Autonomic nerves in pulmonary veins

Risk factors associated with atrial fibrillation following lung cancer surgery: A multi-center case-control study

BACKGROUND

Postoperative atrial fibrillation (POAF) is a common complication after major thoracic operations. The objective of this case-control study was to identify the risk factors for POAF following lung cancer surgery.

METHODS

In total, 216 patients with lung cancer who were selected from three different hospitals were followed up between May 2020 and May 2022. They were divided into two groups: case group, patients with POAF and control group, patients without POAF (case-control). Risk factors associated with POAF were investigated using univariate and multivariate logistic regression analyses.

RESULTS

Risk factors that were significantly associated with POAF were preoperative brain-type natriuretic peptide (BNP) levels [odds ratio (OR): 4.46; 95% confidence interval (CI): 1.52-13.06; P = 0.0064], sex (OR: 0.07; 95%CI: 0.02-0.28; P = 0.0001), preoperative white blood cell (WBC) count (OR: 3.00; 95%CI: 1.89-4.77; P < 0.0001), lymph node dissection (OR: 11.49; 95%CI: 2.81-47.01; P = 0.0007), and cardiovascular disease (OR: 4.93; 95%CI: 1.14-21.31; P = 0.0326).

CONCLUSION

In summary, data from the three hospitals suggested that preoperative BNP levels, sex, preoperative WBC count, lymph node dissection, and hypertension/coronary heart disease/myocardial infarction were associated with a significantly high risk of POAF following lung cancer surgery.

Chronic intermittent hypoxia remodels catecholaminergic nerve innervation in mouse atria

Chronic intermittent hypoxia (CIH, a model for sleep apnoea) is a major risk factor for several cardiovascular diseases. Autonomic imbalance (sympathetic overactivity and parasympathetic withdrawal) has emerged as a causal contributor of CIH-induced cardiovascular disease. Previously, we showed that CIH remodels the parasympathetic pathway. However, whether CIH induces remodelling of the cardiac sympathetic innervation remains unknown. Mice (male, C57BL/6J, 2-3 months) were exposed to either room air (RA, 21% O2 ) or CIH (alternating 21% and 5.7% O2 , every 6 min, 10 h day-1 ) for 8-10 weeks. Flat-mounts of their left and right atria were immunohistochemically labelled for tyrosine hydroxylase (TH, a sympathetic marker). Using a confocal microscope (or fluorescence microscope) and Neurlocudia 360 digitization and tracing system, we scanned both the left and right atria and quantitatively analysed the sympathetic axon density in both groups. The segmentation data was mapped onto a 3D mouse heart scaffold. Our findings indicated that CIH significantly remodelled the TH immunoreactive (-IR) innervation of the atria by increasing its density at the sinoatrial node, the auricles and the major veins attached to the atria (P < 0.05, n = 7). Additionally, CIH increased the branching points of TH-IR axons and decreased the distance between varicosities. Abnormal patterns of TH-IR axons around intrinsic cardiac ganglia were also found following CIH. We postulate that the increased sympathetic innervation may further amplify the effects of enhanced CIH-induced central sympathetic drive to the heart. Our work provides an anatomical foundation for the understanding of CIH-induced autonomic imbalance. KEY POINTS: Chronic intermittent hypoxia (CIH, a model for sleep apnoea) causes sympathetic overactivity, cardiovascular remodelling and hypertension. We determined the effect of CIH on sympathetic innervation of the mouse atria. In vivo CIH for 8-10 weeks resulted in an aberrant axonal pattern around the principal neurons within intrinsic cardiac ganglia and an increase in the density, branching point, tortuosity of catecholaminergic axons and atrial wall thickness. Utilizing mapping tool available from NIH (SPARC) Program, the topographical distribution of the catecholaminergic innervation of the atria were integrated into a novel 3D heart scaffold for precise anatomical distribution and holistic quantitative comparison between normal and CIH mice. This work provides a unique neuroanatomical understanding of the pathophysiology of CIH-induced autonomic remodelling.

Transcriptional profile of the rat cardiovascular system at single cell resolution

Background

Despite the critical role of the cardiovascular system, our understanding of its cellular and transcriptional diversity remains limited. We therefore sought to characterize the cellular composition, phenotypes, molecular pathways, and communication networks between cell types at the tissue and sub-tissue level across the cardiovascular system of the healthy Wistar rat, an important model in preclinical cardiovascular research. We obtained high quality tissue samples under controlled conditions that reveal a level of cellular detail so far inaccessible in human studies.

Methods and Results

We performed single nucleus RNA-sequencing in 78 samples in 10 distinct regions including the four chambers of the heart, ventricular septum, sinoatrial node, atrioventricular node, aorta, pulmonary artery, and pulmonary veins (PV), which produced an aggregate map of 505,835 nuclei. We identified 26 distinct cell types and additional subtypes, including a number of rare cell types such as PV cardiomyocytes and non-myelinating Schwann cells (NMSCs), and unique groups of vascular smooth muscle cells (VSMCs), endothelial cells (ECs) and fibroblasts (FBs), which gave rise to a detailed cell type distribution across tissues. We demonstrated differences in the cellular composition across different cardiac regions and tissue-specific differences in transcription for each cell type, highlighting the molecular diversity and complex tissue architecture of the cardiovascular system. Specifically, we observed great transcriptional heterogeneities among ECs and FBs. Importantly, several cell subtypes had a unique regional localization such as a subtype of VSMCs enriched in the large vasculature. We found the cellular makeup of PV tissue is closer to heart tissue than to the large arteries. We further explored the ligand-receptor repertoire across cell clusters and tissues, and observed tissue-enriched cellular communication networks, including heightened Nppa - Npr1/2/3 signaling in the sinoatrial node.

Conclusions

Through a large single nucleus sequencing effort encompassing over 500,000 nuclei, we broadened our understanding of cellular transcription in the healthy cardiovascular system. The existence of tissue-restricted cellular phenotypes suggests regional regulation of cardiovascular physiology. The overall conservation in gene expression and molecular pathways across rat and human cell types, together with our detailed transcriptional characterization of each cell type, offers the potential to identify novel therapeutic targets and improve preclinical models of cardiovascular disease.

