Mechanisms of sudden cardiac death

Percutaneous left stellate ganglion block for refractory ventricular tachycardia in structural heart disease: our single-centre experience

INTRODUCTION

When electrical storm (ES) is amenable to neither antiarrhythmic drugs, nor deep sedation or catheter ablation, autonomic modulation may be considered. We report our experience with percutaneous left stellate ganglion block (PSGB) to temporarily suppress refractory ventricular arrhythmia (VA) in patients with structural heart disease.

METHODS

A retrospective analysis was performed at our institution of patients with structural heart disease and an implantable cardioverter defibrillator (ICD) who had undergone PSGB for refractory VA between January 2018 and October 2021. The number of times antitachycardia pacing (ATP) was delivered and the number of ICD shocks/external cardioversions performed in the week before and after PSGB were evaluated. Charts were checked for potential complications.

RESULTS

Twelve patients were identified who underwent a combined total of 15 PSGB and 5 surgical left cardiac sympathetic denervation procedures. Mean age was 73 ± 5.8 years and all patients were male. Nine of 12 (75%) had ischaemic cardiomyopathy, with the remainder having non-ischaemic dilated cardiomyopathy. Mean left ventricular ejection fraction was 35% (± 12.2%). Eight of 12 (66.7%) patients were already being treated with both amiodarone and beta-blockers. The reduction in ATP did not reach statistical significance (p = 0.066); however, ICD shocks (p = 0.028) and ATP/shocks combined were significantly reduced (p = 0.04). At our follow-up electrophysiology meetings PSGB was deemed ineffective in 4 of 12 patients (33%). Temporary anisocoria was seen in 2 of 12 (17%) patients, and temporary hypotension and hoarseness were reported in a single patient.

DISCUSSION

In this limited series, PSGB showed promise as a method for temporarily stabilising refractory VA and ES in a cohort of male patients with structural heart disease. The side effects observed were mild and temporary.

Biomarker Periodic Repolarization Dynamics Indicates Enhanced Risk for Arrhythmias and Sudden Cardiac Death in Myocardial Infarction in Pigs

BACKGROUND

Periodic repolarization dynamics (PRD) is an electrocardiographic biomarker that captures repolarization instability in the low frequency spectrum and is believed to estimate the sympathetic effect on the ventricular myocardium. High PRD indicates an increased risk for postischemic sudden cardiac death (SCD). However, a direct link between PRD and proarrhythmogenic autonomic remodeling has not yet been shown.

METHODS AND RESULTS

We investigated autonomic remodeling in pigs with myocardial infarction (MI)-related ischemic heart failure induced by balloon occlusion of the left anterior descending artery (n=17) compared with pigs without MI (n=11). Thirty days after MI, pigs demonstrated enhanced sympathetic innervation in the infarct area, border zone, and remote left ventricle paralleled by altered expression of autonomic marker genes/proteins. PRD was enhanced 30 days after MI compared with baseline (pre-MI versus post-MI: 1.75±0.30 deg2 versus 3.29±0.79 deg2, P<0.05) reflecting pronounced autonomic alterations on the level of the ventricular myocardium. Pigs with MI-related ventricular fibrillation and SCD had significantly higher pre-MI PRD than pigs without tachyarrhythmias, suggesting a potential role for PRD as a predictive biomarker for ischemia-related arrhythmias (no ventricular fibrillation versus ventricular fibrillation: 1.50±0.39 deg2 versus 3.18±0.53 deg2 [P<0.05]; no SCD versus SCD: 1.67±0.32 deg2 versus 3.91±0.63 deg2 [P<0.01]).

CONCLUSIONS

We demonstrate that ischemic heart failure leads to significant proarrhythmogenic autonomic remodeling. The concomitant elevation of PRD levels in pigs with ischemic heart failure and pigs with MI-related ventricular fibrillation/SCD suggests PRD as a biomarker for autonomic remodeling and as a potential predictive biomarker for ventricular arrhythmias/survival in the context of MI.

Manipulation of Glutamatergic Neuronal Activity in the Primary Motor Cortex Regulates Cardiac Function in Normal and Myocardial Infarction Mice

Cardiac function is under neural regulation; however, brain regions in the cerebral cortex responsible for regulating cardiac function remain elusive. In this study, retrograde trans-synaptic viral tracing is used from the heart to identify a specific population of the excitatory neurons in the primary motor cortex (M1) that influences cardiac function in mice. Optogenetic activation of M1 glutamatergic neurons increases heart rate, ejection fraction, and blood pressure. By contrast, inhibition of M1 glutamatergic neurons decreased cardiac function and blood pressure as well as tyrosine hydroxylase (TH) expression in the heart. Using viral tracing and optogenetics, the median raphe nucleus (MnR) is identified as one of the key relay brain regions in the circuit from M1 that affect cardiac function. Then, a mouse model of cardiac injury is established caused by myocardial infarction (MI), in which optogenetic activation of M1 glutamatergic neurons impaired cardiac function in MI mice. Moreover, ablation of M1 neurons decreased the levels of norepinephrine and cardiac TH expression, and enhanced cardiac function in MI mice. These findings establish that the M1 neurons involved in the regulation of cardiac function and blood pressure. They also help the understanding of the neural mechanisms underlying cardiovascular regulation.

Cardiac arrhythmogenesis: roles of ion channels and their functional modification

Cardiac arrhythmias cause significant morbidity and mortality and pose a major public health problem. They arise from disruptions in the normally orderly propagation of cardiac electrophysiological activation and recovery through successive cardiomyocytes in the heart. They reflect abnormalities in automaticity, initiation, conduction, or recovery in cardiomyocyte excitation. The latter properties are dependent on surface membrane electrophysiological mechanisms underlying the cardiac action potential. Their disruption results from spatial or temporal instabilities and heterogeneities in the generation and propagation of cellular excitation. These arise from abnormal function in their underlying surface membrane, ion channels, and transporters, as well as the interactions between them. The latter, in turn, form common regulatory targets for the hierarchical network of diverse signaling mechanisms reviewed here. In addition to direct molecular-level pharmacological or physiological actions on these surface membrane biomolecules, accessory, adhesion, signal transduction, and cytoskeletal anchoring proteins modify both their properties and localization. At the cellular level of excitation-contraction coupling processes, Ca2+ homeostatic and phosphorylation processes affect channel activity and membrane excitability directly or through intermediate signaling. Systems-level autonomic cellular signaling exerts both acute channel and longer-term actions on channel expression. Further upstream intermediaries from metabolic changes modulate the channels both themselves and through modifying Ca2+ homeostasis. Finally, longer-term organ-level inflammatory and structural changes, such as fibrotic and hypertrophic remodeling, similarly can influence all these physiological processes with potential pro-arrhythmic consequences. These normal physiological processes may target either individual or groups of ionic channel species and alter with particular pathological conditions. They are also potentially alterable by direct pharmacological action, or effects on longer-term targets modifying protein or cofactor structure, expression, or localization. Their participating specific biomolecules, often clarified in experimental genetically modified models, thus constitute potential therapeutic targets. The insights clarified by the physiological and pharmacological framework outlined here provide a basis for a recent modernized drug classification. Together, they offer a translational framework for current drug understanding. This would facilitate future mechanistically directed therapeutic advances, for which a number of examples are considered here. The latter are potentially useful for treating cardiac, in particular arrhythmic, disease.

Electrocardiographic frontal QRS-T angle is independently associated with panic disorder

OBJECTIVE

Panic disorder (PD) may cause serious cardiac arrhythmias by causing electrical abnormalities. Abnormal P-wave axis (aPwa), presence of fragmented QRS (fQRS), wide frontal QRS-T angle (fQRSTa), QRS duration corrected (QRSdc) and log/ logQRS duration/RR interval (log/logQRS/RR) have been correlated with increased risk of serious supraventricular and ventricular cardiac arrhythmias in a general population. The purpose of this study was to compare these newly explored atrial and ventricular arrhythmia indicators in patients with PD and in healthy subjects.

METHOD

A total of 169 newly diagnosed PD patients and 128 healthy subjects were included in the study. The Panic and Agoraphobia Scale (PAS) was administered, and 12-lead electrocardiography (ECG) measurements were obtained. Electrocardiographic parameters including aPwa, fQRSTa, presence of fQRS, QRS duration corrected (QRSdc), and log/logQRS duration/RR distance (log/logQRS/RR) were compared between the two groups.

RESULTS

aPwa and fQRS, in addition to fQRSTa, QRSdc, and log/ logQRS/RR ratio values, were significantly increased in the PD group compared to healthy controls. Correlation analyses revealed that wider fQRSTa, number of fQRS derivation, number of total fQRS, wider QRSdc, and log/logQRS/RR ratio significantly correlated with PAS score. Logistic regression analysis demonstrated that fQRSTa and the number of total fQRS were independently associated with PD.

CONCLUSION

PD is associated with wider fQRSTa, QRSdc, and log/logQRS/RR in addition to the increased abnormal aPwa and presence of fQRS. These findings suggest that untreated PD patients may be susceptible to supraventricular and ventricular arrhythmia, indicating that ECG should be routinely obtained in the management of PD patients.

Mechanism of Ventricular Tachycardia Occurring in Chronic Myocardial Infarction Scar

Cardiac arrest is the leading cause of death in the more economically developed countries. Ventricular tachycardia associated with myocardial infarct is a prominent cause of cardiac arrest. Ventricular arrhythmias occur in 3 phases of infarction: during the ischemic event, during the healing phase, and after the scar matures. Mechanisms of arrhythmias in these phases are distinct. This review focuses on arrhythmia mechanisms for ventricular tachycardia in mature myocardial scar. Available data have shown that postinfarct ventricular tachycardia is a reentrant arrhythmia occurring in circuits found in the surviving myocardial strands that traverse the scar. Electrical conduction follows a zigzag course through that area. Conduction velocity is impaired by decreased gap junction density and impaired myocyte excitability. Enhanced sympathetic tone decreases action potential duration and increases sarcoplasmic reticular calcium leak and triggered activity. These elements of the ventricular tachycardia mechanism are found diffusely throughout scar. A distinct myocyte repolarization pattern is unique to the ventricular tachycardia circuit, setting up conditions for classical reentry. Our understanding of ventricular tachycardia mechanisms continues to evolve as new data become available. The ultimate use of this information would be the development of novel diagnostics and therapeutics to reliably identify at-risk patients and prevent their ventricular arrhythmias.

