Changes In Cardiac Electrophysiology Research Articles

Compound Yuye Decoction protects diabetic rats against cardiomyopathy by inhibiting myocardial apoptosis and inflammation via regulating the PI3K/Akt signaling pathway

To explore the therapeutic mechanism of compound Yuye Decoction against diabetic cardiomyopathy (DCM). Drugbank, Gene Cards, OMIM and PharmGKb databases were used to obtain DCM-related targets, and the core targets were identified and functionally annotated by protein-protein interaction network analysis followed by GO and KEGG enrichment analysis. The "Traditional Chinese Medicine-Key Component-Key Target-Key Pathway" network was constructed using Cytoscape 3.9.1, and molecular docking was carried out for the key components and the core targets. In the animal experiment, Wistar rat models of DCM were treated with normal saline or Yuye Decoction by gavage at low (0.29 g/kg) and high (1.15 g/kg) doses for 8 weeks, and the changes in cardiac electrophysiology and histopathology were evaluated. The changes in serum levels of LDH, CK, and CK-MB were examined, and myocardial expressions of PI3K, P-PI3K, Akt, P-AKT, BAX, IL-6, and TNF-α were detected using Western blotting. We identified 61 active compounds in Yuye Decoction with 1057 targets, 3682 DCM-related disease targets, and 551 common targets between them. Enrichment of the core targets suggested that apoptosis, inflammation and the PI3K/Akt pathways were the key signaling pathways for DCM treatment. Molecular docking studies showed that the active components in Yuye Decoction including gold amidohydroxyethyl ester and kaempferol had strong binding activities with AKT1 and PIK3R1. In DCM rat models, treatment with Yuye Decoction significantly alleviated myocardial pathologies, reduced serum levels of LDH, CK and CK-MB, lowered myocardial expressions of BAX, IL-6 and TNF-α, and increased the expressions of P-PI3K and P-AKT. The therapeutic effect of compound Yuye Decoction against DCM is mediated by its multiple active components that act on multiple targets and pathways to inhibit cardiomyocyte apoptosis and inflammatory response by regulating the PI3K/Akt signaling pathway.

Feeding behavior modifies the circadian variation in RR and QT intervals by distinct mechanisms in mice.

Rhythmic feeding behavior is critical for regulating phase and amplitude in the ≈24-h variation of heart rate (RR intervals), ventricular repolarization (QT intervals), and core body temperature in mice. We hypothesized changes in cardiac electrophysiology associated with feeding behavior were secondary to changes in core body temperature. Telemetry was used to record electrocardiograms and core body temperature in mice during ad libitum-fed conditions and after inverting normal feeding behavior by restricting food access to the light cycle. Light cycle-restricted feeding modified the phase and amplitude of 24-h rhythms in RR and QT intervals, and core body temperature to realign with the new feeding time. Changes in core body temperature alone could not account for changes in phase and amplitude in the ≈24-h variation of the RR intervals. Heart rate variability analysis and inhibiting β-adrenergic and muscarinic receptors suggested that changes in the phase and amplitude of 24-h rhythms in RR intervals were secondary to changes in autonomic signaling. In contrast, changes in QT intervals closely mirrored changes in core body temperature. Studies at thermoneutrality confirmed that the daily variation in QT interval, but not RR interval, primarily reflected daily changes in core body temperature (even in ad libitum-fed conditions). Correcting the QT interval for differences in core body temperature helped unmask QT interval prolongation after starting light cycle-restricted feeding and in a mouse model of long QT syndrome. We conclude feeding behavior alters autonomic signaling and core body temperature to regulate phase and amplitude in RR and QT intervals, respectively.NEW & NOTEWORTHY We used time-restricted feeding and thermoneutrality to demonstrate that different mechanisms regulate the 24-h rhythms in heart rate and ventricular repolarization. The daily rhythm in heart rate reflects changes in autonomic input, whereas daily rhythms in ventricular repolarization reflect changes in core body temperature. This novel finding has major implications for understanding 24-h rhythms in mouse cardiac electrophysiology, arrhythmia susceptibility in transgenic mouse models, and interpretability of cardiac electrophysiological data acquired in thermoneutrality.

