Temporal patterns of progression and regression of electrical and mechanical remodeling of the atrium

Chronic stimulation of the sigma-1 receptor ameliorates autonomic nerve dysfunction and atrial fibrillation susceptibility in a rat model of depression

The present study aimed to assess the effect of sigma-1 receptor (S1R) stimulation on autonomic nerve dysfunction and susceptibility to atrial fibrillation (AF) in a rat depression model. Male rats were randomly divided into one of the following four treatment groups: saline [control (CTL)]; saline + intragastric administration of SA4503, an agonist of S1R (CTS); chronic unpredictable mild stress (CUMS) to produce depression (MDD); and CUMS + intragastric administration of SA4503 (MDS). Depression-like behaviors, such as reduced sucrose preference, decreased body weight gain, and increased immobility time during forced swimming, improved in the MDS group after 4 wk of SA4503 treatment. Compared with rats in the CTL group, rats in the MDD group showed significantly augmented sympathetic activity, reduced parasympathetic activity, decreased heart rate variability, and lowered S1R expression in the atrium and hippocampus (all P < 0.01). However, rats in the MDS group showed mitigated aforementioned alterations and improved electrical remodeling compared with rats in the MDD group (all P < 0.01). Furthermore, rats in the MDS group showed shortened activation latencies, increased effective refractory periods, and lowered frequency of AF incidence duration and fibrosis compared with rats in the MDD group (all P < 0.01). The results indicate that S1R stimulation reduces sympathetic activity and susceptibility to AF by improving depressive behaviors, modulating cardiac autonomic nerve balance, lightening nerve remodeling, and upregulating S1R and ion channel protein expression. NEW & NOTEWORTHY Chronic stimulation of the sigma-1 receptor (S1R) ameliorates depression-induced autonomic nerve dysfunction by modulating the imbalance between overactivated sympathetic activity and decreased vagal activity. Chronic S1R stimulation alleviates atrial electrical remodeling, fibrosis, and susceptibility to atrial fibrillation (AF). The S1R agonist may target the underlying mechanisms related to AF occurrence. The results indicate that the S1R could be a potential clinical target for atrial arrhythmia, especially when it is combined with major depressive disorders.

[Thrombus formation and its embolic risk in atrial fibrillation]

Mural thrombus due to blood stasis develops in the left atrium as atrial fibrillation (AF) persists longer. Characteristically, its development depends on the endothelial function of the atrium, and the prevention and control of each component of CHADS2 score are thus important. Treatment of hypertension is essential in the primary prevention of AF, but once AF develops, its suppression will be the next step to address and catheter ablation is a useful intervention for this purpose. If these efforts fail, anticoagulation therapy for those with a substantial risk is mandatory. After the duration of AF and the bleeding risk are carefully taken into account, new oral anticoagulants with the risk of cerebral bleeding much less than warfarin are indicated.

Atrial reverse remodeling: restitution of early tachycardia-induced alterations of atrial ion currents after termination of rapid atrial pacing in rabbits

BACKGROUND AND PURPOSE

Studies report on the reversal of electrophysiological parameters altered by atrial tachycardia after cessation of the latter. However, there is no data concerning reversal of tachycardia-induced alterations of ion currents. Reverse remodeling of atrial ion currents (I(Ca,L), I(to), I(sus)) was studied in our rabbit model of tachycardia-induced electrical remodeling.

METHODS

Three groups each with four animals were built. Rapid atrial pacing (600/min) for 5 days was applied in all groups. Thereafter, different time intervals (5, 10, 20 days) were awaited before the patch clamp experiments.

RESULTS

Similar to I(to) remodeling in our model, within 20 days after cessation of atrial tachycardia, time course of I(to) reverse remodeling was also U-shaped. In contrast, there was no significant recovery of I(Ca,L) which was initially reduced by rapid atrial pacing.

CONCLUSION

Relevance of a missing recovery of I(Ca,L) is likely as this current is closely linked with intracellular calcium handling.

Atrial Remodeling And Atrial Fibrillation: Mechanistic Interactions And Clinical Implications

Atrial fibrillation (AF) is the most common arrhythmia in clinical practice. The prevalence of AF increases dramatically with age and is seen in as high as 9% of individuals by the age of 80 years. In high-risk patients, the thromboembolic stroke risk can be as high as 9% per year and is associated with a 2-fold increase in mortality. Although the pathophysiological mechanism underlying the genesis of AF has been the focus of many studies, it remains only partially understood. Conventional theories focused on the presence of multiple re-entrant circuits originating in the atria that are asynchronous and conducted at various velocities through tissues with various refractory periods. Recently, rapidly firing atrial activity in the muscular sleeves at the pulmonary veins ostia or inside the pulmonary veins have been described as potential mechanism,. AF results from a complex interaction between various initiating triggers and development of abnormal atrial tissue substrate. The development of AF leads to structural and electrical changes in the atria, a process known as remodeling. To have effective surgical or catheter ablation of AF good understanding of the possible mechanism(s) is crucial.Once initiated, AF alters atrial electrical and structural properties that promote its maintenance and recurrence. The role of atrial remodeling (AR) in the development and maintenance of AF has been the subject of many animal and human studies over the past 10-15 years. This review will discuss the mechanisms of AR, the structural, electrophysiologic, and neurohormonal changes associated with AR and it is role in initiating and maintaining AF. We will also discuss briefly the role of inflammation in AR and AF initiation and maintenance, as well as, the possible therapeutic interventions to prevent AR, and hence AF, based on the current understanding of the interaction between AF and AR.

Structural and functional remodeling of the left atrium: clinical and therapeutic implications for atrial fibrillation

Left atrial (LA) structural and functional remodeling reflects a spectrum of pathophysiological changes that have occurred in response to specific stressors. These changes include alterations at the levels of ionic channels, cellular energy balance, neurohormonal expression, inflammatory response, and physiologic adaptations. There is convincing evidence demonstrating an important pathophysiological association between LA remodeling and atrial fibrillation (AF). Measures that will prevent, attenuate, or halt these processes of LA remodeling may have a major public health impact with respect to the epidemic of AF. In this review, we describe the mechanisms involved in LA remodeling and highlight the existing and potential therapeutic options for its reversal, and implications for AF development.

Does left atrial appendage peak emptying flow velocity predict the electrical energy required to achieve successful direct-current cardioversion in patients with persistent atrial fibrillation?

BACKGROUND

The relation of left atrial (LA) appendage peak emptying flow velocity (LAAEV) with energy requirement for successful direct-current cardioversion (DCCV) in persistent atrial fibrillation (AF) is unknown. LAAEV correlates with success of cardioversion of AF to sinus rhythm, both of which are related to the LA size and the chronicity of AF. We tested the hypothesis that LAAEV can predict optimal energy required for DCCV in persistent AF (>48 hours).

METHODS

We studied 1050 consecutive patients with persistent AF who underwent successful transesophageal echocardiographically guided DCCV from 2000 to 2005. After excluding patients with atrial flutter and those receiving antiarrhythmic drugs, 454 patients qualified for the study.

RESULTS

LAAEV did not correlate with cardioversion energy (r = 0.06, P = .23) or number of shocks required for successful DCCV (r = 0.05, P = .33). The only predictor of energy required for successful cardioversion was the chronicity of AF.

CONCLUSION

LAAEV does not predict electrical energy required for successful cardioversion in persistent AF.