Novel insights into the role of the sympathetic nervous system in cardiac arrhythmogenesis

Emerging Strategies and Effective Prevention Measures for Investigating the Association Between Stroke and Sudden Cardiac Fatality

Stroke-related cardiac death is a significant concern for patients with stroke and their healthcare providers. It is a complex and multifaceted condition that requires careful management of both modifiable and non-modifiable risk factors. This review provides an overview of the pathophysiology, risk factors, and prevention strategies for stroke-related cardiac death. The review highlights the importance of identifying and managing modifiable risk factors such as hypertension, diabetes, and lifestyle factors, as well as non-modifiable risk factors such as age and genetics. Additionally, the review explores emerging strategies for prevention, including the use of wearable devices and genetic testing to identify patients at risk, stem cell therapy and gene therapy for cardiac dysfunction, and precision medicine for personalized treatment plans. Despite some limitations to this review, it provides valuable insights into the current understanding of stroke-related cardiac death and identifies important areas for future research. Ultimately, the implementation of evidence-based prevention strategies and personalized treatment plans has the potential to improve outcomes for patients with stroke and reduce the burden of stroke-related cardiac death in the population.

Mapping of Neuro-Cardiac Electrophysiology: Interlinking Epilepsy and Arrhythmia

The interplay between neurology and cardiology has gained significant attention in recent years, particularly regarding the shared pathophysiological mechanisms and clinical comorbidities observed in epilepsy and arrhythmias. Neuro-cardiac electrophysiology mapping involves the comprehensive assessment of both neural and cardiac electrical activity, aiming to unravel the intricate connections and potential cross-talk between the brain and the heart. The emergence of artificial intelligence (AI) has revolutionized the field by enabling the analysis of large-scale data sets, complex signal processing, and predictive modeling. AI algorithms have been applied to neuroimaging, electroencephalography (EEG), electrocardiography (ECG), and other diagnostic modalities to identify subtle patterns, classify disease subtypes, predict outcomes, and guide personalized treatment strategies. In this review, we highlight the potential clinical implications of neuro-cardiac mapping and AI in the management of epilepsy and arrhythmias. We address the challenges and limitations associated with these approaches, including data quality, interpretability, and ethical considerations. Further research and collaboration between neurologists, cardiologists, and AI experts are needed to fully unlock the potential of this interdisciplinary field.

Epilepsy and long-term risk of arrhythmias

BACKGROUND AND AIMS

Previous evidence has mainly supported transient changes in cardiac function during interictal or peri-ictal phases in people with epilepsy, but the long-term risk of cardiac arrhythmias is poorly described. This study aimed to assess the long-term association of epilepsy with cardiac arrhythmias, considering the potential role of genetic predisposition and antiseizure medications (ASMs) in any associations observed.

METHODS

This population-based study evaluated UK Biobank data for individuals recruited between 2006 and 2010. Cox proportional hazards models and competing risk models were used to examine the association of epilepsy history with the long-term incidence risk of cardiac arrhythmias and arrhythmias subtypes. Polygenic risk scores (PRS) were calculated to investigate the effect of genetic susceptibility. The role of ASMs was also evaluated by integrating observational and drug target Mendelian randomization (MR) evidence.

RESULTS

The study included 329 432 individuals, including 2699 people with epilepsy. Compared with those without epilepsy, people with epilepsy experienced an increased risk of all cardiac arrhythmias [hazard ratio (HR) 1.36, 95% confidence interval (CI) 1.21-1.53], atrial fibrillation (HR 1.26, 95% CI 1.08-1.46), and other cardiac arrhythmias (HR 1.56, 95% CI 1.34-1.81). The associations were not modified by genetic predisposition as indicated by PRS. Competing and sensitivity analyses corroborated these results. Individuals with epilepsy using ASMs, especially carbamazepine and valproic acid, were at a higher risk for cardiac arrhythmias. This observation was further supported by drug target MR results (PSMR < .05 and PHEIDI > .05).

CONCLUSION

This study revealed the higher risk of cardiac arrhythmias persists long term in people with epilepsy, especially among those using carbamazepine and valproic acid. These findings highlight the need for regular heart rhythm monitoring and management in people with epilepsy in order to reduce the risk of further cardiovascular complications.

Adrenoceptor sub-type involvement in Ca2+ current stimulation by noradrenaline in human and rabbit atrial myocytes

Atrial fibrillation (AF) from elevated adrenergic activity may involve increased atrial L-type Ca²⁺ current (I_CaL) by noradrenaline (NA). However, the contribution of the adrenoceptor (AR) sub-types to such I_CaL-increase is poorly understood, particularly in human. We therefore investigated effects of various broad-action and sub-type-specific α- and β-AR antagonists on NA-stimulated atrial I_CaL. I_CaL was recorded by whole-cell-patch clamp at 37 °C in myocytes isolated enzymatically from atrial tissues from consenting patients undergoing elective cardiac surgery and from rabbits. NA markedly increased human atrial I_CaL, maximally by ~ 2.5-fold, with EC₇₅ 310 nM. Propranolol (β₁ + β₂-AR antagonist, 0.2 microM) substantially decreased NA (310 nM)-stimulated I_CaL, in human and rabbit. Phentolamine (α₁ + α₂-AR antagonist, 1 microM) also decreased NA-stimulated I_CaL. CGP20712A (β₁-AR antagonist, 0.3 microM) and prazosin (α₁-AR antagonist, 0.5 microM) each decreased NA-stimulated I_CaL in both species. ICI118551 (β₂-AR antagonist, 0.1 microM), in the presence of NA + CGP20712A, had no significant effect on I_CaL in human atrial myocytes, but increased it in rabbit. Yohimbine (α₂-AR antagonist, 10 microM), with NA + prazosin, had no significant effect on human or rabbit I_CaL. Stimulation of atrial I_CaL by NA is mediated, based on AR sub-type antagonist responses, mainly by activating β₁- and α₁-ARs in both human and rabbit, with a β₂-inhibitory contribution evident in rabbit, and negligible α₂ involvement in either species. This improved understanding of AR sub-type contributions to noradrenergic activation of atrial I_CaL could help inform future potential optimisation of pharmacological AR-antagonism strategies for inhibiting adrenergic AF.

Comorbid Hypertension Reduces the Risk of Ventricular Arrhythmia in Chronic Heart Failure Patients with Implantable Cardioverter-Defibrillators

AIMS

Low blood pressure (BP) has been shown to be associated with increased mortality in patients with chronic heart failure. This study was designed to evaluate the relationships between diagnosed hypertension and the risk of ventricular arrhythmia (VA) and all-cause death in chronic heart failure (CHF) patients with implantable cardioverter-defibrillators (ICD), including those with preserved left ventricular ejection fraction (HFpEF) and indication for ICD secondary prevention. We hypothesized that a stable hypertension status, along with an increasing BP level, is associated with a reduction in the risk of VA in this population, thereby limiting ICD efficacy.

METHODS

We retrospectively enrolled 964 CHF patients, with hypertension diagnosis and hospitalized BP measurements obtained before ICD implantation. The primary outcome measure was defined as the composite of SCD, appropriate ICD therapy, and sustained VT. The secondary endpoint was time to death or heart transplantation (HTx). We performed multivariable Cox proportional hazard regression and entropy balancing to calculate weights to control for baseline imbalances with or without hypertension. The Fine-Gray subdistribution hazard model was used to confirm the results. The effect of random BP measurements on the primary outcome was illustrated in the Cox model with inverse probability weighting.

RESULTS

The 964 patients had a mean (SD) age of 58.9 (13.1) years; 762 (79.0%) were men. During the interrogation follow-up [median 2.81 years (interquartile range: 1.32-5.27 years)], 380 patients (39.4%) reached the primary outcome. A total of 244 (45.2%) VA events in non-hypertension patients and 136 (32.1%) in hypertension patients were observed. A total of 202 (21.0%) patients died, and 31 (3.2%) patients underwent heart transplantation (incidence 5.89 per 100 person-years; 95% CI: 5.16-6.70 per 100 person-years) during a median survival follow-up of 4.5 (IQR 2.8-6.8) years. A lower cumulative incidence of VA events was observed in hypertension patients in the initial unadjusted Kaplan-Meier time-to-event analysis [hazard ratio (HR): 0.65, 95% confidence interval (CI): 0.53-0.80]. The protective effect was robust after entropy balancing (HR: 0.71, 95% CI: 0.56-0.89) and counting death as a competing risk (HR: 0.71, 95% CI: 0.51-1.00). Hypertension diagnosis did not associate with all-cause mortality in this population. Random systolic blood pressure was negatively associated with VA outcomes (p = 0.065).