Wide Antral Circumferential Re-Ablation for Recurrent Atrial Fibrillation after Prior Pulmonary Vein Isolation Guided by High-Density Mapping Increases Freedom from Atrial Arrhythmias

Performing repeated pulmonary vein isolation (re-PVI) after recurrent atrial fibrillation (AF) following prior PVI is a standard procedure. However, no consensus exists regarding the most effective approach in redo procedures. We assessed the efficacy of re-PVI using wide antral circumferential re-ablation (WACA) supported by high-density electroanatomical mapping (HDM) as compared to conventional re-PVI. Consecutive patients with AF recurrences showing true PV reconnection (residual intra-PV and PV antral electrical potentials within the initial ablation line) or exclusive PV antral potentials (without intra-PV potentials) in the redo procedure were prospectively enrolled and received HDM-guided WACA (Re-WACA group). Conventional re-PVI patients treated using pure ostial gap ablation guided by a circular mapping catheter served as a historical control (Re-PVI group). Patients with durable PVI and no antral PV potentials were excluded. Arrhythmia recurrences ≥30 s were calculated as recurrences. In total, 114 patients were investigated (Re-WACA: n = 56, 68 ± 10 years, Re-PVI: n = 58, 65 ± 10 years). There were no significant differences in clinical characteristics including the AF type or the number of previous PVIs. In the Re-WACA group, 11% of patients showed electrical potentials only in the antrum but not inside any PV. At 402 ± 71 days of follow-up, the estimated freedom from arrhythmia was 89% in the Re-WACA group and 69% in the Re-PVI group (p = 0.01). Re-WACA independently predicted arrhythmia-free survival (HR = 0.39, 95% CI 0.16-0.93, p = 0.03), whereas two previous PVI procedures predicted recurrences (HR = 2.35, 95% CI 1.20-4.46, p = 0.01). The Re-WACA strategy guided by HDM significantly improved arrhythmia-free survival as compared to conventional ostial re-PVI. Residual PV antral potentials after prior PVI are frequent and can be easily visualized by HDM.

Alteration of Skin Sympathetic Nerve Activity after Pulmonary Vein Isolation in Patients with Paroxysmal Atrial Fibrillation

Autonomic system plays a pivotal role in the pathogenesis of paroxysmal atrial fibrillation (AF). Skin sympathetic nerve activity (SKNA) is a noninvasive tool for assessing sympathetic tone. However, data on changes in SKNA after ablation are limited. Here, we retrospectively enrolled 37 patients with symptomatic drug-refractory paroxysmal AF who underwent pulmonary vein isolation (PVI) with radiofrequency ablation (RFA) or cryoablation (CBA). SKNA was measured from the chest and right arm 1 day prior to ablation, as well as 1 day and 3 months after ablation. One day after ablation, the SKNA-Arm increased from 517.1 µV (first and third quartiles, 396.0 and 728.0, respectively) to 1226.2 µV (first and third quartiles, 555.2 and 2281.0), with an increase of 179.8% (125% and 376.0%) (p < 0.001); the SKNA-Chest increased from 538.2 µV (first and third quartiles, 432.9 and 663.9) to 640.0 µV (first and third quartiles, 474.2 and 925.6), with an increase of 108.3% (95.6% and 167.9%) (p = 0.004), respectively. In those without recurrence, there was a significant increase in SKNA 1 day after ablation as compared with those before ablation. Twelve patients received SKNA measurement 3 months after ablation; both SKNA-Arm (p = 0.31) and SKNA-Chest (p = 0.27) were similar to those before ablation, respectively. Among patients with symptomatic drug-refractory paroxysmal AF receiving PVI, increased SKNA was observed 1 day after ablation and returned to the baseline 3 months after ablation. Elevation of SKNA was associated with lower early and late recurrences following ablation.

Preferential Expression of Ca2+-Stimulable Adenylyl Cyclase III in the Supraventricular Area, Including Arrhythmogenic Pulmonary Vein of the Rat Heart

Ectopic excitability in pulmonary veins (PVs) is the major cause of atrial fibrillation. We previously reported that the inositol trisphosphate receptor in rat PV cardiomyocytes cooperates with the Na+-Ca2+ exchanger to provoke ectopic automaticity in response to norepinephrine. Here, we focused on adenylyl cyclase (AC) as another effector of norepinephrine stimulation. RT-PCR, immunohistochemistry, and Western blotting revealed that the abundant expression of Ca2+-stimulable AC3 was restricted to the supraventricular area, including the PVs. All the other AC isotypes hardly displayed any region-specific expressions. Immunostaining of isolated cardiomyocytes showed an enriched expression of AC3 along the t-tubules in PV myocytes. The cAMP-dependent response of L-type Ca2+ currents in the PV and LA cells is strengthened by the 0.1 mM intracellular Ca2+ condition, unlike in the ventricular cells. The norepinephrine-induced automaticity of PV cardiomyocytes was reversibly suppressed by 100 µM SQ22536, an adenine-like AC inhibitor. These findings suggest that the specific expression of AC3 along t-tubules may contribute to arrhythmogenic automaticity in rat PV cardiomyocytes.

Vagus Nerve Stimulation and Atrial Fibrillation: Revealing the Paradox

BACKGROUND AND OBJECTIVE

The cardiac autonomic nervous system (CANS) plays an important role in the pathophysiology of atrial fibrillation (AF). Cardiovascular disease can cause an imbalance within the CANS, which may contribute to the initiation and maintenance of AF. Increased understanding of neuromodulation of the CANS has resulted in novel emerging therapies to treat cardiac arrhythmias by targeting different circuits of the CANS. Regarding AF, neuromodulation therapies targeting the vagus nerve have yielded promising outcomes. However, targeting the vagus nerve can be both pro-arrhythmogenic and anti-arrhythmogenic. Currently, these opposing effects of vagus nerve stimulation (VNS) have not been clearly described. The aim of this review is therefore to discuss both pro-arrhythmogenic and anti-arrhythmogenic effects of VNS and recent advances in clinical practice and to provide future perspectives for VNS to treat AF.

MATERIALS AND METHODS

A comprehensive review of current literature on VNS and its pro-arrhythmogenic and anti-arrhythmogenic effects on atrial tissue was performed. Both experimental and clinical studies are reviewed and discussed separately.

RESULTS

VNS exhibits both pro-arrhythmogenic and anti-arrhythmogenic effects. The anatomical site and stimulation settings during VNS play a crucial role in determining its effect on cardiac electrophysiology. Since the last decade, there is accumulating evidence from experimental studies and randomized clinical studies that low-level VNS (LLVNS), below the bradycardia threshold, is an effective treatment for AF.