Nitric Oxide Modulates Ca2+ Leak and Arrhythmias via S-Nitrosylation of CaMKII

BACKGROUND

Nitric oxide (NO) has been identified as a signaling molecule generated during β-adrenergic receptor stimulation in the heart. Furthermore, a role for NO in triggering spontaneous Ca2+ release via S-nitrosylation of CaMKIIδ (Ca2+/calmodulin kinase II delta) is emerging. NO donors are routinely used clinically for their cardioprotective effects on the heart, but it is unknown how NO donors modulate the proarrhythmic CaMKII to alter cardiac arrhythmia incidence. We test the role of S-nitrosylation of CaMKIIδ at the Cysteine-273 inhibitory site and cysteine-290 activating site in cardiac Ca2+ handling and arrhythmogenesis before and during β-adrenergic receptor stimulation.

METHODS

We measured Ca2+-handling in isolated cardiomyocytes from C57BL/6J wild-type (WT) mice and mice lacking CaMKIIδ expression (CaMKIIδ-KO) or with deletion of the S-nitrosylation site on CaMKIIδ at cysteine-273 or cysteine-290 (CaMKIIδ-C273S and -C290A knock-in mice). Cardiomyocytes were exposed to NO donors, S-nitrosoglutathione (GSNO; 150 μM), sodium nitroprusside (200 μM), and β-adrenergic agonist isoproterenol (100 nmol/L).

RESULTS

Both WT and CaMKIIδ-KO cardiomyocytes responded to isoproterenol with a full inotropic and lusitropic Ca2+ transient response as well as increased Ca2+ spark frequency. However, the increase in Ca2+ spark frequency was significantly attenuated in CaMKIIδ-KO cardiomyocytes. The protection from isoproterenol-induced Ca2+ sparks and waves was mimicked by GSNO pretreatment in WT cardiomyocytes but lost in CaMKIIδ-C273S cardiomyocytes. When GSNO was applied after isoproterenol, this protection was not observed in WT or CaMKIIδ-C273S but was apparent in CaMKIIδ-C290A. In Langendorff-perfused isolated hearts, GSNO pretreatment limited isoproterenol-induced arrhythmias in WT but not CaMKIIδ-C273S hearts, while GSNO exposure after isoproterenol sustained or exacerbated arrhythmic events.

CONCLUSIONS

We conclude that prior S-nitrosylation of CaMKIIδ at cysteine-273 can limit subsequent β-adrenergic receptor-induced arrhythmias, but that S-nitrosylation at cysteine-290 might worsen or sustain β-adrenergic receptor-induced arrhythmias. This has important implications for the administration of NO donors in the clinical setting.

Possible organ-protective effects of renal denervation: insights from basic studies

Inappropriate sympathetic nervous activation is the body's response to biological stress and is thought to be involved in the development of various lifestyle-related diseases through an elevation in blood pressure. Experimental studies have shown that surgical renal denervation decreases blood pressure in hypertensive animals. Recently, minimally invasive catheter-based renal denervation has been clinically developed, which results in a reduction in blood pressure in patients with resistant hypertension. Accumulating evidence in basic studies has shown that renal denervation exerts beneficial effects on cardiovascular disease and chronic kidney disease. Interestingly, recent studies have also indicated that renal denervation improves glucose tolerance and inflammatory changes. In this review article, we summarize the evidence from animal studies to provide comprehensive insight into the organ-protective effects of renal denervation beyond changes in blood pressure.

USP38 regulates inflammatory cardiac remodeling after myocardial infarction

BACKGROUND

The inflammatory response and subsequent ventricular remodeling are key factors contributing to ventricular arrhythmias (VAs) after myocardial infarction (MI). Ubiquitin-specific protease 38 (USP38) is a member of the USP family, but the impact of USP38 in arrhythmia substrate generation after MI remains unclear. This study aimed to determine the role of USP38 in post-MI VAs and its underlying mechanisms.

METHODS AND RESULTS

Surgical left descending coronary artery ligation was used to construct MI models. Morphological, biochemical, histological, and electrophysiological studies and molecular analyses were performed after MI on days 3 and 28. We found that the USP38 expression was remarkably increased after MI. Cardiac-conditional USP38 knockout (USP38-CKO) reduces the expression of the inflammatory marker CD68 as well as the inflammatory factors TNF-α and IL-1β after MI, thereby alleviating advanced cardiac fibrosis, electrical remodeling, ion channel remodeling, and susceptibility to VAs. In contrast, cardiac-specific USP38 overexpression (USP38-TG) showed a significant opposite effect, exacerbating the early inflammatory response and cardiac remodeling after MI. Mechanistically, USP38 knockout inhibited activation of the TAK1/NF-κB signaling pathway after MI, whereas USP38 overexpression enhanced activation of the TAK1/NF-κB signaling pathway after MI.

CONCLUSIONS

Our study confirms that USP38-CKO attenuates the inflammatory response, improves ventricular remodeling after myocardial infarction, and reduces susceptibility to malignant VA by inhibiting the activation of the TAK1/NF-κB pathway, with USP38-TG playing an opposing role. These results suggest that USP38 may be an important target for the treatment of cardiac remodeling and arrhythmias after MI.

Plasma Ceramides and Sphingomyelins and Sudden Cardiac Death in the Cardiovascular Health Study

Importance

Sphingolipids, including ceramides and sphingomyelins, may influence the pathophysiology and risk of sudden cardiac death (SCD) through multiple biological activities. Whether the length of the fatty acid acylated to plasma sphingolipid species is associated with SCD risk is not known.

Objective

To determine whether the saturated fatty acid length of plasma ceramides and sphingomyelins influences the association with SCD risk.

Design, Setting, and Participants

In this cohort study, multivariable Cox proportional hazards regression models were used to examine the association of sphingolipid species with SCD risk. The study population included 4612 participants in the Cardiovascular Health Study followed up prospectively for a median of 10.2 (IQR, 5.5-11.6) years. Baseline data were collected from January 1992 to December 1995 during annual examinations. Data were analyzed from February 11, 2020, to September 9, 2023.

Exposures

Eight plasma sphingolipid species (4 ceramides and 4 sphingomyelins) with saturated fatty acids of 16, 20, 22, and 24 carbons.

Main Outcome and Measure

Association of plasma ceramides and sphingomyelins with saturated fatty acids of different lengths with SCD risk.

Results

Among the 4612 CHS participants included in the analysis (mean [SD] age, 77 [5] years; 2724 [59.1%] women; 6 [0.1%] American Indian; 4 [0.1%] Asian; 718 [15.6%] Black; 3869 [83.9%] White, and 15 [0.3%] Other), 215 SCD cases were identified. In adjusted Cox proportional hazards regression analyses, plasma ceramides and sphingomyelins with palmitic acid (Cer-16 and SM-16) were associated with higher SCD risk per higher SD of log sphingolipid levels (hazard ratio [HR] for Cer-16, 1.34 [95% CI, 1.12-1.59]; HR for SM-16, 1.37 [95% CI, 1.12-1.67]). Associations did not differ by baseline age, sex, race, or body mass index. No significant association of SCD with sphingolipids with very-long-chain saturated fatty acids was observed after correction for multiple testing (HR for ceramide with arachidic acid, 1.06 [95% CI, 0.90-1.24]; HR for ceramide with behenic acid, 0.92 [95% CI, 0.77-1.10]; HR for ceramide with lignoceric acid, 0.92 [95% CI, 0.77-1.09]; HR for sphingomyelin with arachidic acid, 0.83 [95% CI, 0.71-0.98]; HR for sphingomyelin with behenic acid, 0.84 [95% CI, 0.70-1.00]; HR for sphingomyelin with lignoceric acid, 0.86 [95% CI, 0.72-1.03]).

Conclusions and Relevance

The findings of this large, population-based cohort study of SCD identified that higher plasma levels of Cer-16 and SM-16 were associated with higher risk of SCD. Future studies are needed to examine the underlying mechanism of these associations.

Pro-arrhythmic role of adrenergic spatial densities in the human atria: An in-silico study

Chronic stress among young patients (≤ 45 years old) could result in autonomic dysfunction. Autonomic dysfunction could be exhibited via sympathetic hyperactivity, sympathetic nerve sprouting, and diffuse adrenergic stimulation in the atria. Adrenergic spatial densities could alter atrial electrophysiology and increase arrhythmic susceptibility. Therefore, we examined the role of adrenergic spatial densities in creating arrhythmogenic substrates in silico. We simulated three 25 cm2 atrial sheets with varying adrenergic spatial densities (ASD), activation rates, and external transmembrane currents. We measured their effects on spatial and temporal heterogeneity of action potential durations (APD) at 50% and 20%. Increasing ASD shortens overall APD, and maximum spatial heterogeneity (31%) is achieved at 15% ASD. The addition of a few (5% to 10%) adrenergic elements decreases the excitation threshold, below 18 μA/cm2, while ASDs greater than 10% increase their excitation threshold up to 22 μA/cm2. Increase in ASD during rapid activation increases APD50 and APD20 by 21% and 41%, respectively. Activation times of captured beats during rapid activation could change by as much as 120 ms from the baseline cycle length. Rapidly activated atrial sheets with high ASDs significantly increase temporal heterogeneity of APD50 and APD20. Rapidly activated atrial sheets with 10% ASD have a high likelihood (0.7 ± 0.06) of fragmenting otherwise uniform wavefronts due to the transient inexcitability of adrenergically stimulated elements, producing an effective functional block. The likelihood of wave fragmentation due to ASD highly correlates with the spatial variations of APD20 (ρ = 0.90, p = 0.04). Our simulations provide a novel insight into the contributions of ASD to spatial and temporal heterogeneities of APDs, changes in excitation thresholds, and a potential explanation for wave fragmentation in the human atria due to sympathetic hyperactivity. Our work may aid in elucidating an electrophysiological link to arrhythmia initiation due to chronic stress among young patients.

