Interrelationships Between the Autonomic Nervous System and Atrial Fibrillation

Spectrum of Non-Obstructive Coronary Artery Disease and Its Relationship with Atrial Fibrillation

This article aims to analyze the relationship between non-obstructive coronary artery disease (NOCAD) and atrial fibrillation (AF), exploring the underlying pathophysiological mechanisms and implications for clinical management. NOCAD and AF are prevalent cardiovascular conditions that often coexist, yet their interrelation is not well understood. NOCAD can lead to ischemic necrosis of cardiomyocytes and their replacement with fibrous tissue, sustaining focal ectopic activity in atrial myocardium. Atrial fibrillation, on the other hand, the most common sustained cardiac arrhythmia, is able to accelerate atherosclerosis and increase oxygen consumption in the myocardium, creating a mismatch between supply and demand, and thus promoting the development or worsening of coronary ischemia. Therefore, NOCAD and AF seem to be a complex interplay with one begets another.

Postoperative QRS duration to left ventricular end-diastolic diameter ratio as a predictor for the risk of postoperative atrial fibrillation in cardiac surgery: A single-center prospective study

Background and aims

Postoperative atrial fibrillation (POAF) is a frequent complication following cardiac surgery and is associated with adverse clinical outcomes. Our study aimed at determining the clinical and echocardiographic predictors of POAF in patients with cardiac surgery and management of this group of patients may improve their outcome.

Methods

We prospectively enrolled patients from the department of cardiovascular surgery in the Second Hospital of Tianjin Medical University from October 23, 2020 to October 30, 2022, without a history of atrial fibrillation. Cox regression was used to identify significant predictors of POAF.

Results

A total of 217 patients (79 [36.41 %] were female, 63.96 ± 12.32 years) were included. 88 (40.55 %) patients met the criteria for POAF. Cox regression showed that preoperative left atrial diameter (LAD) (HR: 1.040, 95 % CI 1.008-1.073, p = 0.013) and postoperative QRS/LVEDD (HR: 0.398, 95 % CI 0.193-0.824, p = 0.013) and E/e' (HR: 1.029, 95 % CI 1.002-1.057，p = 0.033) were predictors of POAF.

Conclusion

Preoperative LAD and postoperative QRS/LVEDD and E/e' were predictors of POAF in patients undergoing cardiac surgery.

Trial registration site

http://www.chictr.org.cn.

Registration number

ChiCTR2200063344.

A multiscale predictive digital twin for neurocardiac modulation

Cardiac function is tightly regulated by the autonomic nervous system (ANS). Activation of the sympathetic nervous system increases cardiac output by increasing heart rate and stroke volume, while parasympathetic nerve stimulation instantly slows heart rate. Importantly, imbalance in autonomic control of the heart has been implicated in the development of arrhythmias and heart failure. Understanding of the mechanisms and effects of autonomic stimulation is a major challenge because synapses in different regions of the heart result in multiple changes to heart function. For example, nerve synapses on the sinoatrial node (SAN) impact pacemaking, while synapses on contractile cells alter contraction and arrhythmia vulnerability. Here, we present a multiscale neurocardiac modelling and simulator tool that predicts the effect of efferent stimulation of the sympathetic and parasympathetic branches of the ANS on the cardiac SAN and ventricular myocardium. The model includes a layered representation of the ANS and reproduces firing properties measured experimentally. Model parameters are derived from experiments and atomistic simulations. The model is a first prototype of a digital twin that is applied to make predictions across all system scales, from subcellular signalling to pacemaker frequency to tissue level responses. We predict conditions under which autonomic imbalance induces proarrhythmia and can be modified to prevent or inhibit arrhythmia. In summary, the multiscale model constitutes a predictive digital twin framework to test and guide high-throughput prediction of novel neuromodulatory therapy. KEY POINTS: A multi-layered model representation of the autonomic nervous system that includes sympathetic and parasympathetic branches, each with sparse random intralayer connectivity, synaptic dynamics and conductance based integrate-and-fire neurons generates firing patterns in close agreement with experiment. A key feature of the neurocardiac computational model is the connection between the autonomic nervous system and both pacemaker and contractile cells, where modification to pacemaker frequency drives initiation of electrical signals in the contractile cells. We utilized atomic-scale molecular dynamics simulations to predict the association and dissociation rates of noradrenaline with the β-adrenergic receptor. Multiscale predictions demonstrate how autonomic imbalance may increase proclivity to arrhythmias or be used to terminate arrhythmias. The model serves as a first step towards a digital twin for predicting neuromodulation to prevent or reduce disease.

Prediction, prevention and management of new onset peri-operative atrial fibrillation and flutter in patients undergoing non-cardiac thoracic surgery: a narrative review

Peri-operative atrial fibrillation and flutter (POAF) is recognized as a common complication of non-cardiac thoracic surgery. It is associated with hemodynamic instability, prolonged hospital stay, a risk of stroke and increased risk of mortality. The potential pathogenesis for POAF after non-cardiac thoracic surgery is multifactorial and not fully understood yet. Evaluation of risk factors and prediction of POAF can be beneficial for prevention and management of POAF in patients undergoing non-cardiac thoracic surgery. In this article, we reviewed related studies in order to provide a practically and clinically applicable strategy for anesthesiologists to effectively predict, prevent and manage new onset POAF in patients undergoing non-cardiac thoracic surgery.

Atrial Branch Coronary Artery Stenosis as a Mechanism for Atrial Fibrillation

BACKGROUND

The etiology of atrial fibrillation (AF) is multifactorial and incompletely understood.

OBJECTIVE

Evaluate the association between coronary artery disease (CAD) affecting atrial tissue and AF.

METHODS

Patients from a single center with obstructive CAD during cardiac catheterization (1/12007-12/1/2013) were included in a matched case-control analysis, based on the presence or absence of new-onset AF within 12 months post-catheterization. Quantitative measurements of stenosis severity were performed for sinoatrial (SA) nodal artery, atrioventricular (AV) nodal artery, and right intermediate atrial artery (RIAA), as well as the right coronary, left circumflex, and left anterior descending proximal to the take-off for each atrial-level artery. A multivariable logistic regression model identified factors associated with AF.