CONCLUSIONS

In hospitalized chronic heart failure patients with implantable cardioverter-defibrillators, the hypertension status and higher systolic blood pressure measurements are independently associated with a lower risk of combined endpoints of ventricular arrhythmia and sudden cardiac death but not with all-cause mortality. Randomized controlled trials are needed to confirm the protective effect of hypertension on ventricular arrhythmia in chronic heart failure patients.

Anatomical Evidence for the Neural Connection from the Emotional Brain to Autonomic Innervation in the Anterior Chamber Structures of the Eye

OBJECTIVE

Previous studies have shown that the autonomic nervous system (ANS), which can be affected by emotions, is important in the occurrence or progression of glaucoma. The autonomic innervation distributed in the anterior chamber (AC) structures might play an efferent role in the neural regulation of intraocular pressure (IOP). This study aimed to investigate the anatomic neural connection from the emotional brain to autonomic innervation in the AC.

METHODS

A retrograde trans-multisynaptic pseudorabies virus encoded with an enhanced green fluorescent protein (PRV531) and non-trans-synaptic tracer FAST Dil were injected into the right eye of mice, respectively. Fluorescent localization in the emotional brain and preganglionic nuclei was studied. Five and a half days after PRV531 injection into the right AC, fluorescent signals were observed in several emotional brain regions, including the amygdala, agranular insular cortex, lateral septal nuclei, periaqueductal gray, and hypothalamus. Autonomic preganglionic nuclei, including Edinger-Westphal nucleus, superior salivatory nucleus, and intermediolateral nucleus, were labeled using PRV531.

RESULTS

The sensory trigeminal nuclei were not labeled using PRV531. The fluorescence signals in the nuclei mentioned above showed bilateral distribution, primarily on the ipsilateral side. Seven days after injecting FAST Dil into the AC, we observed no FAST Dil-labeled neurons in the central nervous system.

CONCLUSION

Our results indicate a neural connection from the emotional brain to autonomic innervation in the AC, which provides anatomical support for the emotional influence of IOP via the ANS.

Increased sympathetic tone is associated with illness burden in bipolar disorder

BACKGROUND

We recently described an association between reduced heart rate variability (HRV) and illness burden in bipolar disorder (BD) using a novel Illness Burden Index (IBI). We aimed to further characterize this association by using spectral analyses to assess whether the IBI is also associated with autonomic imbalance in BD patients.

METHODS

In this cross-sectional study, 53 participants with BD wore a device for 24 h to assess association between HRV spectral measures and the IBI or each of its components (age of onset, number and type of previous episode(s), duration of the most severe episode, history of suicide attempts or psychotic symptoms during episodes, co-morbid psychiatric disorders, and family history). We ran both unadjusted models and models controlling for age, sex, years of education, marital status, BMI, pharmacotherapy, and baseline functional cardiovascular capacity.

RESULTS

HRV low-frequency (LF) normalized values were almost twice as high as published in healthy controls. Higher IBI was associated with higher LF and lower High Frequency (HF) values, resulting in a higher LF/HF ratio, indicating an increased sympathetic tone. Four individual components of the IBI were similarly associated with measures of increased sympathetic tone: earlier age of onset, number of depressive episodes, co-morbid anxiety disorders, and family history of suicide. Adjusted and unadjusted models had similar results.

LIMITATIONS

Our models used mean LF and HF and do not consider their dynamic variations over 24 h or phase of the illness.

CONCLUSIONS

Burden of illness is associated with increased sympathetic tone in patients with BD, putting them at risk for arrythmias and sudden death.

Hourly variability in outflow tract ectopy as a predictor of its site of origin

INTRODUCTION

Before ablation, predicting the site of origin (SOO) of outflow tract ventricular arrhythmia (OTVA), can inform patient consent and facilitate appropriate procedural planning. We set out to determine if OTVA variability can accurately predict SOO.

METHODS

Consecutive patients with a clear SOO identified at OTVA ablation had their prior 24-h ambulatory ECGs retrospectively analysed (derivation cohort). Percentage ventricular ectopic (VE) burden, hourly VE values, episodes of trigeminy/bigeminy, and the variability in these parameters were evaluated for their ability to distinguish right from left-sided SOO. Effective parameters were then prospectively tested on a validation cohort of consecutive patients undergoing their first OTVA ablation.

RESULTS

High VE variability (coefficient of variation ≥0.7) and the presence of any hour with <50 VE, were found to accurately predict RVOT SOO in a derivation cohort of 40 patients. In a validation cohort of 29 patients, the correct SOO was prospectively identified in 23/29 patients (79.3%) using CoV, and 26/29 patients (89.7%) using VE < 50. Including current ECG algorithms, VE < 50 had the highest Youden Index (78), the highest positive predictive value (95.0%) and the highest negative predictive value (77.8%).

CONCLUSION

VE variability and the presence of a single hour where VE < 50 can be used to accurately predict SOO in patients with OTVA. Accuracy of these parameters compares favorably to existing ECG algorithms.

Comparison of EQ-5D-3L and metabolic components between patients with hyperhidrosis and the general population: a propensity score matching analysis

PURPOSE

It is important to understand the characteristics of patients with hyperhidrosis, which are different from the general population, for treating hyperhidrosis. Sympathetic overactivity, which might play an important role in hyperhidrosis, can contribute to metabolic diseases and the decreased quality of life (QoL). We compared the metabolic components and health-related QoL between patients with hyperhidrosis and the general population.

METHODS

We conducted a case-control study and compared the characteristics of the patients (N = 196) with hyperhidrosis and propensity score-matched controls (N = 196) selected from the Korean National Health and Nutrition Examination Survey. Metabolic components and EQ-5D-3L (EQ-5D) index were compared using a two-way mixed analysis of covariance after adjusting for confounders.

RESULTS

Patients with hyperhidrosis had significantly higher waist circumference (estimated mean values ± SD for patients and the control group, 85.5  ±  10.8 cm vs 81.3  ±  10.3 cm, p < 0.001), blood pressure (SBP, 121.1  ±  16.9 vs 111.7  ±  10.3, p < 0.001 AND DBP, 77.5  ±  12.8 vs 73.6  ±  8.6, p < 0.001, respectively), fasting glucose (97.1  ±  11.3 vs 91.5  ±  9.2, p < 0.001), and the number of components of metabolic syndrome (1.4  ±  1.3 vs 1.0  ±  1.2, p = 0.002), and significantly lower estimated glomerular filtration rate (144.3  ±  53.2 vs 158.3  ±  55.7, p = 0.002) and EQ-5D values (estimated mean values (standard error) for patients and the control group, 0.92 (0.01) vs 0.97 (0.01), p < 0.001) compared to the control group after adjustment.

CONCLUSION

The patients with hyperhidrosis had more central obesity and unfavorable metabolic parameters and a lower EQ-5D index compared with the general population, emphasizing clinical importance of hyperhidrosis to be cured in aspect of metabolic components as well as patients' QOL.

Location of Parasympathetic Innervation Regions From Electrograms to Guide Atrial Fibrillation Ablation Therapy: An in silico Modeling Study

The autonomic nervous system (ANS) plays an essential role in the generation and maintenance of cardiac arrhythmias. The cardiac ANS can be divided into its extrinsic and intrinsic components, with the latter being organized in an epicardial neural network of interconnecting axons and clusters of autonomic ganglia called ganglionated plexi (GPs). GP ablation has been associated with a decreased risk of atrial fibrillation (AF) recurrence, but the accurate location of GPs is required for ablation to be effective. Although GP stimulation triggers both sympathetic and parasympathetic ANS branches, a predominance of parasympathetic activity has been shown. This study aims was to develop a method to locate atrial parasympathetic innervation sites based on measurements from a grid of electrograms (EGMs). Electrophysiological models representative of non-AF, paroxysmal AF (PxAF), and persistent AF (PsAF) tissues were developed. Parasympathetic effects were modeled by increasing the concentration of the neurotransmitter acetylcholine (ACh) in randomly distributed circles across the tissue. Different circle sizes of ACh and fibrosis geometries were considered, accounting for both uniform diffuse and non-uniform diffuse fibrosis. Computational simulations were performed, from which unipolar EGMs were computed in a 16 × 1 6 electrode mesh. Different distances of the electrodes to the tissue (0.5, 1, and 2 mm) and noise levels with signal-to-noise ratio (SNR) values of 0, 5, 10, 15, and 20 dB were tested. The amplitude of the atrial EGM repolarization wave was found to be representative of the presence or absence of ACh release sites, with larger positive amplitudes indicating that the electrode was placed over an ACh region. Statistical analysis was performed to identify the optimal thresholds for the identification of ACh sites. In all non-AF, PxAF, and PsAF tissues, the repolarization amplitude rendered successful identification. The algorithm performed better in the absence of fibrosis or when fibrosis was uniformly diffuse, with a mean accuracy of 0.94 in contrast with a mean accuracy of 0.89 for non-uniform diffuse fibrotic cases. The algorithm was robust against noise and worked for the tested ranges of electrode-to-tissue distance. In conclusion, the results from this study support the feasibility to locate atrial parasympathetic innervation sites from the amplitude of repolarization wave.

