The Brain-Heart Connection in Sympathetically Triggered Inherited Arrhythmia Syndromes

Molecular and cellular neurocardiology in heart disease

This paper updates and builds on a previous White Paper in this journal that some of us contributed to concerning the molecular and cellular basis of cardiac neurobiology of heart disease. Here we focus on recent findings that underpin cardiac autonomic development, novel intracellular pathways and neuroplasticity. Throughout we highlight unanswered questions and areas of controversy. Whilst some neurochemical pathways are already demonstrating prognostic viability in patients with heart failure, we also discuss the opportunity to better understand sympathetic impairment by using patient specific stem cells that provides pathophysiological contextualization to study 'disease in a dish'. Novel imaging techniques and spatial transcriptomics are also facilitating a road map for target discovery of molecular pathways that may form a therapeutic opportunity to treat cardiac dysautonomia.

Cardiac response to water activities in children with Long QT syndrome type 1

BACKGROUND

Swimming is a genotype-specific trigger in long QT syndrome type 1 (LQT1).

OBJECTIVE

To examine the autonomic response to water activities in children and adolescents with LQT1.

METHODS

In this cross-sectional study, LQT1 patients were age and sex matched to one healthy control subject. Electrocardiograms (ECGs) were recorded during face immersion (FI), swimming, diving, and whole-body submersion (WBS). Heart rate (HR) and heart rate variability (HRV) was measured. The high frequency (HF) component of HRV was interpreted to reflect parasympathetic activity, while the low frequency (LF) component was interpreted as reflecting the combined influence of sympathetic and parasympathetic activity on autonomic nervous modulation of the heart.

RESULTS

Fifteen LQT1 patients (aged 7-19 years, all on beta-blocker therapy) and fifteen age and sex matched non-medicated controls were included. No significant ventricular arrhythmias were observed in the LQT1 population during the water activities. Out of these 15 matched pairs, 12 pairs managed to complete FI and WBS for more than 10 seconds and were subsequently included in HR and HRV analyses. In response to FI, the LQT1 group experienced a drop in HR of 48 bpm, compared to 67 bpm in the control group (p = 0.006). In response to WBS, HR decreased by 48 bpm in the LQT1 group and 70 bpm in the control group (p = 0.007). A significantly lower PTOT (p < 0.001) and HF (p = 0.011) component was observed before, during and after FI in LQT1 patients compared with the controls. Before, during and after WBS, a significantly lower total power (p < 0.001), LF (p = 0.002) and HF (p = 0.006) component was observed in the LQT1 patients.

CONCLUSION

A significantly lower HR decrease in response to water activities was observed in LQT1 subjects on beta-blocker therapy, compared to matched non-medicated controls. The data suggests an impaired parasympathetic response in LQT1 children and adolescents. An aberrant autonomic nervous system (ANS) response may cause an autonomic imbalance in this patient group.

Human in vitro neurocardiac coculture (ivNCC) assay development for evaluating cardiac contractility modulation

Two of the most prominent organ systems, the nervous and the cardiovascular systems, are intricately connected to maintain homeostasis in mammals. Recent years have shown tremendous efforts toward therapeutic modulation of cardiac contractility and electrophysiology by electrical stimulation. Neuronal innervation and cardiac ganglia regulation are often overlooked when developing in vitro models for cardiac devices, but it is likely that peripheral nervous system plays a role in the clinical effects. We developed an in vitro neurocardiac coculture (ivNCC) model system to study cardiac and neuronal interplay using human induced pluripotent stem cell (hiPSC) technology. We demonstrated significant expression and colocalization of cardiac markers including troponin, α-actinin, and neuronal marker peripherin in neurocardiac coculture. To assess functional coupling between the cardiomyocytes and neurons, we evaluated nicotine-induced β-adrenergic norepinephrine effect and found beat rate was significantly increased in ivNCC as compared to monoculture alone. The developed platform was used as a nonclinical model for the assessment of cardiac medical devices that deliver nonexcitatory electrical pulses to the heart during the absolute refractory period of the cardiac cycle, that is, cardiac contractility modulation (CCM) therapy. Robust coculture response was observed at 14 V/cm (5 V, 64 mA), monophasic, 2 ms pulse duration for pacing and 20 V/cm (7 V, 90 mA) phase amplitude, biphasic, 5.14 ms pulse duration for CCM. We observed that the CCM effect and kinetics were more pronounced in coculture as compared to cardiac monoculture, supporting a hypothesis that some part of CCM mechanism of action can be attributed to peripheral nervous system stimulation. This study provides novel characterization of CCM effects on hiPSC-derived neurocardiac cocultures. This innervated human heart model can be further extended to investigate arrhythmic mechanisms, neurocardiac safety, and toxicity post-chronic exposure to materials, drugs, and medical devices. We present data on acute CCM electrical stimulation effects on a functional and optimized coculture using commercially available hiPSC-derived cardiomyocytes and neurons. Moreover, this study provides an in vitro human heart model to evaluate neuronal innervation and cardiac ganglia regulation of contractility by applying CCM pulse parameters that closely resemble clinical setting. This ivNCC platform provides a potential tool for investigating aspects of cardiac and neurological device safety and performance.