RESULTS

Among 1,794 patients, 115 (6%) developed AF within 1-year post-catheterization. The matched cohort included 110 patients with and 110 patients without AF within 12 months post-catheterization. Higher odds of AF at 1 year were associated with increasing lesion stenosis severity in the RIAA (OR 1.41 per 10% increase >50%, 95% CI 1.01-1.97, p=0.047) and AV nodal artery (OR 1.58 per 10% increase >50%, 95% CI 1.00-2.49, p=0.050). Odds of AF diagnosis during the year post-catheterization increased with the number of atrial arteries with >50% lesion (OR 1.53 for each additional artery, 95% CI 1.08-2.15, p=0.015).

CONCLUSIONS

Among patients with obstructive CAD, disease of the AV nodal artery and RIAA, as well as higher burden of CAD within all arteries supplying blood flow to the atrial myocardium were associated with higher odds of new-onset AF at 1 year.

Correlation of heart rate recovery and heart rate variability with atrial fibrillation progression

Objective

To examine the combination of heart rate recovery (HRR) and heart rate variability (HRV) in predicting atrial fibrillation (AF) progression.

Methods

Data from patients with a first detected episode of AF who underwent treadmill exercise testing and 24-h Holter electrocardiography were retrospectively analysed. Autonomic dysfunction was verified using HRR values. Sympathetic and parasympathetic modulation was analysed by HRV. AF progression was defined as transition from the first detected paroxysmal episode to persistent/permanent AF.

Results

Of 306 patients, mean LF/HF ratio and HRR did not differ significantly by AF progression regardless of age (< or ≥65 years). However, when the LF/HF ratio was divided into tertiles, in patients aged <65 years, the mid LF/HF (1.60–2.40) ratio was significantly associated with lower AF progression rates and longer maintenance of normal sinus rhythm. For patients aged <65 years, less metabolic equivalents were related to higher AF progression rates. For patients aged ≥65 years, a low HRR was associated with high AF progression rates.

Conclusion

In relatively younger age, high physical capacity and balanced autonomic nervous system regulation are important predictors of AF progression. Evaluation of autonomic function assessed by age could predict AF progression.

Heart rate recovery is useful for evaluating the recovery of exercise tolerance in patients with heart failure and atrial fibrillation

This study aimed to examine the factors that contribute to improvement of exercise tolerance in patients with heart failure (HF) and atrial fibrillation (AF) following cardiac rehabilitation. Our hypothesis is that parasympathetic values are important for recovering exercise tolerance in those patients. We included 84 consecutive patients with HF and AF (mean age: 69 ± 15 years, 80% men). All of the patients underwent a cardiopulmonary exercise test and had pre and post 5 month cardiac rehabilitation assessed. After 155 ± 11 days and 44 ± 8 sessions, 73 patients (86%) showed an increase in peak oxygen uptake (VO₂) and VO₂ at the anaerobic threshold. In univariate linear regression analysis, the % change in heart rate recovery, plasma B-type natriuretic peptide levels, resting heart rate, and the minute ventilation /carbon dioxide output slope were significantly related to that of peak VO₂ (p < 0.01, p = 0.03, p = 0.02, p < 0.01, respectively). Stepwise multivariate linear regression analysis showed that the % change in heart rate recovery was independently related to that of peak VO₂ (p < 0.05). Our results suggest that heart rate recovery is closely associated with recovery of exercise tolerance in patients with HF and AF after CR.

The role of the tripartite synapse in the heart: how glial cells may contribute to the physiology and pathophysiology of the intracardiac nervous system

One of the major roles of the intracardiac nervous system (ICNS) is to act as the final site of signal integration for efferent information destined for the myocardium to enable local control of heart rate and rhythm. Multiple subtypes of neurons exist in the ICNS where they are organized into clusters termed ganglionated plexi (GP). The majority of cells in the ICNS are actually glial cells; however, despite this, ICNS glial cells have received little attention to date. In the central nervous system, where glial cell function has been widely studied, glia are no longer viewed simply as supportive cells but rather have been shown to play an active role in modulating neuronal excitability and synaptic plasticity. Pioneering studies have demonstrated that in addition to glia within the brain stem, glial cells within multiple autonomic ganglia in the peripheral nervous system, including the ICNS, can also act to modulate cardiovascular function. Clinically, patients with atrial fibrillation (AF) undergoing catheter ablation show high plasma levels of S100B, a protein produced by cardiac glial cells, correlated with decreased AF recurrence. Interestingly, S100B also alters GP neuron excitability and neurite outgrowth in the ICNS. These studies highlight the importance of understanding how glial cells can affect the heart by modulating GP neuron activity or synaptic inputs. Here, we review studies investigating glia both in the central and peripheral nervous systems to discuss the potential role of glia in controlling cardiac function in health and disease, paying particular attention to the glial cells of the ICNS.

Preventive effect of low-dose landiolol on postoperative atrial fibrillation study (PELTA study)

Objective

To investigate the efficacy of prophylactic administration of low-dose landiolol on postoperative atrial fibrillation (POAF) in patients after cardiovascular surgery.

Methods

Consecutive 150 patients over 70 years of age who underwent cardiovascular surgery for valvular, ischemic heart, and aortic diseases were enrolled in this single-center prospective randomized control study from 2010 to 2014. They were assigned to three treatment groups: 1γ group (landiolol at 1 μg/kg/min), 2γ group (landiolol at 2 μg/kg/min), or control group (no landiolol). In the two landiolol groups, landiolol hydrochloride was intravenously administered for a period of 4 days postoperatively. Electrocardiography was continuously monitored during the study period, and cardiologists eventually assessed whether POAF occurred or not.

Results

POAF occurred in 24.4% of patients in the control group, 18.2% in 1γ group, and 11.1% in 2γ group (p = 0.256). Multivariate logistic regression analysis showed that the incidence of POAF tended to decrease depending on the dose of landiolol (trend-p = 0.120; 1γ group: OR = 0.786, 95% CI 0.257–2.404; 2γ group: OR = 0.379, 95% CI 0.112–1.287). Subgroup analysis showed a significant dose-dependent reduction in POAF among categories of female sex, non-use of angiotensin II receptor blockers (ARBs) before surgery, and valve surgery (each trend-p = 0.02, 0.03, and 0.004).

