Role of autonomic reflexes in syncope associated with paroxysmal atrial fibrillation

2024 HRS expert consensus statement on arrhythmias in the athlete: Evaluation, treatment, and return to play

Youth and adult participation in sports continues to increase, and athletes may be diagnosed with potentially arrhythmogenic cardiac conditions. This international multidisciplinary document is intended to guide electrophysiologists, sports cardiologists, and associated health care team members in the diagnosis, treatment, and management of arrhythmic conditions in the athlete with the goal of facilitating return to sport and avoiding the harm caused by restriction. Expert, disease-specific risk assessment in the context of athlete symptoms and diagnoses is emphasized throughout the document. After appropriate risk assessment, management of arrhythmias geared toward return to play when possible is addressed. Other topics include shared decision-making and emergency action planning. The goal of this document is to provide evidence-based recommendations impacting all areas in the care of athletes with arrhythmic conditions. Areas in need of further study are also discussed.

Differential hemodynamic adaptations to tilt test in patients with idiopathic atrial fibrillation

The hemodynamic response during the transition from the supine to standing position in idiopathic atrial fibrillation (AF) patients is not completely understood. This study aimed to analyze the hemodynamic changes that occur during the head-up tilt test in idiopathic AF patients. We investigated the hemodynamic changes during the head-up tilt test with impedance cardiography in 40 AF patients (12 with AF rhythm-AFr and 28 with sinus rhythm-AFsr) and 38 non-AF controls. Patients with AFr had attenuated SVI decrease after standing when compared to AFsr and non-AF [ΔSVI in mL/m2: -1.3 (-3.4 to 1.7) vs. -6.4 (-17.3 to -0.1) vs. -11.8 (-18.7 to -8.0), respectively; p < 0.001]. PVRI decreased in AFr but increased in AFsr and non-AF [ΔPVRI in dyne.seg.m2/cm5: -477 (-1148 to 82.5) vs. 131 (-525 to 887) vs. 357 (-29 to 681), respectively; p < 0.01]. Similarly, compared with non-AF patients, AFr patients also had a greater HR and greater CI increase after standing. The haemodynamic response to orthostatic challenge suggests differential adaptations between patients with AF rhythm and those reverted to sinus rhythm or healthy controls. Characterizing the hemodynamic phenotype may be relevant for the individualized treatment of AF patients.

Pharmacologic prevention of recurrent vasovagal syncope: A systematic review and network meta-analysis of randomized controlled trials

Vasovagal syncope (VVS) is a transient loss of consciousness that currently imposes a high burden on health care systems with limited evidence of the comparative efficacy of available pharmacologic interventions. This study aims to compare all pharmacologic therapies suggested in randomized controlled trials (RCTs) through systematic review and network meta-analysis. A systematic search in PubMed, Embase, Web of Science, and Cochrane Library was conducted to identify RCTs evaluating pharmacologic therapies for patients with VVS. The primary outcome was spontaneous VVS recurrence. The secondary outcome was a positive head-up tilt test (HUTT) after receiving intervention, regarded as a lower level of evidence. Pooled risk ratio (RR) with 95% confidence interval (CI) was calculated using random-effect network meta-analysis. Pairwise meta-analysis for comparison with placebo was also performed when applicable. The surface under the cumulative ranking curve analysis was conducted to rank the treatments for each outcome. Twenty-eight studies with 1744 patients allocated to different medications or placebo were included. Network meta-analysis of the reduction in the primary outcome showed efficacy for midodrine (RR 0.55; 95% CI 0.35-0.85) and fluoxetine (especially in patients with concomitant anxiety) (RR 0.36; 95% CI 0.16-0.84). In addition, midodrine and atomoxetine were superior to other treatment options, considering positive HUTT (RR 0.37; 95% CI 0.23-0.59; and RR 0.49; 95% CI 0.28-0.86, respectively). Overall, midodrine was the only agent shown to reduce spontaneous syncopal events. Fluoxetine also seems to be beneficial but should be studied further in RCTs. Our network meta-analysis did not find evidence of the efficacy of any other medication.