Clocks, Rhythms, Sex, and Hearts: How Disrupted Circadian Rhythms, Time-of-Day, and Sex Influence Cardiovascular Health

Cardiovascular diseases are the top cause of mortality in the United States, and ischemic heart disease accounts for 16% of all deaths around the world. Modifiable risk factors such as diet and exercise have often been primary targets in addressing these conditions. However, mounting evidence suggests that environmental factors that disrupt physiological rhythms might contribute to the development of these diseases, as well as contribute to increasing other risk factors that are typically associated with cardiovascular disease. Exposure to light at night, transmeridian travel, and social jetlag disrupt endogenous circadian rhythms, which, in turn, alter carefully orchestrated bodily functioning, and elevate the risk of disease and injury. Research into how disrupted circadian rhythms affect physiology and behavior has begun to reveal the intricacies of how seemingly innocuous environmental and social factors have dramatic consequences on mammalian physiology and behavior. Despite the new focus on the importance of circadian rhythms, and how disrupted circadian rhythms contribute to cardiovascular diseases, many questions in this field remain unanswered. Further, neither time-of-day nor sex as a biological variable have been consistently and thoroughly taken into account in previous studies of circadian rhythm disruption and cardiovascular disease. In this review, we will first discuss biological rhythms and the master temporal regulator that controls these rhythms, focusing on the cardiovascular system, its rhythms, and the pathology associated with its disruption, while emphasizing the importance of the time-of-day as a variable that directly affects outcomes in controlled studies, and how temporal data will inform clinical practice and influence personalized medicine. Finally, we will discuss evidence supporting the existence of sex differences in cardiovascular function and outcomes following an injury, and highlight the need for consistent inclusion of both sexes in studies that aim to understand cardiovascular function and improve cardiovascular health.

Systolic Blood Pressure and Risk for Ventricular Arrhythmia in Patients With an Implantable Cardioverter Defibrillator

Low systolic blood pressure (SBP) was previously suggested to be a marker for heart failure and mortality in patients with low left ventricular ejection fraction. We aimed to explore the association of SBP on risk of ventricular tachyarrhythmias (VTA) and atrial arrhythmias as well as appropriate and inappropriate Implantable Cardioverter Defibrillator (ICD) therapy. The study population comprised 1,481 of 1,500 (99%) patients enrolled in the Multicenter Automatic Defibrillator Implantation Trial - Reduce Inappropriate Therapy trial. Multivariate Cox proportional hazards regression modeling was used to identify the association of baseline SBP (recorded prior to ICD implantation) with the risk of VTA > 170 beats/min during follow-up (primary end point) and atrial arrhythmia, appropriate and inappropriate ICD therapy, hospitalization and death (secondary end points). SBP was dichotomized at 120 mm Hg (approximate mean and median) and was also assessed as a continuous measure. Multivariate analysis showed that each 10 mm Hg decrement in SBP was associated with corresponding 11% increased risk for VTA (p = 0.008). Low SBP (≤120 mm Hg) was associated with a significant 58% (p = 0.002) increased risk for VTA ≥170 beats/min; 53% (p = 0.019) increased risk for VTA ≥200 beats/min; and 65% (p = 0.001) increased risk for appropriate ICD therapy, as compared with SBP >120 mm Hg. Low SBP was not associated with increased risk of atrial arrhythmias, and inappropriate ICD therapy. In conclusion, in MADIT-RIT, SBP (≤120 mm Hg) predicted higher rates of VTA. These findings suggest that SBP may be utilized for VTA risk stratification in candidates for primary ICD therapy.

Association between Respiratory Sleep Indices and Cardiovascular Disease in Sleep Apnea-A Community-Based Study in Cyprus

Obstructive sleep apnea (OSA) is a chronic and prevalent disorder, strongly associated with cardiovascular disease (CVD). The apnea-hypopnea index (AHI), or respiratory event index (REI), and the oxygen desaturation index (ODI) are the clinical metrics of sleep apnea in terms of diagnosis and severity. However, AHI, or REI, does not quantify OSA-related hypoxemia and poorly predicts the consequences of sleep apnea in cardiometabolic diseases. Moreover, it is unclear whether ODI correlates with CVD in OSA. Our study aimed to examine the possible associations between respiratory sleep indices and CVD in OSA, in a non-clinic-based population in Cyprus. We screened 344 subjects of a stratified, total sample of 4118 eligible responders. All participants were adults (age 18+), residing in Cyprus. Each patient answered with a detailed clinical history in terms of CVD. A type III sleep test was performed on 282 subjects (81.97%). OSA (REI ≥ 15) was diagnosed in 92 patients (32.62%, Group A). REI < 15 was observed in the remaining 190 subjects (67.37%, Group B). In OSA group A, 40 individuals (43%) reported hypertension, 17 (18.5%) arrhythmias, 10 (11%) heart failure, 9 (9.8%) ischemic heart disease and 2 (2%) previous stroke, versus 46 (24%), 21 (11%), 7 (3.7%), 12 (6.3%) and 6 (3%), in Group B, respectively. Hypertension correlated with REI (p = 0.001), ODI (p = 0.003) and mean SaO₂ (p < 0.001). Arrhythmias correlated with mean SaO₂ (p = 0.001) and time spent under 90% oxygen saturation (p = 0.040). Heart failure correlated with REI (p = 0.043), especially in the supine position (0.036). No statistically significant correlations were observed between ischemic heart disease or stroke and REI, ODI and mean SaO₂. The pathogenesis underlying CVD in OSA is variable. According to our data, hypertension correlated with REI, ODI and mean SaO₂. Arrhythmias correlated only with hypoxemia (mean SaO₂), whereas heart failure correlated only with REI, especially in the supine position.

Association Between Heart Rate and Reversibility of the Symptom, Refractoriness to Palliative Treatment, and Survival in Dyspneic Cancer Patients

CONTEXT

Dyspnea is one of the most distressing symptoms for terminally ill cancer patients and a predictor of poor prognosis. Identification of simple clinical signs, such as heart rate, indicating clinical course of each patient is of value.

OBJECTIVES

To explore the potential association between heart rate and reversibility of the symptom, treatment response to palliative intervention, and survival in terminally ill cancer patients with dyspnea at rest.

METHODS

This is a secondary analysis of a multicenter prospective cohort study of patients with advanced cancer to validate multiple prognostic tools. In the patients with dyspnea at rest at the baseline, we examined a potential association between heart rate and the reversibility of dyspnea and refractoriness to palliative treatment using logistic regression analysis. Survivals were compared using the Cox proportional hazards model among four groups with different levels of the heart rate (≤74, 75-84, 85-97, and ≥98).

RESULTS

A total of 2298 patients were enrolled, and 418 patients (18%) had dyspnea at rest. Reversibility of dyspnea was significantly higher in the patients with lower heart rate (P for trend = 0.008), and the refractoriness to palliative treatment tended to be higher in the patients with higher heart rate (P for trend = 0.101). The median survival for each heart rate quartile groups was significantly higher in the lower heart rate group (24 vs. 21 vs. 14 vs. 9 days; heart rate ≤74, 75-84, 85-97, and ≥98, respectively; log-rank P < 0.001).

CONCLUSION

Heart rate may help clinicians to make the prediction of the patient's clinical course more accurate.

Relation between resting heart rate and the risk of ventricular tachyarrhythmias in MADIT-RIT

AIMS

To explore the association between resting heart rate (RHR) and ventricular tachyarrhythmias (VTA) events among patients who were enrolled in MADIT-RIT.

METHODS AND RESULTS

Multivariate Cox proportional hazards regression modelling was employed to evaluate the association between baseline RHR [dichotomized at the lower quartile (≤63 b.p.m.) and further assessed as a continuous measure] and the risk for any VTA, fast VTA (>200 b.p.m.), and appropriate implantable cardioverter-defibrillator (ICD) therapy, among 1500 patients who were enrolled in MADIT-RIT. Kaplan-Meier survival analysis showed that at 2 years of follow-up the rate of any VTA was significantly lower among patients with low baseline RHR (≤63 b.p.m.) as compared with faster RHR (11% vs. 19%, respectively; P = 0.001 for the overall difference during follow-up). Similar results were shown for the association with the rate of fast VTA (8% vs. 14%, respectively; P = 0.016), and appropriate ICD therapy (10% vs. 18%, respectively; P = 0.004). Multivariate analysis, after adjustment for medical therapy, showed that low baseline RHR was associated with a significant 45% (P = 0.002) reduction in the VTA risk as compared with faster baseline RHRs. When assessed as a continuous measure, each 10 b.p.m. decrement in RHR was associated with a corresponding 13% (P = 0.014) reduction in the VTA risk.

