Circadian Regulation of Cardiac Arrhythmias and Electrophysiology.

Circadian rhythms in physiology and behavior are ≈24-hour biological cycles regulated by internal biological clocks (ie, circadian clocks) that optimize organismal homeostasis in response to predictable environmental changes. These clocks are present in virtually all cells in the body, including cardiomyocytes. Many decades ago, clinicians and researchers became interested in studying daily patterns of triggers for sudden cardiac death, the incidence of sudden cardiac death, and cardiac arrhythmias. This review highlights historical and contemporary studies examining the role of day/night rhythms in the timing of cardiovascular events, delves into changes in the timing of these events over the last few decades, and discusses cardiovascular disease-specific differences in the timing of cardiovascular events. The current understanding of the environmental, behavioral, and circadian mechanisms that regulate cardiac electrophysiology is examined with a focus on the circadian regulation of cardiac ion channels and ion channel regulatory genes. Understanding the contribution of environmental, behavioral, and circadian rhythms on arrhythmia susceptibility and the incidence of sudden cardiac death will be essential in developing future chronotherapies.

Extracellular Kir2.1C122Y Mutant Upsets Kir2.1-PIP2 Bonds and Is Arrhythmogenic in Andersen-Tawil Syndrome.

BACKGROUND: Andersen-Tawil syndrome type 1 is a rare heritable disease caused by mutations in the gene coding the strong inwardly rectifying K+ channel Kir2.1. The extracellular Cys (cysteine)122-to-Cys154 disulfide bond in the channel structure is crucial for proper folding but has not been associated with correct channel function at the membrane. We evaluated whether a human mutation at the Cys122-to-Cys154 disulfide bridge leads to Kir2.1 channel dysfunction and arrhythmias by reorganizing the overall Kir2.1 channel structure and destabilizing its open state. METHODS: We identified a Kir2.1 loss-of-function mutation (c.366 A>T; p.Cys122Tyr) in an ATS1 family. To investigate its pathophysiological implications, we generated an AAV9-mediated cardiac-specific mouse model expressing the Kir2.1C122Y variant. We employed a multidisciplinary approach, integrating patch clamping and intracardiac stimulation, molecular biology techniques, molecular dynamics, and bioluminescence resonance energy transfer experiments. RESULTS: Kir2.1C122Y mice recapitulated the ECG features of ATS1 independently of sex, including corrected QT prolongation, conduction defects, and increased arrhythmia susceptibility. Isolated Kir2.1C122Y cardiomyocytes showed significantly reduced inwardly rectifier K+ (IK1) and inward Na+ (INa) current densities independently of normal trafficking. Molecular dynamics predicted that the C122Y mutation provoked a conformational change over the 2000-ns simulation, characterized by a greater loss of hydrogen bonds between Kir2.1 and phosphatidylinositol 4,5-bisphosphate than wild type (WT). Therefore, the phosphatidylinositol 4,5-bisphosphate-binding pocket was destabilized, resulting in a lower conductance state compared with WT. Accordingly, on inside-out patch clamping, the C122Y mutation significantly blunted Kir2.1 sensitivity to increasing phosphatidylinositol 4,5-bisphosphate concentrations. In addition, the Kir2.1C122Y mutation resulted in channelosome degradation, demonstrating temporal instability of both Kir2.1 and NaV1.5 proteins. CONCLUSIONS: The extracellular Cys122-to-Cys154 disulfide bond in the tridimensional Kir2.1 channel structure is essential for the channel function. We demonstrate that breaking disulfide bonds in the extracellular domain disrupts phosphatidylinositol 4,5-bisphosphate-dependent regulation, leading to channel dysfunction and defects in Kir2.1 energetic stability. The mutation also alters functional expression of the NaV1.5 channel and ultimately leads to conduction disturbances and life-threatening arrhythmia characteristic of Andersen-Tawil syndrome type 1.

Acute Adenoviral Infection Elicits an Arrhythmogenic Substrate Prior to Myocarditis.