Conclusions

These findings indicate that prophylactic administration of low-dose landiolol may not be effective for preventing the occurrence of POAF in overall patients after cardiovascular surgery, but the administration could be beneficial to female patients, patients not using ARBs preoperatively, and those after valvular surgery.

The characteristics and regularities of cardiac adverse drug reactions induced by Chinese materia medica: A bibliometric research and association rules analysis

ETHNOPHARMACOLOGICAL RELEVANCE

Chinese materia medica (CMM) has been widely used as an approach of ethnomedicine worldwide. Recently, there are growing concerns related to the potential cardiotoxicity of herbal medicines but comprehensive studies are limited.

METHODS

Comprehensive literature retrieval via publicly available electronic databases was performed to identify the case reports that focused on cardiac adverse reactions (ADRs) triggered by oral CMMs. And a bibliometric survey was conducted to analyze the most commonly suspected risk factors in terms of responsible CMMs, susceptible patients and clinical administration of cardiac ADRs. Moreover, the techniques of data mining were utilized to investigate the regularities and association between the ADRs status and major contributory factors.

RESULTS

The available evidence of current research indicated that many influential factors were strongly associated with cardiac ADRs caused by oral CMMs inevitably, including pediatric patients, poisonous CMMs (especially herbs of Aconitum species), overdose and self-medication. Specifically, the timely and effective resuscitation could attribute their favorable capacity to reduce mortality for cardiac ADRs. Notably, the cardiac ADRs cases had often concomitant the ADRs of the nervous system and digestive system.

CONCLUSION

The comprehensive features and risk factors of cardiac ADRs induced by oral CMMs can be discovered and elucidated through the approaches of bibliometric research, association rules analysis, and data mining technology, which raise the profile and awareness of the rational applications of CMMs and pharmacovigilance within relevant heart side effects.

A Novel Loss-of-Function Variant in the Chloride Ion Channel Gene Clcn2 Associates with Atrial Fibrillation

Atrial Fibrillation (AF) is the most common cardiac arrhythmia. Its pathogenesis is complex and poorly understood. Whole exome sequencing of Danish families with AF revealed a novel four nucleotide deletion c.1041_1044del in CLCN2 shared by affected individuals. We aimed to investigate the role of genetic variation of CLCN2 encoding the inwardly rectifying chloride channel ClC-2 as a risk factor for the development of familiar AF. The effect of the CLCN2 variant was evaluated by electrophysiological recordings on transiently transfected cells. We used quantitative PCR to assess CLCN2 mRNA expression levels in human atrial and ventricular tissue samples. The nucleotide deletion CLCN2 c.1041_1044del results in a frame-shift and premature stop codon. The truncated ClC-2 p.V347fs channel does not conduct current. Co-expression with wild-type ClC-2, imitating the heterozygote state of the patients, resulted in a 50% reduction in macroscopic current, suggesting an inability of truncated ClC-2 protein to form channel complexes with wild type channel subunits. Quantitative PCR experiments using human heart tissue from healthy donors demonstrated that CLCN2 is expressed across all four heart chambers. Our genetic and functional data points to a possible link between loss of ClC-2 function and an increased risk of developing AF.

A comparison of the incidence of supraventricular arrhythmias between thoracic paravertebral and intercostal nerve blocks in patients undergoing thoracoscopic surgery: A randomised trial

BACKGROUND

Postoperative supraventricular arrhythmias are common in patients after thoracoscopic lobectomy. Inadequate pain control has long been recognised as a significant risk factor for arrhythmias. The performance of ultrasound-guided (USG) thoracic paravertebral block (PVB) is increasing as an ideal technique for postoperative analgesia.

OBJECTIVE

We conducted this study to evaluate whether a single-shot USG thoracic PVB would result in fewer postoperative supraventricular tachycardias (SVT) than intercostal nerve blocks (ICNBs) after thoracoscopic pulmonary resection.

DESIGN

A randomised controlled study.

SETTING

A single university hospital.

PATIENTS

Sixty-eight patients undergoing thoracoscopic lobectomy were randomised into two equal groups of 34.

INTERVENTIONS

For postoperative pain control, all patients received a total of 0.3 ml kg of a mixture containing 0.5% ropivacaine and 1/200 000 epinephrine after placement of needles for either a single thoracic PVB or two individual ICNBs, both guided by ultrasound. Data were obtained during the first 48 postoperative hours.

MAIN OUTCOME MEASURES

The primary outcome was the incidence of SVT after thoracoscopic pulmonary resection.

RESULTS

During the first 48 postoperative hours, the incidences of SVT and atrial fibrillation were lower in the USG thoracic PVB group (14.7 vs. 46.9%, P = 0.004 and 3.0 vs. 18.8%, P = 0.037, respectively). The requirement for β-receptor blockade was more frequent in the ICNBs group than in the PVB group (5.9 vs. 25%, P = 0.033).

CONCLUSION

After placement of the needle using ultrasound guidance, a single-shot thoracic PVB is a well tolerated and effective technique to reduce the incidences of postoperative SVT and atrial fibrillation in patients undergoing thoracoscopic pulmonary resection.

TRIAL REGISTRATION

http://www.chictr.org/cn/, registration number: ChiCTR-IOR-17010952.

QT prolongation and variability: new ECG signs of atrial potentials dispersion before atrial fibrillation onset

AIMS

QT interval may be considered an indirect marker of atrial repolarization. Aim of our study was to verify if QT interval variations precede the onset of atrial fibrillation (AF).

METHODS

We analyzed 21 AF onsets recorded at 24-h Holter ECG. Triggering supraventricular extrabeats (TSVEB) were identified and matched to nontriggering supraventricular extrabeats (NTSVEB) with the same prematurity index. QT and QTc intervals and their variability (max-min QT interval) were measured in the 10 beats preceding TSVEB and NTSVEB.