The Impact of Mental Stress on Cardiovascular Health—Part II

Endothelial dysfunction is one of the earliest manifestations of atherosclerosis, contributing to its development and progression. Mental stress induces endothelial dysfunction through increased activity of the sympathetic nervous system, release of corticotropin-releasing hormone from the hypothalamus, inhibition of nitric oxide (NO) synthesis by cortisol, and increased levels of pro-inflammatory cytokines. Mental-stress-induced increased output of the sympathetic nervous system and concomitant withdrawal of the parasympathetic inflammatory reflex results in systemic inflammation and activation of a neural–hematopoietic–arterial axis. This includes the brainstem and subcortical regions network, bone marrow activation, release of leukocytes into the circulation and their migration to the arterial wall and atherosclerotic plaques. Low-grade, sterile inflammation is involved in all steps of atherogenesis, from coronary plaque formation to destabilisation and rupture. Increased sympathetic tone may cause arterial smooth-muscle-cell proliferation, resulting in vascular hypertrophy, thus contributing to the development of hypertension. Emotional events also cause instability of cardiac repolarisation due to brain lateralised imbalance of cardiac autonomic nervous stimulation, which may lead to asymmetric repolarisation and arrhythmia. Acute emotional stress can also provoke severe catecholamine release, leading to direct myocyte injury due to calcium overload, known as myocytolysis, coronary microvascular vasoconstriction, and an increase in left ventricular afterload. These changes can trigger a heart failure syndrome mimicking acute myocardial infarction, characterised by transient left ventricular dysfunction and apical ballooning, known as stress (Takotsubo) cardiomyopathy. Women are more prone than men to develop mental-stress-induced myocardial ischemia (MSIMI), probably reflecting gender differences in brain activation patterns during mental stress. Although guidelines on CV prevention recognise psychosocial factors as risk modifiers to improve risk prediction and decision making, the evidence that their assessment and treatment will prevent CAD needs further evaluation.

A Systematic Review on the Role of Βeta-Blockers in Reducing Cardiac Arrhythmias in Long QT Syndrome Subtypes 1-3

Long QT syndrome (LQTS) is one of the most common inherited cardiac channelopathies with a prevalence of 1:2000. The condition can be congenital or acquired with 15 recognized genotypes; the most common subtypes are LQTS 1, 2, and 3 making up to 85%-90% of the cases. LQTS is characterized by delayed ventricular cardiomyocyte repolarization manifesting on the surface electrocardiogram (EKG) by a prolonged corrected QT (QTc) interval. The mainstay of treatment for this condition involves in part or combination medical therapy via β-blockers as first-line (or other anti-arrhythmic), left cardiac sympathectomy, or implantable cardiac defibrillator placement. Given the high rate of adverse cardiac events (ACE) or sudden cardiac death (SCD) in this population of patients with this disease, this review seeks to highlight the genotype-specific treatment consensus in β-blocker therapy of the most common subtypes. A database search of PubMed, PMC, and Medline was conducted to ascertain the most recent data in the last five years on the management of LQTS types 1-3 and the role of β-blockers in reducing ACE in these types. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were adhered to in the study selection, and selected studies focused on humans, written in the English Language, and within the last five years of LQTS subtypes 1, 2, and 3. Eleven relevant studies were selected after considering inclusion criteria, exclusion criteria, and quality appraisal within the last five years, focusing on β-blocker selection directed based on the subtypes of LQTS. Two meta-analyses, one cohort study, and eight reviews provided significant data that non-selective β-blockers unequivocally are of benefit in these LQTS types. Summary of findings suggested nadolol followed by propranolol yields the best results in LQTS 1, while nadolol would yield the best effect in LQTS 2 and 3.

