Sick Sinus Syndrome

Pacemaker Channels and the Chronotropic Response in Health and Disease

Loss or dysregulation of the normally precise control of heart rate via the autonomic nervous system plays a critical role during the development and progression of cardiovascular disease-including ischemic heart disease, heart failure, and arrhythmias. While the clinical significance of regulating changes in heart rate, known as the chronotropic effect, is undeniable, the mechanisms controlling these changes remain not fully understood. Heart rate acceleration and deceleration are mediated by increasing or decreasing the spontaneous firing rate of pacemaker cells in the sinoatrial node. During the transition from rest to activity, sympathetic neurons stimulate these cells by activating β-adrenergic receptors and increasing intracellular cyclic adenosine monophosphate. The same signal transduction pathway is targeted by positive chronotropic drugs such as norepinephrine and dobutamine, which are used in the treatment of cardiogenic shock and severe heart failure. The cyclic adenosine monophosphate-sensitive hyperpolarization-activated current (If) in pacemaker cells is passed by hyperpolarization-activated cyclic nucleotide-gated cation channels and is critical for generating the autonomous heartbeat. In addition, this current has been suggested to play a central role in the chronotropic effect. Recent studies demonstrate that cyclic adenosine monophosphate-dependent regulation of HCN4 (hyperpolarization-activated cyclic nucleotide-gated cation channel isoform 4) acts to stabilize the heart rate, particularly during rapid rate transitions induced by the autonomic nervous system. The mechanism is based on creating a balance between firing and recently discovered nonfiring pacemaker cells in the sinoatrial node. In this way, hyperpolarization-activated cyclic nucleotide-gated cation channels may protect the heart from sinoatrial node dysfunction, secondary arrhythmia of the atria, and potentially fatal tachyarrhythmia of the ventricles. Here, we review the latest findings on sinoatrial node automaticity and discuss the physiological and pathophysiological role of HCN pacemaker channels in the chronotropic response and beyond.

Case Report: SCN5A mutations in three young patients with sick sinus syndrome

Background

Sick Sinus Syndrome (SSS) is generally regarded as a degenerative disease with aging; however, genetic mutations have been confirmed to be associated with SSS. Among them, mutations in SCN5A are common in patients with SSS. We report three young SSS patients with SCN5A mutations at different sites that have not been previously reported in Asian patients.

Case presentation

The three patients were all young females who presented with symptoms of severe bradycardia and paroxysmal atrial flutter, for which two patients received ablation therapy. However, after ablation, Holter monitoring indicated a significant long cardiac arrest; therefore, the patients received pacemaker implantation. The three patients had familial SSS, and genetic testing was performed. Mutations were found in SCN5A at different sites in the three families. All three patients received pacemaker implantation, resulting in the symptoms of severe bradycardia disappearing.

Conclusion

SCN5A heterozygous mutations are common among patients clinically affected by SSS. Their causative role is confirmed by our data and by the co-occurrence of genetic arrhythmias among our patients. Genetic testing for SSS cannot be performed as a single gene panel because of feasible literature results, but in presence of familial and personal history of SSS in association with arrhythmias can provide clinically useful information.

D-galactose causes sinoatrial node dysfunction: from phenotype to mechanism

With the population aging, age-related sinoatrial node dysfunction (SND) has been on the rise. Sinoatrial node (SAN) degeneration is an important factor for the age-related SND development. However, there is no suitable animal modeling method in this field. Here, we investigated whether D-galactose could induce SAN degeneration and explored the associated mechanism. In vivo, twelve C57BL/6 mice were divided into Control and D-galactose group to receive corresponding treatments. Senescence was confirmed by analyzing the hair and weight; cardiac function was evaluated through echocardiography, cerebral blood flux and serum-BNP; the SAN function was evaluated by electrocardiogram; fibrotic change was evaluated by Masson's trichrome staining and oxidative stress was assessed through DHE staining and serum indicators. Mechanism was verified through immunofluorescence-staining and Western blotting. In vitro, mouse-atrial-myocytes were treated with D-galactose, and edaravone was utilized as the ROS scavenger. Senescence, oxidative stress, proliferation ability and mechanism were verified through various methods, and intuitive evidence was obtained through electrophysiological assay. Finally, we concluded that D-galactose can be used to induce age-related SND, in which oxidative stress plays a key role, causing PITX2 ectopic expression and downregulates SHOX2 expression, then through the downstream GATA4/NKX2-5 axis, results in pacing-related ion channels dysfunction, and hence SND development.

Case Report: Hypertrophic cardiomyopathy with recurrent episodes of ventricular fibrillation and concurrent sinus arrest

Background

Hypertrophic cardiomyopathy (HCM) is a serious hereditary cardiomyopathy. It is characterized morphologically by an increased left ventricular wall thickness and mass and functionally by enhanced global chamber function and myocellular contractility, diastolic dysfunction, and myocardial fibrosis development. Typically, patients with HCM experience atrial fibrillation (AF), syncope, and ventricular fibrillation (VF), causing severe symptoms and cardiac arrest. In contrast, sinoatrial node (SAN) arrest in the setting of HCM is uncommon. In particular, during VF, it has not been described so far.