RESULTS

QTc (470.1 ± 56.7 vs. 436.7 ± 25.6 ms; P = 0.006), QT (36.8 ± 13.1 vs. 21.1 ± 10.1 ms; P = 0.001) and QTc variability (41.5 ± 15.8 vs. 23.1 ± 11.9; P = 0.001) significantly varied between TSVEB and NTSVEB. By stratifying AF onsets in vagal (n = 10) and adrenergic (n = 11) according to Heart Rate Variability, significant differences emerged concerning QT (35.20 ± 16.48 vs. 22.70 ± 10.23 ms, P = 0.006) and QTc variability (39.30 ± 18.32 vs. 25.60 ± 12.91 ms, P = 0.029) for vagal onsets and QTc (477.73 ± 57.50 vs. 438.00 ± 28.55 ms, P = 0.045), QT (38.36 ± 9.79 vs. 19.73 ± 10.21 ms, P = 0.005) and QTc variability (43.55 ± 13.72 vs. 20.82 ± 11.01 ms, P = 0.004) for adrenergic onsets. By stratifying AF onsets in type I (n = 7) or II (n = 14) according to a cycle length variation in the 30 s before the onset greater or smaller than 10% respectively, significant differences were noted concerning QTc (477.73 ± 57.50 vs. 438 ± 28.55 ms, P = 0.045), QT (43.55 ± 13.72 vs. 20.82 ± 11.01 ms, P = 0.005) and QTc variability (43.55 ± 13.72 vs. 20.82 ± 11.01 ms, P = 0.004) in type I and QT (35.20 ± 16.48 vs. 22.70 ± 10.23 ms, P = 0.006) and QTc variability (39.30 ± 18.32 vs. 25.60 ± 12.91 ms, P = 0.029) in type II onsets.

CONCLUSION

Prolongation and QT variability represent a relevant substrate marker in the genesis of AF, independently of the trigger type.

Gastrointestinal and liver diseases and atrial fibrillation: a review of the literature

Atrial fibrillation (AF) is the most common arrhythmia worldwide and is associated with significant morbidity and mortality. A number of risk factors have been associated with AF, though few studies have explored the association between gastrointestinal and liver diseases and AF. Additionally, AF and treatment for AF may predispose to gastrointestinal and liver diseases. We review the current literature on the bidirectional associations between gastrointestinal and liver diseases and AF. We highlight the gaps in knowledge and areas requiring future investigation.

Cardiac autonomic regulation in patients undergoing pulmonary vein isolation for atrial fibrillation

AIMS

Ablation procedures for the treatment of atrial fibrillation lead to changes in autonomic heart control; however, there are insufficient data on the possible association of these changes with atrial fibrillation recurrence. The study aim was to assess the effects of pulmonary vein isolation (PVI) on cardiac autonomic modulation and atrial fibrillation recurrence.

METHODS

We screened 52 patients with atrial fibrillation referred for PVI, of whom 20 patients met inclusion and exclusion criteria, and were enrolled in the study and followed over 6 months. Beat-to-beat blood pressure monitoring was performed 1-2 days before PVI, 1 and 6 months after PVI. We estimated pulse interval variability and spontaneous baroreflex sensitivity (BRS) both in the time and frequency domains, and performed the Valsalva manoeuvre assessing the Valsalva ratio.

RESULTS

During 6 months after PVI, atrial fibrillation recurrence was observed in six patients. One month after PVI, pulse interval variability and BRS (sequence method) significantly decreased in all patients, returning to preintervention values by 6 months. Patients without atrial fibrillation recurrence at 1 month showed a transient reduction in pulse interval variability (frequency domain) and in BRS (both methods) in contrast to those with atrial fibrillation recurrence. A significant decrease in the Valsalva ratio observed at 1 month was maintained at 6 months after PVI in both groups.

CONCLUSION

Successful PVI may lead to transient autonomic alterations reflected by a reduction in pulse interval variability and BRS, with more prolonged changes in the Valsalva ratio. The efficacy of PVI in preventing atrial fibrillation recurrence seems to be related to transient parasympathetic atrial denervation.

Low heart deceleration capacity imply higher atrial fibrillation-free rate after ablation

How deceleration capacity (DC) and acceleration capacity (AC) of heart rate associated with atrial fibrillation (AF) and ablation is still not clear. The dynamic changes of AC, DC and conventional heart rate variability (HRV) parameters were characterized in 154 subjects before circumferential pulmonary veins isolation (CPVI) and three days, 3 months and 6 months after CPVI. The DCs of the recurrent group decreased significantly at each time point after CPVI; the DCs of the recurrence-free group before CPVI and three days, 3 months and 6 months after CPVI were 7.06 ± 1.77, 3.79 ± 1.18, 4.22 ± 1.96 and 3.97 ± 0.98 ms respectively, which also decreased significantly at each time point and were significantly lower than these of recurrent group. Conversely, the AC of recurrent and recurrence-free groups increased significantly at each time point after CPVI; the ACs of recurrence-fee group were significantly higher than these of recurrent group at each time point. No stable difference trend of HRV parameters was found between two groups. Further Kaplan–Meier analysis showed that DC < 4.8 ms or AC ≥ −5.1 ms displayed significant higher recurrence-free rates. In conclusion, high AC and low DC imply higher AF-free rate after ablation.

Decreased gene expression of fatty acid binding protein 3 in the atrium of patients with new onset of atrial fibrillation in cardiac perioperative phase

BACKGROUND

Post-operative atrial fibrillation (POAF) frequently occurs after cardiac surgery. However, the mechanisms of POAF have not been fully elucidated. We aimed to examine whether pre-operative atrial gene expression related to cardiac metabolism is changed in patients with POAF.

METHODS

Right atrial tissue was obtained during surgery from 38 patients who underwent cardiac surgery from 2013 to 2015. Atrial expression levels were determined by reverse transcription polymerase chain reaction for the following genes: glucose transporter type 4, peroxisome proliferator-activated receptor-α, fatty acid translocase, carnitine palmitoyltransferase 1B, and fatty acid binding protein 3 (FABP3). To investigate fatty acid β-oxidation and tricarboxylic acid cycle capacities in the mitochondria, β-hydroxyacyl CoA dehydrogenase and citrate synthase activity levels were spectrophotometrically determined.