Influence of age and sex on physical, cardiac electrical and functional alterations in progressive hyperoxia treatment: A time course study in a murine model

Oxygen supplementation is a widely used treatment for ICU patients. However, it can lead to hyperoxia, which in turn can result in oxidative stress, cardiac remodeling, and even mortality. This paper expands upon previous research conducted by our lab to establish time-dependent cardiac changes under hyperoxia. In this study, both young and aged mice (male and female) underwent 72 h of hyperoxia exposure and were monitored at 24-hour intervals for cardiac electrophysiological and functional parameters using ECG and electrocardiogram data. Our analysis showed that young male mice experienced significant weight loss as well as significant lung edema by 48 h. Although young male mice were highly susceptible to physical changes, they were resistant to early cardiac functional and electrophysiological changes compared to the other groups. Both young and aged female and aged males developed functional impairments by 24 h of hyperoxia exposure. Furthermore, sex and age differences were noted in the onset of electrophysiological changes. While some groups could resist early cardiac remodeling, our data suggests that 72 h of hyperoxia exposure is sufficient to induce significant cardiac remodeling across all age and sex groups. Our data establishes that time-dependent cardiac changes due to oxygen supplementation can have devastating consequences even with short exposure periods. These findings can aid in developing clinical practices for individuals admitted to the ICU by elucidating the impact of aging, sex, and length of stay under mechanical ventilation to limit hyperoxia-induced cardiac remodeling.

Dapagliflozin Pretreatment Prevents Cardiac Electrophysiological Changes in a Diet and Streptozotocin Induction of Type 2 Diabetes in Rats: A Potential New First-Line?

Dapagliflozin exerts cardioprotective effects in Type 2 Diabetes Mellitus (T2DM). However, whether these effects prevent electrocardiographic changes associated with T2DM altogether remain unknown. Our aim was to investigate the prophylactic effect of dapagliflozin pretreatment on the rat ECG using a high-fat, high-fructose (HFHf) diet and a low dose streptozotocin (STZ) model of T2DM. Twenty-five (25) rats were randomized into five (5) groups: normal control receiving a normal diet while the other groups received an 8-week HFHf and 40mg/kg STZ on day 42, and either: saline for the diabetic control (1 mg/kg/d), low dose (1.0 mg/kg/d) and high dose dapagliflozin (1.6 mg/kg/d), or metformin (250 mg/kg/d). Oral glucose tolerance (OGT), electrocardiograms (ECGs), paracardial adipose mass, and left ventricular fibrosis were determined. Data were analyzed using GraphPad version 9.0.0.121, with the level of significance at p < 0.05. Compared to the diabetic control group, a high dose of dapagliflozin preserved the OGT (p = 0.0001), QRS-duration (p = 0.0263), QT-interval (p = 0.0399), and QTc intervals (p = 0.0463). Furthermore, the high dose dapagliflozin group had the lowest paracardial adipose mass (p = 0.0104) and fibrotic area (p = 0.0001). In contrast, while metformin showed favorable effects on OGT (p = 0.0025), paracardial adiposity (p = 0.0153) and ventricular fibrosis (p = 0.0291), it did not demonstrate significant antiarrhythmic effects. Pretreatment with higher doses of Dapagliflozin exhibits prophylactic cardioprotective characteristics against diabetic cardiomyopathy that include antifibrotic and antiarrhythmic qualities. This suggests that higher doses of dapagliflozin could be a more effective initial therapeutic option in T2DM.

Food-grade titanium dioxide (E171) and zinc oxide nanoparticles induce mitochondrial permeability and cardiac damage after oral exposure in rats