Case summary

In this study, we report an 18-year-old woman patient with sudden cardiac arrest due to VF and successful cardiopulmonary resuscitation as the first clinical manifestation of non-obstructive HCM. Subsequently, a subcutaneous implantable cardioverter-defibrillator (ICD) was implanted for secondary VF prophylaxis. However, additional episodes of VF occurred. During these, device interrogation revealed a combined occurrence of VF, bradycardia, and SAN arrest, requiring a device exchange into a dual-chamber ICD. A heterozygous, pathogenic variant of the MYH7 gene (c.2155C>T; p.Arg719Trp) was identified as causative for HCM.

Discussion

First published in 1994, the particular MYH7 variant (p.Arg719Trp) was described in HCM patients with a high incidence of premature cardiac death and a reduced life expectancy. Electrophysiological studies on HCM patients are mainly performed to treat AF and ventricular tachycardia. Further extraordinary arrhythmic phenotypes were reported only in a few HCM patients. Taken together, the present case with documented co-existing VF and SAN arrest is rare and also emphasizes addressing the presence of SAN arrest (in particular, during VF episodes) in HCM patients when a distinct ICD device is considered for implantation.

The W101C KCNJ5 Mutation Induces Slower Pacing by Constitutively Active GIRK Channels in hiPSC-Derived Cardiomyocytes

Mutations in the KCNJ5 gene, encoding one of the major subunits of cardiac G-protein-gated inwardly rectifying K+ (GIRK) channels, have been recently linked to inherited forms of sinus node dysfunction. Here, the pathogenic mechanism of the W101C KCNJ5 mutation underlying sinus bradycardia in a patient-derived cellular disease model of sinus node dysfunction (SND) was investigated. A human-induced pluripotent stem cell (hiPSCs) line of a mutation carrier was generated, and CRISPR/Cas9-based gene targeting was used to correct the familial mutation as a control line. Both cell lines were further differentiated into cardiomyocytes (hiPSC-CMs) that robustly expressed GIRK channels which underly the acetylcholine-regulated K+ current (IK,ACh). hiPSC-CMs with the W101C KCNJ5 mutation (hiPSCW101C-CM) had a constitutively active IK,ACh under baseline conditions; the application of carbachol was able to increase IK,ACh, further indicating that not all available cardiac GIRK channels were open at baseline. Additionally, hiPSCW101C-CM had a more negative maximal diastolic potential (MDP) and a slower pacing frequency confirming the bradycardic phenotype. Of note, the blockade of the constitutively active GIRK channel with XAF-1407 rescued the phenotype. These results provide further mechanistic insights and may pave the way for the treatment of SND patients with GIRK channel dysfunction.

Conversion of Unmodified Stem Cells to Pacemaker Cells by Overexpression of Key Developmental Genes

Arrhythmias of the heart are currently treated by implanting electronic pacemakers and defibrillators. Unmodified adipose tissue-derived stem cells (ASCs) have the potential to differentiate into all three germ layers but have not yet been tested for the generation of pacemaker and Purkinje cells. We investigated if-based on overexpression of dominant conduction cell-specific genes in ASCs-biological pacemaker cells could be induced. Here we show that by overexpression of certain genes that are active during the natural development of the conduction system, the differentiation of ASCs to pacemaker and Purkinje-like cells is feasible. Our study revealed that the most effective procedure consisted of short-term upregulation of gene combinations SHOX2-TBX5-HCN2, and to a lesser extent SHOX2-TBX3-HCN2. Single-gene expression protocols were ineffective. Future clinical implantation of such pacemaker and Purkinje cells, derived from unmodified ASCs of the same patient, could open up new horizons for the treatment of arrythmias.

Sinus node dysfunction and related permanent pacemaker implantation after major cardiac surgeries, systematic review, and meta-analysis

Background

There is no concise evidence or clinical guidelines regarding the incidence of sinus node dysfunction (SND) and permanent pacemaker (PPM) implantation following cardiac surgeries and their management approaches.

Objective

We aim to systematically review current evidence on the prevalence of SND, PPM implantation concerning it, and its risk factors in patients undergoing cardiac surgery.

Method

Four electronic databases (Cochrane Library, Medline, SCOPUS, and Web of Science) were systematically searched for articles regarding SND after cardiovascular surgeries and reviewed by two independent researchers, and a third review in case of discrepancies. Using the random-effects model, a proportion meta-analysis was performed on data regarding PPM implantation. Subgroup analysis was performed for different interventions, and the possible effect of different covariates was evaluated using meta-regression.

Results

From the initial 2012 unique records, 87 were included in the study, and results were extracted. Pooled data from 38,519 patients indicated that the overall prevalence of PPM implantation due to SND after cardiac surgery was 2.87% (95% CI [2.09; 3.76]). The incidence of PPM implantation in the first post-surgical month was 2.707% (95% CI [1.657; 3.952]). Among the four main intervention groups, including valve, maze, valve-maze, and combined surgeries, maze surgery was associated with the highest prevalence (4.93%; CI [3.24; 6.92]). The pooled prevalence of SND among studies was 13.71% (95% CI [8.13; 20.33]). No significant relationship was observed between PPM implantation and age, gender, cardiopulmonary bypass time, or aortic cross-clamp time.

Conclusion

Based on the present report, patients undergoing the maze and maze-valve procedures are at higher risk of post-op SND, whereas lone valve surgery had the lowest prevalence of PPM implantation.

Systematic Review Registration

PROSPERO (CRD42022341896).