RESULTS

POAF within 7 days after surgery was observed in 18 (47%) patients. POAF patients were significantly older, had a larger left atrial diameter, and had reduced expression of FABP3, a fatty acids transport gene in the cytosol, compared to those in the non-POAF group. Reduced FABP3 expression predicted POAF independent of age and atrial size. In contrast, fatty acid β-oxidation enzymatic activity was comparable between the groups.

CONCLUSIONS

FABP3 gene expression in the atrium was reduced in patients with POAF. These findings suggest a potential link between altered fatty acid transport in the atrium and increased AF onset after cardiac surgery.

Tissue-Level Cardiac Electrophysiology Studied in Murine Myocardium Using a Microelectrode Array: Autonomic and Thermal Modulation

Cardiac electrophysiology is regulated by the autonomic nervous system, and this has both pathophysiological, and possibly therapeutic importance. Furthermore, chamber differences in electrophysiology exist between atria and ventricles, yet there have been few direct comparisons. There is substantial literature on ion channel modulation at the single-cell level but less work on how this affects tissue-level parameters. We used a microelectrode array system to explore these issues using murine atrial and ventricular tissue slices. Activation time, conduction velocity and repolarisation were measured, and their modulation by temperature and pharmacological autonomic agonists were assessed. The system recorded reliable measurements under control conditions in the absence of drug/thermal challenge, and significant baseline differences were found in chamber electrophysiology. The sodium channel blocker mexiletine, produced large magnitude changes in all three measured parameters. Carbachol and isoprenaline induced differing effects in atria and ventricles, whereas temperature produced similar effects on activation and repolarisation.

Conversion of atrial dissociation with lidocaine in a dog

A 3-year-old healthy dog was presented for abdominal surgery following ingestion of razor blades. An electrocardiogram revealed a regular sinus bradycardia with normal P waves at a heart rate of 45 bpm. In addition, low-amplitude positive deflections (p' waves) were visualized at a regular interval and rapid rate of 250 bpm, dissociated from the normal sinus P waves. A tentative diagnosis of atrial dissociation was proposed. Administration of lidocaine abolished the p' waves. This case describes atrial dissociation observed following premedication that was successfully terminated using lidocaine in a healthy dog.

Relations of Liver Fat With Prevalent and Incident Atrial Fibrillation in the Framingham Heart Study

Background

Obesity is an important risk factor for nonalcoholic fatty liver disease and atrial fibrillation (AF). Less is known about the relations between nonalcoholic fatty liver disease and AF. We sought to evaluate the association between fatty liver and prevalent and incident AF in the community.

Methods and Results

We examined Framingham Heart Study participants who underwent a study‐directed computed tomography scan, had hepatic steatosis (HS) evaluated, and did not report heavy alcohol use between 2002 and 2005. We evaluated cross‐sectional associations between liver fat and prevalent AF with logistic regression models. We assessed the relations between liver fat and incident AF during 12‐year follow‐up with Cox proportional hazards models. Of 2122 participants (53% women; mean age, 59.0±9.6 years), 20% had HS. AF prevalence (n=62) among individuals with HS was 4% compared to 3% among those without HS. There was no significant association between HS (measured as continuous or dichotomous variables) and prevalent AF in age‐ and sex‐adjusted or multivariable‐adjusted models. Incidence of AF (n=153) among participants with and without HS was 8.7 cases and 7.8 cases per 1000 person‐years, respectively. In age‐ and sex‐adjusted and multivariable‐adjusted models, there were no significant associations between continuous or dichotomous measures of HS and incident AF.

Conclusions

In our community‐based, longitudinal cohort study, liver fat by computed tomography scan was not significantly associated with increased prevalence or incidence of AF over 12 years of follow‐up.

Novel perspectives on arrhythmia-induced cardiomyopathy: pathophysiology, clinical manifestations and an update on invasive management strategies

Arrhythmia-induced cardiomyopathy is a partially or completely reversible form of myocardial dysfunction due to sustained supraventricular and ventricular arrhythmias. Asynchrony, rapid cardiac rates and rhythm irregularities are the main factors involved in the development of the disease. The reversible nature of arrhythmia-induced cardiac dysfunction allows only for a retrospective diagnosis of the disease once cardiac function is restored following heart rate control. A high level of suspicion is needed to make a diagnosis at an early stage and prevent further progression of the disease. Although reversible, arrhythmia-induced cellular and molecular changes may remain, increasing the risk for sudden death even when normal ejection fraction is restored as well as causing rapid deterioration of cardiac function and development of heart failure symptoms if arrhythmia recurs. Appropriate management based on a combination of pharmacologic and nonpharmacologic strategies to achieve rate control and prevent arrhythmia recurrence is pivotal to avoid further cardiac function deterioration and to control symptoms, significantly reducing the risk of heart failure and sudden cardiac death.

β1-Adrenergic and M2 Muscarinic Autoantibodies and Thyroid Hormone Facilitate Induction of Atrial Fibrillation in Male Rabbits

Activating autoantibodies to the β1-adrenergic and M2 muscarinic receptors are present in a very high percentage of patients with Graves' disease and atrial fibrillation (AF). The objective of this study was to develop a reproducible animal model and thereby to examine the impact of these endocrine-like autoantibodies alone and with thyroid hormone on induction of thyroid-associated atrial tachyarrhythmias. Five New Zealand white rabbits were coimmunized with peptides from the second extracellular loops of the β1-adrenergic and M2 muscarinic receptors to produce both sympathomimetic and parasympathomimetic antibodies. A catheter-based electrophysiological study was performed on anesthetized rabbits before and after immunization and subsequent treatment with thyroid hormone. Antibody expression facilitated the induction of sustained sinus, junctional and atrial tachycardias, but not AF. Addition of excessive thyroid hormone resulted in induced sustained AF in all animals. AF induction was blocked acutely by the neutralization of these antibodies with immunogenic peptides despite continued hyperthyroidism. The measured atrial effective refractory period as one parameter of AF propensity shortened significantly after immunization and was acutely reversed by peptide neutralization. No further decrease in the effective refractory period was observed after the addition of thyroid hormone, suggesting other cardiac effects of thyroid hormone may contribute to its role in AF induction. This study demonstrates autonomic autoantibodies and thyroid hormone potentiate the vulnerability of the heart to AF, which can be reversed by decoy peptide therapy. These data help fulfill Witebsky's postulates for an increased autoimmune/endocrine basis for Graves' hyperthyroidism and AF.

