Autonomic function and ventricular tachyarrhythmias during acute myocardial infarction

Autonomic Responses During Acute Anterior Versus Inferior Myocardial Infarction: A Systematic Review and Meta-Analysis

Autonomic responses elicited by myocardial infarction vary depending on the site of injury, but accurate assessment using heart rate variability during the acute phase is limited. We systematically searched PubMed without language restrictions throughout July 2023. We reviewed studies reporting autonomic indices separately for anterior and inferior infarcts, followed by a meta-analysis of those reporting the standard deviation of the inter-beat interval between normal sinus beats during the initial 24 hours after the onset of symptoms. Six studies were included, comprising 341 patients (165 anterior, 176 inferior infarcts), all with satisfactory scores on the Newcastle-Ottawa quality scale. The estimated average of the standardized mean difference (based on the random-effects model) was -0.722 (95% confidence intervals: -0.943 to -0.501), which differed from zero (z=-6.416, p<0.0001). This finding indicates sympathetic and vagal dominance during acute anterior and inferior infarcts, respectively, with excessive responses likely contributing to early arrhythmogenesis. Despite the amelioration of autonomic dysfunction by revascularization, infarct location should be considered when commencing β-adrenergic receptor blockade, especially after delayed procedures.

Glial cell activity in cardiovascular diseases and risk of acute myocardial infarction

Growing evidence indicates that the pathophysiological link between the brain and heart underlies cardiovascular diseases, specifically acute myocardial infarction (AMI). Astrocytes are the most abundant glial cells in the central nervous system and provide support/protection for neurons. Astrocytes and peripheral glial cells are emerging as key modulators of the brain-heart axis in AMI, by affecting sympathetic nervous system activity (centrally and peripherally). This review, therefore, aimed to gain an improved understanding of glial cell activity and AMI risk. This includes discussions on the potential role of contributing factors in AMI risk, i.e., autonomic nervous system dysfunction, glial-neurotrophic and ischemic risk markers [glial cell line-derived neurotrophic factor (GDNF), astrocytic S100 calcium-binding protein B (S100B), silent myocardial ischemia, and cardiac troponin T (cTnT)]. Consideration of glial cell activity and related contributing factors in certain brain-heart disorders, namely, blood-brain barrier dysfunction, myocardial ischemia, and chronic psychological stress, may improve our understanding regarding the pathological role that glial dysfunction can play in the development/onset of AMI. Here, findings demonstrated perturbations in glial cell activity and contributing factors (especially sympathetic activity). Moreover, emerging AMI risk included sympathovagal imbalance, low GDNF levels reflecting prothrombic risk, hypertension, and increased ischemia due to perfusion deficits (indicated by S100B and cTnT levels). Such perturbations impacted blood-barrier function and perfusion that were exacerbated during psychological stress. Thus, greater insights and consideration regarding such biomarkers may help drive future studies investigating brain-heart axis pathologies to gain a deeper understanding of astrocytic glial cell contributions and unlock potential novel therapies for AMI.

Endothelin System and Ischemia-Induced Ventricular Tachyarrhythmias

Despite the contemporary treatment of acute coronary syndromes, arrhythmic complications occurring prior to medical attendance remain significant, mandating in-depth understanding of the underlying mechanisms. Sympathetic activation has long been known to play a key role in the pathophysiology of ischemia-induced arrhythmias, but the regulating factors remain under investigation. Several lines of evidence implicate the endothelin system (a family of three isopeptides and two specific receptors) as an important modulator of sympathetic activation in the setting of acute coronary syndromes. Such interaction is present in the heart and in the adrenal medulla, whereas less is known on the effects of the endothelin system on the central autonomic network. This article summarizes the current state-of-the-art, placing emphasis on early-phase arrhythmogenesis, and highlights potential areas of future research.