Adenosine and Adenosine Receptors: Advances in Atrial Fibrillation

Atrial fibrillation (AF) is the most common arrhythmia in the world. Because the key to developing innovative therapies that limit the onset and the progression of AF is to fully understand the underlying molecular mechanisms of AF, the aim of the present narrative review is to report the most recent advances in the potential role of the adenosinergic system in the pathophysiology of AF. After a comprehensive approach describing adenosinergic system signaling and the mechanisms of the initiation and maintenance of AF, we address the interactions of the adenosinergic system's signaling with AF. Indeed, adenosine release can activate four G-coupled membrane receptors, named A₁, A_2A, A_2B and A₃. Activation of the A_2A receptors can promote the occurrence of delayed depolarization, while activation of the A₁ receptors can shorten the action potential's duration and induce the resting membrane's potential hyperpolarization, which promote pulmonary vein firing, stabilize the AF rotors and allow for functional reentry. Moreover, the A_2B receptors have been associated with atrial fibrosis homeostasis. Finally, the adenosinergic system can modulate the autonomous nervous system and is associated with AF risk factors. A question remains regarding adenosine release and the adenosine receptors' activation and whether this would be a cause or consequence of AF.

Healing the Broken Hearts: A Glimpse on Next Generation Therapeutics

Cardiovascular diseases are the leading cause of death worldwide, accounting for 32% of deaths globally and thus representing almost 18 million people according to WHO. Myocardial infarction, the most prevalent adult cardiovascular pathology, affects over half a million people in the USA according to the last records of the AHA. However, not only adult cardiovascular diseases are the most frequent diseases in adulthood, but congenital heart diseases also affect 0.8–1.2% of all births, accounting for mild developmental defects such as atrial septal defects to life-threatening pathologies such as tetralogy of Fallot or permanent common trunk that, if not surgically corrected in early postnatal days, they are incompatible with life. Therefore, both congenital and adult cardiovascular diseases represent an enormous social and economic burden that invariably demands continuous efforts to understand the causes of such cardiovascular defects and develop innovative strategies to correct and/or palliate them. In the next paragraphs, we aim to briefly account for our current understanding of the cellular bases of both congenital and adult cardiovascular diseases, providing a perspective of the plausible lines of action that might eventually result in increasing our understanding of cardiovascular diseases. This analysis will come out with the building blocks for designing novel and innovative therapeutic approaches to healing the broken hearts.

Shenxian-Shengmai Oral Liquid Evoke Autophagy of Fibroblast to Attenuate Sinoatrial Node Fibrosis in Sick Sinus Syndrome Mice via the AKT/mTOR Pathway

Sick sinus syndrome (SSS) is closely associated with cardiac syncope and sudden death, wherein sinoatrial node (SAN) fibrosis is one of the main pathological changes that occur. Shenxian-Shengmai oral liquid (SXSM) has been clinically proven to significantly improve the heart rate of SSS patients. In this study, we aimed to explore the mechanism of SXSM in reducing the SAN fibrosis by combining in vitro and in vivo experiments. Accordingly, the SSS model was constructed by slowly pumping angiotensin II (AngII) with a micro-osmotic pump. The degree of fibrosis was evaluated by Masson's trichrome staining and immunofluorescence staining of the fibrosis marker protein. In addition, NIH-3T3 mouse fibroblasts were used to simulate SAN fibroblasts to further explore the mechanism, with AngII used as the cellular fibrosis inducer. Monodansylcadaverine (MDC) staining and transmission electron microscopy were employed to assay the autophagy content, whereas immunofluorescence staining and Western blotting were employed to elucidate the related protein expression. Finally, fibroblasts were given the AKT phosphorylation agonist SC79 to reversely verify the effects of SXSM. The results showed that SXSM could significantly increase the heart rate of SSS mice by reducing the deposition of extracellular matrix (ECM) in SAN induced by AngII. According to in vivo experiments, when compared with the model group, SSS mice treated with SXSM developed less fibrosis in the SAN area. In vitro experiments revealed that AngII could restrain autophagy by activating the phosphorylation of the AKT/mTOR pathway, thereby increasing the deposition of ECM. Moreover, SXSM pretreatment prevented this upregulation. After the intervention of SC79, the protective effect of SXSM was weakened. In conclusion, SXSM activated autophagy through the AKT/mTOR pathway, which in turn reduced the deposition of the ECM in SAN induced by AngII, attenuated the fibrosis of SAN, and improved the decreased heart rate in the SSS mice.

NRF-2/HO-1 Pathway-Mediated SHOX2 Activation Is a Key Switch for Heart Rate Acceleration by Yixin-Fumai Granules