Evaluating the Atrial Myopathy Underlying Atrial Fibrillation: Identifying the Arrhythmogenic and Thrombogenic Substrate

Atrial disease or myopathy forms the substrate for atrial fibrillation (AF) and underlies the potential for atrial thrombus formation and subsequent stroke. Current diagnostic approaches in patients with AF focus on identifying clinical predictors with the evaluation of left atrial size by echocardiography serving as the sole measure specifically evaluating the atrium. Although the atrial substrate underlying AF is likely developing for years before the onset of AF, there is no current evaluation to identify the preclinical atrial myopathy. Atrial fibrosis is 1 component of the atrial substrate that has garnered recent attention based on newer MRI techniques that have been applied to visualize atrial fibrosis in humans with prognostic implications regarding the success of treatment. Advanced ECG signal processing, echocardiographic techniques, and MRI imaging of fibrosis and flow provide up-to-date approaches to evaluate the atrial myopathy underlying AF. Although thromboembolic risk is currently defined by clinical scores, their predictive value is mediocre. Evaluation of stasis via imaging and biomarkers associated with thrombogenesis may provide enhanced approaches to assess risk for stroke in patients with AF. Better delineation of the atrial myopathy that serves as the substrate for AF and thromboembolic complications might improve treatment outcomes. Furthermore, better delineation of the pathophysiologic mechanisms underlying the development of the atrial substrate for AF, particularly in its earlier stages, could help identify blood and imaging biomarkers that could be useful to assess risk for developing new-onset AF and suggest specific pathways that could be targeted for prevention.

A peptidomimetic inhibitor suppresses the inducibility of β1-adrenergic autoantibody-mediated cardiac arrhythmias in the rabbit

PURPOSE

Previous studies demonstrated that burst pacing and subthreshold infusion of acetylcholine in β1-adrenergic receptor (β1AR)-immunized rabbits induced sustained sinus tachycardia. The aim of this study was to examine the anti-arrhythmogenic effect of a newly designed retro-inverso (RI) peptidomimetic inhibitor that specifically targets the β1AR antibodies in the rabbit.

METHODS

Six New Zealand white rabbits were immunized with a β1AR second extracellular loop peptide to produce sympathomimetic β1AR antibodies. A catheter-based electrophysiological study was performed on anesthetized rabbits before and after immunization and subsequent treatment with the RI peptide inhibitor. Each rabbit served as its own control.

RESULTS

No sustained arrhythmias were induced at preimmune baseline. At 6 weeks after immunization, there was a marked increase in induced sustained tachyarrhythmias, predominantly sinus tachycardia, which was largely suppressed by the RI peptide. The atrial effective refractory period was shortened significantly in immunized rabbits compared to their preimmune state. The RI peptide reversed and prolonged this shortening. β1AR antibody levels were negatively correlated with the atrial effective refractory period. Postimmune sera-induced β1AR activation in transfected cells in vitro was also blocked by the RI peptide.

CONCLUSIONS

β1AR-activating autoantibodies are associated with reduction of the atrial effective refractory period and facilitate arrhythmia induction in this model. The RI peptide reversal may have important therapeutic implications in subjects who harbor these autoantibodies.

Postoperative atrial fibrillation in non-cardiac and cardiac surgery: an overview

Postoperative atrial fibrillation (POAF) is the most common perioperative cardiac arrhythmia. A major risk factor for POAF is advanced age, both in non-cardiac and cardiac surgery. Following non-cardiac surgery, it is important to correct reversible conditions such as electrolytes imbalances to prevent the occurrence of POAF. Management of POAF consists of rate control and therapeutic anticoagulation if POAF persists for > 48 h and CHADS2 score > 2. After cardiac surgery, POAF affects a larger amount of patients. In addition to age, valve surgery carries the greatest risk for new AF. Rate control is the mainstay therapy in these patients. Prediction, prevention, and management of POAF should be further studied.

Activating autoantibodies to the β1/2-adrenergic and M2 muscarinic receptors associate with atrial tachyarrhythmias in patients with hyperthyroidism

We have previously demonstrated that activating autoantibodies to β1-adrenergic receptor (β1AR) and M2 muscarinic receptor (M2R) facilitate atrial fibrillation (AF) in patients with Graves' disease (GD). The objectives of this expanded study were to examine the prevalence of β1AR, β2AR, and M2R autoantibodies in hyperthyroidism subjects. Sera from 81 patients including 31 with GD and AF, 36 with GD and sinus rhythm, 9 with toxic multinodular goiter, 5 with subacute thyroiditis, and 10 control subjects were examined for these autoantibodies by ELISA. Sera from 20 ELISA-positive GD subjects, 10 with AF and 10 with sinus rhythm, were assayed for autoantibody bioactivity using cell-based bioassays. In patients with GD and AF, 45, 65, and 77 % were ELISA positive for β1AR, M2R, and β2AR autoantibodies, respectively. In patients with GD and sinus rhythm, 17, 39, and 75 % were ELISA positive for β1AR, M2R, and β2AR autoantibodies, respectively. β1AR and M2R autoantibodies were co-present in 39 % of patients with GD and AF compared to 14 % in GD with sinus rhythm (p = 0.026). Patients with toxic multinodular goiter or subacute thyroiditis had a low prevalence of autoantibodies. The mean β1AR and M2R autoantibody activity was elevated in both GD groups but higher in those with AF than those with sinus rhythm. β2AR autoantibody activity was also increased in both groups. In conclusion, β1AR, β2AR, and M2R autoantibodies were elevated in GD. β1AR and M2R autoantibodies appear to be related to concurrent AF, while β2AR autoantibodies were equally prevalent in those with a sinus tachycardia and those with AF.