Food-grade titanium dioxide (E171) and zinc oxide nanoparticles (ZnO NPs) are found in diverse products for human use. E171 is used as whitening agent in food and cosmetics, and ZnO NPs in food packaging. Their potential multi-organ toxicity has raised concerns on their safety. Since mitochondrial dysfunction is a key aspect of cardio-pathologies, here, we evaluate the effect of chronic exposure to E171 and ZnO NPs in rats on cardiac mitochondria. Changes in cardiac electrophysiology and body weight were measured. E171 reduced body weight more than 10% after 5 weeks. Both E171 and ZnO NPs increased systolic blood pressure (SBP) from 110–120 to 120–140 mmHg after 45 days of treatment. Both NPs altered the mitochondrial permeability transition pore (mPTP), reducing calcium requirement for permeability by 60% and 93% in E171- and ZnO NPs-exposed rats, respectively. Treatments also affected conformational state of adenine nucleotide translocase (ANT). E171 reduced the binding of EMA to Cys 159 in 30% and ZnO NPs in 57%. Mitochondrial aconitase activity was reduced by roughly 50% with both NPs, indicating oxidative stress. Transmission electron microscopy (TEM) revealed changes in mitochondrial morphology including sarcomere discontinuity, edema, and hypertrophy in rats exposed to both NPs. In conclusion, chronic oral exposure to NPs induces functional and morphological damage in cardiac mitochondria, with ZnO NPs being more toxic than E171, possibly due to their dissociation in free Zn2+ ion form. Therefore, chronic intake of these food additives could increase risk of cardiovascular disease.

Measuring of cardiac electrical system function among salbutamol inhaled children – A cohort study

Background: Salbutamol is widely recognized as an effective rescue therapy for acute asthma attacks. However, the usage of inhaled β2-agonists, including salbutamol, has been related to an amplified hazard of cardiovascular disease, as suggested by several studies. Despite this association, there is an absence of sufficient facts regarding the cardiac electrophysiological possessions of inhaled β2-agonists in children. Aim and Objectives: The present study was to explore the cardiac electrophysiological effects of inhaled salbutamol in children. By examining the specific impact of salbutamol on cardiac electrophysiology, this study aimed to contribute valuable insights into the potential cardiovascular effects of inhaled β2-agonists in the pediatric population. Materials and Methods: This cohort study involved 130 individuals of both sexes, levels in age from 1 to 12 years. Salbutamol nebulization was administered to the children at a dosage of 0.15 mg/kg/dose, mixed with normal saline at a ratio of 1:3, using a nebulizer. Cardiac parameters including heart rate, T axis, P axis, QTc interval, QRS axis, QRS interval, and PR interval were recorded before and after nebulization using a computerized electrocardiogram (ECG). Results: The outcomes of the work presented that following nebulization, there was a major rise in heart rate and a notable decline in the PR interval, T axis, and P axis. However, no analytical significant deviations were observed in the QRS axis, QTc interval, and QRS interval. Conclusion: The study demonstrates that within a time frame of 5–15 min after inhaling a single standard dose of salbutamol, significant changes in the ECG parameters occur. These changes in cardiac electrophysiology may contribute to an amplified occurrence of arrhythmias in some patients getting salbutamol treatment. It is important to note that the frequent use of high doses of salbutamol for asthmatic exacerbations may potentially lead to more severe cardiac adverse effects.

Six-Lead Electrocardiography Enables Identification of Rhythm and Conduction Anomalies of Patients in the Telemedicine-Based, Hospital-at-Home Setting: A Prospective Validation Study.

The hospital-at-home (HAH) model is a viable alternative for conventional in-hospital stays worldwide. Serum electrolyte abnormalities are common in acute patients, especially in those with many comorbidities. Pathologic changes in cardiac electrophysiology pose a potential risk during HAH stays. Periodical electrocardiogram (ECG) tracing is therefore advised, but few studies have evaluated the accuracy and efficiency of compact, self-activated ECG devices in HAH settings. This study aimed to evaluate the reliability of such a device in comparison with a standard 12-lead ECG. We prospectively recruited consecutive patients admitted to the Sheba Beyond Virtual Hospital, in the HAH department, during a 3-month duration. Each patient underwent a 12-lead ECG recording using the legacy device and a consecutive recording by a compact six-lead device. Baseline patient characteristics during hospitalization were collected. The level of agreement between devices was measured by Cohen's kappa coefficient for inter-rater reliability (Ϗ). Fifty patients were included in the study (median age 80 years, IQR 14). In total, 26 (52%) had electrolyte disturbances. Abnormal D-dimer values were observed in 33 (66%) patients, and 12 (24%) patients had elevated troponin values. We found a level of 94.5% raw agreement between devices with regards to nine of the options included in the automatic read-out of the legacy device. The calculated Ϗ was 0.72, classified as a substantial consensus. The rate of raw consensus regarding the ECG intervals' measurement (PR, RR, and QT) was 78.5%, and the calculated Ϗ was 0.42, corresponding to a moderate level of agreement. This is the first report to our knowledge regarding the feasibility of using a compact, six-lead ECG device in the setting of an HAH to be safe and bearing satisfying agreement level with a legacy, 12-lead ECG device, enabling quick, accessible arrythmia detection in this setting. Our findings bear a promise to the future development of telemedicine-based hospital-at-home methodology.