CONCLUSION

LLVNS is a promising novel therapeutic modality to treat AF and further research will further elucidate the underlying anti-arrhythmogenic mechanisms, optimal stimulation settings, and site to apply LLVNS.

Autonomic Testing Optimizes Therapy for Heart Failure and Related Cardiovascular Disorders

PURPOSE OF REVIEW

Cardiovascular autonomic control is an intricately balanced dynamic process. Autonomic dysfunction, regardless of origin, promotes and sustains the disease processes, including in patients with heart failure (HF). Autonomic control is mediated through the two autonomic branches: parasympathetic and sympathetic (P&S). HF is arguably the disease that stands to most benefit from P&S manipulation to reduce mortality risk. This review article briefly summarizes some of the more common types of autonomic dysfunction (AD) that are found in heart failure, suggests a mechanism by which AD may contribute to HF, reviews AD involvement in common HF co-morbidities (e.g., ventricular arrhythmias, AFib, hypertension, and Cardiovascular Autonomic Neuropathy), and summarizes possible therapy options for treating AD in HF.

RECENT FINDINGS

Autonomic assessment is important in diagnosing and treating CHF, and its possible co-morbidities. Autonomic assessment may also have importance in predicting which patients may be susceptible to sudden cardiac death. This is important since most CHF patients with sudden cardiac death have preserved left ventricular ejection fraction and better discriminators are needed. Many life-threatening cardiovascular disorders will require invasive testing for precise diagnoses and therapy planning when modulating the ANS is important. In cases of non-life-threatening disorders, non-invasive ANS testing techniques, especially those that individually assess both ANS branches simultaneously and independently, are sufficient to diagnose and treat serially.

Automatic Activity Arising in Cardiac Muscle Sleeves of the Pulmonary Vein

Ectopic activity in the pulmonary vein cardiac muscle sleeves can both induce and maintain human atrial fibrillation. A central issue in any study of the pulmonary veins is their difference from the left atrial cardiac muscle. Here, we attempt to summarize the physiological phenomena underlying the occurrence of ectopic electrical activity in animal pulmonary veins. We emphasize that the activation of multiple signaling pathways influencing not only myocyte electrophysiology but also the means of excitation–contraction coupling may be required for the initiation of triggered or automatic activity. We also gather information regarding not only the large-scale structure of cardiac muscle sleeves but also recent studies suggesting that cellular heterogeneity may contribute to the generation of arrythmogenic phenomena and to the distinction between pulmonary vein and left atrial heart muscle.

Cardiac Autonomic Nervous System Remodeling May Play a Role in Atrial Fibrillation: A Study of the Autonomic Nervous System and Myocardial Receptors

BACKGROUND

The primary factors that originate and perpetuate atrial fibrillation (AF) are electrical and anatomical substrate alterations. However, the central mechanisms governing AF perpetuation have not been elucidated yet, which is reflected on the modest results of the treatment in patients with long persistent AF.

OBJECTIVE

To evaluate if human intrinsic cardiac autonomic nervous system (ICANS) remodeling, including nervous system fibers and muscarinic and β-adrenergic receptors, play a role in permanent AF.

METHODS

Heart necropsy samples from thirteen patients with heart disease and permanent AF and thirteen controls without AF were used. By using immunoperoxidase and histomorphometry quantification, we identified the following: the density of all fibers of the ICANS, sympathetic and parasympathetic fibers; and the percentage of myocardium positive for β-adrenergic receptors 1, 2 and 3; G protein-coupled receptor kinase-5 (GRK-5); and muscarinic receptors M1 to M5. The results were compared using ANOVA and nested ANOVA and were adjusted according to the left atrium volume for all variables, and β-blocker use to evaluate the expression of β-receptors and GRK-5.

RESULTS

There was an overall increase in the density of fibers of the ICANS (p=0.006), especially in atrial sympathetic nerve fibers (p=0.017). Only M1 muscarinic receptors were increased (5.87 vs 2.35, p=0.032). For adrenergic receptors, the results were positive for increased expression of β-3 (37.41 vs 34.18, p=0.039) and GRK-5 (51.16 vs 47.66; p<0.001). β-blocker use had no impact on β-receptor expression.

CONCLUSION

Increased ICANS innervation and remodeling receptor expression in regions prone to triggering AF may play a role in permanent AF.

Atrial fibrillation and alteration of heart rate variability after video-assisted pulmonary lobectomy versus thoracotomy pulmonary lobectomy

Objective

To compare the incidence of atrial fibrillation (AF) and alteration of heart rate variability (HRV) after pulmonary lobectomy through video assisted thoracic surgery or thoracotomy, and to explore the role of autonomic nerves in the pathogenesis of atrial fibrillation after pulmonary lobectomy.

Methods

In a single institution, 224 patients (age > 60) with normal sinus rhythm were enrolled in the study. Experienced surgeons and anesthetists carried out operation and anesthesia according to the same procedure. The hearts were monitored using Holter for more than 96 h. Any new-onset AF was recorded and HRV was analyzed at different time intervals.

Results

One hundred twelve patients undergoing video-assisted thoracic surgery (VATS) and 112 patients undergoing thoracotomy (THOR) were matched for age and gender. Atrial fibrillation occurred in 39 patients, with a similar incidence between the two groups (VATS: 19/112, 16.9% and THOR: 20/112, 17.9%, P = 0.82). The post-operational heart variability at different time intervals was comparable between the two groups.

Conclusion

Pulmonary lobectomy through video assisted thoracic surgery does not reduce the postoperative atrial fibrillation. Autonomic nerve mechanism may be involved in the pathogenesis of postoperative atrial fibrillation.

Can local infiltration of lidocaine reduce the postoperative atrial fibrillation rate in patients undergoing lobectomy for lung cancer?