Increased prevalence of atrial fibrillation in the endurance athlete: potential mechanisms and sport specificity

Atrial fibrillation is a common, often symptomatic, and concerning arrhythmia that can lead to heart failure, decreased athletic tolerance, and thromboembolic events; it has also been associated with increased mortality. Although atrial fibrillation is an uncommon condition in younger and otherwise healthy people, recent emerging evidence indicates that endurance athletes may be at particularly high risk of developing atrial fibrillation. We review the evidence that atrial fibrillation is associated with intense endurance athletics and we also explore the mechanisms by which this may occur. Finally, we consider some of the options that are available to treat athletes who develop atrial fibrillation.

Prolonged atrial fibrillation precipitated by new-onset seizures and marijuana abuse

We report a case of prolonged atrial fibrillation (AF) precipitated by new-onset generalized tonic-clonic convulsions and marijuana abuse in a developmentally normal 18-year-old adolescent with a structurally normal heart. Our case highlights an interesting association and a unique pathophysiology between generalized tonic-clonic convulsions, marijuana abuse, and AF. We suggest that seizures and marijuana abuse should be considered in the differential diagnosis of the etiology of AF in children.

Contemporary approaches to persistent atrial fibrillation

Atrial fibrillation (AF) is currently the most commonly treated cardiac arrhythmia. It is generally a progressive disease, often more difficult to control as electromechanical remodeling alters the underlying substrate. Patients typically evolve from infrequent, self-terminating episodes, to more frequent and sustained events. In addition, atrial remodeling may make sinus rhythm more challenging to achieve. Although an ablation strategy limited to pulmonary vein isolation may be curative in those with paroxysmal AF, a more extensive approach is often required in those with persistent AF. This article discusses the current approaches and most recent advances in the ablation of persistent and long-standing persistent AF.

Autonomic cardiac innervation: development and adult plasticity

Autonomic cardiac neurons have a common origin in the neural crest but undergo distinct developmental differentiation as they mature toward their adult phenotype. Progenitor cells respond to repulsive cues during migration, followed by differentiation cues from paracrine sources that promote neurochemistry and differentiation. When autonomic axons start to innervate cardiac tissue, neurotrophic factors from vascular tissue are essential for maintenance of neurons before they reach their targets, upon which target-derived trophic factors take over final maturation, synaptic strength and postnatal survival. Although target-derived neurotrophins have a central role to play in development, alternative sources of neurotrophins may also modulate innervation. Both developing and adult sympathetic neurons express proNGF, and adult parasympathetic cardiac ganglion neurons also synthesize and release NGF. The physiological function of these “non-classical” cardiac sources of neurotrophins remains to be determined, especially in relation to autocrine/paracrine sustenance during development.

 

Cardiac autonomic nerves are closely spatially associated in cardiac plexuses, ganglia and pacemaker regions and so are sensitive to release of neurotransmitter, neuropeptides and trophic factors from adjacent nerves. As such, in many cardiac pathologies, it is an imbalance within the two arms of the autonomic system that is critical for disease progression. Although this crosstalk between sympathetic and parasympathetic nerves has been well established for adult nerves, it is unclear whether a degree of paracrine regulation occurs across the autonomic limbs during development. Aberrant nerve remodeling is a common occurrence in many adult cardiovascular pathologies, and the mechanisms regulating outgrowth or denervation are disparate. However, autonomic neurons display considerable plasticity in this regard with neurotrophins and inflammatory cytokines having a central regulatory function, including in possible neurotransmitter changes. Certainly, neurotrophins and cytokines regulate transcriptional factors in adult autonomic neurons that have vital differentiation roles in development. Particularly for parasympathetic cardiac ganglion neurons, additional examinations of developmental regulatory mechanisms will potentially aid in understanding attenuated parasympathetic function in a number of conditions, including heart failure.

Relation of heart-rate recovery to new onset heart failure and atrial fibrillation in patients with diabetes mellitus and preserved ejection fraction

Diabetic autonomic neuropathy is a possible link between abnormal metabolism in type 2 diabetes mellitus (T2DM) and risk for atrial fibrillation (AF) and heart failure (HF). The aim of this study was to elucidate the association between attenuated heart rate recovery (HRR) and these manifestations of myocardial dysfunction in T2DM. Nine hundred fourteen consecutive patients with T2DM (mean age 56 ± 11 years, 508 men) without diabetes mellitus complications, with negative results on stress echocardiography, were enrolled. Patients with known cardiac disease were excluded. Demographics, clinical assessment, co-morbidities, and insulin use were collected prospectively. The association of HRR with new-onset HF and AF was sought using a Cox proportional-hazards model. There were 47 events (22 HF and 25 AF) during a median follow-up period of 7.8 years. Events were associated with age, exercise capacity, HRR, and left atrial volume index but not with baseline glycosylated hemoglobin, left ventricular mass index, or standard markers of diastolic function. In sequential Cox models for the combined outcomes, the model based on clinical data (age and gender; overall chi-square = 5.5) was not significantly improved by left atrial volume index (chi-square = 8.6, p = 0.10) or maximum METs (chi-square = 8.7, p = 0.07) but was significantly improved by adding HRR (chi-square = 19.7, p = 0.004). In addition, HRR provided significant incremental prognostic value regarding the composite end point (net reclassification improvement 19.2%, p = 0.04; integrated discrimination improvement 1.58%, p = 0.004). In conclusion, the association of HRR with subsequent HF and AF, independent of and incremental to left atrial volume index and other markers of abnormal cardiac structure and function, indicates a role for autonomic neuropathy as the link between metabolic and cardiac risk in patients with T2DM.