Nitric Oxide modulates spontaneous Ca2+ release and ventricular arrhythmias during β-adrenergic signalling through S-nitrosylation of Calcium/Calmodulin dependent kinase II

Rationale

Nitric oxide (NO) has been identified as a signalling molecule generated during β-adrenergic receptor (AR) stimulation in the heart. Furthermore, a role for NO in triggering spontaneous Ca2+ release via S-nitrosylation of Ca2+/calmodulin kinase II delta (CaMKIIδ) is emerging. NO donors are routinely used clinically for their cardioprotective effects in the heart, but it is unknown how NO donors modulate the pro-arrhythmic CaMKII to alter cardiac arrhythmia incidence.

Objective

We test the role of S-nitrosylation of CaMKIIδ at the Cys-273 inhibitory site and Cys-290 activating site in cardiac Ca2+ handling and arrhythmogenesis before and during β-AR stimulation.

Methods and Results

We measured Ca2+-handling in isolated cardiomyocytes from C57BL/6J wild-type (WT) mice and mice lacking CaMKIIδ expression (CaMKIIδ-KO) or with deletion of the S-nitrosylation site on CaMKIIδ at Cys-273 or Cys-290 (CaMKIIδ-C273S and -C290A knock-in mice). Cardiomyocytes were exposed to NO donors, S-nitrosoglutathione (GSNO; 150 μM), sodium nitroprusside (SNP; 200 μM) and/or β-adrenergic agonist isoproterenol (ISO; 100 nM). WT and CaMKIIδ-KO cardiomyocytes treated with GSNO showed no change in Ca2+ transient or spark properties under baseline conditions (0.5 Hz stimulation frequency). Both WT and CaMKIIδ-KO cardiomyocytes responded to ISO with a full inotropic and lusitropic Ca2+ transient response as well as increased Ca2+ spark frequency. However, the increase in Ca2+ spark frequency was significantly attenuated in CaMKIIδ-KO cardiomyocytes. The protection from ISO-induced Ca2+ sparks and waves was mimicked by GSNO pre-treatment in WT cardiomyocytes, but lost in CaMKIIδ-C273S cardiomyocytes that displayed a robust increase in Ca2+ waves. This observation is consistent with CaMKIIδ-C273 S-nitrosylation being critical in limiting ISO-induced arrhythmogenic sarcoplasmic reticulum Ca2+ leak. When GSNO was applied after ISO this protection was not observed in WT or CaMKIIδ-C273S but was apparent in CaMKIIδ-C290A. In Langendorff-perfused isolated hearts, GSNO pre-treatment limited ISO-induced arrhythmias in WT but not CaMKIIδ-C273S hearts, while GSNO exposure after ISO sustained or exacerbated arrhythmic events.

Conclusions

We conclude that prior S-nitrosylation of CaMKIIδ at Cys-273 can limit subsequent β-AR induced arrhythmias, but that S-nitrosylation at Cys-290 might worsen or sustain β-AR-induced arrhythmias. This has important implications for the administration of NO donors in the clinical setting.

Spinal neuromodulation mitigates myocardial ischemia-induced sympathoexcitation by suppressing the intermediolateral nucleus hyperactivity and spinal neural synchrony

Introduction

Myocardial ischemia disrupts the cardio-spinal neural network that controls the cardiac sympathetic preganglionic neurons, leading to sympathoexcitation and ventricular tachyarrhythmias (VTs). Spinal cord stimulation (SCS) is capable of suppressing the sympathoexcitation caused by myocardial ischemia. However, how SCS modulates the spinal neural network is not fully known.

Methods

In this pre-clinical study, we investigated the impact of SCS on the spinal neural network in mitigating myocardial ischemia-induced sympathoexcitation and arrhythmogenicity. Ten Yorkshire pigs with left circumflex coronary artery (LCX) occlusion-induced chronic myocardial infarction (MI) were anesthetized and underwent laminectomy and a sternotomy at 4-5 weeks post-MI. The activation recovery interval (ARI) and dispersion of repolarization (DOR) were analyzed to evaluate the extent of sympathoexcitation and arrhythmogenicity during the left anterior descending coronary artery (LAD) ischemia. Extracellular in vivo and in situ spinal dorsal horn (DH) and intermediolateral column (IML) neural recordings were performed using a multichannel microelectrode array inserted at the T2-T3 segment of the spinal cord. SCS was performed for 30 min at 1 kHz, 0.03 ms, 90% motor threshold. LAD ischemia was induced pre- and 1 min post-SCS to investigate how SCS modulates spinal neural network processing of myocardial ischemia. DH and IML neural interactions, including neuronal synchrony as well as cardiac sympathoexcitation and arrhythmogenicity markers were evaluated during myocardial ischemia pre- vs. post-SCS.

Results

ARI shortening in the ischemic region and global DOR augmentation due to LAD ischemia was mitigated by SCS. Neural firing response of ischemia-sensitive neurons during LAD ischemia and reperfusion was blunted by SCS. Further, SCS showed a similar effect in suppressing the firing response of IML and DH neurons during LAD ischemia. SCS exhibited a similar suppressive impact on the mechanical, nociceptive and multimodal ischemia sensitive neurons. The LAD ischemia and reperfusion-induced augmentation in neuronal synchrony between DH-DH and DH-IML pairs of neurons were mitigated by the SCS.

Discussion

These results suggest that SCS is decreasing the sympathoexcitation and arrhythmogenicity by suppressing the interactions between the spinal DH and IML neurons and activity of IML preganglionic sympathetic neurons.

Characteristics and predictors of out-of-hospital cardiac arrest in young adults hospitalized with acute coronary syndrome: A retrospective cohort study of 30,000 patients in the Gulf region

INTRODUCTION

The characteristics of young adults with out-of-hospital cardiac arrest (OHCA) due to acute coronary syndrome (ACS) has not been well described. The mean age of gulf citizens in ACS registries is 10-15 years younger than their western counterparts, which provided us with a unique opportunity to investigate the characteristics and predictors of OHCA in young adults presenting with ACS.

METHODOLOGY

This was a retrospective cohort study using data from 7 prospective ACS registries in the Gulf region. In brief, all registries included consecutive adults who were admitted with ACS. OHCA was defined as cardiac arrest upon presentation (i.e., before admission to the hospital). We described the characteristics of young adults (< 50 years) who had OHCA and performed multivariate logistic regression analysis to assess independent predictors of OHCA.

RESULTS

A total of 31,620 ACS patients were included in the study. There were 611 (1.93%) OHCA cases in the whole cohort [188/10,848 (1.73%) in young adults vs 423/20,772 (2.04%) in older adults, p = 0.06]. Young adults were predominantly males presenting with ST-elevation myocardial infarction (STEMI) [182/188 (96.8%) and 172/188 (91.49%), respectively]. OHCA was the sentinel event of coronary artery disease (CAD) in 70% of young adults. STEMI, male sex, and non-smoking status were found to be independent predictors of OHCA [OR = 5.862 (95% CI 2.623-13.096), OR: 4.515 (95% CI 1.085-18.786), and OR = 2.27 (95% CI 1.335-3.86), respectively].

CONCLUSION

We observed a lower prevalence of OHCA in ACS patients in our region as compared to previous literature from other regions. Moreover, OHCA was the sentinel event of CAD in the majority of young adults, who were predominantly males with STEMIs. These findings should help risk-stratify patients with ACS and inform further research into the characteristics of OHCA in young adults.

EHRA expert consensus document on the management of arrhythmias in frailty syndrome, endorsed by the Heart Rhythm Society (HRS), Asia Pacific Heart Rhythm Society (APHRS), Latin America Heart Rhythm Society (LAHRS), and Cardiac Arrhythmia Society of Southern Africa (CASSA)

There is an increasing proportion of the general population surviving to old age with significant chronic disease, multi-morbidity, and disability. The prevalence of pre-frail state and frailty syndrome increases exponentially with advancing age and is associated with greater morbidity, disability, hospitalization, institutionalization, mortality, and health care resource use. Frailty represents a global problem, making early identification, evaluation, and treatment to prevent the cascade of events leading from functional decline to disability and death, one of the challenges of geriatric and general medicine. Cardiac arrhythmias are common in advancing age, chronic illness, and frailty and include a broad spectrum of rhythm and conduction abnormalities. However, no systematic studies or recommendations on the management of arrhythmias are available specifically for the elderly and frail population, and the uptake of many effective antiarrhythmic therapies in these patients remains the slowest. This European Heart Rhythm Association (EHRA) consensus document focuses on the biology of frailty, common comorbidities, and methods of assessing frailty, in respect to a specific issue of arrhythmias and conduction disease, provide evidence base advice on the management of arrhythmias in patients with frailty syndrome, and identifies knowledge gaps and directions for future research.

Role of purinergic receptors in cardiac sympathetic nerve injury in diabetes mellitus

Diabetic cardiac autonomic neuropathy is a common and serious chronic complication of diabetes, which can lead to sympathetic and parasympathetic nerve imbalance and a relative excitation of the sympathetic nerve. Purinergic receptors play a crucial role in this process. Diabetic cardiac sympathetic nerve injury affects the expression of purinergic receptors, and activated purinergic receptors affect the phosphorylation of different signaling pathways and the regulation of inflammatory processes. This paper introduces the abnormal changes of sympathetic nerve in diabetes mellitus and summarizes the recently published studies on the role of several purinergic receptor subtypes in diabetic cardiac sympathetic nerve injury. These studies suggest that purinergic receptors as novel drug targets are of great significance for the treatment of diabetic autonomic neuropathy. This article is part of the Special Issue on "Purinergic Signaling: 50 years".