Atrial Fibrillation Is Associated With Syncope and Falls in Older Adults: A Systematic Review and Meta-analysis

OBJECTIVE

To examine the potential association of atrial fibrillation (AF) to syncope and falls, we undertook a systematic review and meta-analysis given the increasing prevalence of AF in older adults as well as emerging data that it is a risk factor for dementia.

PATIENTS AND METHODS

CENTRAL, PubMed, and EMBASE databases were searched from inception to January 31, 2019, to retrieve relevant studies. Search terms consisted of MeSH, tree headings, and keywords relating patients with "AF," "falls," "syncope," and "postural hypotension." When possible; results were pooled using a random-effects model.

RESULTS

A total of 10 studies were included, with 7 studies (36,444 patients; mean ± SD age, 72±10 years) reporting an association between AF and falls and 3 studies (6769 patients; mean ± SD age, 65±3 years) reporting an association between AF and syncope. Pooled analyses demonstrate that AF is independently associated with falls (odds ratio, 1.19; 95% CI, 1.07-1.33; P=.001) and syncope (odds ratio, 1.88; 95% CI, 1.20-2.94; P=.006). There was overall moderate bias and low-moderate heterogeneity (I²=37%; P=.11) for falls and moderate bias with low statistical heterogeneity (I²=0%; P=.44) for syncope. Persistent AF, but not paroxysmal AF, was associated with orthostatic intolerance in 1 study (4408 patients; mean ± SD age, 66±6 years).

CONCLUSION

AF is independently associated with syncope and falls in older adults. Further studies are needed to delineate mechanistic links and to guide management to improve outcomes in these patients.

TRIAL REGISTRATION

PROSPERO: trial identifier: CRD4201810721.

[Differential diagnostics of unclear syncope]

The clarification of syncope is a diagnostic challenge as possible causes often occur only intermittently. Therefore, a detailed and standardized anamnesis is essential as it 1) differentiates syncope from other transient losses of consciousness (TLOC) and 2) directly clarifies possible causes of syncope. The risk stratification plays a central and very important role in order to avoid unnecessary examinations in patients with benign syncope and to provide patients with life-threatening, mostly cardiac syncopal episodes with timely diagnostics and treatment. In cases where the cause of syncope is still unclear, a standardized approach is indicated using extended diagnostics, such as a tilt table examination, a carotid sinus pressure test, prolonged telemetric monitoring or clarification with an implantable loop recorder (ILR).

Syncope in the German Nationwide inpatient sample - Syncope in atrial fibrillation/flutter is related to pulmonary embolism and is accompanied by higher in-hospital mortality

AIMS

Syncope is a common phenomenon in the general population. Although most of the causes are of benign origin, some comorbidities are accompanied by high mortality. We aimed to compare the in-hospital mortality of patients with syncope related to different comorbities and investigate the impact of syncope in patients with atrial fibrillation/flutter (AF).

METHODS

The nationwide inpatient sample of Germany of the years 2011-2014 was used for this analysis. Patients with syncope (ICD-code R55) were stratified by presence of selected comorbidities. Additionally, AF patients with and without syncope were compared. Incidence of syncope and in-hospital mortality were calculated. Syncope as a predictor of adverse outcome in AF patients was investigated.

RESULTS

In total, 1,628,859 hospitalizations of patients with syncope were identified; incidence was 504.6/100,000 citizens/year with case-fatality rate of 1.6%. Patients with syncope revealed frequently comorbidities as AF, heart failure and pneumonia. In-hospital mortality was high in syncope patients with pulmonary embolism (PE, 13.0%), pneumonia (12.8%), myocardial infarction (MI, 9.7%) and stroke (8.5%). We analysed 1,106,019 hospitalizations (52.9% females, 54.9% aged > 70 years) of patients with AF (2011-2014). Among these, 23,694 (2.1%) were coded with syncope and 0.7% died. Syncope had no significant impact on in-hospital mortality (OR 1.04, 95%CI 0.92-1.17, P = .503) independently of age, sex and comorbidities, but was associated with PE (OR 1.83, 95%CI 1.42-2.36, P < .001), MI (OR 1.68, 95%CI 1.48-1.90, P < .001), stroke (OR 1.66, 95%CI 1.42-1.94, P < .001) and pneumonia (OR 1.26, 95%CI 1.16-1.37, P < .001).