The role of the autonomic nervous system in cardiac arrhythmias

Autonomic nervous system activity exerts potent and diverse effects on cardiac rhythm through elaborate neurocircuitry that is integrated at multiple levels. Adrenergic activity such as is associated with mental or physical stress or as a reflex response to myocardial ischemia is capable of generating significant rhythm abnormalities including ventricular fibrillation, the arrhythmia responsible for sudden cardiac death. With respect to the ventricles, vagus nerve activity is generally antiarrhythmic as it inhibits the profibrillatory effects of sympathetic nerve activation, whereas atrial arrhythmias generally derive from heightened levels of both vagus and sympathetic nerve activity. Containment of neural influences by pharmacological and electrical targeted neuromodulation is being pursued as an antiarrhythmic modality.

Effects of acute autonomic modulation on atrial conduction delay and local electrograms duration in paroxysmal atrial fibrillation

Slowed atrial conduction may contribute to reentry circuits and vulnerability for atrial fibrillation (AF). The autonomic nervous system (ANS) has modulating effects on electrophysiological properties. However, complex interactions of the ANS with the arrhythmogenic substrate make it difficult to understand the mechanisms underlying induction and maintenance of AF.

AIM

To determine the effect of acute ANS modulation in atrial activation times in patients (P) with paroxysmal AF (PAF).

METHODS AND RESULTS

16P (9 men; 59±14years) with PAF, who underwent electrophysiological study before AF ablation, and 15P (7 men; 58±11years) with atrioventricular nodal reentry tachycardia, without documentation or induction of AF (control group). Each group included 7P with arterial hypertension but without underlying structural heart disease. The study was performed while off drugs. Multipolar catheters were placed at the high right atrium (HRA), right atrial appendage (RAA), coronary sinus (CS) and His bundle area (His). At baseline and with HRA pacing (600ms, shortest propagated S2) we measured: i) intra-atrial conduction time (IACT, between RAA and atrial deflection in the distal His), ii) inter-atrial conduction time (interACT, between RAA and distal CS), iii) left atrial activation time (LAAT, between atrial deflection in the distal His and distal CS), iv) bipolar electrogram duration at four atrial sites (RAA, His, proximal and distal CS). In the PAF group, measurements were also determined during handgrip and carotid sinus massage (CSM), and after pharmacological blockade of the ANS (ANSB). AF was induced by HRA programmed stimulation in 56% (self-limited - 6; sustained - 3), 68.8% (self-limited - 6; sustained - 5), and 50% (self-limited - 5; sustained - 3) of the P, in basal, during ANS maneuvers, and after ANSB, respectively (p=NS). IACT, interACT and LAAT significantly lengthened during HRA pacing in both groups (600ms, S2). P with PAF have longer IACT (p<0.05), a higher increase in both IACT, interACT (p<0.01) and electrograms duration (p<0.05) with S2, and more fragmented activity, compared with the control group. Atrial conduction times and electrograms duration were not significantly changed during ANS stimulation. Nevertheless, ANS maneuvers increased heterogeneity of the local electrograms duration. Also, P with sustained AF showed longer interACT and LAAT during CSM.

CONCLUSION

Atrial conduction times, electrograms duration and fractionated activity are increased in PAF, suggesting a role for conduction delays in the arrhythmogenic substrate. Acute vagal stimulation is associated with prolonged interACT and LAAT in P with inducible sustained AF and ANS modulation may influence the heterogeneity of atrial electrograms duration.

Heart Rate Predicts Outcomes in an Implantable Cardioverter-Defibrillator Population

Background— Elevated heart rate (HR) is associated with adverse cardiovascular events and total mortality in the general population and in individuals with heart disease. Our hypothesis was that mean HR predicts total mortality and heart failure hospitalization in patients undergoing implantable cardioverter-defibrillator (ICD) implantation.

Methods and Results— The Inhibition of Unnecessary RV Pacing With AV Search Hysteresis in ICDs (INTRINSIC RV) trial included 1530 patients undergoing ICD implantation. After implantation of a dual-chamber ICD, patients were followed for a mean of 10.4 months. The mean HR for 1436 patients over the follow-up period was determined from device histograms. Patients were grouped into strata by mean HR, and the relationship between the primary end point and mean HR was analyzed with Mantel-Haenszel ordinal χ 2 tests. Higher intrinsic (unpaced) HR was associated with greater risk of achieving the primary end point of death or heart failure hospitalization ( P <0.001). Of patients with a mean HR <75 bpm, 5.8% died or were hospitalized for heart failure, whereas 20.9% with a mean HR >90 bpm achieved the same end point, a 3.6-fold difference ( P <0.0001). In a multivariate model with the use of Cox regression, HR was a significant predictor with a hazard ratio of 1.34 ( P =0.0001; 95% confidence interval, 1.19 to 1.50), as were age, New York Heart Association functional class, and percent right ventricular pacing, but it was independent of gender and β-blocker dosing. When considered as continuous or discrete variables grouped by 5-bpm increments, HR remained a significant predictor.

Conclusions— In this ICD population, the mean intrinsic HR was strongly associated with outcomes.

Clinical Trial Registration— http://www.clinicaltrials.gov. Identifier: NCT00148967.

Use of vitamins C and E as a prophylactic therapy to prevent postoperative atrial fibrillation

Oxidative stress has been strongly involved in the underlying mechanism of atrial fibrillation, particularly in the arrhythmia occurring in patients undergoing cardiac surgery with extracorporeal circulation (postoperative atrial fibrillation). The ischemia/reperfusion injury thus occurring in the myocardial tissue contributes to the development of tissue remodeling, thought to be responsible for the functional heart impairment. Consequently, structural changes due to the cardiac tissue biomolecules attack by reactive oxygen and/or nitrogen species could account for functional changes in ion channels, transporters, membrane conductance, cytosolic transduction signals, and other events, all associated with the occurrence of arrhythmic consequences. The lack of success and significant side effects of anti-arrhythmic drugs have given rise to attempts aimed to develop alternative novel pharmacologic treatments. On this line, the biological properties of the antioxidant vitamins C and E suggest that they could decrease the vulnerability of the heart to the oxidative damage. Nevertheless, very few studies to assess their anti-arrhythmic effects have been reported in humans. The clinical and experimental evidence supporting the view that the pharmacological use of antioxidant vitamins could contribute to prevent postoperative atrial fibrillation is presented.