Heart Rate Variability Analysis May Identify Individuals With Williams-Beuren Syndrome at Risk of Sudden Death

BACKGROUND

Williams-Beuren syndrome (WBS) (Online Mendelian Inheritance in Man #194050) is a rare genetic multisystem disorder resulting from a chromosomal microdeletion at 7q11.23. The condition is characterized by distinct facies, intellectual disability, and supravalvar aortic stenosis. Those with WBS have an increased risk of sudden death, but mechanisms underlying this phenotype are incompletely understood.

OBJECTIVES

The aim of this study was to quantify and compare autonomic activity as reflected by heart rate variability (HRV) measures in a cohort of individuals with WBS (n = 18) and age- and sex-matched control subjects (n = 18).

METHODS

We performed HRV analysis on 24-hour electrocardiography recordings using nonlinear, time and frequency domain analyses on a cohort of subjects with WBS and age- and sex-matched control subjects enrolled in a prospective cross-sectional study designed to characterize WBS disease natural history.

RESULTS

WBS subjects demonstrated diminished HRV (reflected by the SD of the NN intervals [P = 0.0001], SD of the average NN interval for 5-minute intervals over 24 hours [P < 0.0001], average of the 5-minute SDs of NN intervals for 24 hours [P = 0.0002], root mean square of successive differences of NN intervals [P = 0.0004], short axis of the Poincaré plot (SD1) [P < 0.0001], and long axis of the Poincaré plot [P < 0.0001]) and indirect markers of parasympathetic activity (reflected by the percent of NN intervals different from previous by 50% or more of local average [P < 0.0007], root mean square of successive differences of NN intervals [P = 0.0004], natural log high-frequency power [P = 0.0038], and SD1 [P < 0.0001]). Additional parameters were also significantly different, including natural log very low-frequency power (decreased; P = 0.0002), natural log low-frequency power (decreased; P = 0.0024), and SD1 divided by the long axis of the Poincaré plot (decreased; P < 0.0001).

CONCLUSIONS

Individuals with WBS demonstrate significant HRV abnormalities consistent with diminished autonomic reserve. Future studies will be needed to determine the relationship between autonomic dysregulation observed and sudden death risk seen in these patients. (Impact of Elastin Mediated Vascular Stiffness on End Organs; NCT02840448).

Circadian and Seasonal Pattern of Arrhythmic Events in Arrhythmogenic Cardiomyopathy Patients

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited cardiac disease associated with an increased risk of life-threatening arrhythmias. The aim of the present study was to evaluate the association of ventricular arrhythmias (VA) with circadian and seasonal variation in ARVC. One hundred two ARVC patients with an implantable cardioverter defibrillator (ICD) were enrolled in the study. Arrhythmic events included (a) any initial ventricular tachycardia (VT) or fibrillation (VF) prompting ICD implantation, (b) any VT or non-sustained VT (NSVT) recorded by the ICD, and (c) appropriate ICD shocks/therapy. Differences in the annual incidence of events across seasons (winter, spring, summer, autumn) and period of the day (night, morning, afternoon, evening) were assessed both for all cardiac events and major arrhythmic events. In total, 67 events prior to implantation and 263 ICD events were recorded. These included 135 major (58 ICD therapies, 57 self-terminating VT, 20 sustained VT) and 148 minor (NSVT) events. A significant increase in the frequency of events was observed in the afternoon versus in the nights and mornings (p = 0.016). The lowest number of events was registered in the summer, with a peak in the winter (p < 0.001). Results were also confirmed when excluding NSVT. Arrhythmic events in ARVC follow a seasonal variation and a circadian rhythm. They are more prevalent in the late afternoon, the most active period of the day, and in the winter, supporting the role of physical activity and inflammation as triggers of events.

Effects and mechanism of renal denervation on ventricular arrhythmia after acute myocardial infarction in rats

BACKGROUND

Renal denervation (RDN) can reduce ventricular arrhythmia after acute myocardial infarction (AMI), but the mechanism is not clear. The purpose of this study is to study its mechanism.

METHODS

Thirty-two Sprague-Dawley rats were divided into four groups: control group, AMI group, RDN-1d + AMI group, RDN-2w + AMI group. The AMI model was established 1 day after RDN in the RDN-1d + AMI group and 2 weeks after RDN in the RDN-2w + AMI group. At the same time, 8 normal rats were subjected to AMI modelling (the AMI group). The control group consisted of 8 rats without RDN intervention or AMI modelling.

RESULTS

The study confirmed that RDN can reduce the occurrence of ventricular tachycardia in AMI rats, reduce renal sympathetic nerve discharge, and inhibit the activity of local sympathetic nerves and cell growth factor (NGF) protein expression in the heart after AMI. In addition, RDN decreased the expression of norepinephrine (NE) and glutamate in the hypothalamus,and NE in cerebrospinal fluid, and increased the expression level of γ aminobutyric acid (GABA) in the hypothalamus after AMI.

CONCLUSION

RDN can effectively reduce the occurrence of ventricular arrhythmia after AMI, and its main mechanism may be via the inhibition of central sympathetic nerve discharge.

Median nerve stimulation elevates ventricular fibrillation threshold via the cholinergic anti-inflammatory pathway in myocardial infarction canine model

Background

Median nerve stimulation (MNS) diminishes regional myocardial ischemia and ventricular arrhythmia; however, the underlying mechanism has not been elucidated.

Methods

In this study, we randomly categorized 22 adult mongrel dogs into a control group, MNS group 1, and MNS group 2. After a 4-week experimental myocardial infarction (MI), ventricular electrophysiology was measured in the MNS group 1 before and after 30 min of MNS. The same measurements were performed in the MNS group 2 dogs via bilateral vagotomy. Venous blood and ventricular tissue were collected to detect molecular indicators related to inflammation and cholinergic pathways by enzyme-linked immunosorbent assay (ELISA), immunohistochemistry (IHC), and Western blot (WB).

Results

No significant changes were reported in the ventricular effective refractory period (ERP) in the MNS group 1 and MNS group 2 dogs before and after MNS. The ventricular fibrillation threshold (VFT) in the MNS group 1 was significantly higher than that in the MNS group 2 (20.3 ± 3.7 V vs. 8.7 ± 2.9 V, P &lt; 0.01). The levels of tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and nuclear transcription factor-κB (NF-κB) were lower (P &lt; 0.01), whereas the levels of Ach were higher in the peri-infarct zone tissues in the MNS group 1 dogs than those in the MNS group 2 dogs (P &lt; 0.01).

Conclusion

This study demonstrated that MNS increases VFT in a canine model with MI. The effects of MNS on VFT are potentially associated with the cholinergic anti-inflammatory pathway.

Hippo-Yap Signaling Maintains Sinoatrial Node Homeostasis

BACKGROUND

The sinoatrial node (SAN) functions as the pacemaker of the heart, initiating rhythmic heartbeats. Despite its importance, the SAN is one of the most poorly understood cardiac entities because of its small size and complex composition and function. The Hippo signaling pathway is a molecular signaling pathway fundamental to heart development and regeneration. Although abnormalities of the Hippo pathway are associated with cardiac arrhythmias in human patients, the role of this pathway in the SAN is unknown.

METHODS

We investigated key regulators of the Hippo pathway in SAN pacemaker cells by conditionally inactivating the Hippo signaling kinases Lats1 and Lats2 using the tamoxifen-inducible, cardiac conduction system-specific Cre driver Hcn4CreERT2 with Lats1 and Lats2 conditional knockout alleles. In addition, the Hippo-signaling effectors Yap and Taz were conditionally inactivated in the SAN. To determine the function of Hippo signaling in the SAN and other cardiac conduction system components, we conducted a series of physiological and molecular experiments, including telemetry ECG recording, echocardiography, Masson Trichrome staining, calcium imaging, immunostaining, RNAscope, cleavage under targets and tagmentation sequencing using antibodies against Yap1 or H3K4me3, quantitative real-time polymerase chain reaction, and Western blotting. We also performed comprehensive bioinformatics analyses of various datasets.

RESULTS

We found that Lats1/2 inactivation caused severe sinus node dysfunction. Compared with the controls, Lats1/2 conditional knockout mutants exhibited dysregulated calcium handling and increased fibrosis in the SAN, indicating that Lats1/2 function through both cell-autonomous and non-cell-autonomous mechanisms. It is notable that the Lats1/2 conditional knockout phenotype was rescued by genetic deletion of Yap and Taz in the cardiac conduction system. These rescued mice had normal sinus rhythm and reduced fibrosis of the SAN, indicating that Lats1/2 function through Yap and Taz. Cleavage Under Targets and Tagmentation sequencing data showed that Yap potentially regulates genes critical for calcium homeostasis such as Ryr2 and genes encoding paracrine factors important in intercellular communication and fibrosis induction such as Tgfb1 and Tgfb3. Consistent with this, Lats1/2 conditional knockout mutants had decreased Ryr2 expression and increased Tgfb1 and Tgfb3 expression compared with control mice.

CONCLUSIONS

We reveal, for the first time to our knowledge, that the canonical Hippo-Yap pathway plays a pivotal role in maintaining SAN homeostasis.