Background: Postoperative atrial fibrillation (POAF) occurs frequently after lung cancer surgery. Unfortunately, owing to the multifactorial etiology of POAF, no single drug or intervention can prevent POAF in all cases. The effects of local interventions after lung cancer surgery are unknown. This study investigated the effects of local infiltration of an anesthetic (lidocaine) on the post-lobectomy POAF rate.Methods: This non-randomized study included 81 patients who underwent lobectomy for lung cancer. Patients were divided into a lidocaine-infiltration group comprising patients who received lidocaine infiltration around the pulmonary veins and a no-intervention group. Patients were monitored for the development of POAF during hospitalization. Pre- and postoperative demographic and clinical data were analyzed.Results: AF occurred in 3 (7.5%) of 40 patients in the lidocaine-infiltration group and in 10 (24.39%) of 41 patients in the standard surgical resection group. Overall, it was observed that intraoperative lidocaine infiltration resulted in a lower POAF rate (p < .05).Conclusion: Local infiltration of lidocaine around the pulmonary veins in patients undergoing lobectomy for lung cancer was associated with a lower incidence of POAF, which is attributable to the local anesthetic and autonomic effects of lidocaine.

Cardiac glial cells release neurotrophic S100B upon catheter-based treatment of atrial fibrillation

Atrial fibrillation (AF), the most common sustained heart rhythm disorder worldwide, is linked to dysfunction of the intrinsic cardiac autonomic nervous system (ICNS). The role of ICNS damage occurring during catheter-based treatment of AF, which is the therapy of choice for many patients, remains controversial. We show here that the neuronal injury marker S100B is expressed in cardiac glia throughout the ICNS and is released specifically upon catheter ablation of AF. Patients with higher S100B release were more likely to be AF free during follow-up. Subsequent in vitro studies revealed that murine intracardiac neurons react to S100B with diminished action potential firing and increased neurite growth. This suggests that release of S100B from cardiac glia upon catheter-based treatment of AF is a hallmark of acute neural damage that contributes to nerve sprouting and can be used to assess ICNS damage.

Pulmonary Vein Ganglia Are Remodeled in the Diabetic Heart

Background Cardiac autonomic neuropathy is thought to cause adverse cardiovascular effects in diabetes mellitus. Pulmonary vein ganglia ( PVG ), which have been implicated in normal and abnormal heart rhythm regulation, have not been fully investigated in type 1 diabetes mellitus (T1D). We examined the functional and anatomical effects of T1D on PVG and studied the details of T1D-induced remodeling on the PVG structure and function. Methods and Results We used a mouse model of T1D (Akita mouse), immunofluorescence, isolated Langendorff-perfused hearts, and mathematical simulations to explore the effects of T1D on PVG . Whole-mount atrial immunofluorescence of choline acetyltransferase and tyrosine hydroxylase labeling showed that sympathetic and parasympathetic somas of the PVG neurons were significantly hypotrophied in T1D hearts versus wild type. Stimulation of PVG in isolated Langendorff-perfused hearts caused more pronounced P-P interval prolongation in wild type compared with Akita hearts. Propranolol resulted in a comparable P-P prolongation in both phenotypes, and atropine led to more pronounced P-P interval shortening in wild type compared with Akita hearts. Numerical modeling using network simulations revealed that a decrease in the sympathetic and parasympathetic activities of PVG in T1D could explain the experimental results. Conclusions T1D leads to PVG remodeling with hypotrophy of sympathetic and parasympathetic cell bodies and a concomitant decrease in the PVG sympathetic and parasympathetic activities.

Angiotensin II Induces Automatic Activity of the Isolated Guinea Pig Pulmonary Vein Myocardium through Activation of the IP₃ Receptor and the Na⁺-Ca2+ Exchanger

The automaticity of the pulmonary vein myocardium is known to be the major cause of atrial fibrillation. We examined the involvement of angiotensin II in the automatic activity of isolated guinea pig pulmonary vein preparations. In tissue preparations, application of angiotensin II induced an automatic contractile activity; this effect was mimicked by angiotensin I and blocked by losartan, but not by PD123,319 or carvedilol. In cardiomyocytes, application of angiotensin II induced an increase in the frequency of spontaneous Ca²⁺ sparks and the generation of Ca²⁺ transients; these effects were inhibited by losartan or xestospongin C. In tissue preparations, angiotensin II caused membrane potential oscillations, which lead to repetitive generation of action potentials. Angiotensin II increased the diastolic depolarization slope of the spontaneous or evoked action potentials. These effects of angiotensin II were inhibited by SEA0400. In tissue preparations showing spontaneous firing of action potentials, losartan, xestospongin C or SEA0400 decreased the slope of the diastolic depolarization and inhibited the firing of action potentials. In conclusion, in the guinea pig pulmonary vein myocardium, angiotensin II induces the generation of automatic activity through activation of the IP₃ receptor and the Na⁺-Ca²⁺ exchanger.

Risk factors for atrial fibrillation in hypertrophic cardiomyopathy

Atrial fibrillation is the most common sustained arrhythmia in hypertrophic cardiomyopathy (HCM), occurring in approximately 25% of patients, which is four to six times more common than in similarly aged patients of the general population. Atrial fibrillation is poorly tolerated by HCM patients, largely due to their dependence on atrial systole for left ventricular filling. HCM patients who develop atrial fibrillation have an increased rate of heart failure related mortality and disabling or fatal thromboembolic events, as well as functional deterioration due to progressive heart failure when left untreated. Atrial fibrillation is both common in HCM and may lead to significant morbidity and mortality. Accurate risk stratification for atrial fibrillation in this population is crucial as contemporary treatments are highly successful. In this paper, we review the current understanding of known risk factors for atrial fibrillation, including different imaging-based parameters that assess left atrial structural and functional remodeling, electrocardiographic changes that reflect left atrial electrical remodeling, and a focus on comorbid obstructive sleep apnea, and in addition we review variables that have been reported to be predictive of atrial fibrillation. Last, we summarize the accumulating evidence for HCM patients having an intrinsic atrial myopathy.

