, this begins a chain of events that leads to the activation of the renin aldosterone angiotensin system (RAAS) and subsequent increase in matrix metaloproteinases and disintegrin, which leads to atrial remodeling and fibrosis, with loss of atrial muscle mass. In addition any inflammatory state that affects the heart can cause fibrosis of the atria. This is typically due to sarcoidosis but may also be due to autoimmune disorders that create autoantibodies against myosin heavy chains. There are numerous evidences for presence of a relationship between autonomic nervous system and it's function and the atrial electrophysiology and atrial fibrillation development. Multiple associated genes to atrial fibrillation have been found. Connexin 40, potassium voltage-gated channels, natriuretic peptide precursor A and lamin A/C are some of the known genes that are related to atrial fibrillation pathogenesis. The presence of atrial fibrillation often reflects the presence of an underlying cardiac or lung disease. Indeed, the proportion of patients with lone atrial fibrillation is low (approximately 12% of cases). On gross pathology atrial enlargement has been found with echocardiographic evaluations as a consequence of atrial fibrillation. On microscopic pathology lateralization of gap junctional proteins (such as connexin 43 (Cx43), connexin 40 (Cx40) and N-cadherin) have been found. Furthermore there is an approximately 57% reduce in connexin 43 (Cx43) in right atrium appendages and walls.

Pathophysiology

Pathogenesis

Onset of atrial fibrillation is dependent upon specific triggers and tissue substrates capable of maintaining atrial fibrillation. The following triggers are know to initiate atrial fibrillation:[1][2][3][4]

Ectopic Foci in the Pulmonary Vein

Re-enterant Wavelets or Multiple Wavelets Phenomenon

Molecular Pathogenesis and Role of Mechano-electric Feedback

Role of Dilation of the Atria/Atrial Stress

Inflammation

Fibrosis of the SA Node

Autonomic nervous system

Genetics

Multiple associated genes to atrial fibrillation have been found. The following table is a summary of these genes:[34][35][36][37][38][39][40][41][42][43][44][45]

Gene Locus
Connexin 40 GJA5
Potassium voltage-gated channel (KQT-like subfamily) KCNQ1
Natriuretic peptide precursor A NPPA
Lamin A/C LMNA
Potassium voltage-gated channel (shaker-related subfamily) KCNA5
Potassium voltage-gated channel (Isk-related family) KCNE2
Potassium voltage-gated channel (subfamily H) KCNH2
Potassium inwardly rectifying channel (subfamily J) KCNJ2
Sodium channel, voltage-gated (type V, α-subunit) SCN5A
Angiotensin-converting enzyme ACE
Angiotensinogen AGT

Associated Conditions

Gross Pathology

On gross pathology atrial enlargement has been found with echocardiographic evaluations as a consequence of atrial fibrillation. [51]

Microscopic Pathology

References

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