Stellate Ganglia and Cardiac Sympathetic Overactivation in Heart Failure

Heart failure (HF) is a major public health problem worldwide, especially coronary heart disease (myocardial infarction)-induced HF with reduced ejection fraction (HFrEF), which accounts for over 50% of all HF cases. An estimated 6 million American adults have HF. As a major feature of HF, cardiac sympathetic overactivation triggers arrhythmias and sudden cardiac death, which accounts for nearly 50–60% of mortality in HF patients. Regulation of cardiac sympathetic activation is highly integrated by the regulatory circuitry at multiple levels, including afferent, central, and efferent components of the sympathetic nervous system. Much evidence, from other investigators and us, has confirmed the afferent and central neural mechanisms causing sympathoexcitation in HF. The stellate ganglion is a peripheral sympathetic ganglion formed by the fusion of the 7th cervical and 1st thoracic sympathetic ganglion. As the efferent component of the sympathetic nervous system, cardiac postganglionic sympathetic neurons located in stellate ganglia provide local neural coordination independent of higher brain centers. Structural and functional impairments of cardiac postganglionic sympathetic neurons can be involved in cardiac sympathetic overactivation in HF because normally, many effects of the cardiac sympathetic nervous system on cardiac function are mediated via neurotransmitters (e.g., norepinephrine) released from cardiac postganglionic sympathetic neurons innervating the heart. This review provides an overview of cardiac sympathetic remodeling in stellate ganglia and potential mechanisms and the role of cardiac sympathetic remodeling in cardiac sympathetic overactivation and arrhythmias in HF. Targeting cardiac sympathetic remodeling in stellate ganglia could be a therapeutic strategy against malignant cardiac arrhythmias in HF.

QTc interval diurnal variations in patients treated with psychotropic medications: implications for the evaluation of drug induced QTc changes

Psychotropic drugs such as antipsychotics may prolong the QTc interval, increasing the risk of torsades de pointes (TdP) and sudden cardiac death. To assess QTc prolongation by psychotropic drugs, an electrocardiogram (EKG) is usually recorded before and after starting treatment. Circadian variations in the QTc interval have been described but have not been adequately studied in patients taking psychotropic drugs. In psychiatric clinical practice, EKGs before and after treatment initiation are often compared, without considering the time of day at which the two EKGs are recorded. To determine whether there is a circadian change in the QTc interval in patients treated with psychotropic drugs, we evaluated the EKGs of a group of patients treated with psychotropic drugs (85% on antipsychotics) and the EKGs of a group of patients that were not treated with medications. In each group, we compared the EKGs recorded before 11:00 am with those recorded after 5:00 pm. The QTc value was significantly longer in the group treated with psychotropic drugs than in the group without drugs at both morning and evening evaluations (p ≤ 0.001). In each group, a statistically significant difference was found between the EKGs recorded before 11:00 a.m. and the EKGs recorded after 5:00 p.m. In patients treated with medications, the mean QTc in the morning was 453.3 ± 25.4 while the mean QTc in the afternoon was 428.4 ± 24.7 (p < 0.0001). In patients who were not receiving any medication, the morning mean QTc was 422.4 ± 22.6 while the mean afternoon QTc was 409.4 ± 19.6 (p = 0.002). These results suggest that a circadian variation in QTc is observed both in patients taking psychotropic drugs and in patients not taking medication. We conclude that any comparison of EKGs to test the effect on QTc of a medication, should be referred to EKGs recorded at the same time of day.

m6A methyltransferase METTL3 participated in sympathetic neural remodeling post-MI via the TRAF6/NF-κB pathway and ROS production

OBJECTIVE

Sudden cardiac death caused by ventricular arrhythmias (VAs) is the main cause of high mortality in patients with myocardial infarction (MI). Sympathetic neural remodeling caused by inflammation after MI is closely associated with the occurrence of VAs. METTL3, the earliest identified m⁶A methyltransferase, is critical in mediating inflammatory responses. Our aim was to investigate whether the m⁶A methyltransferase METTL3 was involved in sympathetic remodeling post-MI and its specific mechanism.

METHODS AND RESULTS

A rat MI model was established via left coronary artery ligation. The expression of METTL3, TRAF6, NOX2, and NF-κB increased at 3 days and remained elevated at 7 days after MI, as determined via Western blotting. METTL3 was primarily present in macrophages, as determined via immunofluorescence. Intramyocardial injection of lentivirus carrying METTL3-shRNA inhibited METTL3 expression in vivo. Methylated immunoprecipitation-qPCR determined the METTL3 knockdown inhibited the m⁶A level of TRAF6 mRNA 3'-UTR. The co-immunoprecipitation experiment proved that METTL3 combines with TRAF6. Western blotting showed that silencing METTL3 inhibited TRAF6 level, NF-κB activation, and ROS production; decreased cytokine release (TNF-α and IL-1β); and downregulated nerve growth factor expression. Finally, METTL3 knockdown reduced sympathetic remodeling after MI, as determined via immunofluorescence assays of tyrosine hydroxylase and growth-associated protein 43. Programmed electrical stimulation, renal sympathetic nerve activity recording, and haemodynamic measurements showed that METTL3 inhibition decreased sympathetic activity and improved cardiac function.

CONCLUSIONS

Downregulation of METTL3 expression attenuated the excessive sympathetic neural remodeling induced by MI, further reducing the incidence of VAs and improving cardiac function. This was partly associated with the inhibition of the TRAF6/NF-κB pathway and ROS production.

Neonatal Deletion of Hand1 and Hand2 within Murine Cardiac Conduction System Reveals a Novel Role for HAND2 in Rhythm Homeostasis

The cardiac conduction system, a network of specialized cells, is required for the functioning of the heart. The basic helix loop helix factors Hand1 and Hand2 are required for cardiac morphogenesis and have been implicated in cardiac conduction system development and maintenance. Here we use embryonic and post-natal specific Cre lines to interrogate the role of Hand1 and Hand2 in the function of the murine cardiac conduction system. Results demonstrate that loss of HAND1 in the post-natal conduction system does not result in any change in electrocardiogram parameters or within the ventricular conduction system as determined by optical voltage mapping. Deletion of Hand2 within the post-natal conduction system results in sex-dependent reduction in PR interval duration in these mice, suggesting a novel role for HAND2 in regulating the atrioventricular conduction. Surprisingly, results show that loss of both HAND factors within the post-natal conduction system does not cause any consistent changes in cardiac conduction system function. Deletion of Hand2 in the embryonic left ventricle results in inconsistent prolongation of PR interval and susceptibility to atrial arrhythmias. Thus, these results suggest a novel role for HAND2 in homeostasis of the murine cardiac conduction system and that HAND1 loss potentially rescues the shortened HAND2 PR phenotype.

Arrhythmic risk stratification in ischemic, non-ischemic and hypertrophic cardiomyopathy: A two-step multifactorial, electrophysiology study inclusive approach

Annual arrhythmic sudden cardiac death ranges from 0.6% to 4% in ischemic cardiomyopathy (ICM), 1% to 2% in non-ischemic cardiomyopathy (NICM), and 1% in hypertrophic cardiomyopathy (HCM). Towards a more effective arrhythmic risk stratification (ARS) we hereby present a two-step ARS with the usage of seven non-invasive risk factors: Late potentials presence (≥ 2/3 positive criteria), premature ventricular contractions (≥ 30/h), non-sustained ventricular tachycardia (≥ 1episode/24 h), abnormal heart rate turbulence (onset ≥ 0% and slope ≤ 2.5 ms) and reduced deceleration capacity (≤ 4.5 ms), abnormal T wave alternans (≥ 65μV), decreased heart rate variability (SDNN < 70ms), and prolonged QT_c interval (> 440 ms in males and > 450 ms in females) which reflect the arrhythmogenic mechanisms for the selection of the intermediate arrhythmic risk patients in the first step. In the second step, these intermediate-risk patients undergo a programmed ventricular stimulation (PVS) for the detection of inducible, truly high-risk ICM and NICM patients, who will benefit from an implantable cardioverter defibrillator. For HCM patients, we also suggest the incorporation of the PVS either for the low HCM Risk-score patients or for the patients with one traditional risk factor in order to improve the inadequate sensitivity of the former and the low specificity of the latter.

Sudden death syndrome in broiler chickens: a review on the etiology and prevention of the syndrome

Sudden death syndrome (SDS) is a condition in which apparently healthy broiler chickens die suddenly. There are short convulsions and frantic wing-beating prior to death, and the weight of internal organs is the same as in healthy chickens. The exact etiology of SDS is unknown. Heart problems have been implicated as a potential cause of the disease in broiler chickens. Despite considerable research, effective methods of prevention are still being sought. Furthermore, the prophylactic measures often make production less profitable (reduced body weight gain resulting from restricted feeding) and prolong the growth period. It is necessary to continue research on SDS, in particular on stimulation of the cardiovascular system to reduce the susceptibility of broilers to sudden death syndrome under intensive production systems.

Periodic Repolarization Dynamics Identifies ICD-responders in Non-ischemic Cardiomyopathy: A DANISH Substudy

Background: Identification of patients with non-ischemic cardiomyopathy who benefit from prophylactic implantation of a cardioverter-defibrillator (ICD) remains an unmet clinical need. We hypothesized that periodic repolarization dynamics (PRD), a marker of repolarization instability associated with sympathetic activity, could be used to identify patients that benefit from prophylactic ICD-implantation. Methods: Heart-failure (DANISH) study, in which patients with non-ischemic cardiomyopathy, left-ventricular ejection fraction (LVEF) ≤35% and elevated N-terminal pro-brain natriuretic peptides (NT-proBNP) were randomized to ICD-implantation or control group. Patients were included in the PRD-substudy if they had a 24-hour Holter monitor recording at baseline with technically acceptable ECG signals during the night hours (00:00-06.00 AM). PRD was assessed using wavelet analysis according to previously validated methods. Primary endpoint was all-cause mortality. Cox-regression models were adjusted for age, sex, NT-proBNP, estimated glomerular filtration rate, LVEF, atrial fibrillation, ventricular pacing, diabetes mellitus, cardiac resynchronization therapy and mean heart rate. We proposed PRD ≥10deg² as exploratory cut-off value for ICD-implantation. Results: Seven-hundred and forty-eight of the 1,116 DANISH patients qualified for the PRD-substudy. During a mean follow-up period of 5.1±2.0 years, 82 of 385 patients died in the ICD group and 85 of 363 patients died in the control group (p-value=0.40). In Cox-regression analysis, PRD was independently associated with mortality (HR 1.28 [1.09-1.50] per SD increase; p-value = 0.003). Moreover, PRD was significantly associated with mortality in the control group (HR 1.51 [1.25-1.81]; p<0.001) but not in the ICD-group 1.04 [0.83-1.54]; p-value=0.71). There was a significant interaction between PRD and the effect of ICD-implantation on mortality (p-value 0.008), with patients with higher PRD having the greater benefit in terms of mortality reduction. ICD-implantation was associated with an absolute mortality reduction of 17.5% in the 280 patients with PRD ≥10deg² (HR 0.54 [0.34-0.84]; p-value=0.006; number needed to treat 6), but not in the 468 patients with PRD<10deg² (HR 1.17 [0.77-1.78]; p-value=0.46; p-value for interaction 0.01). Conclusions: Increased PRD identified patients with non-ischemic cardiomyopathy, where prophylactic ICD-implantation led to significant mortality reduction.