Multifractal Desynchronization of the Cardiac Excitable Cell Network During Atrial Fibrillation. I. Multifractal Analysis of Clinical Data

Atrial fibrillation (AF) is a cardiac arrhythmia characterized by rapid and irregular atrial electrical activity with a high clinical impact on stroke incidence. Best available therapeutic strategies combine pharmacological and surgical means. But when successful, they do not always prevent long-term relapses. Initial success becomes all the more tricky to achieve as the arrhythmia maintains itself and the pathology evolves into sustained or chronic AF. This raises the open crucial issue of deciphering the mechanisms that govern the onset of AF as well as its perpetuation. In this study, we develop a wavelet-based multi-scale strategy to analyze the electrical activity of human hearts recorded by catheter electrodes, positioned in the coronary sinus (CS), during episodes of AF. We compute the so-called multifractal spectra using two variants of the wavelet transform modulus maxima method, the moment (partition function) method and the magnitude cumulant method. Application of these methods to long time series recorded in a patient with chronic AF provides quantitative evidence of the multifractal intermittent nature of the electric energy of passing cardiac impulses at low frequencies, i.e., for times (≳0.5 s) longer than the mean interbeat (≃ 10-1 s). We also report the results of a two-point magnitude correlation analysis which infers the absence of a multiplicative time-scale structure underlying multifractal scaling. The electric energy dynamics looks like a "multifractal white noise" with quadratic (log-normal) multifractal spectra. These observations challenge concepts of functional reentrant circuits in mechanistic theories of AF, still leaving open the role of the autonomic nervous system (ANS). A transition is indeed observed in the computed multifractal spectra which group according to two distinct areas, consistently with the anatomical substrate binding to the CS, namely the left atrial posterior wall, and the ligament of Marshall which is innervated by the ANS. In a companion paper (II. Modeling), we propose a mathematical model of a denervated heart where the kinetics of gap junction conductance alone induces a desynchronization of the myocardial excitable cells, accounting for the multifractal spectra found experimentally in the left atrial posterior wall area.

Atrial Fibrillation: The Science behind Its Defiance

Atrial fibrillation (AF) is the most prevalent arrhythmia in the world, due both to its tenacious treatment resistance, and to the tremendous number of risk factors that set the stage for the atria to fibrillate. Cardiopulmonary, behavioral, and psychological risk factors generate electrical and structural alterations of the atria that promote reentry and wavebreak. These culminate in fibrillation once atrial ectopic beats set the arrhythmia process in motion. There is growing evidence that chronic stress can physically alter the emotion centers of the limbic system, changing their input to the hypothalamic-limbic-autonomic network that regulates autonomic outflow. This leads to imbalance of the parasympathetic and sympathetic nervous systems, most often in favor of sympathetic overactivation. Autonomic imbalance acts as a driving force behind the atrial ectopy and reentry that promote AF. Careful study of AF pathophysiology can illuminate the means that enable AF to elude both pharmacological control and surgical cure, by revealing ways in which antiarrhythmic drugs and surgical and ablation procedures may paradoxically promote fibrillation. Understanding AF pathophysiology can also help clarify the mechanisms by which emerging modalities aiming to correct autonomic imbalance, such as renal sympathetic denervation, may offer potential to better control this arrhythmia. Finally, growing evidence supports lifestyle modification approaches as adjuncts to improve AF control.

Meta-Analysis of Continuous Positive Airway Pressure as a Therapy of Atrial Fibrillation in Obstructive Sleep Apnea

Atrial fibrillation (AF) is a significant health care problem for patients with obstructive sleep apnea (OSA). Continuous positive airway pressure (CPAP) as a therapy for OSA is underused, and it is unknown if CPAP might reduce rates of AF. We systematically reviewed the published reports on CPAP use and risk of AF. MEDLINE, EMBASE, CINAHL, Web of Science, meeting abstracts, and Cochrane databases were searched from inception to June 2015. Studies needed to report the rates of AF in participants who were and were not on CPAP. Data were extracted by 2 authors. A total of 8 studies on OSA were identified (1 randomized controlled trial) with 698 CPAP users and 549 non-CPAP users. In a random effects model, patients treated with CPAP had a 42% decreased risk of AF (pooled risk ratio, 0.58; 95% confidence interval, 0.47 to 0.70; p <0.001). There was low heterogeneity in the results (I(2) = 30%). In metaregression analysis, benefits of CPAP were stronger for younger, obese, and male patients (p <0.05). An inverse relationship between CPAP therapy and AF recurrence was observed. Results suggest that more patients with AF also should be tested for OSA.

Left atrial function and maximum volume as determined by MDCT are independently associated with atrial fibrillation

RATIONALE AND OBJECTIVES

To assess whether left atrial (LA) volume, function, and diameter as determined by multidetector computed tomography (MDCT) are associated with the presence and chronicity of atrial fibrillation (AF).

MATERIALS AND METHODS

A total of 232 subjects, 156 with AF (43 with chronic and 113 with paroxysmal) and 76 normal subjects, formed the study population. AF subjects underwent MDCT of the pulmonary veins and LA, and normal subjects underwent coronary computed tomography (CT), on which LA volume, function, and diameter were measured. Associations between each MDCT LA parameter and presence and chronicity of AF were assessed using logistic regression analysis.

RESULTS

The indexed LA maximum volume (odds ratio [OR]=2.42; 95% confidence interval [CI], 1.43-4.08; P=.0009) was significantly associated with chronicity and presence of AF (OR=1.06; 95% CI, 1.03-1.10; P=.0003) after adjustment for traditional risk factors. The LA function was associated with presence of AF (OR=0.93; 95% CI, 0.89-0.97; P=.0005), but not with AF chronicity (OR=1.12; 95% CI, 0.93-1.33; P=.21).

CONCLUSIONS

Decreased LA function is associated with presence of AF, and increased LA maximum volume is associated with presence and chronicity of AF, independent of traditional risk factors.

Atrial fibrillation in obstructive sleep apnea

Atrial fibrillation (AF) is a common arrhythmia with rising incidence. Obstructive sleep apnea (OSA) is prevalent among patients with AF. This observation has prompted significant research in understanding the relationship between OSA and AF. Multiple studies support a role of OSA in the initiation and progression of AF. This association has been independent of obesity, body mass index and hypertension. Instability of autonomic tone and wide swings in intrathoracic pressure are seen in OSA. These have been mechanistically linked to initiation of AF in OSA patients by lowering atrial effective refractory period, promoting pulmonary vein discharges and atrial dilation. OSA not only promotes initiation of AF but also makes management of AF difficult. Drug therapy and electrical cardioversion for AF are less successful in presence of OSA. There has been higher rate of early and overall recurrence after catheter ablation of AF in patients with OSA. Treatment of OSA with continuous positive airway pressure has been shown to improve control of AF. However, additional studies are needed to establish a stronger relationship between OSA treatment and success of AF therapies. There should be heightened suspicion of OSA in patients with AF. There is a need for guidelines to screen for OSA as a part of AF management.