CONCLUSION

In MADIT-RIT, low RHR was independently associated with a lower risk for life-threatening arrhythmic events. These findings suggest a possible role for RHR for improved selection of candidates for ICD therapy.

The NACA score as a predictor of ventricular cardiac arrhythmias - A retrospective six-year study

BACKGROUND

Helicopter Emergency Medical Service (HEMS) conducts the evaluation of a patient's condition using NACA score before transporting the patient to hospital. The conditions inside the rescue helicopter limit or even make it impossible to conduct some medical procedures. An appropriate classification of the patient may lead to a lower possibility of occurrence of adverse events during the flight. The aim of the research was to evaluate the correlation of NACA score with the cardiac arrhythmia that may be life threatening.

METHODS

A retrospective observational study included a group of 47,131 patients, who were transported by HEMS services between 2012 and 2017. The research was conducted using the analysis of variance ANOVA running a post hoc test. In order to calculate the correlation of variables, Kruskal-Wallis and r-Pearson tests were carried out, interpreting the results according to J. Gilville's scale. The significance level was set at α = 0,05.

RESULTS

The average number of points using NACA score for the studied group was 4,06 (SD ± 1,38). Twelve heart rhythms were selected while evaluating correlations using NACA score. There was a significant relation between the ECG variable and NACA score (p = 0,003). There was a very strong correlation between NACA score and the following: VF/pVT (r-Pearson = 0,856; p = 0,006), PEA (r-Pearson = 0,810; p = 0,015) and Asystole (r-Pearson = 0,728; p = 0,026).

CONCLUSIONS

NACA score allows to predict the risk of occurrence of ventricular arrhythmia of the myocardium as well as cardiac arrest. The possibility of occurrence of a life-threatening rhythm is significantly higher in patients classified as NACA IV or higher.

Region-specific parasympathetic nerve remodeling in the left atrium contributes to creation of a vulnerable substrate for atrial fibrillation

Atrial fibrillation (AF) is the most common heart rhythm disorder and a major cause of stroke. Unfortunately, current therapies for AF are suboptimal, largely because the molecular mechanisms underlying AF are poorly understood. Since the autonomic nervous system is thought to increase vulnerability to AF, we used a rapid atrial pacing (RAP) canine model to investigate the anatomic and electrophysiological characteristics of autonomic remodeling in different regions of the left atrium. RAP led to marked hypertrophy of parent nerve bundles in the posterior left atrium (PLA), resulting in a global increase in parasympathetic and sympathetic innervation throughout the left atrium. Parasympathetic fibers were more heterogeneously distributed in the PLA when compared with other left atrial regions; this led to greater fractionation and disorganization of AF electrograms in the PLA. Computational modeling revealed that heterogeneously distributed parasympathetic activity exacerbates sympathetic substrate for wave break and reentry. We further discovered that levels of nerve growth factor (NGF) were greatest in the left atrial appendage (LAA), where AF was most organized. Preferential NGF release by the LAA - likely a direct function of frequency and regularity of atrial stimulation - may have important implications for creation of a vulnerable AF substrate.

Nocturnal ventricular arrhythmias are associated with the severity of cardiovascular autonomic neuropathy in type 2 diabetes

BACKGROUND

Cardiovascular autonomic neuropathy (CAN) is a risk factor for arrhythmias and adverse cardiovascular events, but the relationship between CAN severity and nocturnal arrhythmias needs to be clarified. This study evaluated the association between nocturnal arrhythmias and CAN severity in patients with type 2 diabetes (T2D).

METHODS

In all, 219 T2D patients were recruited from January 2017 to May 2018. Subjects were classified into no CAN (NCAN), early CAN (ECAN), definite CAN (DCAN), or advanced CAN (ACAN) based on cardiovascular autonomic reflex tests (CARTs). A 24-hour electrocardiogram was recorded and daytime (0700-2300 hours) and night-time (2300-0700 hours) heartbeats were analyzed separately.

RESULTS

After adjusting for age, the incidence of ventricular arrhythmias increased with CAN severity at night-time (18.6%, 29.9%, 36.2%, and 60.0% in the NCAN, ECAN, DCAN, and ACAN groups, respectively; P_trend  = 0.034). Patients with nocturnal ventricular arrhythmias (NVAs) had higher CART scores (2.0 ± 1.0 vs 1.5 ± 0.9; P < 0.001) and lower heart rate variability (HRV) during deep breathing (9.5 ± 5.7 vs 11.6 ± 6.6 b. p. m; P = 0.021), HRV during the Valsalva maneuver (1.2 ± 0.1 vs 1.2 ± 0.2; P = 0.006), and postural blood pressure change (-8.8 ± 15.5 vs -4.1 ± 11.2 mmHg; P = 0.023). Multivariate regression analysis revealed that CAN stage (odds ratio 1.765; 95% confidence interval 1.184-2.632; P = 0.005) was independently associated with NVAs.

CONCLUSIONS

In T2D, CAN stage was independently associated with the presence of NVAs. Early detection, diagnosis, and treatment of CAN may help predict and prevent adverse cardiovascular events and cardiovascular mortality in diabetes.

Sympatho-Vagal Imbalance is Associated with Sarcopenia in Male Patients with Heart Failure

Background

Resting sympathetic hyperactivity and impaired parasympathetic reactivation after exercise have been described in patients with heart failure (HF). However, the association of these autonomic changes in patients with HF and sarcopenia is unknown.

Objective

The aim of this study was to evaluate the impact of autonomic modulation on sarcopenia in male patients with HF.

Methods

We enrolled 116 male patients with HF and left ventricular ejection fraction < 40%. All patients underwent a maximal cardiopulmonary exercise testing. Maximal heart rate was recorded and delta heart rate recovery (∆HRR) was assessed at 1^st and 2^nd minutes after exercise. Muscle sympathetic nerve activity (MSNA) was recorded by microneurography. Dual-energy X-ray absorptiometry was used to measure body composition and sarcopenia was defined by the sum of appendicular lean muscle mass (ALM) divided by height in meters squared and handgrip strength.

Results

Sarcopenia was identified in 33 patients (28%). Patients with sarcopenia had higher MSNA than those without (47 [41-52] vs. 40 [34-48] bursts/min, p = 0.028). Sarcopenic patients showed lower ∆HRR at 1^st (15 [10-21] vs. 22 [16-30] beats/min, p < 0.001) and 2^nd min (25 [19-39] vs. 35 [24-48] beats/min, p = 0.017) than non-sarcopenic. There was a positive correlation between ALM and ∆HRR at 1^st (r = 0.26, p = 0.008) and 2^nd min (r = 0.25, p = 0.012). We observed a negative correlation between ALM and MSNA (r = -0.29, p = 0.003).

Conclusion

Sympatho-vagal imbalance seems to be associated with sarcopenia in male patients with HF. These results highlight the importance of a therapeutic approach in patients with muscle wasting and increased peripheral sympathetic outflow.

Cardiac rhythm disorders in obstructive sleep apnea

Obstructive sleep apnea (OSA) is common among patients with cardiac rhythm disorders. OSA may contribute to arrhythmias due to acute mechanisms, such as generation of negative intrathoracic pressure during futile efforts to breath, intermittent hypoxia, and surges in sympathetic activity. In addition, OSA may lead to heart remodeling and increases arrhythmia susceptibility. Atrial distension and remodeling, that has been shown to be associated with OSA, is a well-known anatomical substrate for atrial fibrillation (AF). AF is the arrhythmia most commonly described in patients with OSA. Several observational studies have shown that the treatment of OSA with continuous positive airway pressure (CPAP) reduces recurrence of AF after electrical cardioversion and catheter ablation. There is also evidence that nocturnal hypoxemia, a hallmark of OSA, predicts sudden cardiac death (SCD) independently of well-established cardiovascular risk factors. Among patients with an implantable cardiac defibrillator, those with OSA have a higher risk of receiving treatment for life-threatening arrhythmias. Nocturnal hypoxemia may also increase vagal tone, which increases susceptibility to bradycardic and conduction rhythm disorders that have also been described in patients with OSA. In conclusion, there are several biological pathways linking OSA and increased cardiac arrhythmogenesis propensity. However, the independent association is derived from observational studies and the direction of the association still needs clarification due to the lack of large clinical trials. This review focuses on the current scientific evidence linking OSA to cardiac rhythm disorders and point out future directions.

Sympathetic overactivity in dialysis patients-Underappreciated and clinically consequential

Cardiovascular morbidity and mortality remain frustratingly common in dialysis patients. A dearth of established evidence-based treatment calls for alternative therapeutic avenues to be embraced. Sympathetic hyperactivity, predominantly due to afferent nerve signaling from the diseased native kidneys, has been established to be prognostic in the dialysis population for over 15 years. Despite this, tangible therapeutic interventions have, to date, been unsuccessful and the outlook for patients remains poor. This narrative review summarizes established experimental and clinical data, highlighting recent developments, and proposes why interventions to ameliorate sympathetic hyperactivity may well be beneficial for this high-risk population.