CONCLUSIONS

Syncope is a frequent cause for referrals in hospitals. While the overall in-hospital mortality rate is low (<2%), syncope in coprevalence with PE, pneumonia, MI and stroke showed a mortality rate > 8%. Syncope in AF patients had no independent impact on in-hospital mortality.

Sympathetic Nervous System Activation and Its Modulation: Role in Atrial Fibrillation

The autonomic nervous system (ANS) has a significant influence on the structural integrity and electrical conductivity of the atria. Aberrant activation of the sympathetic nervous system can induce heterogeneous changes with arrhythmogenic potential which can result in atrial tachycardia, atrial tachyarrhythmias and atrial fibrillation (AF). Methods to modulate autonomic activity primarily through reduction of sympathetic outflow reduce the incidence of spontaneous or induced atrial arrhythmias in animal models and humans, suggestive of the potential application of such strategies in the management of AF. In this review we focus on the relationship between the ANS, sympathetic overdrive and the pathophysiology of AF, and the potential of sympathetic neuromodulation in the management of AF. We conclude that sympathetic activity plays an important role in the initiation and maintenance of AF, and modulating ANS function is an important therapeutic approach to improve the management of AF in selected categories of patients. Potential therapeutic applications include pharmacological inhibition with central and peripheral sympatholytic agents and various device based approaches. While the role of the sympathetic nervous system has long been recognized, new developments in science and technology in this field promise exciting prospects for the future.

Clinical evidence of autonomic dysfunction due to atrial fibrillation: implications for rhythm control strategy

PURPOSE

The role of the autonomic nervous system in the genesis of atrial fibrillation (AF) has been well studied; however, the converse remains poorly understood. Pulmonary veins (PV) contain receptors important in cardiac reflexes. Here, we evaluated reflex responses in patients with paroxysmal AF (PAF) to lower body negative pressure (LBNP).

METHODS

Thirty-four PAF patients (including 14 PAF patients post successful PV Isolation; PVI) were compared to 14 age and sex-matched controls. Mean arterial pressure (MAP), heart rate (HR), systemic vascular resistance index (SVRI), cardiac index (CI), and stroke volume index (SVI) were measured continuously during - 0, - 20, and - 40 mmHg LBNP. LBNP reduces venous return, deactivating atrial receptors, thereby eliciting a reflex increase in SVRI to maintain MAP.

RESULTS

AF patients have higher BMI than the controls (p = 0.02). In control subjects, LBNP did not alter MAP as SVRI increased. In PAF patients, LBNP resulted in a reduction in MAP (- 4.8%) with attenuated SVRI response (+ 4.2%) compared to controls (p < 0.05). However, in the post-PVI group, SVRI increase was similar to controls (p = 0.12) although that was insufficient to maintain MAP. In all patients, both reduction in SVI and CI and increase in HR were similar in response to LBNP.

CONCLUSIONS

This study provides novel clinical evidence of autonomic dysfunction in PAF patients. Successful PVI results in partial recovery of the cardiac reflex. Therefore, not only does autonomic disturbance predispose to AF but it is also a consequence of AF; potentially contributing to disease progression. This could help explain the dictum "AF begets AF."

Atrial fibrillation in elderly patients with implantable loop recorders for unexplained syncope

BACKGROUND

An implantable loop recorder (ILR) assists in the diagnosis of unexplained syncope and atrial fibrillation (AF). Both become prevalent with age. Limited data exist describing the incidence of AF as the diagnostic rhythm underlying syncope in the elderly. This study aims to report the incidence of AF in older adults with ILRs for unexplained syncope and identify clinical characteristics associated with AF in this population.