Population aging has led to increased sick sinus syndrome (SSS) incidence; however, no effective and safe medical therapy has been reported thus far. Yixin-Fumai granules (YXFMs), a Chinese medicine granule designed for bradyarrhythmia treatment, can effectively increase SSS patients' heart rate. Senescence-induced sinoatrial node (SAN) degeneration is an important part of SSS pathogenesis, and older people often show high levels of oxidative stress; reactive oxygen species (ROS) accumulation in the SAN causes abnormal SAN pacing or conduction functions. The current study observed the protective effects of YXFMs on senescent SAN and explored the relationship between the NRF-2/HO-1 pathway, SHOX2, and T-type calcium channels. We selected naturally senescent C57BL/6 mice with bradycardia to simulate SSS; electrocardiography, Masson's trichrome staining, and DHE staining were used to assess SAN function and tissue damage. Immunofluorescence staining and Western blotting were used to assay related proteins. In vitro, we treated human-induced pluripotent stem cell-derived atrial myocytes (hiPSC-AMs) and mouse atrial myocyte-derived cell line HL-1 with D-galactose to simulate senescent SAN-pacemaker cells. CardioExcyte96 was used to evaluate the pulsatile function of the hiPSC-AMs, and the mechanism was verified by DCFH-DA, immunofluorescence staining, RT-qPCR, and Western blotting. The results demonstrated that YXFMs effectively inhibited senescence-induced SAN hypofunction, and this effect possibly originated from scavenging of ROS and promotion of NRF-2, SHOX2, and T-type calcium channel expression. In vitro experiment results indicated that ML385, si-SHOX2, LDN193189, and Mibefradil reversed YXFMs' effects. Moreover, we, for the first time, found that ROS accumulation may hinder SHOX2 expression; YXFMs can activate SHOX2 through the NRF-2/HO-1 pathway-mediated ROS scavenging and then regulate CACNA1G through the SHOX2/BMP4/GATA4/NKX2-5 axis, improve T-type calcium channel function, and ameliorate the SAN dysfunction. Finally, through network pharmacology and molecular docking, we screened for the most stable YXFMs compound that docks to NRF-2, laying the foundation for future studies.

First in human surgical implantation of a leadless pacemaker on the epicardial portion of the right atrial appendage in a patient with a cardiac electronic devices mediated dermatitis

A 33-year-old woman with Sick Sinus Node syndrome and persistent atrial fibrillation underwent a Maze IV procedure in order treat atrial fibrillation and concomitant atrial epicardial implantation of a leadless pacemaker to manage her sinus node insufficiency. Last option has been chosen due to rare pocket complication after previous classic dual-chamber pacemaker implantation.

A phenotype-based forward genetic screen identifies Dnajb6 as a sick sinus syndrome gene

Previously we showed the generation of a protein trap library made with the gene-break transposon (GBT) in zebrafish (Danio rerio) that could be used to facilitate novel functional genome annotation towards understanding molecular underpinnings of human diseases (Ichino et al, 2020). Here, we report a significant application of this library for discovering essential genes for heart rhythm disorders such as sick sinus syndrome (SSS). SSS is a group of heart rhythm disorders caused by malfunction of the sinus node, the heart's primary pacemaker. Partially owing to its aging-associated phenotypic manifestation and low expressivity, molecular mechanisms of SSS remain difficult to decipher. From 609 GBT lines screened, we generated a collection of 35 zebrafish insertional cardiac (ZIC) mutants in which each mutant traps a gene with cardiac expression. We further employed electrocardiographic measurements to screen these 35 ZIC lines and identified three GBT mutants with SSS-like phenotypes. More detailed functional studies on one of the arrhythmogenic mutants, GBT411, in both zebrafish and mouse models unveiled Dnajb6 as a novel SSS causative gene with a unique expression pattern within the subpopulation of sinus node pacemaker cells that partially overlaps with the expression of hyperpolarization activated cyclic nucleotide gated channel 4 (HCN4), supporting heterogeneity of the cardiac pacemaker cells.

Clinical Spectrum of SCN5A Channelopathy in Children with Primary Electrical Disease and Structurally Normal Hearts

Sodium voltage-gated channel α subunit 5 (SCN5A)-mutations may cause an array of arrhythmogenic syndromes most frequently as an autosomal dominant trait, with incomplete penetrance, variable expressivity and male predominance. In the present study, we retrospectively describe a group of Mexican patients with SCN5A-disease causing variants in whom the onset of symptoms occurred in the pediatric age range. The study included 17 patients with clinical diagnosis of primary electrical disease, at least one SCN5A pathogenic or likely pathogenic mutation and age of onset <18 years, and all available first- and second-degree relatives. Fifteen patients (88.2%) were male, and sixteen independent variants were found (twelve missense, three truncating and one complex inframe deletion/insertion). The frequency of compound heterozygosity was remarkably high (3/17, 17.6%), with early childhood onset and severe disease. Overall, 70.6% of pediatric patients presented with overlap syndrome, 11.8% with isolated sick sinus syndrome, 11.8% with isolated Brugada syndrome (BrS) and 5.9% with isolated type 3 long QT syndrome (LQTS). A total of 24/45 SCN5A mutation carriers were affected (overall penetrance 53.3%), and penetrance was higher in males (63.3%, 19 affected/30 mutation carriers) than in females (33.3%, 5 affected/15 carriers). In conclusion, pediatric patients with SCNA-disease causing variants presented mainly as overlap syndrome, with predominant loss-of-function phenotypes of sick sinus syndrome (SSS), progressive cardiac conduction disease (PCCD) and ventricular arrhythmias.