Impact of Yiqi Huoxue Decoction on the Relationship between Remodeling of Cardiac Nerves and Macrophages after Myocardial Infarction in Rats

Sympathetic nerve remodeling after myocardial infarction (MI) has an indispensable role in cardiac remodeling. Numerous works have shown that sympathetic nerve remodeling can be delayed by inhibition of inflammatory response. Earlier studies have shown improvement in ventricular remodeling and inhibited chronic stage neural remodeling by Yiqi Huoxue decoction (YQHX). Therefore, the current study looked at the inhibitory effect of YQHX prescription on proinflammatory mediators and macrophages and the effect on neural remodeling at 3 and 7 days after MI. YQHX inhibited the expression of Toll-like receptor 4 (TLR4) and nuclear factor kappa B (NF-κB) proteins and macrophage infiltration within 7 days after myocardial infarction. YQHX could decrease Th-positive nerve fiber density in the area around infarction and reduce the expression of growth-associated protein 43 (GAP43), nerve growth factor (NGF), and tyrosine hydroxylase (TH) proteins, which was associated with the remodeling of sympathetic nerves. Thus, the nerve remodeling inhibition after MI due to YQHX may be through its anti-inflammatory action. These data provide direct evidence for the potential application of traditional Chinese medicine (TCM) in the remodeling of sympathetic nerves after MI.

LianXia Formula Granule Attenuates Cardiac Sympathetic Remodeling in Rats with Myocardial Infarction via the NGF/TrKA/PI3K/AKT Signaling Pathway

Sympathetic remodeling may cause severe arrhythmia after myocardial infarction (MI). Thus, targeting this process may be an effective strategy for clinical prevention of arrhythmias. LianXia Formula Granule (LXFG) can effectively improve the symptoms of patients with arrhythmia after MI, and modern pharmacological studies have shown that Coptidis Rhizoma and Rhizoma Pinelliae Preparata, the components of LXFG, have antiarrhythmia effects. Here, we investigated whether LXFG can mitigate sympathetic remodeling and suppress arrhythmia and then elucidated its underlying mechanism of action in rats after MI. Sprague-Dawley (SD) rats that had undergone a myocardial infarction model were randomly divided into 6 groups, namely, sham, model, metoprolol, and LXFG groups, with high, medium, and low dosages. We exposed the animals to 30 days of treatment and then evaluated incidence of arrhythmia and arrhythmia scores in vivo using programmed electrical stimulation. Moreover, we determined plasma catecholamines contents via enzyme-linked immunosorbent assay and detected expression of tyrosine hydroxylase (TH) at infarcted border zones via western blot, real-time PCR, and immunohistochemical analyses to assess sympathetic remodeling. Finally, we measured key molecules involved in the NGF/TrKA/PI3K/AKT pathways via western blot and real-time PCR. Compared with the model group, treatment with high dose of LXFG suppressed arrhythmia incidence and arrhythmia scores. In addition, all the LXFG groups significantly decreased protein and mRNA levels of TH, improved the average optical density of TH-positive nerve fibers, and reduced the levels of plasma catecholamines relative to the model group. Meanwhile, expression analysis revealed that key molecules in the NGF/TrKA/PI3K/AKT pathways were downregulated in the LXFG group when compared with model group. Overall, these findings indicate that LXFG suppresses arrhythmia and attenuates sympathetic remodeling in rats after MI. The mechanism is probably regulated by suppression of the NGF/TrKA/PI3K/AKT signaling pathway.

Sympathetic Activation and Arrhythmogenesis after Myocardial Infarction: Where Do We Stand?

Myocardial infarction often leads to progressive structural and electrophysiologic remodeling of the left ventricle. Despite the widespread use of β-adrenergic blockade and implantable defibrillators, morbidity and mortality from chronic-phase ventricular tachyarrhythmias remains high, calling for further investigation on the underlying pathophysiology. Histological and functional studies have demonstrated extensive alterations of sympathetic nerve endings at the peri-infarct area and flow-innervation mismatches that create a highly arrhythmogenic milieu. Such accumulated evidence, along with the previously well-documented autonomic dysfunction as an important contributing factor, has stirred intense research interest for pharmacologic and non-pharmacologic neuromodulation in post-infarction heart failure. In this regard, aldosterone inhibitors, sacubitril/valsartan and sodium-glucose cotransporter type 2 inhibitors have shown antiarrhythmic effects. Non-pharmacologic modalities, currently tested in pre-clinical and clinical trials, include transcutaneous vagal stimulation, stellate ganglion modulation and renal sympathetic denervation. In this review, we provide insights on the pathophysiology of ventricular arrhythmogenesis post-myocardial infarction, focusing on sympathetic activation.