Neurohumoral Cardiac Regulation: Optogenetics Gets Into the Groove

The cardiac autonomic nervous system (ANS) is the main modulator of heart function, adapting contraction force, and rate to the continuous variations of intrinsic and extrinsic environmental conditions. While the parasympathetic branch dominates during rest-and-digest sympathetic neuron (SN) activation ensures the rapid, efficient, and repeatable increase of heart performance, e.g., during the "fight-or-flight response." Although the key role of the nervous system in cardiac homeostasis was evident to the eyes of physiologists and cardiologists, the degree of cardiac innervation, and the complexity of its circuits has remained underestimated for too long. In addition, the mechanisms allowing elevated efficiency and precision of neurogenic control of heart function have somehow lingered in the dark. This can be ascribed to the absence of methods adequate to study complex cardiac electric circuits in the unceasingly moving heart. An increasing number of studies adds to the scenario the evidence of an intracardiac neuron system, which, together with the autonomic components, define a little brain inside the heart, in fervent dialogue with the central nervous system (CNS). The advent of optogenetics, allowing control the activity of excitable cells with cell specificity, spatial selectivity, and temporal resolution, has allowed to shed light on basic neuro-cardiology. This review describes how optogenetics, which has extensively been used to interrogate the circuits of the CNS, has been applied to untangle the knots of heart innervation, unveiling the cellular mechanisms of neurogenic control of heart function, in physiology and pathology, as well as those participating to brain-heart communication, back and forth. We discuss existing literature, providing a comprehensive view of the advancement in the understanding of the mechanisms of neurogenic heart control. In addition, we weigh the limits and potential of optogenetics in basic and applied research in neuro-cardiology.

Functional hyperactivity in long QT syndrome type 1 pluripotent stem cell-derived sympathetic neurons

Sympathetic activation is an established trigger of life-threatening cardiac events in long QT syndrome type 1 (LQT1). KCNQ1 loss-of-function variants, which underlie LQT1, have been associated with both cardiac arrhythmia and neuronal hyperactivity pathologies. However, the LQT1 sympathetic neuronal phenotype is unknown. Here, we aimed to study human induced pluripotent stem cell (hiPSC)-derived sympathetic neurons (SNs) to evaluate neuronal functional phenotype in LQT1. We generated hiPSC-SNs from two patients with LQT1 with a history of sympathetically triggered arrhythmia and KCNQ1 loss-of-function genotypes (c.781_782delinsTC and p.S349W/p.R518X). Characterization of hiPSC-SNs was performed using immunohistochemistry, enzyme-linked immunosorbent assay, and whole cell patch clamp electrophysiology, and functional LQT1 hiPSC-SN phenotypes compared with healthy control (WT) hiPSC-SNs. hiPSC-SNs stained positive for tyrosine hydroxylase, peripherin, KCNQ1, and secreted norepinephrine. hiPSC-SNs at 60 ± 2.2 days in vitro had healthy resting membrane potentials (-60 ± 1.3 mV), and fired rapid action potentials with mature kinetics in response to stimulation. Significant hyperactivity in LQT1 hiPSC-SNs was evident via increased norepinephrine release, increased spontaneous action potential frequency, increased total inward current density, and reduced afterhyperpolarization, compared with age-matched WT hiPSC-SNs. A significantly higher action potential frequency upon current injection and larger synaptic current amplitudes in compound heterozygous p.S349W/p.R518X hiPSC-SNs compared with heterozygous c.781_782delinsTC hiPSC-SNs was also observed, suggesting a potential genotype-phenotype correlation. Together, our data reveal increased neurotransmission and excitability in heterozygous and compound heterozygous patient-derived LQT1 sympathetic neurons, suggesting that the cellular arrhythmogenic potential in LQT1 is not restricted to cardiomyocytes.NEW & NOTEWORTHY Here, we present the first study of patient-derived LQT1 sympathetic neurons that are norepinephrine secreting, and electrophysiologically functional, in vitro. Our data reveal a novel LQT1 sympathetic neuronal phenotype of increased neurotransmission and excitability. The identified sympathetic neuronal hyperactivity phenotype is of particular relevance as it could contribute to the mechanisms underlying sympathetically triggered arrhythmia in LQT1.

Cardiovascular autonomic dysfunction after stroke

Strokes are the paradigmatic example of the sudden impairment of the cerebral regulation of cardiac autonomic regulation. Although several aspects of dysautonomic cardiovascular regulation post stroke remain unanswered, there has been a wealth of research in this area in the last decade. In this article, we present a state-of-the-art review on the anatomical and functional organization of cardiovascular autonomic regulation, and the pathophysiology, incidence, time course, diagnosis, clinical aspects, prognosis, and management of post-stroke cardiovascular autonomic dysfunction.

Functional coculture of sympathetic neurons and cardiomyocytes derived from human-induced pluripotent stem cells

We present data on a functional coculture between human-induced pluripotent stem cell-derived sympathetic neurons and cardiomyocytes. Moreover, this study adds significantly to the available data on the electrophysiological function of human-induced pluripotent stem cell-derived sympathetic neurons.