Parkinson's disease and parkinsonism: Clinicopathological discrepancies on diagnosis in three patients

Parkinson's disease (PD) is one of the most common neurodegenerative disorders. The cardinal neuropathological features of PD include selective and progressive loss of pigmented neurons in the substantia nigra, deficiencies in dopaminergic signaling in the striatum, and occurrence of phosphorylated α-synuclein-identified Lewy bodies in the nervous system. Parkinsonism, the clinical presentation of movement disorders seen in PD, is a feature shared commonly by other pathologically distinct neurodegenerative diseases, such as progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and multiple system atrophy (MSA). Consequently, it is sometimes difficult to distinguish PD from such parkinsonism-related neurological disorders. In addition, parkinsonism is not always a feature of certain neurodegenerative diseases, and it can sometimes develop as a result of various forms of drug intoxication or cerebrovascular disease. Here, we describe the clinicopathological features of three patients (cases 1, 2, and 3) diagnosed as having PSP, MSA, and PD, respectively, in each of whom the postmortem histopathological diagnosis differed from the final clinical diagnosis. Neuropathologically, they had suffered from coexistent disorders: PD, MSA, and argyrophilic grain disease (case 1); PD (case 2); and vascular parkinsonism (case 3). The variety of patients showing features of parkinsonism underlines the importance of careful long-term follow up followed by postmortem neuropathological evaluation.

Yixin-Fumai granules improve sick sinus syndrome in aging mice through Nrf-2/HO-1 pathway: A new target for sick sinus syndrome

ETHNOPHARMACOLOGICAL RELEVANCE

Yixin-Fumai granules (YXFMs)-composed of Ginseng quinquefolium (L.) Alph. Wood, Ophiopogon japonicus (Thunb.) Ker Gawl, Schisandra arisanensis Hayata, Astragalus aaronsohnianus Eig, Salvia cryptantha Montbret & Aucher ex Benth, and Ligusticum striatum DC-are compound granules used in traditional Chinese medicine to increase heart rate and thus treat bradyarrhythmia. It may be effective in treating sick sinus syndrome (SSS).

AIM

To observe the effect of YXFMs on aging-induced SSS in mice and explore whether this effect is related to the Nrf-2/HO-1 signaling pathway.

MATERIALS AND METHODS

Mice with a significant decrease in the heart rate due to natural aging were selected to construct an SSS model. After the mice were administered YXFMs, the damage to their sinoartrial node (SAN) was assessed through electrocardiography, Masson's trichrome staining, and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL). Dihydroethidium staining and immunofluorescence staining were used to assay reactive oxygen species (ROS) content and HCN4, respectively. Moreover, to observe the effects of YXFMs in vitro, the HL-1 cell line, derived from mouse atrial myocytes, was used to simulate SAN pacemaker cells, with H₂O₂ used as the cellular oxidative stress (OS) inducer. 2,7-Dichlorodihydrofluorescein diacetate staining was used to assay ROS content, whereas immunofluorescence staining and Western blotting were used to elucidate the related protein expression. Finally, mice were injected the Nrf-2 inhibitor ML385 to reversely verify the effects of YXFMs.

RESULTS

In our in vivo experiments, YXFMs significantly inhibited aging-induced SSS, shortened the R-R interval, increased heart rate, alleviated fibrosis, reduced apoptosis rate and ROS content, and promote HCN4 expression in the SAN. In our in vitro experiments, YXFMs significantly inhibited H₂O₂-induced cell peroxidation damage, promoted Nrf-2 activation and nuclear metastasis, increased HO-1 expression- thereby inhibiting ROS accumulation-and finally, upregulated HCN4 expression through the inhibition of histone deacetylase 4 (HDAC4) expression and its nuclear metastasis. Finally, injection of the Nrf-2 inhibitor ML385 after YXFMs administration inhibited their protective effect in the mice.

CONCLUSION

Here, we elaborated on the relationship between aging-induced SSS and the Nrf-2/HO-1 pathway for the first time and proposed that YXFMs improve SSS via the Nrf-2/HO-1 axis. Specifically, YXFMs promoted Nrf-2 activation and plasma-nuclear transfer to enhance HO-1 expression via the Nrf-2/HO-1 axis. This inhibited OS and reduced ROS accumulation in the SAN, and then, through the ROS/HDAC4 axis, reduced HDAC4 expression and plasma-nuclear transfer. Thereby, the OS-induced HCN4 loss in the SAN was inhibited-improving the function of I_f channel and thus producing SAN protection effect against SSS and improving the heart rate and R-R interval. In the future, we plan to use bioinformatics analysis technology to execute the next step of our research, namely to determine the effect of isolated, purified components of YXFMs in SSS, to increase its efficiency and reduce the toxicity of YXFMs.

Tongyang Huoxue Decoction (TYHX) Ameliorating Hypoxia/Reoxygenation-Induced Disequilibrium of Calcium Homeostasis and Redox Imbalance via Regulating Mitochondrial Quality Control in Sinoatrial Node Cells