BACKGROUND: Viral cardiac infection represents a significant clinical challenge encompassing several etiological agents, disease stages, complex presentation, and a resulting lack of mechanistic understanding. Myocarditis is a major cause of sudden cardiac death in young adults, where current knowledge in the field is dominated by later disease phases and pathological immune responses. However, little is known regarding how infection can acutely induce an arrhythmogenic substrate before significant immune responses. Adenovirus is a leading cause of myocarditis, but due to species specificity, models of infection are lacking, and it is not understood how adenoviral infection may underlie sudden cardiac arrest. Mouse adenovirus type-3 was previously reported as cardiotropic, yet it has not been utilized to understand the mechanisms of cardiac infection and pathology. METHODS: We have developed mouse adenovirus type-3 infection as a model to investigate acute cardiac infection and molecular alterations to the infected heart before an appreciable immune response or gross cardiomyopathy. RESULTS: Optical mapping of infected hearts exposes decreases in conduction velocity concomitant with increased Cx43Ser368 phosphorylation, a residue known to regulate gap junction function. Hearts from animals harboring a phospho-null mutation at Cx43Ser368 are protected against mouse adenovirus type-3-induced conduction velocity slowing. Additional to gap junction alterations, patch clamping of mouse adenovirus type-3-infected adult mouse ventricular cardiomyocytes reveals prolonged action potential duration as a result of decreased IK1 and IKs current density. Turning to human systems, we find human adenovirus type-5 increases phosphorylation of Cx43Ser368 and disrupts synchrony in human induced pluripotent stem cell-derived cardiomyocytes, indicating common mechanisms with our mouse whole heart and adult cardiomyocyte data. CONCLUSIONS: Together, these findings demonstrate that adenoviral infection creates an arrhythmogenic substrate through direct targeting of gap junction and ion channel function in the heart. Such alterations are known to precipitate arrhythmias and likely contribute to sudden cardiac death in acutely infected patients.

AAV-Mediated Delivery of Plakophilin-2a Arrests Progression of Arrhythmogenic Right Ventricular Cardiomyopathy in Murine Hearts: Preclinical Evidence Supporting Gene Therapy in Humans.

BACKGROUND: Pathogenic variants in PKP2 (plakophilin-2) cause arrhythmogenic right ventricular cardiomyopathy, a disease characterized by life-threatening arrhythmias and progressive cardiomyopathy leading to heart failure. No effective medical therapy is available to prevent or arrest the disease. We tested the hypothesis that adeno-associated virus vector-mediated delivery of the human PKP2 gene to an adult mammalian heart deficient in PKP2 can arrest disease progression and significantly prolong survival. METHODS: Experiments were performed using a PKP2-cKO (cardiac-specific, tamoxifen-activated PKP2 knockout murine model). The potential therapeutic, adeno-associated virus vector of serotype rh.74 (AAVrh.74)-PKP2a (PKP2 variant A; RP-A601) is a recombinant AAVrh.74 gene therapy viral vector encoding the human PKP2 variant A. AAVrh.74-PKP2a was delivered to adult mice by a single tail vein injection either before or after tamoxifen-activated PKP2-cKO. PKP2 expression was confirmed by molecular and histopathologic analyses. Cardiac function and disease progression were monitored by survival analyses, echocardiography, and electrocardiography. RESULTS: Consistent with prior findings, loss of PKP2 expression caused 100% mortality within 50 days after tamoxifen injection. In contrast, AAVrh.74-PKP2a-mediated PKP2a expression resulted in 100% survival for >5 months (at study termination). Echocardiographic analysis revealed that AAVrh.74-PKP2a prevented right ventricle dilation, arrested left ventricle functional decline, and mitigated arrhythmia burden. Molecular and histological analyses showed AAVrh.74-PKP2a-mediated transgene mRNA and protein expression and appropriate PKP2 localization at the cardiomyocyte intercalated disc. Importantly, the therapeutic benefit was shown in mice receiving AAVrh.74-PKP2a after disease onset. CONCLUSIONS: These preclinical data demonstrate the potential for AAVrh.74-PKP2a (RP-A601) as a therapeutic for PKP2-related arrhythmogenic right ventricular cardiomyopathy in both early and more advanced stages of the disease.