The Relationship between Obstructive Sleep Apnea and Atrial Fibrillation: A Complex Interplay

In recent years, growing evidence suggests an association between obstructive sleep apnea (OSA), a common sleep breathing disorder which is increasing in prevalence as the obesity epidemic surges, and atrial fibrillation (AF), the most common cardiac arrhythmia. AF is a costly public health problem increasing a patient's risk of stroke, heart failure, and all-cause mortality. It remains unclear whether the association is based on mutual risk factors, such as obesity and hypertension, or whether OSA is an independent risk factor and causative in nature. This paper explores the pathophysiology of OSA which may predispose to AF, clinical implications of stroke risk in this cohort who display overlapping disease processes, and targeted treatment strategies such as continuous positive airway pressure and AF ablation.

Origins of Western diseases

Recent gynaecological studies show that childbirth, constipation, trauma and surgery cause injuries to autonomic nerves at different anatomical sites in the female pelvis resulting in endometriosis, adenomyosis and fibroids. Re-growth of abnormal nerves causes allodynic symptoms ('light touch causing pain or discomfort') some years later including vulvodynia, dyspareunia, dysmenorrhea, irritative bladder and bowel symptoms. Further consequences of autonomic denervation include tissue hypoplasia and hyperplasia, visceral dysfunction, susceptibility to infection, alcohol, tobacco and drugs, as well as pain with sensitization of the central nervous system. The 'autonomic denervation' view extrapolates these observations from the female pelvis to the varied anatomy of branches of the cardiac and coeliac plexi to provide primary mechanisms for many forms of Western disease. This account sets out the autonomic denervation view, identifies features of autonomic denervation in extrapelvic organs, and, contrasts it with prior accounts of chronic Western diseases including those of DP Burkitt, PRJ Burch and DP Barker.

Stimulation of the intrinsic cardiac autonomic nervous system results in a gradient of fibrillatory cycle length shortening across the atria during atrial fibrillation in humans

INTRODUCTION

The intrinsic cardiac autonomic nervous system (ANS) is implicated in atrial fibrillation (AF) but little is known about its role in maintenance of the electrophysiological substrate during AF in humans. We hypothesized that ANS activation by high-frequency stimulation (HFS) of ganglionated plexi (GP) increases dispersion of atrial AF cycle lengths (AFCLs) via a parasympathetic effect.

METHODS AND RESULTS

During AF in 25 patients, HFS was delivered to presumed GP sites to provoke a bradycardic vagal response and AFCL was continuously monitored from catheters placed in the pulmonary vein (PV), coronary sinus (CS), and high right atrium (HRA). A total of 163 vagal responses were identified from 271 HFS episodes. With a vagal response, the greatest reduction in AFCL was seen in the PV adjacent to the site of HFS (16% reduction, 166 ± 28 to 139 ± 26 ms, P < 0.0001) followed by the PV-atrial junction (9% reduction, 173 ± 21 to 158 ± 20 ms, P < 0.0001), followed by the rest of the atrium (3-7% reduction recorded in HRA and CS). Without a vagal response, AFCL changes were not observed. In 10 patients, atropine was administered in between HFS episodes. Before atropine administration, HFS led to a vagal response and a reduction in PV AFCL (164 ± 28 to 147 ± 26 ms, P < 0.0001). Following atropine, HFS at the same GP sites no longer provoked a vagal response, and the PV AFCL remained unchanged (164 ± 30 to 166 ± 33 ms, P = 0.34).

CONCLUSIONS

Activation of the parasympathetic component of the cardiac ANS may cause heterogenous changes in atrial AFCL that might promote PV drivers.

Autonomic remodeling in the left atrium and pulmonary veins in heart failure: creation of a dynamic substrate for atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) is commonly associated with congestive heart failure (CHF). The autonomic nervous system is involved in the pathogenesis of both AF and CHF. We examined the role of autonomic remodeling in contributing to AF substrate in CHF.

METHODS AND RESULTS

Electrophysiological mapping was performed in the pulmonary veins and left atrium in 38 rapid ventricular-paced dogs (CHF group) and 39 control dogs under the following conditions: vagal stimulation, isoproterenol infusion, β-adrenergic blockade, acetylcholinesterase (AChE) inhibition (physostigmine), parasympathetic blockade, and double autonomic blockade. Explanted atria were examined for nerve density/distribution, muscarinic receptor and β-adrenergic receptor densities, and AChE activity. In CHF dogs, there was an increase in nerve bundle size, parasympathetic fibers/bundle, and density of sympathetic fibrils and cardiac ganglia, all preferentially in the posterior left atrium/pulmonary veins. Sympathetic hyperinnervation was accompanied by increases in β(1)-adrenergic receptor R density and in sympathetic effect on effective refractory periods and activation direction. β-Adrenergic blockade slowed AF dominant frequency. Parasympathetic remodeling was more complex, resulting in increased AChE activity, unchanged muscarinic receptor density, unchanged parasympathetic effect on activation direction and decreased effect of vagal stimulation on effective refractory period (restored by AChE inhibition). Parasympathetic blockade markedly decreased AF duration.

CONCLUSIONS

In this heart failure model, autonomic and electrophysiological remodeling occurs, involving the posterior left atrium and pulmonary veins. Despite synaptic compensation, parasympathetic hyperinnervation contributes significantly to AF maintenance. Parasympathetic and/or sympathetic signaling may be possible therapeutic targets for AF in CHF.

Novel insights into the cellular basis of atrial fibrillation

Atrial fibrillation is the most common clinical cardiac arrhythmia. It is often initiated by ectopic beats arising from the pulmonary veins and atria. While pulmonary vein myocytes most likely contribute to atrial ectopic beats initiating atrial fibrillation, emerging evidence suggests the existence of other cell populations that may also contribute to atrial arrhythmias. In addition to sinus node-like and intestinal Cajal-like cells, we recently characterized a novel, melanocyte-like cell population in murine and human hearts that may contribute to atrial arrhythmogenic triggers in mice. Murine cardiac melanocyte-like cells are electrically excitable, and express adrenergic and muscarinic receptors. Adult mice lacking the gene encoding dopachrome tautomerase (Dct) are susceptible to atrial arrhythmias, and Dct is expressed by both murine and human cardiac melanocytes. While Dct-expressing cells are present in human hearts in regions from which atrial arrhythmias often arise, the contribution of these cells to clinical atrial arrhythmias remains to be determined.

Characteristics of the conduction of the left atrium in atrial fibrillation using non-contact mapping

BACKGROUND

We evaluated the conduction properties of the posterior left atrium (LA) using a non-contact mapping (NCM) system as well as the significance of linear ablation at the roof of the posterior LA (LA roof) and inferior region of the posterior LA (LA bottom).