Sick sinus syndrome (SSS) is a disease with bradycardia or arrhythmia. The pathological mechanism of SSS is mainly due to the abnormal conduction function of the sinoatrial node (SAN) caused by interstitial lesions or fibrosis of the SAN or surrounding tissues, SAN pacing dysfunction, and SAN impulse conduction accompanied by SAN fibrosis. Tongyang Huoxue Decoction (TYHX) is widely used in SSS treatment and amelioration of SAN fibrosis. It has a variety of active ingredients to regulate the redox balance and mitochondrial quality control. This study mainly discusses the mechanism of TYHX in ameliorating calcium homeostasis disorder and redox imbalance of sinoatrial node cells (SANCs) and clarifies the protective mechanism of TYHX on the activity of SANCs. The activity of SANCs was determined by CCK-8 and the TUNEL method. The levels of apoptosis, ROS, and calcium release were analyzed by flow cytometry and immunofluorescence. The mRNA and protein levels of calcium channel regulatory molecules and mitochondrial quality control-related molecules were detected by real-time quantitative PCR and Western Blot. The level of calcium release was detected by laser confocal. It was found that after H/R treatment, the viability of SANCs decreased significantly, the levels of apoptosis and ROS increased, and the cells showed calcium overload, redox imbalance, and mitochondrial dysfunction. After treatment with TYHX, the cell survival level was improved, calcium overload and oxidative stress were inhibited, and mitochondrial energy metabolism and mitochondrial function were restored. However, after the SANCs were treated with siRNA (si-β-tubulin), the regulation of TYHX on calcium homeostasis and redox balance was counteracted. These results suggest that β-tubulin interacts with the regulation of mitochondrial function and calcium release. TYHX may regulate mitochondrial quality control, maintain calcium homeostasis and redox balance, and protect SANCs through β-tubulin. The regulation mechanism of TYHX on mitochondrial quality control may also become a new target for SSS treatment.

Clinical review of sick sinus syndrome and atrial fibrillation

Sick sinus syndrome (SSS) is a set of diseases with abnormal cardiac pacing, which manifests as diverse cardiac arrhythmias, especially bradycardia. The clinical presentation is inconspicuous in the early stage, but with the progression of this disease, patients may present with symptoms and signs of end-organ hypoperfusion. As a common result in the natural history of the disease, SSS coexisting with atrial fibrillation (AF) forms the basis of bradycardia-tachycardia syndrome. Age-related interstitial fibrosis is considered to be the common pathophysiological mechanism between SSS and AF. The combination of these diseases will adversely affect the condition of patients and the efficiency of subsequent treatment. Although the exact mechanism is not clear to date, the extensive structural and electrical remodeling of the atrium are considered to be the important mechanism for the occurrence of AF in patients with SSS. Pacemaker implantation is the first-line treatment for symptomatic patients with SSS and documented bradycardia history. In view of the adverse effects of AF on the treatment of SSS, researchers have focused on evaluating different pacing modes and algorithms to reduce the risk of AF during pacing. Catheter ablation may also be used as an alternative second-line therapy for some patients with SSS and AF.

Shenxian-Shengmai Oral Liquid Improves Sinoatrial Node Dysfunction through the PKC/NOX-2 Signaling Pathway

Sick sinus syndrome (SSS) is one of the common causes of cardiac syncope and sudden death; the occurrence of SSS is associated with the accumulation of ROS in the sinoatrial node (SAN). Shenxian-shengmai (SXSM) is a traditional Chinese medicine available as oral liquid that causes a significant increase in heart rate. The objective of this study is to observe the improvement of SXSM on SAN function in SSS mice and explore its potential mechanism. In the current study, SSS was simulated in mice by inducing SAN dysfunction using a micro-osmotic pump to inject angiotensin II (Ang II). The mouse model with SSS was used to determine the effect of SXSM on SAN function and to explore its potential mechanism. Furthermore, the HL-1 cell line, derived from mouse atrial myocytes, was used to simulate SAN pacemaker cells. Our results indicated that SXSM significantly increased the heart rate of SSS mice by reducing the AngII-induced accumulation of ROS in the SAN and by inhibiting the expression of HDAC4, thereby reducing the loss of HCN4, a critical component of the cardiac conduction system. MASSON staining revealed a reduction of SAN damage in SSS mice that were treated with SXSM compared with controls. In vitro experiments showed that AngII treatment caused an upregulation of the PKC/NOX-2 signaling pathway in HL-1 cells which could be prevented by pretreatment with SXSM. The protective effect of SXSM was attenuated upon treatment with the PCK agonist PMA. In conclusion, SXSM reduced the AngII-induced accumulation of ROS in the SAN through the PKC/NOX2 signaling pathway, improving the functioning of the SAN and preventing the decrease of heart rate in SSS mice.

Genetic Complexity of Sinoatrial Node Dysfunction

The pacemaker cells of the cardiac sinoatrial node (SAN) are essential for normal cardiac automaticity. Dysfunction in cardiac pacemaking results in human sinoatrial node dysfunction (SND). SND more generally occurs in the elderly population and is associated with impaired pacemaker function causing abnormal heart rhythm. Individuals with SND have a variety of symptoms including sinus bradycardia, sinus arrest, SAN block, bradycardia/tachycardia syndrome, and syncope. Importantly, individuals with SND report chronotropic incompetence in response to stress and/or exercise. SND may be genetic or secondary to systemic or cardiovascular conditions. Current management of patients with SND is limited to the relief of arrhythmia symptoms and pacemaker implantation if indicated. Lack of effective therapeutic measures that target the underlying causes of SND renders management of these patients challenging due to its progressive nature and has highlighted a critical need to improve our understanding of its underlying mechanistic basis of SND. This review focuses on current information on the genetics underlying SND, followed by future implications of this knowledge in the management of individuals with SND.