Unraveling Complexities in Genetically Elusive Long QT Syndrome.

Genetic testing has become standard of care for patients with long QT syndrome (LQTS), providing diagnostic, prognostic, and therapeutic information for both probands and their family members. However, up to a quarter of patients with LQTS do not have identifiable Mendelian pathogenic variants in the currently known LQTS-associated genes. This absence of genetic confirmation, intriguingly, does not lessen the severity of LQTS, with the prognosis in these gene-elusive patients with unequivocal LQTS mirroring genotype-positive patients in the limited data available. Such a conundrum instigates an exploration into the causes of corrected QT interval (QTc) prolongation in these cases, unveiling a broad spectrum of potential scenarios and mechanisms. These include multiple environmental influences on QTc prolongation, exercise-induced repolarization abnormalities, and the profound implications of the constantly evolving nature of genetic testing and variant interpretation. In addition, the rapid advances in genetics have the potential to uncover new causal genes, and polygenic risk factors may aid in the diagnosis of high-risk patients. Navigating this multifaceted landscape requires a systematic approach and expert knowledge, integrating the dynamic nature of genetics and patient-specific influences for accurate diagnosis, management, and counseling of patients. The role of a subspecialized expert cardiogenetic clinic is paramount in evaluation to navigate this complexity. Amid these intricate aspects, this review outlines potential causes of gene-elusive LQTS. It also provides an outline for the evaluation of patients with negative and inconclusive genetic test results and underscores the need for ongoing adaptation and reassessment in our understanding of LQTS, as the complexities of gene-elusive LQTS are increasingly deciphered.

Fluoroquinolones do not provide added risk of out-of-hospital cardiac arrest: a nationwide study.

AIM: Conflicting results have been reported regarding the association between fluoroquinolones (FQs) and the risk of out-of-hospital cardiac arrest (OHCA). In particular, it has not become clear whether OHCA in FQ users is related to the inherent comorbidities or whether there is a direct pro-arrhythmic effect of FQs. Therefore, we studied the relation between FQs and OHCA in the general population. METHODS: Through Danish nationwide registries, we conducted a nested case-control study with OHCA cases of presumed cardiac causes and age/sex/OHCA date-matched non-OHCA controls from the general population. Conditional logistic regression models with adjustments for well-known risk factors of OHCA were employed to estimate the OR with 95% CI of OHCA comparing FQs with amoxicillin. RESULTS: The study population consisted of 46 578 OHCA cases (mean: 71 years (SD: 14.40), 68.8% men) and 232 890 matched controls. FQ was used by 276 cases and 328 controls and conferred no increase in the odds of OHCA compared with amoxicillin use after controlling for the relevant confounders (OR: 0.91 (95% CI: 0.71 to 1.16)). The OR of OHCA associated with FQ use did not vary significantly by age (OR≤65: 0.96 (95% CI: 0.53 to 1.74), OR>65: 0.88 (95% CI: 0.67 to 1.16), p value interaction=0.7818), sex (ORmen: 0.96 (95% CI: 0.70 to 1.31), ORwomen: 0.80 (95% CI: 0.53 to 1.20), p value interaction=0.9698) and pre-existing cardiovascular disease (ORabsent: 1.02 (95% CI: 0.57 to 1.82), ORpresent: 0.98 (95% CI: 0.75 to 1.28), p value interaction=0.3884), including heart failure (ORabsent: 0.93 (95% CI: 0.72 to 1.22), ORpresent: 1.11 (95% CI: 0.61 to 2.02), p value interaction=0.7083) and ischaemic heart disease (ORabsent: 0.85 (95% CI: 0.64 to 1.12), ORpresent: 1.38 (95% CI: 0.86 to 2.21), p value interaction=0.6230). CONCLUSION: Our findings do not support an association between FQ exposure and OHCA in the general population. This lack of association was consistent in men and women, in all age categories, and in the presence or absence of cardiovascular disease.

Sudden Cardiac Death in National Collegiate Athletic Association Athletes: A 20-Year Study.