METHODS

Retrospective observational study on patients with unexplained syncope seen in syncope clinics from two Canadian centers. Participants were ≥65 years old, without a history of AF, and received an ILR for unexplained syncope. Data were collected from patient's clinic charts. Arrhythmia diagnosis was based on ILR electrocardiogram reading during syncope (symptom-rhythm correlation). Fisher's exact test and the Student's t test were used to compare participants with and without AF.

RESULTS

In our cohort of 222 patients, 124 were females and 98 were males. Mean age at implant was 80 ± 8 years. Arrhythmia was diagnosed in 98 patients (44.1%). Median time to diagnosis was 18 months. AF was diagnosed in 17 (7.7%) participants. There were fewer males in the AF group than the no AF group (11.8%, 46.8%, p = 0.01). Age, baseline EKG, and prevalence of hypertension, diabetes, stroke, or ischemic heart disease were not statistically different between patients with AF and without AF.

CONCLUSIONS

Atrial fibrillation was a common diagnostic rhythm in this cohort of adults, aged 65 and older, with ILRs for unexplained syncope. It was observed more frequently in females.

Atrial fibrillation occurring during head-up tilt testing: Once detected, atrial fibrillation should be monitored, regardless of how it is detected

BACKGROUND

Atrial fibrillation (AF) often progresses to more sustained forms and increases the risk of ischemic stroke or sinus node dysfunction. However, there have been no data on the clinical outcomes of patients who developed AF during head-up tilt testing (HUT).

OBJECTIVE

The purpose of this study was to evaluate the clinical significance of AF detected during HUT performed for syncope evaluation.

METHODS

We analyzed incidence, short- and long-term prognosis, and predictors of adverse outcomes of AF detected during HUT, which was performed in 6780 consecutive patients without AF history.

RESULTS

Of the 6780 patients, 52 (0.8%) developed AF during passive tilting (n = 5), isoproterenol infusion (n = 32), and recovery phase (n = 15) of HUT, respectively. There was no short-term adverse event: spontaneous sinus conversion occurred in 43 patients (83%) within 48 hours. Over a median follow-up of 34.8 months, 24 patients (46%) had AF recurrence with initial presentation as ischemic stroke (n = 2), sinus node dysfunction requiring pacemaker (n = 10), and AF alone (n = 12). In addition, 19 of 24 recurred AF cases (79.2%) progressed to persistent/permanent forms. The index AF duration was identified as an independent predictor of AF recurrence. Patients with longer AF duration (≥1.0 hour) showed worse prognosis than did those with shorter AF duration (<1.0 hour).

CONCLUSION

The incidence of AF during HUT was ∼0.8%, and short-term prognosis was favorable. However, about half of the cases were complicated by long-term adverse outcomes. Therefore, regular follow-up might be warranted for patients with HUT-induced AF, particularly when AF duration is long.

Role of autonomic nervous system in atrial fibrillation

Atrial fibrillation is the most common sustained arrhythmia and is associated with significant morbidity and mortality. The autonomic nervous system has a significant role in the milieu predisposing to the triggers, perpetuators and substrate for atrial fibrillation. It has direct electrophysiological effects and causes alterations in atrial structure. In a significant portion of patients with atrial fibrillation, the autonomic nervous system activity is likely a composite of reflex excitation due to atrial fibrillation itself and contribution of concomitant risk factors such as hypertension, obesity and sleep-disordered breathing. We review the role of autonomic nervous system activation, with focus on changes in reflex control during atrial fibrillation and the role of combined sympatho-vagal activation for atrial fibrillation initiation, maintenance and progression. Finally, we discuss the potential impact of combined aggressive risk factor management as a strategy to modify the autonomic nervous system in patients with atrial fibrillation and to reverse the arrhythmogenic substrate.

[Management of syncope in clinical practice : What has changed according to the new ESC guidelines 2018?]