Protective effects of limb remote ischemic per-conditioning on the heart injury induced by renal ischemic-reperfusion through the interaction of the apelin with the RAS/iNOS pathway.

Remote ischemic conditioning upregulates endogenous protective pathways in response to ischemia-reperfusion injury. This study tested the hypothesis that limb remote ischemic per- conditioning (RIPerC) exerts cardioprotective effects via the renin-angiotensin system (RAS)/inducible nitric oxide synthase (iNOS)/apelin pathway. Renal ischemia-reperfusion injury (I/R) was induced by bilateral occlusion of the renal pedicles for 60 minutes, followed by 24 hours of reperfusion; sham-operated rats served as controls. RIPerC was induced by four cycles (5 minutes) of limb ischemia-reperfusion along with bilateral renal ischemia. The functional disturbance was evaluated by renal (BUN and creatinine) and cardiac (troponin I and lactate dehydrogenase) injury biomarkers. Renal I/R injury increased renal and cardiac injury biomarkers that were reduced in the RIPerC group. Histopathological findings of the kidney and heart were also suggestive of amelioration injury-induced changes in the RIPerC group. Assessment of cardiac electrophysiology revealed that RIPerC ameliorated the decline in P wave duration without significantly affecting other cardiac electrophysiological changes. Further, renal I/R injury increased the plasma (322.40±34.01 IU/L), renal (8.27±1.10 mIU/mg of Protein), and cardiac (68.28±10.28 mIU/mg of protein) angiotensin-converting enzyme (ACE) activities in association with elevations in the plasma and urine nitrite (25.47±2.01 & 16.62±3.05 μmol/L) and nitrate (15.47±1.33 & 5.01±0.96 μmol/L) levels; these changes were reversed by RIPerC. Further, renal ischemia-reperfusion injury significantly (P=0.047) decreased the renal (but not cardiac) apelin mRNA expression, while renal and cardiac ACE2 (P<0.05) and iNOS (P=0.043) mRNA expressions were significantly increased compared to the sham group; these effects were largely reversed by RIPerC. Our results indicated that RIPerC protects the heart against renal ischemia- reperfusion injury, likely via interaction of the apelin with the RAS/iNOS pathway.

Transient cardiac electrophysiological changes in a rat model of subarachnoid haemorrhage: a brain-heart interaction.

Subarachnoid haemorrhage (SAH) is one of the causes of sudden cardiac death (SCD). However, the time course of ventricular arrhythmias and potential mechanisms responsible for this effect after SAH remain unknown. This study aims to investigate the effect of SAH on ventricular electrophysiological changes and its potential mechanisms in long-term phase. We examined the ventricular electrophysiological remodelling and potential mechanisms in a Sprague Dawley rat model of SAH at six time points (baseline, and Days 1, 3, 7, 14 and 28) and explored the potential mechanisms. We measured the ventricular effective refractory period (ERP), ventricular fibrillation threshold (VFT) and left stellate ganglion (LSG) activity at different time points before and after SAH. We also detected neuropeptide Y (NPY) levels in plasma and myocardial tissues by enzyme-linked immunosorbent assay, and quantified NPY 1 receptor (NPY1R) protein and mRNA expression levels by western blotting and quantitative real-time reverse transcription-polymerase chain reaction, respectively. Subarachnoid haemorrhage gradually prolonged QTc intervals, shortened ventricular ERP and reduced VFT during the acute phase, peaking at Day 3. However, no significant changes were observed from Days 14 to 28 compared to Day 0. Subarachnoid haemorrhage gradually increased LSG activity, increased NPY concentrations and up-regulated NPY1R expression in the acute phase of SAH, peaking at Day 3. However, no significant variations were found from Days 14 to 28 compared to Day 0. Subarachnoid haemorrhage increases the transient susceptibility of VAs in the acute phase, and the underlying mechanisms for this response included increased sympathetic activity and up-regulated NPY1R expression.