Sympathetic and Vagal Responses Elicited by Acute Stress in Rats

Introduction

Acute emotional stress triggers autonomic responses that affect sympathovagal balance. However, the temporal pattern of changes in each autonomic arm during stress and recovery remains unclear. Therefore, we analyzed separately sympathetic and vagal activity, elicited by acute unpredictable stress in a rat model.

Methods

Continuous electrocardiographic recording was performed during (32 minutes) and after (two hours) successive use of restraint and air-jet stress in 10 rats, whereas five rats served as controls. Sympathetic and vagal indices were calculated non-invasively after heart rate variability analysis. Voluntary motion was quantified during recovery, as an index of continuing anxiety.

Results

The sympathetic nervous system index increased during stress and remained elevated during the initial stage of recovery. The parasympathetic nervous system index decreased immediately after the onset of stress and remained low throughout the observational period. During recovery, voluntary activity was more pronounced in the stress group than in the controls.

Conclusion

Successive restraint and air-jet stress in rats increased sympathetic activity and decreased vagal activity. These changes displayed only partial recovery post-stress and were accompanied by enhanced voluntary motion. Our findings may be important in the evaluation of the cardiac electrophysiologic implications of autonomic changes elicited by acute emotional stress.

Endothelin receptors in the brain modulate autonomic responses and arrhythmogenesis during acute myocardial infarction in rats

AIMS

Endothelin has been implicated in various processes in the brain, including the modulation of sympathetic responses. The present study examined the pathophysiologic role of brain endothelin-receptors in the setting of acute myocardial infarction, characterized by high incidence of ventricular tachyarrhythmias.

MAIN METHODS

We investigated the effects of intracerebroventricular administration of antagonists of endothelin-receptors ET_A, ET_B, or both, during a 24 h-observation period post-coronary ligation in (n = 70) rats. Continuous recording was performed via implanted telemetry transmitters, followed by arrhythmia-analysis and calculation of autonomic indices derived from heart rate variability. The regional myocardial electrophysiologic properties were assessed by monophasic action potentials and multi-electrode recordings.

KEY FINDINGS

Sympathetic-activity was decreased and vagal-activity was enhanced after intracerebroventricular ET_A-receptor blockade, thus attenuating regional myocardial repolarization inhomogeneity. As a result, the incidence of ventricular tachyarrhythmias was markedly lower in this group. Such effects were also observed after intracerebroventricular blockade of ET_B-, or both, ET_A- and ET_B-receptors, although to a lesser extent.

SIGNIFICANCE

ET_A-receptors in the brain modulate sympathetic and vagal responses and alter arrhythmogenesis during evolving myocardial necrosis in rats. These findings provide insights into arrhythmogenic mechanisms during acute myocardial infarction and call for further investigation on the role of endothelin in the central autonomic network.

Intracerebroventricular endothelin receptor-A blockade in rats decreases phase-II ventricular tachyarrhythmias during acute myocardial infarction

Endothelin alters central sympathetic responses, but the resultant effects on arrhythmogenesis are unknown. We examined ventricular tachyarrhythmias after endothelin receptor-A blockade in the brain of Wistar rats with acute myocardial infarction. For this aim, BQ-123 (n=6) or phosphate-buffered saline (n=6) were injected intracerebroventricularly. After 10 min, the left coronary artery was ligated, followed by implantation of telemetry transmitters. Electrocardiography and voluntary activity (as a surrogate of acute left ventricular failure) were continuously monitored for 24 h. Infarct-size was similar in the two groups. There were fewer episodes of ventricular tachyarrhythmias of shorter average duration in treated rats, leading to markedly shorter total duration (12.3+/-8.9 s), when compared to controls (546.2+/-130.3 s). Voluntary activity increased in treated rats during the last hours of recording, but bradyarrhythmic episodes were comparable between the two groups. Endothelin receptor-A blockade in the brain of rats decreases the incidence of ventricular tachyarrhythmias post-ligation, without affecting bradyarrhythmic episodes. These findings call for further research on the pathophysiologic role of endothelin during acute myocardial infarction.