Syncope is a common problem in clinical practice, which affects approximately 1% of patients admitted to European emergency departments. The clinical practice guidelines for the diagnosis and management of syncope published by the European Society of Cardiology (ESC) are based on the newest scientific data in the field and have provided clinical cardiologists with a structured therapeutic approach for affected patients over many years. The previous ESC guidelines on syncope were published in 2009 and are compared to the most recent edition, which was published in 2018. This review summarizes the most important innovations with respect to the diagnostic principles and treatment of syncope. The initial assessment of the patient and the risk stratification in the emergency department are the focus of the review. Another important topic that is adequately covered in the current guidelines is the rising significance of implantable loop recorders for the evaluation of unexplained syncope and the assessment of potential indications for a definitive treatment with a pacemaker or implantable cardioverter defibrillator (ICD). Additional changes involve the evidence level with respect to the use of other diagnostic (ECG monitoring, tilt testing) and therapeutic measures (indications for pacemaker implantation, catheter ablation of tachycardiac rhythm disorders).

Syncope: Electrocardiographic and Clinical Correlation

Syncope is a frequent condition, owing to a transient global cerebral hypoperfusion, that may depend on a reduction of vascular total peripheral resistance and/or cardiac output. Cardiac syncope doubled the risk of death from any cause and increased the risk of nonfatal and fatal cardiovascular events. Arrhythmias are the most common cardiac causes of syncope. Both bradyarrhythmias and tachyarrhythmias may predispose to syncope. The first line evaluation relies on clinical history, physical examination, active standing test, 12-lead echocardiogram. The diagnostic yield of electrophysiological study in detecting the cause of syncope depends highly on the pretest probability.

[Syncope: electrocardiogram and autonomic function tests]

Syncope represents one of the most frequent reasons for consultation in the emergency department. A proper identification will allow a precise etiologic approach and the optimization of delivery of health resources.
Once knowing the classification of syncope; it is the clinical interrogatory what enables to discriminate which of these patients present with a neurogenic mediated syncope or a cardiac mediated syncope. The use of diagnostic methods such as the tilt test, will clarify what type of neurally mediated syncope predominates in the patient.
The electrocardiogram is the cornerstone in the identification of those patients who had a true episode of self-limited or aborted sudden death as the first manifestation of their syncope, a fact which provides prognostic and therapeutic information that will impact the morbidity and mortality.

AF is associated with self-reported syncope and falls in a general population cohort

BACKGROUND

syncope is an important, but underestimated clinical problem in older persons. It is often overlooked in clinical practice or mistaken for falls. Atrial fibrillation (AF) is the most common cardiac arrhythmia, but little evidence exists regarding the association between AF, falls and syncope in the general population.

METHODS

cross-sectional analyses within a population sample of people aged 50+, taken from The Irish Longitudinal Study on Ageing. Ten-minute electrocardiogram recordings (n = 4,885) were analysed to detect AF. Syncope (self-reported faints or blackouts) and falls in the past year, co-morbidities, health measures and medications were gathered through computer-aided personal interviews. Multivariable logistic regression was performed to study associations between AF, falls and syncope.

RESULTS

mean age was 62 years (range: 50-91), 54% were female. Prevalence of AF was 3%, increasing to 8% in participants aged 75+. Of participants, 5% (n = 223) reported syncope and 20% (n = 972) reported falls. After adjustment for confounders, AF was significantly associated with faints and blackouts (odds ratio (OR) 2.0 [95% confidence interval (CI) 1.0-3.9]). After stratification by age category, we found that this association was strongest and only significant in participants aged 50-64 years (OR 4.4 [1.5-12.6]). Stratified for age group, AF was significantly associated with falls in participants aged 65-74 years (OR 2.0 [1.0-4.1]).

CONCLUSIONS

adults aged 50+ with self-reported syncope and adults aged 65-74 years with falls are twice as likely to have AF at physical examination. These associations are independent of stroke, cardiovascular and psychotropic drugs and other confounders. Further longitudinal studies are needed to explore this association and potential causality further.

Syncope due to Autonomic Dysfunction: Diagnosis and Management

Syncope is one of several disorders that cause transient loss of consciousness. Cerebral hypoperfusion is the proximate cause of syncope. Transient or fixed autonomic nervous system dysfunction is a major contributor in many causes. A structured approach to the evaluation of syncope allows for more effective therapy.