METHODS AND RESULTS

In 133 patients with atrial fibrillation (AF) (83 paroxysmal type, 50 persistent/long-lasting persistent type), we performed complete isolation of the posterior LA including pulmonary veins (Box isolation) using NCM. Isochronal activation maps were analyzed during sinus rhythm (SR), during pacing from the proximal coronary sinus (CS), and during pacing within the posterior LA before and after ablation. In sinus rhythm, horizontal conduction along the LA roof line, but not into the posterior LA wall, was observed in 59% of the patients. During paroxysmal CS pacing, horizontal conduction along the LA bottom line was observed in 69% of the patients. Posterior wall pacing conducted vertically over the LA roof and bottom lines in 98% and 83% of the patients, respectively. During AF, rotor wave conduction into the posterior LA through the LA roof and bottom lines was observed in 85% of the patients. Heterogeneous conduction directions in the posterior LA at the LA roof and bottom lines were observed in 60% of the patients.

CONCLUSIONS

Heterogeneous conduction was observed at the roof and inferior region of the posterior LA in most of these AF patients. The conduction properties of the posterior LA are affected by the direction of the wavefronts, and this may play an important role in the initiation and maintenance of AF. The complete isolation of the posterior LA may prevent AF.

Anatomy of the Pericardial Space and Mediastinum: Relevance to Epicardial Mapping and Ablation

The pericardial space is a fairly new portal for interventional cardiac electrophysiologists to access the heart and requires an understanding of its anatomic peculiarities to maneuver safely around the epicardial surfaces of the heart and great veins. Subxiphoid puncture should allow the diaphragm and fibrous pericardium to be crossed without entering the right ventricle, which is the most anteriorly situated cardiac chamber. The phrenic nerves descend on the fibrous pericardium bilaterally. The right nerve is related to the superior caval vein and the superior right pulmonary vein, whereas the left nerve takes variable courses over the left atrial appendage and the left ventricle. Related to the fibrous pericardium overlying the posterior wall of the left atrium is the esophagus.

Correlative anatomy for the electrophysiologist: ablation for atrial fibrillation. Part II: regional anatomy of the atria and relevance to damage of adjacent structures during AF ablation

Ablation procedures for atrial fibrillation have become an established and increasingly used option for managing patients with symptomatic arrhythmia. The anatomic structures relevant to the pathogenesis of atrial fibrillation and ablation procedures are varied and include the pulmonary veins, other thoracic veins, the left atrial myocardium, and autonomic ganglia. Exact regional anatomic knowledge of these structures is essential to allow correlation with fluoroscopy and electrograms and, importantly, to avoid complications from damage of adjacent structures within the chest. We present this information as a series of 2 articles. In a prior issue, we have discussed the thoracic vein anatomy relevant to paroxysmal atrial fibrillation. In the present article, we focus on the atria themselves, the autonomic ganglia, and anatomic issues relevant for minimizing complications during atrial fibrillation ablation.

Autonomic denervation and the origins of chronic Western diseases

Many chronic Western diseases result from lifestyles that include refined diets, poor bowel habits, limited physical exercise and suboptimal patterns of childbirth. Western diets result in reduced stool weights, increased bowel transit times and persistent physical efforts during defaecation. Prolonged physical efforts during defaecation and childbirth cause latent, or direct, injuries to branches of the cardiac (thorax), coeliac (abdomen) and hypogastric (pelvis) plexi. Injuries to autonomic nerves result in impaired visceral function including visceral dysmotility, tissue hypoplasia and hyperplasia, increased susceptibility to infection, and, aberrant reinnervation with sensitisation of the central nervous system (CNS). These unrecognised injuries are vulnerable to the long list of causes of autonomic Dysfunction, e.g. stress, alcohol, drugs, infection, trauma, cancer, etc. Specific injuries at different anatomical locations in midline autonomic pathways give rise to a wide range of Western diseases from infancy to old age, through diverse and cumulative mechanisms.

VEGF-A and Semaphorin3A: modulators of vascular sympathetic innervation

Sympathetic nerve activity regulates blood pressure by altering peripheral vascular resistance. Variations in vascular sympathetic innervation suggest that vascular-derived cues promote selective innervation of particular vessels during development. As axons extend towards peripheral targets, they migrate along arterial networks following gradients of guidance cues. Collective ratios of these gradients may determine whether axons grow towards and innervate vessels or continue past non-innervated vessels towards peripheral targets. Utilizing directed neurite outgrowth in a three-dimensional (3D) co-culture, we observed increased axon growth from superior cervical ganglion explants (SCG) towards innervated compared to non-innervated vessels, mediated in part by vascular endothelial growth factor (VEGF-A) and Semaphorin3A (Sema3A) which both signal via neuropilin-1 (Nrp1). Exogenous VEGF-A, delivered by high-expressing VEGF-A-LacZ vessels or by rhVEGF-A/alginate spheres, increased sympathetic neurite outgrowth while exogenous rhSema3A/Fc decreased neurite outgrowth. VEGF-A expression is similar between the innervated and non-innervated vessels examined. Sema3A expression is higher in non-innervated vessels. Spatial gradients of Sema3A and VEGF-A may promote differential Nrp1 binding. Vessels expressing high levels of Sema3A favor Nrp1-PlexinA1 signaling, producing chemorepulsive cues limiting sympathetic neurite outgrowth and vascular innervation; while low Sema3A expressing vessels favor Nrp1-VEGFR2 signaling providing chemoattractive cues for sympathetic neurite outgrowth and vascular innervation.

Diagnosis and management of premature ventricular complexes-associated chronic cough

BACKGROUND

Chronic cough frequently remains unexplained. Although various cardiac arrhythmias have already been reported as a cause of chronic cough, this phenomenon has not been evaluated prospectively. Therefore, we studied the incidence and management of cough associated with premature ventricular complexes (PVCs) in a population of patients with this condition.

METHODS

Patients without organic heart disease who had been referred for the management of symptomatic PVC were evaluated prospectively. PVC-associated cough was recognized if cough episodes occurred just after spontaneous or induced PVC or observed in an ECG or a multichannel recording system that included ECG. A differential diagnosis of cough was performed according to the guidelines on cough. Afterward, antiarrhythmic therapy was instituted to eliminate PVC and cough.