Oral adenosine 5'-triphosphate supplementation improved hemodynamic and autonomic parameters after exercise in hypertensive women

The aim of this study was to verify the autonomic modulation and blood pressure after adenosine-5'-triphosphate (ATP) supplementation associated to acute aerobic exercise in hypertensive women. Eleven hypertensive women (age, 61.8±5.0 years) completed a randomized, double blind trial: ATP supplement condition (ATP=400 mg) or placebo. After 30 min of supplementation or placebo intake, the subjects performed 30 min of aerobic exercise (70%-75% of maximum heart rate). The autonomic modulation was assessed by heart rate variability during rest and recovery (postexercise until 30 min of recovery), the square root of the mean squared difference between adjacent RR intervals (RMSSD), standard deviation of successive values (SDNN), low frequency (LF) and high frequency (HF) were measured. The blood pressure (systolic blood pressure [SBP] and diastolic blood pressure, mmHg) were recorded at rest, immediately postexercise, post-10, post-20, and post-30 min after exercise. For RMSSD, there was statistically significant difference during recovery, with higher RMSSD for ATP compared to placebo (rest=16.4±8.5 vs. placebo=11.6±4.0; ATP=18.5±9.7 msec; P=0.020). When analyzing the delta (recovery minus rest), the RMSSD (ATP=2.1± 7.2 msec vs. placebo=-4.7±7.5 msec; P=0.009), LF (ATP=-19.8±122.7 vs. placebo=-94.1±200.2 msec2; P=0.02), and SDNN (ATP=-2.8±12.2 msec vs. placebo=-10.6±10.5 msec; P=0.010) were higher for ATP than placebo. Furthermore, there was a greater postexercise hypotension at 20 min for ATP (SBP: ATP=-13.2±8.4 mmHg vs. placebo=-6.1±9.9 mmHg; P=0.006). Acute ATP supplementation promoted greater postexercise hypotension for systolic blood pressure and induced faster recovery of heart rate variability in hypertensive women.

Healthy hearts at hectic pace: From daily life stress to abnormal cardiomyocyte function and arrhythmias

The hectic pace of contemporary life is a major source of acute and chronic stress, which may have a deleterious impact on body health . In the field of cardiovascular disease, acute emotional stress has been associated with coronary spasm and Takotsubo cardiomyopathy, whereas the manifestations of chronic stress have been overlooked, and most underlying pathophysiology remains to be elucidated. Chronic stress affects the neuronal circuitry composed of cortico-limbic structures and the nuclei regulating autonomic function, eliciting a sympatho-vagal imbalance, characterised by adrenergic activation and vagal withdrawal. Sympathetic terminals are connected to cardiomyocytes in a quasi-synaptic way, producing the so called 'neuro-cardiac junction'. During chronic stress, norepinephrine release is increased, leading to overstimulation of cardiomyocytes via β₁-adrenergic receptors, influencing mainly calcium dynamics, and β₂-adrenergic receptors, which control housekeeping functions. The circadian rhythm of cardiomyocytes is then impaired, with elongation of the catabolic ('light' phase) over the anabolic ('nocturnal') phase. This leads to a depletion of cell energy storage, and a decreased turnover of cell constituents. Even cell interactions are affected, as coupling between cardiomyocytes decreases while coupling between cardiomyocytes and fibroblasts increases. The ultimate results are changes in the shape and velocity of action potential, fibroblast activation and deposition of extracellular matrix. These alterations may predispose to arrhythmias and may favour the development of a stress-related cardiomyopathy. A better comprehension of this cascade of events may allow us to identify screening protocols and treatment strategies (meditation, yoga, physical activity, psychological assistance, β-blockers) to prevent or relieve ongoing cardiac damage.

Postexercise hypotension and autonomic modulation response after full versus split body resistance exercise in trained men

To investigate the effects of full versus split body resistance exercise on postexercise hypotension and autonomic modulation in trained men. Sixteen resistance recreationally trained males (age, 24.9±5.3 years) performed three randomized trials: upper body (UB), lower body (LB), and full body (FB) conditions. Blood pressure and heart rate variability were collected at rest, immediately postexercise, post-10, and post-30 min during recovery. For systolic blood pressure, delta (30 min minus rest) was lower for the FB condition compared to the UB (−10.1±7.4 mmHg [FB] vs. −3.3±12.6 mmHg [LB] vs. −1.9±8.1 mmHg [UB], P=0.004). For diastolic blood pressure (−8.2±10.9 mmHg [FB] vs. −1.5±9.8 mmHg [LB] vs. −8.7±11.4 mmHg [UB], P=0.038) and mean blood pressure delta during recovery (−11.7±14 mmHg [FB] vs. −2.2±10.6 mmHg [LB] vs. −5.2±6.8 mmHg [UB], P=0.045), there were statistically significant lower values in the FB condition in relation to the LB condition. Regarding heart rate variability, there were no significant differences between conditions, however, the square root of the mean squared difference between adjacent RR intervals presented an increase until post-30 during recovery (P<0.001), and there was a higher values of low frequency and lower values of high frequency across time (P<0.001). Postexercise hypotension was influenced by the amount of muscle mass involved in a bout of resistance exercise, with the FB condition inducing lower systolic blood pressure in relation to the UB after exercise, as well as a great decrease in postexercise diastolic and mean blood pressure compared with the LB. The autonomic modulation response was similar between conditions during recovery.

Inhibition of Small Conductance Calcium-Activated Potassium (SK) Channels Prevents Arrhythmias in Rat Atria During β-Adrenergic and Muscarinic Receptor Activation

Sympathetic and vagal activation is linked to atrial arrhythmogenesis. Here we investigated the small conductance Ca²⁺-activated K⁺ (SK)-channel pore-blocker N-(pyridin-2-yl)-4-(pyridine-2-yl)thiazol-2-amine (ICA) on action potential (AP) and atrial fibrillation (AF) parameters in isolated rat atria during β-adrenergic [isoprenaline (ISO)] and muscarinic M2 [carbachol (CCh)] activation. Furthermore, antiarrhythmic efficacy of ICA was benchmarked toward the class-IC antiarrhythmic drug flecainide (Fleca). ISO increased the spontaneous beating frequency but did not affect other AP parameters. As expected, CCh hyperpolarized resting membrane potential (-6.2 ± 0.9 mV), shortened APD₉₀ (24.2 ± 1.6 vs. 17.7 ± 1.1 ms), and effective refractory period (ERP; 20.0 ± 1.3 vs. 15.8 ± 1.3 ms). The duration of burst pacing triggered AF was unchanged in the presence of CCh compared to control atria (12.8 ± 5.3 vs. 11.2 ± 3.6 s), while β-adrenergic activation resulted in shorter AF durations (3.3 ± 1.7 s) and lower AF-frequency compared to CCh. Treatment with ICA (10 μM) in ISO -stimulated atria prolonged APD₉₀ and ERP, while the AF burden was reduced (7.1 ± 5.5 vs. 0.1 ± 0.1 s). In CCh-stimulated atria, ICA treatment also resulted in APD₉₀ and ERP prolongation and shorter AF durations. Fleca treatment in CCh-stimulated atria prolonged APD₉₀ and ERP and abbreviated the AF duration to a similar extent as with ICA. Muscarinic activated atria constitutes a more arrhythmogenic substrate than β-adrenoceptor activated atria. Pharmacological inhibition of SK channels by ICA is effective under both conditions and equally efficacious to Fleca.

Connexin 43 reduces susceptibility to sympathetic atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmia reported in clinical practice. Connexin 43 (Cx43) is a member of the connexin protein family, which serves important roles in signal transduction in vivo. The aim of the present study was to investigate the role of Cx43 in the induction and maintenance of atrial fibrillation by using an animal model of sympathomimetic atrial fibrillation. Cx43 was successfully knocked down in the myocardium with gene‑specific small interfering (si)RNA via lentiviral infection. A total of 25 dogs were randomly and evenly divided into five groups: Normal (N), rapid atrial pacing (RAP), isoproterenol (ISO) + RAP, RAP + Cx43 siRNA and ISO + RAP + Cx43 siRNA. The mRNA and protein levels, as well as the distribution of Cx43 on the cell membrane, were gradually decreased in each group compared with the N group following treatment (P<0.05). The induction rate of the atrial effective refractory period was not significantly affected in the RAP and RAP + Cx43 siRNA groups, whereas it was significantly reduced in the ISO + RAP and ISO + RAP + Cx43 siRNA groups compared with the N group (P<0.05). The induction rate of AF was gradually increased in the RAP + Cx43 siRNA, ISO + RAP and ISO + RAP + Cx43 siRNA groups compared with the N group (P<0.05). The expression of nerve growth factor (NGF) and tyrosine hydroxylase (TH) was gradually increased in the ISO + RAP and ISO + RAP + Cx43 siRNA groups compared with their respective controls (RAP and RAP + Cx43 siRNA groups, respectively). However, no significant difference in the levels of NGF and TH was observed between the RAP, RAP + Cx43 siRNA, ISO + RAP and ISO + RAP + Cx43 siRNA groups. The mitochondrial morphology in each group was notably altered compared with the N group. The mitochondrial reactive oxygen species production and apoptotic index were gradually increased in each group compared with the N group (P<0.05). The results of the present study suggest that Cx43 reduces susceptibility to AF. Downregulation of Cx43 mediates the induction and maintenance of sympathetic AF.