Atrial Fibrillation in the Young: A Neurologist's Nightmare

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia seen in clinical practice with prevalence in excess of 33 million worldwide. Although often asymptomatic and until recently considered a "benign" arrhythmia, it is now appreciated that thromboembolism resulting from AF results in significant morbidity and mortality predominantly due to stroke. Although an arrhythmia more commonly affecting the elderly, AF can also occur in the young. This review focuses on the impact of AF in the younger population and discusses the dilemmas of managing younger patients with AF.

[Syncope : epidemiology, definition, classification, pathophysiology and prognosis]

Syncope is a common clinical issue. Around 40 % of the total population experience syncope during their lifetime. Serious injuries and reduced quality of life are often observed after syncope. Furthermore, in some cases syncope can be associated with an unfavorable prognosis. Due to the complex etiology and pathophysiology, syncope provides challenges for doctors both in private and in clinical practices. This review is based on the latest European guidelines for syncope which were formulated by internists, neurologists, emergency physicians and cardiologists and gives an overview of the current epidemiology, definition, classification, pathophysiology and prognosis of syncope.

"Vasovagal" response during ventricular fibrillation: incidence and implications

BACKGROUND

The purpose of this study was to assess the relationship between changes in sinus node cycle length (SNCL) during ventricular fibrillation (VF) and the peripheral changes in blood pressure (BP) and sympathetic nerve activity (SNA) in human subjects. We hypothesized that patients with no SNCL shortening during VF have a vasovagal-like response with a greater decrease in BP and SNA when compared to patients with SNCL shortening.

METHODS

SNCL, BP, and SNA recordings were attempted in 24 patients undergoing the implantation of a dual-chamber implantable defibrillator. Changes were measured during the first 5 seconds of VF and compared with the 5 seconds prior to VF induction.

RESULTS

SNCL shortened during VF in nine patients (mean%∆SNCL = -12 ± 8%) and remained unchanged or lengthened in seven patients (mean%∆SNCL = 7 ± 7%). Eight patients had ventriculoatrial (VA) conduction prohibiting assessment of SNCL changes. In patients with SNCL shortening, the %∆MBP (mean BP) was -47 ± 6% compared to -58 ± 8% in patients with no SNCL shortening (P < 0.01). In patients with VA conduction, the %∆MBP was -54 ± 3%. SNA recordings were successfully obtained in four patients. When compared to baseline, SNA increased by 34 ± 30% in two patients with SNCL shortening, decreased by 25% in one patient with SNCL lengthening, and by 90% in the fourth patient with VA conduction.

CONCLUSIONS

We have shown that patients with no SNCL shortening have a significantly greater decrease in MBP during VF when compared to patients with SNCL shortening. The underlying mechanism appears to be reflex mediated with a vasovagal-like response in patients with no SNCL shortening.

Syncope: diagnosis and management

Syncope is defined as transient loss of consciousness due to global cerebral hypoperfusion. It is characterized by having a relatively rapid onset, brief duration with spontaneous and full recovery. The major challenge in the evaluation of patients with syncope is that most patients are asymptomatic at the time of their presentation. A thorough history and physical examination including orthostatic assessment are crucial for making the diagnosis. After initial evaluation, short-term risk assessment should be performed to determine the need for admission. If the short-term risk is high, inpatient evaluation is needed. If the short-term risk is low, outpatient evaluation is recommended. In patients with suspected cardiac syncope, monitoring is indicated until a diagnosis is made. In patients with suspected reflex syncope or orthostatic hypotension, outpatient evaluation with tilt-table testing is appropriate. Syncope units have been shown to improve the rate of diagnosis while reducing cost and thus are highly recommended.

Autonomic modulation in a patient with syncope and paroxysmal atrial-fibrillation

We report a case of a patient with recurrent syncope and paroxysmal atrial fibrillation whose clinical status greatly improved after a period of orthostatic training. The potential efficacy of this non-pharmacological measure in modulating the autonomic tone is discussed below.