Abstract 15535: A Case of Suspected Menstruation Induced QTc Prolongation Leading to Torsades De Pointes

Estrogen is known to produce changes in cardiac electrophysiology specifically in premenopausal women, increasing the risk of arrhythmias. We report a case of Torsades de Pointes (TdP) in a young premenopausal female. A 25-year-old female with a history of anxiety presented to the emergency room (ED) with several days of vomiting. While in the ED, she had an unwitnessed syncopal event, and was found to be in pulseless ventricular fibrillation (V-Fib) . She required one defibrillation to obtain return of spontaneous circulation (ROSC). Initial work up showed calcium 7.6 mg/dl, phosphorous 1.1 mg/dl, magnesium 2.4 mg/dl, potassium 4.0 mg/dl. Remainder of electrolytes were normal. Toxicology screen was positive for cannabinoids. Post ROSC EKG showed sinus tachycardia at a rate of 103bpm with a prolonged QTc of 531ms. Patient was not on any medications outpatient. On further discussion, patient reported no prior history of syncopal episodes, palpitations, and denied any family history of sudden cardiac death. She did report she was presently on her menses. Shortly after admission, she had recurrent polymorphic ventricular tachycardia which degenerated to TdP. She was loaded with magnesium. Echocardiogram showed an ejection fraction (EF) of 35-39% and global hypokinesis. Diagnostic left heart catheterization was performed revealing clean coronaries. Cardiac MRI revealed EF of 43% without any late gadolinium enhancement. Her QTc remained prolonged even with electrolyte normalization. She underwent successful ICD placement and remained event free during the remainder of the hospital course. She will undergo genetic work up for long QT syndrome. Female sex hormones, specifically estrogen, have been described in literature as pro-arrhythmic given its effects on QT prolongation and ion gated channels. Prior cases of menstruation dependent arrhythmias have speculated that the abrupt reduction in estradiol prior to menstruation is associated with increased cyclic adenosine monophosphate dependent arrhythmogenicity. This case highlights the multifactorial etiology of sudden V-Fib arrest in a young female, and the importance of understanding the role that sex hormones play in the underlying pathogenesis.

Changes in heart rate variability of healthy subjects shortly exposed to printing shop particles and the effect of air purifier intervention

Particulate matter (PM) released by printers may cause airway inflammation and cardiac electrophysiological changes. We conducted a two-stage crossover study to examine the association between short-term exposure to printing shop particles (PSPs) and the heart rate variability (HRV) among healthy volunteers, as well as to evaluate the effect of air purifier intervention. The on-site assessments of PSPs and individual HRV parameters of the volunteers were used to analyze the influence of size-fractionated PSPs and air purifier intervention on HRV at different lag times after PSPs exposure (0 min, 5 min, 15 min, and 30 min) by using the linear mixed-effects models. We observed that changes in 6 HRV parameters were associated with particle mass concentration (PMC) of PSPs, and changes in 8 HRV parameters were associated with particle number concentration (PNC) of PSPs. The sensitive HRV parameters were the square root of the mean of the sum of the squares of differences between adjacent NN intervals (rMSSD), NN50 count divided by the total number of all NN intervals (pNN50), normalized high frequency power (nHF), very high frequency power (VHF), normalized low frequency power (nLF), and the ratio of low frequency power to high frequency power (LF/HF). Most HRV parameters exhibited the strongest effect associated with PMC and PNC at a lag time of 30 min. The air purifier intervention markedly reduced the PNC and PMC of size-fractionated PSPs, enhanced 5 HRV parameters, and decreased the nLF and LF/HF. Our study suggests that short-term exposure to PSPs can affect HRV parameters, reflecting changes in cardiac autonomic nervous activity, and the use of an air purifier can reduce the concentration of PSPs and improve the autonomic nervous system activity of the exposed individuals.

Cardiac Electrophysiological Changes and Downregulated Connexin 43 Prompts Reperfusion Arrhythmias Induced by Hypothermic Ischemia-Reperfusion Injury in Isolated Rat Hearts.