Beta blockers in patients with end-stage renal disease-Evidence-based recommendations

For patients who require hemodialysis, beta blockers offer a simultaneous opportunity and challenge in the treatment of cardiovascular disease. Beta blockers are well supported by data from nondialysis populations and directly mitigate the sympathetic overactivity that links chronic kidney disease with cardiovascular sequelae. However, the evidence supporting their use in patients receiving hemodialysis is sparse and the heterogeneity of the beta blocker class makes it difficult to prescribe these medications with confidence. Despite these limitations, both trial and observational data exist that can help guide the use of these medications. In this review, we outline the reasons to consider beta blockers for patients receiving hemodialysis, discuss the barriers to their use, and provide specific evidence-based recommendations for beta blocker use in patients with heart failure, hypertension, ischemic heart disease and arrhythmia.

Promising effects of xanthine oxidase inhibition by allopurinol on autonomic heart regulation estimated by heart rate variability (HRV) analysis in rats exposed to hypoxia and hyperoxia

Background

It has long been suggested that reactive oxygen species (ROS) play a role in oxygen sensing via peripheral chemoreceptors, which would imply their involvement in chemoreflex activation and autonomic regulation of heart rate. We hypothesize that antioxidant affect neurogenic cardiovascular regulation through activation of chemoreflex which results in increased control of sympathetic mechanism regulating heart rhythm. Activity of xanthine oxidase (XO), which is among the major endogenous sources of ROS in the rat has been shown to increase during hypoxia promote oxidative stress. However, the mechanism of how XO inhibition affects neurogenic regulation of heart rhythm is still unclear.

Aim

The study aimed to evaluate effects of allopurinol-driven inhibition of XO on autonomic heart regulation in rats exposed to hypoxia followed by hyperoxia, using heart rate variability (HRV) analysis.

Material and methods

16 conscious male Wistar rats (350 g): control-untreated (N = 8) and pretreated with Allopurinol-XO inhibitor (5 mg/kg, followed by 50 mg/kg), administered intraperitoneally (N = 8), were exposed to controlled hypobaric hypoxia (1h) in order to activate chemoreflex. The treatment was followed by 1h hyperoxia (chemoreflex suppression). Time-series of 1024 RR-intervals were extracted from 4kHz ECG recording for heart rate variability (HRV) analysis in order to calculate the following time-domain parameters: mean RR interval (RRi), SDNN (standard deviation of all normal NN intervals), rMSSD (square root of the mean of the squares of differences between adjacent NN intervals), frequency-domain parameters (FFT method): TSP (total spectral power) as well as low and high frequency band powers (LF and HF). At the end of experiment we used rat plasma to evaluate enzymatic activity of XO and markers of oxidative stress: protein carbonyl group and 8-isoprostane concentrations. Enzymatic activity of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) were measures in erythrocyte lysates.

Results

Allopurinol reduced oxidative stress which was the result of hypoxia/hyperoxia, as shown by decreased 8-isoprostane plasma concentration. XO inhibition did not markedly influence HRV parameters in standard normoxia. However, during hypoxia, as well as hyperoxia, allopurinol administration resulted in a significant increase of autonomic control upon the heart as shown by increased SDNN and TSP, with an increased vagal contribution (increased rMSSD and HF), whereas sympathovagal indexes (LF/HF, SDNN/rMSSD) remained unchanged.

Conclusions

Observed regulatory effects of XO inhibition did not confirm preliminary hypothesis which suggested that an antioxidant such as allopurinol might activate chemoreflex resulting in augmented sympathetic discharge to the heart. The HRV regulatory profile of XO inhibition observed during hypoxia as well as post-hypoxic hyperoxia corresponds to reported reduced risk of sudden cardiovascular events. Therefore our data provide a new argument for therapeutical use of allopurinol in hypoxic conditions.

Impact of presynaptic sympathetic imbalance in long-QT syndrome by positron emission tomography

OBJECTIVE

We investigated the impact of cardiac presynaptic norepinephrine recycling in patients with long-QT syndrome (LQTS) using positron emission tomography (PET) with ¹¹C-meta-hydroxyephedrine ([¹¹C]mHED-PET).

METHODS

[¹¹C]mHED-PET was performed in 25 patients with LQTS (LQT1: n=14; LQT2: n=11) and 20 healthy controls and correlated with clinical parameters. [¹¹C]mHED-PET images were analysed for global and regional retention indices (RI) and washout rates (WO) reflecting dynamic parameters of the tracer activity.

RESULTS

Global and regional RI values were similar between patients with LQTS and controls. Although the global WO rates were similar between these groups, regional WO rates were on average higher in the lateral left ventricle (LV) wall in patients with LQTS (dose, mean ±SD; 0.08±0.14 vs 0.00%±0.09% min^-1; p=0.033). In addition, patients with LQTS with a longer QTc interval showed a higher global WO rate. Clinical symptoms correlated with higher global WO rates. In the presence of normal global WO rates, asymptomatic LQTS patients showed higher global RI values.

CONCLUSION

The increased regional WO rate of [¹¹C]mHED in the lateral LV suggests an imbalance of presynaptic catecholamine reuptake and release, resulting in a higher synaptic catecholamine concentration, in particular in LQT1 patients. This might enhance β-adrenoceptor signalling and thereby aggravate inherited ion channel dysfunction and may facilitate occurrence of ventricular tachyarrhythmias. Detection of regional differences in LV sympathetic nervous function may modify disease expression and potentially serve as a non-invasive risk marker in congenital LQTS.

TRIAL REGISTRATION NUMBER

2006-002767-41;Results.

Sympathetic Overactivity in Chronic Kidney Disease: Consequences and Mechanisms

The incidence of chronic kidney disease (CKD) is increasing worldwide, with more than 26 million people suffering from CKD in the United States alone. More patients with CKD die of cardiovascular complications than progress to dialysis. Over 80% of CKD patients have hypertension, which is associated with increased risk of cardiovascular morbidity and mortality. Another common, perhaps underappreciated, feature of CKD is an overactive sympathetic nervous system. This elevation in sympathetic nerve activity (SNA) not only contributes to hypertension but also plays a detrimental role in the progression of CKD independent of any increase in blood pressure. Indeed, high SNA is associated with poor prognosis and increased cardiovascular morbidity and mortality independent of its effect on blood pressure. This brief review will discuss some of the consequences of sympathetic overactivity and highlight some of the potential pathways contributing to chronically elevated SNA in CKD. Mechanisms leading to chronic sympathoexcitation in CKD are complex, multifactorial and to date, not completely understood. Identification of the mechanisms and/or signals leading to sympathetic overactivity in CKD are crucial for development of effective therapeutic targets to reduce the increased cardiovascular risk in this patient group.

Characteristics of diurnal ventricular premature complex variation in right ventricular outflow tract arrhythmias after catheter ablation

Diurnal variations in ventricular tachyarrhythmias (VAs) have been demonstrated in idiopathic arrhythmogenic heart disease. The electrophysiological characteristics of diurnal variations in idiopathic right ventricular outflow tract (RVOT) VA have not previously been elucidated. Sixty-two consecutive patients undergoing catheter ablation for idiopathic RVOT VA (mean age: 42.8 ± 12.3 years, 35 females) were enrolled. The diurnal variation type (group 1, n = 36) was defined as those patients who had most ventricular premature contractions (VPCs) during the night hours by preprocedure Holter recordings. Group 2 (n = 26) was defined as those patients who did not have significant VPC variations. The baseline characteristics and electrophysiological properties were collected and analyzed, and the rates of recurrence after catheter ablation were compared between the 2 groups. In this study, heart rate variability analysis demonstrated lower low frequency/high frequency ratios in group 1 than in group 2 (3.95 ± 3.08 vs 6.26 ± 5.33; P = 0.042). There were no significant differences in baseline characteristics, echocardiography and electrophysiological characteristics between the 2 groups. During a mean follow-up period of 13.5 ± 11.0 months, a total of 16 patients had VA recurrences, including 13 patients from group 1 and 3 patients from group 2 (36.1% vs 12.5%, P = 0.039). This study demonstrated the effect of the autonomic nervous system in idiopathic RVOT VAs and that the diurnal variation type leads to a higher recurrence rate after catheter ablation.