[Cardiac syncope : diagnosis and therapy]

The second most frequent category of syncope is cardiac syncope. In contrast to syncope of noncardiac causes, the 1-year mortality of patients presenting with cardiac syncope without treatment is as high as 33%. Therefore, immediate diagnosis and treatment are necessary. Bradyarrhythmias or tachyarrhythmias are the most common causes of cardiac syncope. In many cases, an initial evaluation including history, physical examination, and electrocardiogram identifies the cause of syncope, so that specific treatment can be initiated immediately. In the remainder of cases, implantable loop recorders are useful to identify arrhythmias, while the presence or absence of structural cardiac disease is diagnosed by echocardiography. Syncope due to arrhythmias is typically treated with implantation of a pacemaker or an implantable cardioverter-defibrillator; treatment of syncope of other cardiac causes requires therapy of the underlying heart disease.

Atrial fibrillation is associated with decreased cardiac sympathetic response to isometric exercise in CHF in comparison to sinus rhythm

BACKGROUND

The presence of atrial fibrillation (AF) in congestive heart failure (CHF) is accompanied by increased mortality, although the exact mechanism is unclear. In previous studies, we have demonstrated cardiac baroreceptor abnormalities in association with AF and CHF. In this study, we sought to examine the effect of cardiac rhythm on the cardiac sympathetic response to exercise in CHF.

METHODS

In 13 CHF patients (six AF, seven SR, left ventricular ejection fraction 31 +/- 2%, age 61 +/- 1 years), we measured the hemodynamic and cardiac sympathetic response isometric handgrip (IHG) exercise.

RESULTS

At baseline the groups were well matched. Baseline hemodynamics and cardiac sympathetic activity did not significantly differ between the cohorts. In response to IHG exercise, both groups demonstrated significant hemodynamic responses. In conjunction, the sinus rhythm (SR) group demonstrated a significant increase in cardiac sympathetic response to exercise (P = 0.04) while in contrast the AF group did not (P = 0.6).

CONCLUSION

In this study, we demonstrate for the first time that the combination of AF and CHF is accompanied by a marked attenuation of the cardiac sympathetic response to acute hemodynamic stress. This implies AF is associated with a further impairment of baroreceptor response in CHF compared to SR. These findings present possible insights to the associated increased mortality and pathogenesis of AF with CHF.

[Atrial fibrillation and the autonomous nervous system]

The autonomic nervous system has a crucial role in the genesis, maintenance and abruption of atrial fibrillation. The substrate and trigger mechanism of atrial fibrillation can be influenced by the changing autonomic tone. The authors summarize the current knowledge on the relationship between autonomic nervous system and atrial fibrillation. The special neuroanatomical status and the role of autonomic reflexes and baroreflex in the initiation, maintenance, and termination of arrhythmia are reviewed. Furthermore, the mechanism and consequences of autonomic effect of the curative radiofrequency catheter ablation of pulmonary vein with atrial vagal neuroablation are discussed. At the end we also summarize the pharmacologic therapy of atrial fibrillation. Classification of atrial fibrillation, as either vagal or adrenergic, has only limited impact on current management.

Back to the Future: The Role of the Autonomic Nervous System in Atrial Fibrillation

The purpose of this manuscript is to review the current literature regarding the role of the autonomic nervous system (ANS) in atrial fibrillation (AF). We will be reviewing its effect on initiation, maintenance, and termination of AF, with emphasis on the role of baroreflex gain (BRG) and autonomic reflexes in the maintenance of this arrhythmia. While it is generally accepted that the ANS plays an important role in AF, the extent of that role remains controversial. Much of the controversy could be explained by the time frame during which the autonomic measurements were made, the differences in patient population, and possibly the differential effect of the autonomic changes on the trigger versus the substrate. While vagal stimulation results in shortening of the atrial effective refractory period and increased dispersion of refractoriness, its effect on the "trigger" might be antiarrhythmic. During AF, cardiac filling pressure increases while arterial blood pressure decreases sending conflicting messages to the medulla. The acute effect is an increase in sympathetic activity to ensure adequate hemodynamic stability. On the other hand, the long-term effects might be impairment in the cardiopulmonary BRG and changes that accentuate the presence of AF. While radiofrequency ablation has provided us with a unique insight into the role of possible denervation in AF suppression, the exact mechanisms involved are far from being completely understood. Today, in an era where great technological advances have occurred, our need to understand the role of the ANS in AF is greater than ever.

