Atrial Fibrillation and Congestive Heart Failure: Risk Factors, Mechanisms, and Treatment

Left stellate ganglion and vagal nerve activity and cardiac arrhythmias in ambulatory dogs with pacing-induced congestive heart failure

OBJECTIVES

The purpose of this study was to determine the patterns of autonomic nerve activity in congestive heart failure (CHF).

BACKGROUND

The relationship between autonomic nerve activity and cardiac arrhythmias in CHF is unclear.

METHODS

We implanted radiotransmitters in 6 dogs for continuous (24/7) simultaneous monitoring of left stellate ganglion nerve activity (SGNA), vagal nerve activity (VNA), and electrocardiography before and after pacing-induced CHF.

RESULTS

Congestive heart failure increased both SGNA and VNA. The SGNA but not VNA manifested a circadian variation pattern. There was extensive sinus node fibrosis. We analyzed 2,263 episodes of prolonged (>3 s) sinus pauses (PSP) and 1,420 long (>10 s) episodes of paroxysmal atrial tachycardia (PAT). Most (95.3%) PSP episodes occurred at night, and 56% were preceded by a short burst of SGNA that induced transient sinus tachycardia. Long PAT episodes were typically (83%) induced by simultaneous SGNA and VNA discharge, followed by VNA withdrawal. Premature ventricular contractions and ventricular tachycardia were preceded by elevated SGNA.

CONCLUSIONS

The reduction of sympathovagal balance at night in ambulatory dogs was due to reduced sympathetic discharge rather than a net increase of vagal discharge. The tachybrady syndrome in CHF might be triggered by an intermittent short burst of SGNA that resulted in tachycardia and sinus node suppression. Simultaneous sympathovagal discharge is a cause of long PAT episodes. These data indicate that there is an association between the specific patterns of autonomic nerve discharges and cardiac arrhythmia during CHF.

Quantitative mRNA analysis of serotonin 5-HT4 receptor isoforms, calcium handling proteins and ion channels in human atrial fibrillation

Serotonin 5-HT(4) receptors are present in human atrial myocytes and have been proposed to contribute to the generation of atrial fibrillation (AF). Here, we quantified 5-HT(4) receptors as well as other key genes involved in cardiac rhythm and contraction in right atrial appendages of patients with chronic AF (CAF) and acute AF (AAF). Right atrial appendages were obtained from eleven patients in sinus rhythm (SR), five with AAF and six with CAF (>12 months). TaqMan real time quantitative RT-PCR was performed on total RNA. Results were normalised to the average of three housekeeping genes, cyclophilin, GADPH and RL-19. The rank order of expression of h5-HT(4) receptors variants was (b)>(a)>(g)>(c) in the group of patients in SR. In AAF, we found a strong decrease in h5-HT(4(b)), h5-HT(4(c),) and h5-HT(4(g)) transcripts. In CAF patients, the mRNA expression level of the h5-HT(4(b)) isoform significantly increased two fold versus SR. A similar increase was reported for beta(1)-adrenergic receptor, connexin 43 and the L-type Ca(2+) channel CaCNA1C subunit. Interestingly, CAF was associated with a strong increase in the expression of Na(+)/Ca(2+) exchanger and the voltage-dependent Na(+) channel SCN5A subunit. Our results indicate that h5-HT(4(b)) is the dominant cardiac isoform of human 5-HT(4) receptors and its expression is increased in CAF. These data support the involvement of 5-HT(4) receptors in atrial arrhythmia.

Left atrial remodelling contributes to the progression of asymptomatic left ventricular systolic dysfunction to chronic symptomatic heart failure

Systolic heart failure (HF) is a progressive disorder that often begins with asymptomatic left ventricular (LV) systolic dysfunction and culminates in symptoms from fluid overload and poor end-organ perfusion. The progression to symptomatic HF is accompanied by marked activation of neurohormonal and cytokine systems, as well as a series of adaptive LV anatomical and functional changes, collectively referred to as LV remodelling. However, the mechanisms underlying symptom appearance have not been delineated and the weight of experimental and clinical evidence suggests that the development of symptomatic HF occurs independently of the haemodynamic status of the patient. The left atrium is a muscular chamber strategically located between the left ventricle and the pulmonary circulation with important mechanical function (modulation of LV filling), which is closely coupled with its endocrine (atrial natriuretic peptide synthesis and secretion) and regulatory (contribution to the control of sympathetic activity and vasopressin release) functions. In this narrative review we provide evidence supporting the concept that left atrial dilation and systolic dysfunction (left atrial remodelling) contributes to the progression of asymptomatic LV dysfunction to chronic symptomatic systolic HF as it is a prerequisite for the development of the pulmonary congestion and marked neuronhormoral activity that characterize the symptomatic state.

Optimising stroke prevention in non-valvular atrial fibrillation

Atrial fibrillation is associated with substantial morbidity and mortality. Pooled data from trials comparing antithrombotic treatment with placebo have shown that warfarin reduces the risk of stroke by 62%, and that aspirin alone reduces the risk by 22%. Overall, in high-risk patients, warfarin is superior to aspirin in preventing strokes, with a relative risk reduction of 36%. Ximelagatran, an oral direct thrombin inhibitor, was found to be as efficient as vitamin K antagonist drugs in the prevention of embolic events, but has been recently withdrawn because of abnormal liver function tests. The ACTIVE-W (Atrial Fibrillation Clopidogrel Trial with Irbesartan for Prevention of Vascular Events) study has demonstrated that warfarin is superior to platelet therapy (clopidogrel plus aspirin) in the prevention af embolic events. Idraparinux, a Factor Xa inhibitor, is being evaluated in patients with atrial fibrillation. Angiotensin-converting enzyme inhibitors and angiotensin II receptor-blocking drugs hold promise in atrial fibrillation through cardiac remodelling. Preliminary studies suggest that statins could interfere with the risk of recurrence after electrical cardioversion. Finally, percutaneous methods for the exclusion of left atrial appendage are under investigation in high-risk patients.