Increased Local Sympathetic Nerve Activity During Pathogenesis of Ventricular Arrhythmias Originating from the Right Ventricular Outflow Tract

Background

The contribution of local sympathetic nerves to ventricular arrhythmia (VA) originating from the right ventricular outflow tract (RVOT) has not been elucidated. This study used a canine model to investigate the anatomical changes of the RVOT associated with VA, and the distribution of local sympathetic nerves.

Material/Methods

The RVOT-VA canine model (6 dogs) was induced with a circular catheter and high-frequency stimulation (100 Hz) in the middle of the pulmonary artery trunk. Six dogs who were not given stimulation served as the control group. The serum levels of neurotransmitters, the extent of myocardial extension, and the sympathetic nerve density of the RVOT were also analyzed.

Results

Ventricular arrhythmias, including premature ventricular contractions, were induced in the experimental group after high-frequency stimulation. Dogs from the RVOT-VA group showed enhanced myocardial extension and sympathetic nerve density in the septal wall as compared with those of the free wall of the RVOT. In the RVOT-VA dogs, serum norepinephrine and neuropeptide Y and the sympathetic nerve density were significantly higher compared with the control group.

Conclusions

Stimulation of the pulmonary artery could activate local sympathetic nerves and enhance myocardial extension, which may be the foundation of RVOT-VA. The RVOT voltage transitional zone positively correlated with myocardial extension, which may serve as an important target for the radiofrequency catheter ablation of RVOT-VA clinically.

Modulation of Autonomic Nervous Activity in the Termination of Paroxysmal Atrial Fibrillation

BACKGROUND

Autonomic nervous activity plays a critical role in the genesis of paroxysmal atrial fibrillation (AF, PAF). However, the role of autonomic nervous activity on AF termination has not been elucidated. Heart rate variability (HRV) is widely used to evaluate autonomic nervous activity in humans. The purpose of this study was to assess whether autonomic nervous activity assessed by HRV contributes to AF termination.

METHODS

Electrocardiograms (ECGs) and HRV were studied in patients with termination of sustained (>30 s) PAF by 24-hour ambulatory Holter monitoring. The 20-minute interval after termination of AF was divided into four segments of 5 minutes each, and a frequency analysis was applied to each 5-minute segment.

RESULTS

In 52 AF episodes, the ultra-low-frequency power, very-low-frequency power, low-frequency power (LF), high-frequency power (HF), and total power significantly decreased with time after episodes of AF termination. The LF/HF (L/H) ratio, normalized LF (LFnu), and normalized HF (HFnu) significantly changed after AF termination. Eighteen (35%) episodes had decreased LFnu and increased HFnu (sympathetic withdrawal and vagal activation), which had slower average AF ventricular responses (92 ± 16 beats/min vs 105 ± 24 beats/min, P < 0.05) than the AF termination episodes (n = 34, 65%) with increased LFnu and decreased HFnu (sympathetic activation and vagal withdrawal). Moreover, older patients (aged >65 years) had a higher incidence (n = 27, 75%) of AF termination with increased LFnu and decreased HFnu than did younger patients (aged ≤65 years, n = 7, 44%, P < 0.05).

CONCLUSION

Autonomic changes critically regulate termination of PAF, which is modulated by aging.

OSA and Cardiac Arrhythmogenesis: Mechanistic Insights

A surge of data has reproducibly identified strong associations of OSA with cardiac arrhythmias. As an extension of epidemiologic and clinic-based findings, experimental investigations have made strides in advancing our understanding of the putative OSA and cardiac arrhythmogenesis mechanistic underpinnings. Although most studies have focused on the links between OSA and atrial fibrillation (AF), relationships with ventricular arrhythmias have also been characterized. Key findings implicate OSA-related autonomic nervous system fluctuations typified by enhanced parasympathetic activation during respiratory events and sympathetic surges subsequent to respiratory events, which contribute to augmented arrhythmic propensity. Other more immediate pathophysiologic influences of OSA-enhancing arrhythmogenesis include intermittent hypoxia, intrathoracic pressure swings leading to atrial stretch, and hypercapnia. Intermediate pathways by which OSA may trigger arrhythmia include increased systemic inflammation, oxidative stress, enhanced prothrombotic state, and vascular dysfunction. Long-term OSA-associated sequelae such as hypertension, atrial enlargement and fibrosis, ventricular hypertrophy, and coronary artery disease also predispose to cardiac arrhythmia. These factors can lead to a reduction in atrial effective refractory period, triggered and abnormal automaticity, and promote slowed and heterogeneous conduction; all of these mechanisms increase the persistence of reentrant arrhythmias and prolong the QT interval. Cardiac electrical and structural remodeling observed in OSA animal models can progress the arrhythmogenic substrate to further enhance arrhythmia generation. Future investigations clarifying the contribution of specific OSA-related mechanistic pathways to arrhythmia generation may allow targeted preventative therapies to mitigate OSA-induced arrhythmogenicity. Furthermore, interventional studies are needed to clarify the impact of OSA pathophysiology reversal on cardiac arrhythmogenesis and related adverse outcomes.

Type 2 Diabetes and Heart Failure: Challenges and Solutions

Increasing numbers of older patients with type 2 diabetes, and their improved survival from cardiovascular events is seeing a massive increase in patients with both diabetes and heart failure. Already, at least a third of all patients with heart failure have diabetes. This close association is partly because all the major risk factors for heart failure also cluster in patients with type 2 diabetes, including obesity, hypertension, advanced age, sleep apnoea, dyslipidaemia, anaemia, chronic kidney disease, and coronary heart disease. However, diabetes may also cause cardiac dysfunction in the absence of overt macrovascular disease, as well as complicate the response to therapy. Current management is focused on targeting modifiable risk factors for heart failure including hyperglycaemia, dyslipidaemia, hypertension, obesity and anemia. But although these are important risk markers, none of these interventions substantially prevents heart failure or improves its outcomes. Much more needs to be done to focus on this issue, including the inclusion of hospital admission for heart failure as a pre-specified component of the primary composite cardiovascular outcomes and new trials in heart failure management specifically in the context of diabetes.

Cardiac Arrhythmias and Abnormal Electrocardiograms After Acute Stroke

Cardiac arrhythmias and electrocardiogram (ECG) abnormalities occur frequently but are often underrecognized after strokes. Acute ischemic and hemorrhagic strokes in some particular area of brain can disrupt central autonomic control of the heart, precipitating cardiac arrhythmias, ECG abnormalities, myocardial injury and sometimes sudden death. Identification of high-risk patients after acute stroke is important to arrange appropriate cardiac monitoring and effective management of arrhythmias, and to prevent cardiac morbidity and mortality. More studies are needed to better clarify pathogenesis, localization of areas associated with arrhythmias and practical management of arrhythmias and abnormal ECGs after acute stroke.

Cardiac arrhythmias during or after epileptic seizures

Seizure-related cardiac arrhythmias are frequently reported and have been implicated as potential pathomechanisms of Sudden Unexpected Death in Epilepsy (SUDEP). We attempted to identify clinical profiles associated with various (post)ictal cardiac arrhythmias. We conducted a systematic search from the first date available to July 2013 on the combination of two terms: 'cardiac arrhythmias' and 'epilepsy'. The databases searched were PubMed, Embase (OVID version), Web of Science and COCHRANE Library. We attempted to identify all case reports and case series. We identified seven distinct patterns of (post)ictal cardiac arrhythmias: ictal asystole (103 cases), postictal asystole (13 cases), ictal bradycardia (25 cases), ictal atrioventricular (AV)-conduction block (11 cases), postictal AV-conduction block (2 cases), (post)ictal atrial flutter/atrial fibrillation (14 cases) and postictal ventricular fibrillation (3 cases). Ictal asystole had a mean prevalence of 0.318% (95% CI 0.316% to 0.320%) in people with refractory epilepsy who underwent video-EEG monitoring. Ictal asystole, bradycardia and AV-conduction block were self-limiting in all but one of the cases and seen during focal dyscognitive seizures. Seizure onset was mostly temporal (91%) without consistent lateralisation. Postictal arrhythmias were mostly found following convulsive seizures and often associated with (near) SUDEP. The contrasting clinical profiles of ictal and postictal arrhythmias suggest different pathomechanisms. Postictal rather than ictal arrhythmias seem of greater importance to the pathophysiology of SUDEP.