Hypotensive and Antihypertensive Properties and Safety for Use of Annona muricata and Persea americana and Their Combination Products

Introduction

In the management of hypertension (a cardiovascular disease and the leading metabolic risk factor in noncommunicable diseases) with herbal medicines, efficacy and safety are of uttermost concern. This study sought to establish hypotensive, antihypertensive, drug interaction, and safety for use of the aqueous leaf extracts of Annona muricata (AME), Persea americana (PAE), or their combination products (CAPE). Methodology. Systolic and diastolic blood pressure (SBP and DBP), mean arterial blood pressure (MAP), and heart rate (HR) were measured in normotensive Sprague-Dawley rats treated with 50-150 mg/kg of AME, PAE, or CAPE to establish a hypotensive effect. "Combination index" was calculated to establish interaction between AME and PAE. The antihypertensive effect of CAPE was established by measuring SBP, DBP, MAP, and HR in ethanol-sucrose- and epinephrine-induced hypertension. Full blood count, liver and kidney function tests, and urinalysis were determined in ethanol/sucrose-induced hypertension to establish safety for use.

Results

AME, PAE, and CAPE significantly (p ≤ 0.001) decreased BP in both normotensive and hypertensive animals. Effects of CAPE 1, CAPE 2, and CAPE 3 were synergistic (combination indices of 0.65 ± 0.07, 0.76 ± 0.09, and 0.87 ± 0.07, respectively). There was a significant decrease (p ≤ 0.01 - 0.001) in SBP and MAP with 100 mg/kg CAPE 1 and 75 mg/kg CAPE 2 treatment in hypertension as well as with nifedipine (p ≤ 0.001) treatment. Epinephrine-induced hypertension in anesthetized cats was significantly and dose-dependently inhibited (p < 0.05 - 0.001) by 25-100 mg/ml CAPE 1 and 37.5-75 mg/ml CAPE 2. CAPE administration had no deleterious effect (p > 0.05) on full blood count, liver and kidney function, and urine composition in hypertensive rats.

Conclusion

The aqueous leaf extracts of Annona muricata, Persea americana, and their combination products possess antihypertensive properties, with combination products showing synergism and safety with use.

Sinus node disfunction in an adolescent with systemic lupus erythematosus

Cardiac involvement in systemic lupus erythematosus (SLE) is well documented. The pericardium, myocardium and endocardium, as well as the coronary arteries, the valves and the conduction system can all be affected. While pericarditis is common, arrythmias are less frequently described.We present a 13-year-old male, who had fatigue, anorexia, weight loss, myalgias and arthralgias for four months. On physical examination, we identified bradycardia (heart rate 31-50 bpm), oral and nasal ulcers and polyarthritis. The laboratory results showed hemolytic anemia, hypocomplementemia, antinuclear and anti-dsDNA antibodies, hematuria and non-nephrotic proteinuria. Renal function was normal. Lupus nephritis class II was diagnosed by kidney biopsy. On the transthoracic echocardiogram we identified a minimal pericardial effusion, suggesting pericarditis, and, on the electrocardiogram, we detected sinus arrest with junctional rhythm, denoting sinus node dysfunction. The patient was diagnosed with juvenile SLE with cardiac, renal, musculoskeletal and hematologic involvement. Disease remission and cardiac rhythm control were obtained with steroids and mycophenolate mofetil. Currently, the patient is asymptomatic, with normal sinus rhythm.We described an adolescent with SLE who had sinus node dysfunction upon diagnosis. Other cases have been reported in adults but none in juvenile SLE. All SLE patients should have a thorough cardiac examination to promptly diagnose and treat the innumerous cardiac manifestations of this disease.

Overexpression of TBX3 in human induced pluripotent stem cells (hiPSCs) increases their differentiation into cardiac pacemaker-like cells

BACKGROUD

The TBX3(T-box 3)transcription factor is considered as an essential factor in sinoatrial node formation. While the effect of TBX3 in the differentiation of sinoatrial node cells from embryonic stem cells(ESCs) has been recognized, its role in human induced pluripotent stem cell derived cardiomyocytes(hiPSCMs) has not been addressed. Therefore, the purpose of the present study was to investigate whether overexpression of TBX3 in hiPSCs could increase their differentiation into pacemaker-like cells.

METHODS

The hiPSCs were transfected with TBX3 gene during differentiation into cardiomyocytes(CMs). The hiPSCMs were analyzed using immunofluorescence, RT-qPCR, flow cytometry, whole-cell patch clamp recording to identify the differentiation effect exerted by TBX3. We discovered that hiPSCs transfected with TBX3 showed more proportions of NKX2.5-cTNT + sinoatrial node cells and faster contracting rates.

RESULTS

The results showed increment in transcription factor TBX18, SHOX2; hyperpolarization-activated cyclic nucleotide (HCN) channel: HCN1, HCN2, HCN4, connexin 45(CX45), Na + Ca2+ exchanger(NCX) in TBX3 transfected hiPSCMs. Sinoatrial node cell specific If current and action potential were also confirmed by patch clamp in TBX3 transfected hiPSCMs and the pacemaker-like cells were able to pace hiPSCMs ex vivo.

CONCLUSION

In conclusion, the present study demonstrated that overexpression of TBX3 could increase the differentiation of hiPSCs into pacemaker-like cells. Our study provide new strategy to construct a biological pacemaker, however, further study is still needed to identify the efficacy and safety of using the pacemaker-like cells to produce biological pacemaker in vivo.