Fragmented QRS is associated with ventricular arrhythmias in heart failure patients: A systematic review and meta-analysis

INTRODUCTION

Many primary prevention heart failure (HF) patients with an implantable cardiac defibrillator (ICD) rarely experience life-threatening ventricular arrhythmias (VA). New strategies are required to identify patients most at risk of VA and sudden cardiac death who would benefit from an ICD. One potential method is the detection of fragmented QRS (fQRS) on the electrocardiogram. The aim was to assess the predictive capacity of fQRS for VA and mortality in ischemic (ICM) and non-ischemic cardiomyopathy (NICM) primary prevention HF patients.

METHODS AND RESULTS

A systematic review and meta-analysis of studies examining fQRS in HF patients with or without an ICD who met primary prevention indications with reduced ejection fraction ≤40%. Outcome measures were VA (or appropriate ICD therapy) and all-cause mortality. Ten studies involving 3885 patients were included for analysis. Most patients were male with non-fQRS patients being significantly younger (-1.5[-2.66, -0.42], p = .03). Diabetes was more likely in fQRS patients (1.12[1.01, 1.25], p = .03) while non-fQRS patients were 28% more likely to have a history of atrial fibrillation (0.82[0.67,1.00], p = .05). Ventricular arrhythmias were significantly 1.5 times more likely in patients with fQRS (1.51[1.02, 2.25], p = .04). HF patients were 1.7 times more likely to die of any cause if fQRS was present (1.68[1.13, 2.52], p = .01). NICM patients with fQRS have a significant 2.6-fold increased incidence of death compared with ICM patients (2.55[1.63, 3.98], p < .0001).

CONCLUSION

fQRS is associated with VA and all-cause mortality and may be a novel marker in the risk stratification of primary prevention HF patients indicated for ICD implantation.

EphrinB2-RhoA upregulation attenuates sympathetic hyperinnervation and decreases the incidence of ventricular arrhythmia after myocardial infarction

BACKGROUND

Cardiac sympathetic hyperinnervation after myocardial infarction (MI) is associated with a high incidence of lethal arrhythmia. Erythropoietin-producing hepatoma interactor B2 (EphrinB2), a diffusible axonal chemorepellent that can induce growth cone collapse and axon repulsion of several neuronal populations, is crucial in neurodevelopment during disease development and progression. However, whether EphrinB2 could inhibit cardiac sympathetic hyperinnervation after MI remains unclear.

METHODS AND RESULTS

A rat model of MI was developed by left anterior descending coronary artery ligation. EphrinB2 expression was markedly increased in the infarcted border at 3 days after MI. Downregulation of EphrinB2 by intramyocardial injection of lentivirus carrying EphrinB2-shRNA significantly increased sympathetic hyperinnervation along with downregulated RhoA expression. In contrast, injection of EphrinB2-overexpressing lentivirus markedly upregulated EphrinB2, concomitant with inhibition of sympathetic sprouting and upregulated RhoA expression, accompanied by decreased incidence of ventricular arrhythmias (VAs). However, co-administering EphrinB2-overexpressing lentivirus and Fasudil (Rho kinase inhibitor) nearly abolished the inhibition of nerve sprouting effect. Additionally, EphrinB2 expression did not affect nerve growth factor level in the infarcted heart.

CONCLUSIONS

Overexpression of EphrinB2 may ameliorate MI-induced sympathetic hyperinnervation and further reduce the incidence of VAs, at least in part by activating RhoA-mediated axonal retraction.

An OpenCV-Based Approach for Automated Cardiac Rhythm Measurement in Zebrafish from Video Datasets

Cardiac arrhythmia has been defined as one of the abnormal heart rhythm symptoms, which is a common problem dealt with by cardiologists. Zebrafish were established as a powerful animal model with a transparent body that enables optical observation to analyze cardiac morphology and cardiac rhythm regularity. Currently, research has observed heart-related parameters in zebrafish, which used different approaches, such as starting from the use of fluorescent transgenic zebrafish, different software, and different observation methods. In this study, we developed an innovative approach by using the OpenCV library to measure zebrafish larvae heart rate and rhythm. The program is designed in Python, with the feature of multiprocessing for simultaneous region-of-interest (ROI) detection, covering both the atrium and ventricle regions in the video, and was designed to be simple and user-friendly, having utility even for users who are unfamiliar with Python. Results were validated with our previously published method using ImageJ, which observes pixel changes. In summary, the results showed good consistency in heart rate-related parameters. In addition, the established method in this study also can be widely applied to other invertebrates (like Daphnia) for cardiac rhythm measurement.

Sudden Unexpected Death after a mild trauma: The complex forensic interpretation of cardiac and genetic findings

A 55-year-old man affected by a psychotic disorder suddenly died during a quarrel with his father. The autopsy excluded traumatic causes of death, and the cardiac examination identified a severe cardiomegaly with biventricular dilatation of very likely multifactorial origin. Toxicological and pharmacogenetic analyses excluded a fatal intoxication and identified the presence of the antipsychotic drug fluphenazine in the therapeutic range in a normal metabolizer. The screening for genetic variations highlighted a novel heterozygous single-nucleotide variant in the exon 36: c 0.4750C>A (p.Pro1584Thr) of the Ryanodine Receptor Type 2 (RYR2) gene. The mutation detected can be classified as Likely Pathogenic according to the American College of Medical Genetics and Genomics (ACMG) criteria. RYR2 variation has been associated to catecholaminergic polymorphic ventricular tachycardia (CPVT), a disease currently recognized as one of the most malignant cardiac channelopathies, expressed mostly in young patients, normally in the absence of structural heart disease. The victim late middle age, compared to juvenile onset of CPVT reported in literature, his clinical history, his structurally altered heart, circumstances at death and the absence of phenotype-related variations of dilated cardiomyopathy genes, suggested that the fatal arrhythmia could have been caused by an acquired form of dilated cardiopathy/cardiomyopathy. However, the contribution of the genetic variant to death cannot be completely ruled out, since the significance of a VUS or of a novel variant depends on the data available at the time of investigation, and should be periodically evaluated. We discuss the contribution of the structural alteration and of the variant detected, as well as the role of the molecular autopsy in forensic examination, which can make a significant contribution for inferring both cause and manner of death.

A red-emissive two-photon fluorescent probe for mitochondrial sodium ions in live tissue

A cyclocyanine (CC)-based organic small molecule two-photon (TP) fluorescent probe (CCNa1) was developed for mitochondrial sodium ion sensing. CCNa1 exhibits a low solvatochromic shift and strong TP fluorescence enhancement at 575 nm upon binding to Na⁺ and is insensitive to other metal ions and to pH. CCNa1 demonstrated fast cell loading ability, biocompatibility, and sensitive response to mitochondrial Na⁺ influx in live cells and mouse brain tissue.

Multi-classification of arrhythmias using a HCRNet on imbalanced ECG datasets

BACKGROUND AND OBJECTIVE

Cardiac arrhythmia, which is an abnormal heart rhythm, is a common clinical problem in cardiology. Arrhythmias can be divided into many Categories, and accurate detection of arrhythmias can effectively prevent heart disease and reduce mortality. However, existing screening methods require long time monitoring and are low cost and low yield. Our goal is to develop a mixed depth model for processing time series to predict multi-classification electrocardiograph (ECG).

METHODS

In this study, we developed a new, more robust network model named Hybrid Convolutional Recurrent Neural Network (HCRNet) for the time-series signal of ECG. This model utilized a nine-class ECG dataset containing tens of thousands of data to automatically detect cardiac arrhythmias. At the same time, a large imbalance arose because some of the cases in our selected MIT-BIH atrial fibrillation database had less than 100 records, but some had more than 10,000 records. Therefore, during data preprocessing, we adopted a scientific and efficient method to solve the ECG data imbalance problem. In the experimental studies, 10-fold cross validation technique is employed to evaluate performance of the model.

RESULTS

In order to fully validate our proposed model, we conducted a comprehensive experiment to investigate the performance of the proposed method. Our proposed HCRNet achieved the average accuracy of 99.01% performance and the average sensitivity of 99.58% performance on this dataset. Results suggest that the proposed model outperformed some state-of-the-art studies in ECG classification with a high overall performance value.

CONCLUSION

The HCRNet model can effectively classify arrhythmia signals in nine categories and obtain high efficiency, accuracy and F1 values. These improvements in efficiency and accuracy explain the rationality and science of setting up the modules in the HCRNet. By using this model, it can help cardiologists to correctly identify heartbeat types and perform arrhythmia diagnosis quickly.

Spinal Cord Stimulation Reduces Ventricular Arrhythmias by Attenuating Reactive Gliosis and Activation of Spinal Interneurons

OBJECTIVES

This study investigated spinal cord neuronal and glial cell activation during cardiac ischemia-reperfusion (IR)-triggered ventricular arrhythmias and neuromodulation therapy by spinal cord stimulation (SCS).