Patients with exercise-associated ventricular ectopy present evidence of myocarditis

BACKGROUND

The origin and clinical relevance of exercise-induced premature ventricular beats (PVBs) in patients without coronary heart disease or cardiomyopathies is unknown. Cardiovascular magnetic resonance enables us to non-invasively assess myocardial scarring and oedema. The purpose of our study was to discover any evidence of myocardial anomalies in patients with exercise-induced ventricular premature beats.

METHODS

We examined 162 consecutive patients presenting palpitations and documented exercise-induced premature ventricular beats (PVBs) but no history or evidence of structural heart disease. Results were compared with 70 controls matched for gender and age. ECG-triggered, T2-weighted, fast spin echo triple inversion recovery sequences and late gadolinium enhancement were obtained as well as LV function and dimensions.

RESULTS

Structural anomalies in the myocardium and/or pericardium were present in 85 % of patients with exercise-induced PVBs. We observed a significant difference between patients with PVBs and controls in late gadolinium enhancement, that is 68 % presented subepicardial or midmyocardial lesions upon enhancement, whereas only 9 % of the controls did so (p < 0.0001). More patients presented pericardial enhancement (35 %) or pericardial thickening (27 %) compared to controls (21 % and 13 %, p < 0.0001). Myocardial oedema was present in 37 % of the patients and in only one control, p < 0.0001. Left ventricular ejection fraction did not differ between patients and controls (63.1 ± 7.9 vs. 64.7 ± 7.0, p = 0.13).

CONCLUSIONS

The majority of patients with exercise-associated premature ventricular beats present evidence of myocardial disease consistent with acute or previous myocarditis or myopericarditis.

Continuous vagal nerve stimulation affects atrial neural remodeling and reduces atrial fibrillation inducibility in rabbits

BACKGROUND

The effects of continuous vagal nerve stimulation (VNS) on atrial neural remodeling during atrial fibrillation (AF) remain unclear.

OBJECTIVE

To test the hypothesis that VNS affects atrial neural remodeling and reduces AF inducibility.

METHODS

Twenty rabbits were randomly divided into two groups: rapid atrial pacing (RAP) group and RAP with VNS group. AF inducibility studies and atrial histologic analyses were performed after 4 weeks.

RESULTS

Five rabbits of RAP group (5/10) in the RAP group developed sustained AF. None of rabbits in RAP with VNS group had developed AF. The incidence of sustained AF in VNS group was significant lower than that in rapid pacing group (P<.01). Treatment with VNS resulted in a significant reduction in atrial neural remodeling and AF duration (P<.01).

CONCLUSIONS

Atrial neural remodeling plays an important role in the initiation and maintenance of AF. Modulating autonomic nerve function with VNS can contribute to AF control.

Evaluation of Cardiovascular Risk Factors in the Wistar Audiogenic Rat (WAR) Strain

Introduction

Risk factors for life-threatening cardiovascular events were evaluated in an experimental model of epilepsy, the Wistar Audiogenic Rat (WAR) strain.

Methods

We used long-term ECG recordings in conscious, one year old, WAR and Wistar control counterparts to evaluate spontaneous arrhythmias and heart rate variability, a tool to assess autonomic cardiac control. Ventricular function was also evaluated using the pressure-volume conductance system in anesthetized rats.

Results

Basal RR interval (RRi) was similar between WAR and Wistar rats (188±5 vs 199±6 ms). RRi variability strongly suggests that WAR present an autonomic imbalance with sympathetic overactivity, which is an isolated risk factor for cardiovascular events. Anesthetized WAR showed lower arterial pressure (92±3 vs 115±5 mmHg) and exhibited indices of systolic dysfunction, such as higher ventricle end-diastolic pressure (9.2±0.6 vs 5.6±1 mmHg) and volume (137±9 vs 68±9 μL) as well as lower rate of increase in ventricular pressure (5266±602 vs 7320±538 mmHg.s-1). Indices of diastolic cardiac function, such as lower rate of decrease in ventricular pressure (-5014±780 vs -7766±998 mmHg.s^-1) and a higher slope of the linear relationship between end-diastolic pressure and volume (0.078±0.011 vs 0.036±0.011 mmHg.μL), were also found in WAR as compared to Wistar control rats. Moreover, Wistar rats had 3 to 6 ventricular ectopic beats, whereas WAR showed 15 to 30 ectopic beats out of the 20,000 beats analyzed in each rat.

Conclusions

The autonomic imbalance observed previously at younger age is also present in aged WAR and, additionally, a cardiac dysfunction was also observed in the rats. These findings make this experimental model of epilepsy a valuable tool to study risk factors for cardiovascular events in epilepsy.

Tetrahydrobiopterin lowers muscle sympathetic nerve activity and improves augmentation index in patients with chronic kidney disease

Chronic kidney disease (CKD) is characterized by overactivation of the sympathetic nervous system (SNS) that contributes to cardiovascular risk. Decreased nitric oxide (NO) bioavailability is a major factor contributing to SNS overactivity in CKD, since reduced neuronal NO leads to increased central SNS activity. Tetrahydrobiopterin (BH4) is an essential cofactor for nitric oxide synthase that increases NO bioavailability in experimental models of CKD. We conducted a randomized, double-blinded, placebo-controlled trial testing the benefits of oral sapropterin dihydrochloride (6R-BH4, a synthetic form of BH4) in CKD. 36 patients with CKD and hypertension were randomized to 12 wk of 1) 200 mg 6R-BH4 twice daily + 1 mg folic acid once daily; vs. 2) placebo + folic acid. The primary endpoint was a change in resting muscle sympathetic nerve activity (MSNA). Secondary endpoints included arterial stiffness using pulse wave velocity (PWV) and augmentation index (AIx), endothelial function using brachial artery flow-mediated dilation and endothelial progenitor cells, endothelium-independent vasodilatation (EID), microalbuminuria, and blood pressure. We observed a significant reduction in MSNA after 12 wk of 6R-BH4 (-7.5 ± 2.1 bursts/min vs. +3.2 ± 1.3 bursts/min; P = 0.003). We also observed a significant improvement in AIx (by -5.8 ± 2.0% vs. +1.8 ± 1.7 in the placebo group, P = 0.007). EID increased significantly (by +2.0 ± 0.59%; P = 0.004) in the 6R-BH4 group, but there was no change in endothelial function. There was a trend toward a reduction in diastolic blood pressure by -4 ± 3 mmHg at 12 wk with 6R-BH4 (P = 0.055). 6R-BH4 treatment may have beneficial effects on SNS activity and central pulse wave reflections in hypertensive patients with CKD.

The potassium current carried by TREK-1 channels in rat cardiac ventricular muscle

We studied the potassium current flowing through TREK-1 channels in rat cardiac ventricular myocytes. We separated the TREK-1 current from other current components by blocking most other channels with a blocker cocktail. We tried to inhibit the TREK-1 current by activating protein kinase A (PKA) with a mixture of forskolin and isobutyl-methylxanthine (IBMX). Activation of PKA blocked an outwardly rectifying current component at membrane potentials positive to -40 mV. At 37 °C, application of forskolin plus IBMX reduced the steady-state outward current measured at positive voltages by about 52 %. Application of the potassium channel blockers quinidine or tetrahexylammonium also reduced the steady-state outward current by about 50 %. Taken together, our results suggest that the increase in temperature from 22 to 37 °C increased the TREK-1 current by a factor of at least 5 and that the average density of the TREK-1 current in rat cardiomyocytes at 37 °C is about 1.5 pA/pF at +30 mV. The contribution of TREK-1 to the action potential was assessed by using a dynamic patch clamp technique. After subtraction of simulated TREK-1 currents, action potential duration at 50 or 90 % repolarisation was increased by about 12 %, indicating that TREK-1 may be functionally important in rat ventricular muscle. During sympathetic stimulation, inhibition of TREK-1 channels via PKA is expected to prolong the action potential primarily in subendocardial myocytes; this may decrease the transmural dispersion of repolarisation and thus may serve to prevent the occurrence of arrhythmias.

Arrhythmia risk associated with sleep disordered breathing in chronic heart failure

The intersecting relationships of sleep disordered breathing (SDB), arrhythmogenic risk and chronic heart failure (HF) are complex and most likely multi-directional and synergistic. Autonomic dysfunction is a common pathophysiological feature of each of these entities. Intermittent hypoxia, hypercapnia, mechanical cardiac influences due to upper airway obstruction and rostral fluid shifts are SDB-specific mechanisms which may trigger, perpetuate and exacerbate HF and arrhythmogenesis. Specific pathophysiological mechanisms will vary according to the predominance of central as compared to obstructive sleep apnea. The risk of cardiac arrhythmias and HF attributable to SDB may be considerable given the high prevalence of SDB and its likely physiologic burden. The current review focuses on the data, which have accrued elucidating the specific contributory mechanisms of SDB in cardiac arrhythmias and HF, highlighting the clinical relevance and effects of standard SDB treatment on these outcomes, and describing the role of novel therapeutics.