Interrelationships Between the Autonomic Nervous System and Atrial Fibrillation

Mechanisms responsible for atrial fibrillation are not completely understood but the autonomic nervous system is a potentially potent modulator of the initiation, maintenance, termination and ventricular rate determination of atrial fibrillation. Complex interactions exist between the parasympathetic and sympathetic nervous systems on the central, ganglionic, peripheral, tissue, cellular and subcellular levels that could be responsible for alterations in conduction and refractoriness properties of the heart as well as the presence and type of triggered activity, all of which could contribute to atrial fibrillation. These dynamic inter-relationships may also be altered dependent upon other neurohumoral modulators and cardiac mechanical effects from ventricular dysfunction and congestive heart failure. The clinical implications regarding the effects of the autonomic nervous system in atrial fibrillation are widespread. The effects of modulating ganglionic input into the atria may alter the presence or absence of atrial fibrillation as has been highlighted from ablation investigations. This article reviews what is known regarding the inter-relationships between the autonomic nervous system and atrial fibrillation and provides state of the art information at all levels of autonomic interactions.

Neurally mediated syncope manifesting during atrial fibrillation: a case report

A 64-year-old male was admitted to hospital because of repeated episodes of syncope and palpitation. Ambulatory monitoring revealed paroxysmal atrial fibrillation (AF) as the cause of palpitation; he did not have structural heart disease. The induction of AF by rapid pacing (50 Hz for 1 s) in an upright position provoked syncope with a vasodepressor response. Atropine sulfate blocked the induction of syncope. The possible etiology was neurally mediated syncope that manifested only during AF, which suggests that the abnormal vagal activity during AF in this case exaggerated the vasodepessor response while upright.

[Atypical sinus node dysfunction. Usefulness of implantable Holter. A case report]

We present an 84 year-old female patient with repeated syncopes/presyncopes in the last nine years. All diagnosis tests were negative, including ECG, 24-hour Holter, tilt table test and EP study. Therefore, a subcutaneous insertable loop recorder was implanted (Reveal). The recording of three episodes showed the association of presyncope with the onset of atrial fibrilation and, in two syncopes, with an atrial pause between AF episodes. Probably an abnormal prolonged sinus node recovery time (more than 6 s) allowed AF to restart before the sinus rhythm.

Impaired autonomic function predicts dizziness at onset of paroxysmal atrial fibrillation

BACKGROUND

Paroxysmal atrial fibrillation is associated with various symptoms, including dizziness, which presumably reflects hemodynamic deterioration. Given the importance of the autonomic nervous system in mitigating the hemodynamic effect of atrial fibrillation, we hypothesized that autonomic function would be predictive of the severity of dizziness.

METHODS

The study group comprised 73 patients with paroxysmal atrial fibrillation (mean age 54.1 years, 51 males). Forty-three (59%) patients had lone atrial fibrillation. Mean ventricular rate during atrial fibrillation was 99+/-16 beats/min. On average, patients had a 3-year history of one paroxysm per week lasting 2 h. Autonomic function was assessed using autonomic function tests, including noninvasive measurement of baroreflex sensitivity. Head up tilting was used to test vasovagal reactivity. Severity of dizziness at onset of atrial fibrillation was quantified by the patients using a five-point scale (1=none; 2=light; 3=mild; 4=moderate; and 5=severe). Multivariate analysis was performed to identify the independent predictors of the severity of dizziness.

RESULTS

Mean severity of dizziness was 3.36+/-1.65. Multivariate predictors of moderate-to-severe dizziness as opposed to none-to-mild dizziness were a low 30-15 ratio after standing up and low baroreflex sensitivity. Though syncope was never reported nine patients showed a full vasovagal response during head up tilting.

CONCLUSIONS

It is concluded that dizziness in patients with "treated" atrial fibrillation in the setting of none to mild structural heart disease is predicted by impaired autonomic function. Vasovagal reactivity appears not to be involved in this connection.