Sinus Node Dysfunction in a Young Patient With COVID-19

A 34-year-old man was admitted with acute lung injury and COVID-19 pneumonia. In the intensive care unit, he experienced episodes of prolonged asystole accompanied by hypotension without loss of consciousness. Once reversible causes were excluded, symptoms were related to dysfunction of the sinus node, and the patient underwent implantation of a pacemaker. (Level of Difficulty: Beginner.)

Aging-associated sinus arrest and sick sinus syndrome in adult zebrafish

Because of its powerful genetics, the adult zebrafish has been increasingly used for studying cardiovascular diseases. Considering its heart rate of ~100 beats per minute at ambient temperature, which is very close to human, we assessed the use of this vertebrate animal for modeling heart rhythm disorders such as sinus arrest (SA) and sick sinus syndrome (SSS). We firstly optimized a protocol to measure electrocardiogram in adult zebrafish. We determined the location of the probes, implemented an open-chest microsurgery procedure, measured the effects of temperature, and determined appropriate anesthesia dose and time. We then proposed an PP interval of more than 1.5 seconds as an arbitrary criterion to define an SA episode in an adult fish at ambient temperature, based on comparison between the current definition of an SA episode in humans and our studies of candidate SA episodes in aged wild-type fish and Tg(SCN5A-D1275N) fish (a fish model for inherited SSS). With this criterion, a subpopulation of about 5% wild-type fish can be considered to have SA episodes, and this percentage significantly increases to about 25% in 3-year-old fish. In response to atropine, this subpopulation has both common SSS phenotypic traits that are shared with the Tg(SCN5A-D1275N) model, such as bradycardia; and unique SSS phenotypic traits, such as increased QRS/P ratio and chronotropic incompetence. In summary, this study defined baseline SA and SSS in adult zebrafish and underscored use of the zebrafish as an alternative model to study aging-associated SSS.

Obstructive Sleep Apnea as a Predictor of Abnormal Heart Rate Turbulence

Obstructive sleep apnea (OSA) causes dysfunction of the autonomic nervous system, but the exact mechanism has not been fully understood. The aim of this study was to analyse the relationship between the incidence and severity of OSA and heart rate turbulence (HRT). Seventy one patients with clinical suspicion of OSA were qualified to participate in the study. All participants took part in a survey and were subjected to laboratory tests, 24-hour electrocardiogram (ECG) Holter monitoring with HRT analysis and polysomnography. The group with OSA manifested significantly higher turbulence onset (TO) and lower turbulence slope (TS) as compared to the group without OSA. Older age, diabetes, hypertension and higher apnea/hypopnea index (AHI) were found to be independent risk factors for increased TO, whereas older age, higher body mass index (BMI), higher blood glucose levels, hypertension and higher AHI were independent risk factors for TS reduction. The AHI ≥65 criterion indicates abnormal HRT in patients with OSA with 94.9% sensitivity and 50.0% specificity, which gives a prediction accuracy of 85.7%. In summary, OSA should be considered as a predictor of abnormal HRT.

Heart rate variability in sick sinus syndrome: does it have a diagnostic role?

BACKGROUND

Hypothesis of our study was that the irregular rhythm of sick sinus syndrome (SSS) was characterized by an augmented HRV. Objective was to assess whether SSS patients had a typical HRV profile.

METHODS

We screened all 1947 consecutive Holter ECGs performed in our Units of Vascular Medicine and Internal Medicine and Cardioangiology at the University of Palermo (Italy) from April 2010 to September 2014. Among these, we selected 30 patients with ECG criteria of SSS. They were compared to 30 patients without SSS matched for age, sex and comorbidities.

RESULTS

The SSS group had a lower mean heart rate (HR) (P=0.003), and a longer mean NN max-min longer (P<0.0005) compared to control group. SSS group had higher mean pNN50 (P=0.043), mean RMSSD (P=0.006), mean SDNN (P=0.021), and mean SDNNi (P=0.005) as compared with control group. Moreover, HR ≤64.5 bpm, NN max-min>1355 msec, pNN50>16.08, RMSSD>50.2, SDNN>151.94, and SDNNi>71.1 showed a predictive value for diagnosis of SSS. The positivity of all 6 variables according to the aforementioned cut-offs ensured a positive predictive value of 100% and the negativity of all 6 variables had a negative predictive value of 94% for diagnosis of SSS. Among SSS patients, we did not observe any correlation between HR and HRV variables.

CONCLUSIONS

SSS patients have a HRV profile characterized by: low HR, long NN max-min interval, and elevated pNN50, RMSSD, SDNN and SDNNi values with specific diagnostic cut-offs for diagnosis of SSS. Moreover, we found the absence of correlation between HR and all time-domain HRV variables in SSS patients.

Advanced Cardiac Signal Recording

Implantable loop recorders allow prolonged and continuous single-lead electrocardiogram recording, with the pivotal addition of remote monitoring. They have significantly shortened time to electrocardiographic diagnosis and appropriate therapy of many bradyarrhythmias/tachyarrhythmias and proved helpful in arrhythmia burden definition, offering invaluable information in the diagnostic workup for syncope and atrial fibrillation. Advanced cardiac signal recording is also possible by transesophageal catheters. They have been used to orient diagnosis during wide and narrow QRS complex tachycardias and also to perform minimally invasive pacing. Intracardiac electrophysiologic study remains, however, essential for diagnosis of several arrhythmias in the perspective of curative catheter ablation.