RESULTS

Of the 120 patients who were referred for the management of PVC, 10 had a chronic cough. After extensive workup for the cause of chronic cough, the cough was thought to be solely due to PVC in one patient, partially due to PVC plus another cause in five patients, and not due to PVC but to nonasthmatic eosinophilic bronchitis, gastroesophageal reflux disease, and chronic sinusitis in four patients. Patients with PVC-associated cough reported more severe perception of symptoms associated with arrhythmia than patients without cough (mean [+/- SD] visual analog scale score, 8.2 +/- 0.5 vs 5.7 +/- 1.6, respectively; p < 0.01). PVC-associated cough disappeared after antiarrhythmic treatment (radiofrequency ablation [n = 4], oral antiarrhythmic agent [n = 1]), or after spontaneous remission of PVC (n = 1).

CONCLUSIONS

PVC may be a cause of chronic cough. Interdisciplinary cooperation is warranted for the proper diagnosis and management of PVC-associated cough.

PDGF-B signaling is important for murine cardiac development: its role in developing atrioventricular valves, coronaries, and cardiac innervation

We hypothesized that PDGF-B/PDGFR-beta-signaling is important in the cardiac contribution of epicardium-derived cells and cardiac neural crest, cell lineages crucial for heart development. We analyzed hearts of different embryonic stages of both Pdgf-b-/- and Pdgfr-beta-/- mouse embryos for structural aberrations with an established causal relation to defective contribution of these cell lineages. Immunohistochemical staining for alphaSMA, periostin, ephrinB2, EphB4, VEGFR-2, Dll1, and NCAM was performed on wild-type and knockout embryos. We observed that knockout embryos showed perimembranous and muscular ventricular septal defects, maldevelopment of the atrioventricular cushions and valves, impaired coronary arteriogenesis, and hypoplasia of the myocardium and cardiac nerves. The abnormalities correspond with models in which epicardial development is impaired and with neuronal neural crest-related innervation deficits. This implies a role for PDGF-B/PDGFR-beta-signaling specifically in the contribution of these cell lineages to cardiac development.

Inducibility of atrial and ventricular arrhythmias along the ligament of marshall: role of autonomic factors

BACKGROUND

The mechanism(s) underlying atrial fibrillation (AF) initiation along the ligament of Marshall (LOM) remains controversial.

OBJECTIVES

We sought to examine the role of the autonomic nervous system in arrhythmogenesis along the LOM.

METHODS

In 31 anesthetized dogs, a left thoracotomy exposed the LOM. During atrial pacing, high-frequency stimulation (HFS: 200 Hz, 0.1 ms pulse width, 40 ms duration, 0.6-12 V) was delivered during atrial refractoriness to different sites of LOM (LOM(CS)= near coronary sinus; LOM(LIPV)= near left inferior pulmonary vein; LOM(LS-LIPV)= between LIPV and left superior pulmonary vein (LSPV); LOM(LSPV)= near LSPV). HFS was repeated after intravenous administration of esmolol (1 mg/kg; n = 9) or atropine (2 mg; n = 12). Norepinephrine (10(-7) M, 0.4 cc) was injected into LOM(LSPV) (n = 5).

RESULTS

The median voltages for HFS to induce AF were 3.2 V, 3.2 V, 8.0 V*(,double dagger), and 12 V*(,double dagger) at LOM(CS), LOM(LIPV), LOM(LS-LIPV), and LOM(LSPV), respectively (*P < 0.01, compared with LOM(CS) and double dagger P < 0.01, compared with LOM(LIPV)). Esmolol or atropine markedly increased the threshold for AF induction. Ventricular tachycardias (VT) and accelerated junctional rhythm were induced in 8 of 12 and 6 of 12 dogs after atropine administration, respectively. Sustained VT occurred within minutes in 5 of 5 dogs receiving norepinephrine injection into the LOM(LSPV.)

CONCLUSION

HFS induced AF along LOM with a gradient of stimulation thresholds from LOM(CS) (lowest) toward LOM(LSPV) (highest). This response was inhibited by esmolol or atropine. These data suggest an autonomic basis for AF initiation in LOM, and both sympathetic and parasympathetic neural elements play an important role in AF initiation. Hyperactivity of the sympathetic neural elements in LOM may be crucial in the initiation of ventricular tachyarrhythmias.

How Does Successful Off-Pump Pulmonary Vein Isolation for Paroxysmal Atrial Fibrillation Influence Heart Rate Variability and Autonomic Activity?

Objective

Surgical pulmonary vein isolation (PVI) for paroxysmal atrial fibrillation (PAF) blocks trigger stimulation from PVs and partially disconnects the atria from sympathetic and parasympathetic neural stimulation. This study describes long-term changes in heart rate variability (HRV) and autonomic activity (AA) after successful bipolar radiofrequency PVI.

Methods

Twenty-seven patients who underwent coronary artery bypass grafting and successful (defined as stable sinus rhythm for 1 year) off-pump bipolar radiofrequency PVI for PAF were prospectively followed 3, 6, and 12 months after surgery including 24 hours Holter electrocardiogram. The following HRV and AA parameters were calculated: mean NN-interval, SD of NN-intervals, SD of averaged NN-intervals, root mean square of successive differences, low frequency (LF) power (0.04–0.15 Hz; a parameter specific for sympathetic activity), high frequency (HF) power (0.15–0.4 Hz; a parameter specific for parasympathetic activity), and the LF:HF ratio.

Results

Preoperatively, high HRV and AA parameters were recorded. In 3-, 6-, and 12-month time, a progressive reduction of HRV and AA was observed, reaching significance after 12 months. Respective rates before surgery and 12 months after it were: for SD of averaged NN-intervals (122.4 ± 113; 80.5 ± 42 milliseconds; P = 0.046), for root mean square of successive differences (79.2 ± 93; 45 ± 20 milliseconds; P = 0.04). The LF:HF ratios were 1.22 and 0.73 before and 12 months after surgery, respectively. The statistically significant continuous reduction in LF:HF ratio (P = 0.02) is suggestive of a progressive parasympathetic dominance 12 months after surgery.

Conclusions

Successful PVI for PAF results in HRV and sympathetic activity reduction with preoperative sympathetic dominance and oncoming vagal dominance after 1 year from surgery. Despite preoperative sympathetic dominance, successful PVI for PAF results in HRV and a reduction in sympathetic activity with emerging parasympathetic dominance 12 months after surgery.