BACKGROUND

Myocardial ischemia induces changes in cardiospinal neural networks leading to sudden cardiac death. Neuromodulation with SCS decreases cardiac sympathoexcitation; however, the molecular mechanisms remain unknown.

METHODS

Yorkshire pigs (n = 16) were randomized to Control, IR, or IR+SCS groups. A 4-pole SCS lead was placed in the T1-T4 epidural space with stimulation for 30 minutes before IR (50 Hz, 0.4-ms duration, 90% motor threshold). Cardiac electrophysiological mapping and Ventricular Arrhythmia Score (VAS) were recorded. Immunohistochemistry of thoracic spinal sections was used to map and identify Fos-positive neuronal and glial cell types during IR with and without SCS.

RESULTS

IR increased cardiac sympathoexcitation and arrhythmias (VAS = 6.2 ± 0.9) that were attenuated in IR + SCS (VAS = 2.8 ± 0.5; P = 0.017). IR increased spinal cellular Fos expression (#Fos+ cells Control = 23 ± 2 vs IR = 88 ± 5; P < 0.0001) in T1-T4, with the greatest increase localized to T3, and the greatest %Fos+ cells being microglia and astrocytes. Fos expression was attenuated by IR + SCS (62 ± 4; P < 0.01), primarily though a reduction in Fos+ microglia and astrocytes, as SCS also led to increase in Fos+ neurons in deep dorsal laminae.

CONCLUSIONS

In a porcine model, cardiac IR was associated with astrocyte and microglial cell activation. Our results suggest that preemptive thoracic SCS decreased IR-induced cardiac sympathoexcitation and ventricular arrhythmias through attenuation of reactive gliosis and activation of inhibitory interneurons in the dorsal horn of spinal cord.

Microvolt T-Wave Alternans Is Modulated by Acute Low-Level Tragus Stimulation in Patients With Ischemic Cardiomyopathy and Heart Failure

Aims: Microvolt T-wave alternans (TWA), an oscillation in T-wave morphology of the electrocardiogram (ECG), has been associated with increased susceptibility to ventricular tachy-arrhythmias, while vagus nerve stimulation has shown promising anti-arrhythmic effects in in vivo and ex vivo animal studies. We aimed to examine the effect of non-invasive, acute low-level tragus stimulation (LLTS) on TWA in patients with ischemic cardiomyopathy and heart failure.

Methods: 26 patients with ischemic cardiomyopathy (left ventricular ejection fraction <35%) and chronic stable heart failure, previously implanted with an automatic implantable cardioverter defibrillator (ICD) device with an atrial lead (dual chamber ICD or cardiac resynchronization therapy defibrillator), were enrolled in the study. Each patient sequentially received, (1) Sham LLTS (electrode on tragus, but no stimulation delivered) for 5 min; (2) Active LLTS at two different frequencies (5 and 20 Hz, 15 min each); and (3) Active LLTS, during concomitant atrial pacing at 100 bpm at two different frequencies (5 and 20 Hz, 15 min each). LLTS was delivered through a transcutaneous electrical nerve stimulation device (pulse width 200 μs, frequency 5/20 Hz, amplitude 1 mA lower than the discomfort threshold). TWA burden was assessed using continuous ECG monitoring during sham and active LLTS in sinus rhythm, as well as during atrial pacing.

Results: Right atrial pacing at 100 bpm led to significantly heightened TWA burden compared to sinus rhythm, with or without LLTS. Acute LLTS at both 5 and 20 Hz, during sinus rhythm led to a significant rise in TWA burden in the precordial leads (p < 0.05).

Conclusion: Acute LLTS results in a heart-rate dependent increase in TWA burden.

Association between thrombolysis in myocardial infarction grade and clinical outcome after emergent percutaneous coronary intervention in patients with acute myocardial infarction who have suffered out-of-hospital cardiac arrest: the Yamagata AMI registry

Despite improvements in the survival rate of acute myocardial infarction (AMI), out-of-hospital cardiac arrest (OHCA) due to AMI is still a devastating condition. Thrombolysis in myocardial infarction (TIMI) grade is used to classify coronary reperfusion after percutaneous coronary intervention (PCI), but it remains unclear whether TIMI grade after emergent PCI is associated with short-term mortality in patients with AMI who have suffered OHCA. We analyzed data collected from 2012 to 2017 and recorded in the Yamagata AMI registry, which is a multicenter surveillance conducted in all institutions in Yamagata prefecture. Among 3332 patients with AMI, 254 had suffered OHCA. There were 564 deaths during the 30 days after the onset of AMI. The survival rate was lower in patients who had suffered OHCA than in those who had not (40% vs. 87%; P < 0.0001). Patients with AMI who had suffered OHCA were divided into three groups based on TIMI grade (TIMI III group, n = 70; TIMI ≤ II group, n = 21; and no coronary angiography [non-CAG] group, n = 163). The survival rates in the TIMI III, TIMI ≤ II, and non-CAG groups were 87%, 38%, and 5%, respectively. Kaplan-Meier analysis demonstrated that the survival rate was highest in the TIMI III group. Multivariate Cox proportional hazard regression analysis demonstrated that TIMI III was closely associated with survival after adjustment for confounding factors. Achieving TIMI grade III during emergent PCI is crucial to improve survival in patients with AMI who have suffered OHCA.

Left ventricular hypertrophy and sudden cardiac death

Sudden cardiac death (SCD) is among the leading causes of death worldwide, and it remains a public health problem, as it involves young subjects. Current guideline-directed risk stratification for primary prevention is largely based on left ventricular (LV) ejection fraction (LVEF), and preventive strategies such as implantation of a cardiac defibrillator (ICD) are justified only for documented low LVEF (i.e., ≤ 35%). Unfortunately, only a small percentage of primary prevention ICDs, implanted on the basis of a low LVEF, will deliver life-saving therapies on an annual basis. On the other hand, the vast majority of patients that experience SCD have LVEF > 35%, which is clamoring for better understanding of the underlying mechanisms. It is mandatory that additional variables be considered, both independently and in combination with the EF, to improve SCD risk prediction. LV hypertrophy (LVH) is a strong independent risk factor for SCD regardless of the etiology and the severity of symptoms. Concentric and eccentric LV hypertrophy, and even earlier concentric remodeling without hypertrophy, are all associated with increased risk of SCD. In this paper, we summarize the physiology and physiopathology of LVH, review the epidemiological evidence supporting the association between LVH and SCD, briefly discuss the mechanisms linking LVH with SCD, and emphasize the need to evaluate LV geometry as a potential risk stratification tool regardless of the LVEF.

Emerging evidence for a mechanistic link between low-frequency oscillation of ventricular repolarization measured from the electrocardiogram T-wave vector and arrhythmia

Strong recent clinical evidence links the presence of prominent oscillations of ventricular repolarization in the low-frequency range (0.04–0.15 Hz) to the incidence of ventricular arrhythmia and sudden death in post-MI patients and patients with ischaemic and non-ischaemic cardiomyopathy. It has been proposed that these oscillations reflect oscillations of ventricular action potential duration at the sympathetic nerve frequency. Here we review emerging evidence to support that contention and provide insight into possible underlying mechanisms for this association.

Role of cardiac hypoxia in the pathogenesis of sudden death syndrome in broiler chickens - A metabolic and molecular study

Sudden death syndrome (SDS) is an economically important disorder in broiler chickens with unknown aetiology. The aim of the present study was to evaluate the metabolic and molecular alterations related to hypoxia in the myocardium of broiler chickens with SDS. Samples from the cardiac muscle of internal control broiler chickens (ICs) (n = 36) and chickens having died of SDS (n = 36) were obtained during the rearing period. The activities of lactate dehydrogenase (LDH) and creatine phosphokinase (CPK) and the concentration of lactate were measured in the cardiac tissue using available commercial kits. The expression of hypoxia-inducing factor 1α (HIF1α), glucose transporter 1 (GLUT1), pyruvate dehydrogenase kinase 4 (PDHK4) and monocarboxylate transporter 4 (MCT4) genes was determined in the myocardium by real-time PCR analysis. The results showed the elevation of lactate level and activities of LDH and CPK in the cardiac muscle of SDS-affected chickens compared with the IC birds (P < 0.05). The cardiac muscle expression of HIF1α, MCT4 and GLUT1 genes was increased, while the PDHK4 mRNA level was decreased in the SDS-affected group compared to those in the IC chickens (P < 0.05). Our results showed that metabolic remodelling associated with hypoxia in the cardiac tissues may have an important role in the pathogenesis of cardiac insufficiency and SDS in broiler chickens.

Integrating proteomic, lipidomic and metabolomic data to construct a global metabolic network of lethal ventricular tachyarrhythmias (LVTA) induced by aconitine

Lethal ventricular tachyarrhythmias (LVTA)-related sudden cardiac death (SCD) is one of the major causes of death worldwide. However, the mechanisms underlying LVTA induced by myocardial ion channel diseases (MICDs) are not yet fully understood. Here, we produced an LVTA rat model induced by aconitine, to mimic MICDs-elicited LVTA, and constructed a global pathway network via integrating proteomic and lipidomic data, and our previously published metabolomic data. Results showed that both proteome and lipidome were disturbed during the LVTA process. Most of the differentially expressed proteins and lipid species were correlated. Proteomic data indicated disturbance of energy metabolism (e.g. fatty acid β-oxidation and the tricarboxylic acid cycle) and activation of the protein kinase C and nicotinamide adenine dinucleotide phosphate (NAPDH) oxidase pathway; these alterations led to lowered ATP and elevated ROS, respectively. Altered levels of the Ca²⁺ handling proteins suggested aberrant intracellular Ca²⁺ homeostasis, which might also be secondary to the shortage of ATP and oxidative stress. Significantly, the disrupted pathways implied by proteomic data were largely confirmed by lipidomic and metabolomic data. Collectively, we have constructed a metabolic pathway network of aconitine-induced LVTA using a multi-omics strategy, which confers great promise for the deeper interpretation of the mechanisms underlying LVTA. SIGNIFICANCE: In this study, we integrated proteomics, lipidomics and metabolomics to explore the pathophysiological processes of LVTA induced by aconitine. It is innovative to try to integrate these three omics in a study exploring the relative mechanisms. Here, based on the DEPs and differentially abundant lipid species (DALPs) between the LVTA groups and the controls, and the different metabolites discovered previously from the same model, we have successfully constructed a global metabolic network. Taken together, the multi-omics integration strategies used in this study show the potential for a new interpretation of the pathophysiological processes of LVTA induced by different conditions and open the possibility to explore deeper and broader mechanisms of other diseases.