The purpose of this study was to determine the utility of the monophasic action potential (MAP) changes as an arrhythmic biomarker in hypothermic ischemia-reperfusion. The hypothermic ischemia-reperfusion model was subjected to 60min of cardioplegic arrest while the isolated rat hearts were preserved with a multidose cold K-H solution at 4°C. During the reperfusion period, the heart's arrhythmia and monophasic action potential were also monitored. The myocardial damage was assessed using HE and TTC stains. Immunohistochemistry and Western blotting were used to assess the expression and distribution of Connexin 43 (Cx43) and Akt. Collectively, prolonged action potential durations, increased dispersion of repolarization, and downregulated and lateralized Cx43 all contribute to the derangement of electrical impulse propagation that may underlie arrhythmogenesis in the cold ischemic heart following cardioplegic arrest. MAP might be used as a biomarker for arrhythmias caused by hypothermic ischemia-reperfusion.

Microbeam Irradiation of the Beating Rodent Heart: An Ex Vivo Study of Acute and Subacute Effects on Cardiac Function

Microbeam radiation therapy (MRT) has shown several advantages compared with conventional broad-beam radiation therapy in small animal models, including a better preservation of normal tissue function and improved drug delivery based on a rapidly increased vascular permeability in the target region. Normal tissue tolerance is the limiting factor in clinical radiation therapy. Knowledge of the normal tissue tolerance of organs at risk is therefore a prerequisite in evaluating any new radiation therapy approach. With an irradiation target in the thoracic cavity, the heart would be the most important organ at risk. We used the ex vivo beating rodent heart in the Langendorff perfusion system at the synchrotron to administer microbeam irradiation (MBI) with a peak dose of 40 or 400 Gy. By continuously recording the electrocardiogram, the left ventricular pressure, and the aortic pressure before, during and after MBI, we were able to assess acute and subacute effects of MBI on electrophysiological and mechanical cardiac function. In addition, we analyzed histologic and ultrastructural sequelae caused by MBI. There were no significant changes in heart rate, heart rate variability, systolic increase of left ventricular pressure or aortic pressure. Moreover, the changes of heart rate, left ventricular pressure and aortic pressure by adding 10-5 mol/L norepinephrine to the perfusate, were also not significant between MBI and sham experiments. However, the rate-pressure product as a surrogate marker for maximum workload after MBI was significantly lower compared with sham-irradiated controls. On the structural level, no severe membranous, sarcomeric, mitochondrial or nuclear changes caused by MBI were detected by desmin immunohistochemistry and electron microscopy. With respect to acute and subacute toxicity, an MBI peak dose up to 400Gy did not result in severe changes in cardiac electrophysiology or mechanics.

Cardiac Electropharmacological Effects of Antidiarrheal Drug Loperamide and Its Antidote Naloxone in Anesthetized Guinea Pigs

Cardiac electropharmacological effects of an antidiarrheal drug loperamide and its antidote naloxone were assessed in isoflurane-anesthetized guinea pigs. Intravenous administration of loperamide at 0.01-0.1 mg/kg did not affect parameters of electrocardiogram (ECG) or monophasic action potential (MAP) of the right ventricle. Additional administration of loperamide at 1 mg/kg prolonged the QT interval and MAP duration of the ventricle accompanied with increments of the PQ interval and QRS width. The potency of loperamide for QT-interval prolongation was about 100-times lower than that of dofetilide, in spite that similar inhibitory effects on the human Ether-a-go-go Related Gene (hERG) K+ channels have been reported between loperamide and dofetilide, implying lower accessibility of loperamide to the K+ channels. Intravenous administration of naloxone at 0.003-0.3 mg/kg, which effectively inhibits µ-opioid receptors, did not affect ECG parameters including QT interval or MAP duration. Furthermore, the loperamide-induced cardiac electrophysiological changes were not modified in the presence of naloxone at 0.3 mg/kg. These results suggest that loperamide has a potential to delay cardiac conduction and repolarization in the in vivo condition. Since naloxone did not modify ECG parameters and loperamide-induced ECG changes, naloxone is confirmed to possess acceptable cardiac safety when used as an antidote.