BACKGROUND: Understanding the incidence, causes, and trends of sudden cardiac death (SCD) among young competitive athletes is critical to inform preventive policies. METHODS: This study included National Collegiate Athletic Association athlete deaths during a 20-year time frame (July 1, 2002, through June 30, 2022). Athlete deaths were identified through 4 separate independent databases and search strategies (National Collegiate Athletic Association resolutions list, Parent Heart Watch database and media reports, National Center for Catastrophic Sports Injury Research database, and insurance claims). Autopsy reports and medical history were reviewed by an expert panel to adjudicate causes of SCD. RESULTS: A total of 143 SCD cases in National Collegiate Athletic Association athletes were identified from 1102 total deaths. The National Collegiate Athletic Association resolutions list identified 117 of 143 (82%), the Parent Heart Watch database or media reports identified 89 of 143 (62%), the National Center for Catastrophic Sports Injury Research database identified 63 of 143 (44%), and insurance claims identified 27 of 143 (19%) SCD cases. The overall incidence of SCD was 1:63 682 athlete-years (95% CI, 1:54 065-1:75 010). Incidence was higher in male athletes than in female athletes (1:43 348 [95% CI, 1:36 228-1:51 867] versus 1:164 504 [95% CI, 1:110 552-1:244 787] athlete-years, respectively) and Black athletes compared with White athletes (1:26 704 [1:20 417-1:34 925] versus 1:74 581 [1:60 247-1:92 326] athlete-years, respectively). The highest incidence of SCD was among Division I male basketball players (1:8188 [White, 1:5848; Black, 1:7696 athlete-years]). The incidence rate for SCD decreased over the study period (5-year incidence rate ratio, 0.71 [95% CI, 0.61-0.82]), whereas the rate of noncardiovascular deaths remained stable (5-year incidence rate ratio, 0.98 [95% CI, 0.94-1.04]). Autopsy-negative sudden unexplained death (19.5%) was the most common postmortem examination finding, followed by idiopathic left ventricular hypertrophy or possible cardiomyopathy (16.9%) and hypertrophic cardiomyopathy (12.7%), in cases with enough information for adjudication (118 of 143). Eight cases of death were attributable to myocarditis over the study period (1 case from January 1, 2020, through June 30, 2022), with none attributed to COVID-19 infection. SCD events were exertional in 50% of cases. Exertional SCD was more common among those with coronary artery anomalies (100%) and arrhythmogenic cardiomyopathy (83%). CONCLUSIONS: The incidence of SCD in college athletes has decreased. Male sex, Black race, and basketball are associated with a higher incidence of SCD.

Impact of serum haemoglobin-to-creatinine ratio after transcatheter aortic valve implantation.

OBJECTIVE: The association between a combined anaemia and renal failure index and 1-year prognosis of patients undergoing transcatheter aortic valve implantation (TAVI) is unexplored. We aimed to investigate a simple risk score in patients undergoing TAVI. METHODS: A total of 469 consecutive patients undergoing TAVI between 2015 and 2021 were enrolled. After excluding patients undergoing dialysis, the remaining 458 patients were classified according to three tertiles of the serum haemoglobin-to-creatinine (Hgb/Cr) ratio 1 day before TAVI. The primary clinical outcome measure was all-cause mortality and heart failure hospitalisation 1 year after TAVI. RESULTS: In the first, second and third tertiles, the 1-year cumulative incidence of all-cause mortality was 16.9% versus 7.2% versus 2.0%, respectively (p<0.01), and that of heart failure hospitalisation was 10.7% versus 3.4% versus 0.7%, respectively (p<0.01). The indexes of the area under the curve of the Hgb/Cr ratio for all-cause mortality and heart failure hospitalisation 1 year after TAVI were both 0.73. Cut-off values were 10.1 for all-cause mortality 1 year after TAVI (OR, 4.78; 95% CI 2.43 to 9.74; p<0.01) and 10.4 for heart failure hospitalisation 1 year after TAVI (OR, 5.3; 95% CI 2.21 to 14.1; p<0.01). In the multivariate analysis, the Hgb/Cr ratio was an independent predictor of all-cause mortality and heart failure hospitalisation 1 year after TAVI. CONCLUSIONS: Hgb/Cr ratio calculation 1 day before TAVI may help predict midterm all-cause mortality and heart failure hospitalisation in patients with severe aortic valve stenosis undergoing TAVI. TRIAL REGISTRATION NUMBER: 4143 (The Institutional Review Board of Kurashiki Central Hospital).