FAT10 protects against ischemia-induced ventricular arrhythmia by decreasing Nedd4-2/Nav1.5 complex formation

The human leukocyte antigen F-associated transcript 10 (FAT10) is a member of the small ubiquitin-like protein family that binds to its target proteins and subjects them to degradation by the ubiquitin-proteasome system (UPS). In the heart, FAT10 plays a cardioprotective role and affects predisposition to cardiac arrhythmias after myocardial ischemia (MI). However, whether and how FAT10 influences cardiac arrhythmias is unknown. We investigated the role of FAT10 in regulating the sodium channel Nav1.5, a major regulator of cardiac arrhythmias. Fat10 was conditionally deleted in cardiac myocytes using Myh6-Cre and Fat10^F/F mice (cFat10^-/-). Compared with their wild-type littermates, cFat10^-/- mice showed prolonged RR, PR, and corrected QT (QTc) intervals, were more likely to develop ventricular arrhythmia, and had increased mortality after MI. Patch-clamp studies showed that the peak Na⁺ current was reduced, and the late Na⁺ current was significantly augmented, resulting in a decreased action potential amplitude and delayed depolarization. Immunoblot and immunofluorescence analyses showed that the expression of the membrane protein Nav1.5 was decreased. Coimmunoprecipitation experiments demonstrated that FAT10 stabilized Nav1.5 expression by antagonizing Nav1.5 ubiquitination and degradation. Specifically, FAT10 bound to the lysine residues in the C-terminal fragments of Nav1.5 and decreased the binding of Nav1.5 to the Nedd4-2 protein, a ubiquitin E3 ligase, preventing degradation of the Nav1.5 protein. Collectively, our findings showed that deletion of the Fat10 in cardiac myocytes led to increased cardiac arrhythmias and increased mortality after MI. Thus, FAT10 protects against ischemia-induced ventricular arrhythmia by binding to Nav1.5 and preventing its Neddylation and degradation by the UPS after MI.

Cardiac adaptation and cardioprotection against arrhythmias and ischemia-reperfusion injury in mammalian hibernators

Hibernation allows animals to enter an energy conserving state to survive severe drops in external temperatures and a shortage of food. It has been observed that the hearts of mammalian hibernators exhibit intrinsic protection against ischemia-reperfusion (I/R) injury and cardiac arrhythmias in the winter whether they are hibernating or not. However, the molecular and ionic mechanisms for cardioprotection in mammalian hibernators remain elusive. Recent studies in woodchucks (Marmota monax) have suggested that cardiac adaptation occurs at different levels and mediates an intrinsic cardioprotection prior to/in the winter. The molecular/cellular remodeling in the winter (with or without hibernation) includes (1) an upregulation of transcriptional factor, anti-apoptotic factor, nitric oxide synthase, protein kinase C-ε, and phosphatidylinositol-4,5-bisphosphate 3-kinase; (2) an upregulation of antioxidant enzymes (e.g. superoxide dismutase and catalase); (3) a reduction in the oxidation level of Ca²⁺/calmodulin-dependent protein kinase II (CaMKII); and (4) alterations in the expression and activity of multiple ion channels/transporters. Therefore, the cardioprotection against I/R injury in the winter is most likely mediated by enhancement in signaling pathways that are shared by preconditioning, reduced cell apoptosis, and increased detoxification of reactive oxygen species (ROS). The resistance to cardiac arrhythmias and sudden cardiac death in the winter is closely associated with an upregulation of the antioxidant catalase and a downregulation of CaMKII activation. This remodeling of the heart is associated with a reduction in the incidence of afterdepolarizations and triggered activities. In this short review article, we will discuss the seasonal changes in gene and protein expression profiles as well as alterations in the function of key proteins that are associated with the occurrence of cardioprotection against myocardial damage from ischemic events and fatal arrhythmias in a mammalian hibernator. Understanding the intrinsic cardiac adaptive mechanisms that confer cardioprotection in hibernators may offer new strategies to protect non-hibernating animals, especially humans, from I/R injury and ischemia-induced fatal cardiac arrhythmias.

Neuromodulation With Thoracic Dorsal Root Ganglion Stimulation Reduces Ventricular Arrhythmogenicity

Introduction: Sympathetic hyperactivity is strongly associated with ventricular arrhythmias and sudden cardiac death. Neuromodulation provides therapeutic options for ventricular arrhythmias by modulating cardiospinal reflexes and reducing sympathetic output at the level of the spinal cord. Dorsal root ganglion stimulation (DRGS) is a recent neuromodulatory approach; however, its role in reducing ventricular arrhythmias has not been evaluated. The aim of this study was to determine if DRGS can reduce cardiac sympathoexcitation and the indices for ventricular arrhythmogenicity induced by programmed ventricular extrastimulation. We evaluated the efficacy of thoracic DRGS at both low (20 Hz) and high (1 kHz) stimulation frequencies. Methods: Cardiac sympathoexcitation was induced in Yorkshire pigs (n = 8) with ventricular extrastimulation (S1/S2 pacing), before and after DRGS. A DRG-stimulating catheter was placed at the left T2 spinal level, and animals were randomized to receive low-frequency (20 Hz and 0.4 ms) or high-frequency (1 kHz and 0.03 ms) DRGS for 30 min. High-fidelity cardiac electrophysiological recordings were performed with an epicardial electrode array measuring the indices of ventricular arrhythmogenicity-activation recovery intervals (ARIs), electrical restitution curve (S_max), and Tpeak-Tend interval (Tp-Te interval). Results: Dorsal root ganglion stimulation, at both 20 Hz and 1 kHz, decreased S1/S2 pacing-induced ARI shortening (20 Hz DRGS -21±7 ms, Control -50±9 ms, P = 0.007; 1 kHz DRGS -13 ± 2 ms, Control -46 ± 8 ms, P = 0.001). DRGS also reduced arrhythmogenicity as measured by a decrease in S_max (20 Hz DRGS 0.5 ± 0.07, Control 0.7 ± 0.04, P = 0.006; 1 kHz DRGS 0.5 ± 0.04, Control 0.7 ± 0.03, P = 0.007), and a decrease in Tp-Te interval/QTc (20 Hz DRGS 2.7 ± 0.13, Control 3.3 ± 0.12, P = 0.001; 1 kHz DRGS 2.8 ± 0.08, Control; 3.1 ± 0.03, P = 0.007). Conclusions: In a porcine model, we show that thoracic DRGS decreased cardiac sympathoexcitation and indices associated with ventricular arrhythmogenicity during programmed ventricular extrastimulation. In addition, we demonstrate that both low-frequency and high-frequency DRGS can be effective neuromodulatory approaches for reducing cardiac excitability during sympathetic hyperactivity.

Firefighters Are More Physically Active On-Duty Compared to Off-Duty

Physical inactivity, coupled with increasing obesity levels, in firefighters plays a key role in aggregated cardiovascular events. The purpose of this study was to investigate device-measured physical activity (PA) for firefighters while on- and off-duty to have a clearer understanding of their overall PA level. Methods: Twenty-nine career firefighters participated in this non-experimental, within-subjects study by wearing an accelerometer to assess PA intensities and step-count. Obesity was classified using body mass index (BMI). Dependent t-tests were used to examine mean differences in PA intensities when on- and off-duty. Pearson product-moment correlations were used to assess the association between PA intensities when on and off-duty. Results: According to the World Health Organization BMI categorizations, 20 firefighters were overweight, 9 were obese, and, thus, none were normal weight. Only light PA (LPA) was statistically significant (p = 0.026) for on- and off-duty days with a small-to-medium effect size (d = 0.47), meaning that on average, firefighters performed more minutes of LPA when on-duty compared to off. There was a significant difference between on- (9060.2 ± 2636.4) and off-duty (7495.3 ± 2835.8) daily step counts (p = 0.011). Conclusion: As the results demonstrate, there is a dire need for increased PA levels in firefighters while on- and off-duty.

Ethnic variability in mortality from ischaemic heart disease/cardiomegaly in Malaysia

The prevalence of ischaemic heart disease with associated cardiomegaly and other chronic diseases such as diabetes mellitus has increased in Malaysia in recent years. As the contribution to mortality from ischaemic heart disease/cardiomegaly in different ethnic populations is unclear, a three year (January 2013-December 2015) retrospective study of autopsy cases was undertaken at the Department of Forensic Pathology, University Malaya Medical Centre. There were 80 cases with lethal ischaemic heart diseases/cardiomegaly. The age range was 30-69 years (mean 50.19 years) with a male to female ratio of 39:01. The most vulnerable age was 50-59 years accounting for 38.75% of cases. Malays accounted for 15% of cases, Indians for 32.5% and Chinese for 36.25%. Although in 35 cases (43.75%) there was a history suggestive of ischaemic heart disease, the remaining 45 cases (56.25%) were apparently healthy until the terminal collapse. It appears that Indian males in the 50-59 year age range are most at risk for lethal cardiac events in this population, most often with no preceding symptoms or signs. The study demonstrates the value of studying subpopulations for disease risk rather than relying on accrued general population data.