Factors influencing deviation from target temperature during targeted temperature management in postcardiac arrest patients.

BACKGROUND: Targeted temperature management (TTM) is a recommended therapy for postcardiac arrest patients. Hyperthermia worsened the patient outcome, and overcooling increased the incidence of complications; therefore, a high-quality TTM is required. The target temperature tended to be modified worldwide after the TTM trial in 2013. Our institute modified the target temperature to 35°C in 2017. This study aimed to compare the conventional and modified protocols, assess the relationship between target temperature deviation and patient outcomes, and identify the factors influencing temperature deviation. METHODS: This single-centre, retrospective, observational study included adult out-of-hospital cardiac arrest patients who underwent TTM between April 2013 and October 2019. We compared the conventional and modified protocol groups to evaluate the difference in the background characteristics and details on TTM. Subsequently, we assessed the relationship of deviation (>±0.5°C, >37°C, or<33°C) rates from the target temperature with mortality and neurological outcomes. We assessed the factors that influenced the deviation from the target temperature. RESULTS: Temperature deviation was frequently observed in the conventional protocol group (p=0.012), and the modified protocol group required higher doses of neuromuscular blocking agents (NMBAs) during TTM (p=0.016). Other background data, completion of protocol, incidence of complications, mortality and rate of favourable neurological outcomes were not significantly different. The performance rate of TTM was significantly higher in the modified group than in the conventional protocol group (p<0.001). Temperature deviation did not have an impact on the outcomes. Age, sex, body surface area, NMBA doses and type of cooling device were the factors influencing temperature deviation. CONCLUSIONS: A target temperature of 35°C might be acceptable and easily attainable if shivering of the patients was well controlled using NMBAs. Temperature deviation did not have an impact on outcomes. The identified factors influencing deviation from target temperature might be useful for ensuring a high-quality TTM.

Increased cardiovascular mortality in patients with mechanically expandable transcatheter aortic valve and without permanent pacemaker.

INTRODUCTION: Use of the mechanically expandable transcatheter aortic valve (MEV) has been recently linked to increased risks of valve dysfunction and cardiovascular mortality. The risk of developing conduction disturbance with the MEV valve is well known, and the negative prognostic impact of permanent pacemaker implantation (PPI) after transcatheter aortic valve implantation is another consideration. AIM: This study aimed to compare the mid-term survival of patients with MEV and self-expandable valves (SEV), and to examine survival of both groups according to the presence or absence of PPI. METHODS: This single-centre, retrospective, observational study examined data from MEV and SEV groups comprising 92 and 373 patients, respectively. The mean clinical follow-up was 2.5±1.7 years. Mortality information was obtained from the National Institutes of Health Information and Statistics. RESULTS: Baseline characteristics were comparable between the groups. The log-rank test showed higher cardiovascular mortality in the MEV group (p=0.042; the relative risk (RR) 1.594 (95% CI 1.013 to 2.508)). The Cox proportional hazards model identified MEV implantation as an independent predictor of cardiovascular mortality. The rate of PPI was twice as high in the MEV vs SEV group (33.7% vs 16.1%; p<0.001). We compared the survival of both groups according to the presence or absence of PPI and found higher mortality in the MEV group without PPI versus the SEV group without PPI (p=0.007; RR 2.156 (95% CI 1.213 to 3.831)). Survival did not differ in the groups with PPI. CONCLUSIONS: A higher mid-term cardiovascular mortality rate was observed with MEV versus SEV implants. Comparing both groups according to the presence or absence of PPI, we observed a higher mortality risk in patients with MEV without PPI than in SEV without PPI. In contrast, mortality did not differ between the groups when PPI was implanted.