Timing of food intake in mice unmasks a role for the cardiomyocyte circadian clock mechanism in limiting QT-interval prolongation

ABSTRACT Cardiac electrophysiological studies demonstrate that restricting the feeding of mice to the light cycle (time restricted feeding or TRF) causes a pronounced change in heart rate and ventricular repolarization as measured by the RR- and QT-interval, respectively. TRF slows heart rate and shifts the peak (acrophase) of the day/night rhythms in the RR- and QT-intervals from the light to the dark cycle. This study tested the hypothesis that these changes in cardiac electrophysiology are driven by the cardiomyocyte circadian clock mechanism. We determined the impact that TRF had on RR- and QT-intervals in control mice or mice that had the cardiomyocyte circadian clock mechanism disrupted by inducing the deletion of Bmal1 in adult cardiomyocytes (iCSΔBmal1 −/− mice). In control and iCSΔBmal1 −/− mice, TRF increased the RR-intervals measured during the dark cycle and shifted the acrophase of the day/night rhythm in the RR-interval from the light to the dark cycle. Compared to control mice, TRF caused a larger prolongation of the QT-interval measured from iCSΔBmal1 −/− mice during the dark cycle. The larger QT-interval prolongation in the iCSΔBmal1 −/− mice caused an increased mean and amplitude in the day/night rhythm of the QT-interval. There was not a difference in the TRF-induced shift in the day/night rhythm of the QT-interval measured from control or iCSΔBmal1 −/− mice. We conclude that the cardiomyocyte circadian clock does not drive the changes in heart rate or ventricular repolarization with TRF. However, TRF unmasks an important role for the cardiomyocyte circadian clock to prevent excessive QT-interval prolongation, especially at slow heart rates.

Transcription factor Meis1 act as a new regulator of ischemic arrhythmias in mice

IntroductionThe principal voltage-gated Na+ channel, NaV1.5 governs heart excitability and conduction. NaV1.5 dysregulation is responsible for ventricular arrhythmias and subsequent sudden cardiac death (SCD) in post-infarct hearts. The transcription factor Meis1 performs a significant role in determining differentiation fate and regenerative capability of cardiomyocytes. However, the functions of Meis1 in ischemic arrhythmias following myocardial infarction (MI) are still largely undefined. ObjectivesHere we aimed to study whether Meis1 could act as a key regulator to mediate cardiac Na+ channel and its underlying mechanisms. MethodsHeart-specific Meis1 overexpression was established by AAV9 virus injection in C57BL/6 mice. The QRS duration, the incidence of ventricular arrhythmias and cardiac conduction velocity were evaluated by ECG, programmed electrical stimulation and optical mapping techniques respectively. The conventional patch clamp technique was performed to explore the INa characteristics of isolated mouse ventricular myocytes. In vitro, Meis1 was also overexpressed in hypoxic-treated neonatal cardiomyocytes. The analysis of immunoblotting and immunofluorescence were used to detect the changes in the expression of NaV1.5 in each group. ResultsWe found that forced expression of Meis1 rescued the prolongation of QRS complex, produced anti-arrhythmic activity and improved epicardial conduction velocity in infarcted mouse hearts. In terms of mechanisms, cardiac electrophysiological changes of MI mice can be ameliorated by the recovery of Meis1, which is characterized by the restoration of INa current density and NaV1.5 expression level of cardiomyocytes in the marginal zone of MI mouse hearts. Furthermore, in vitro studies showed that Meis1 was also able to rescue hypoxia-induced decreased expression and dysfunction of NaV1.5 in ventricular myocytes. We further revealed that E3 ubiquitin ligase CDC20 led to the ubiquitination and degradation of Meis1, which blocked the transcriptional regulation of SCN5A by Meis1 and ultimately led to the electrophysiological remodeling in ischemic-hypoxic cardiomyocytes. ConclusionCDC20 mediates ubiquitination of Meis1 to govern the transcription of SCN5A and cardiac electrical conduction in mouse cardiomyocytes. This finding uncovers a new mechanism of NaV1.5 dysregulation in infarcted heart, and provides new therapeutic strategies for malignant arrhythmias and sudden cardiac death following MI.

MiR133b Microinjection during Early Development Targets Transcripts of Cardiomyocyte Ion Channels and Induces Oil-like Cardiotoxicity in Zebrafish (Danio rerio) Embryos.

Previous studies have shown that altered expression of a family of small noncoding RNAs (microRNAs, or miRs) regulates the expression of downstream mRNAs and is associated with diseases and developmental disorders. miR133b is highly expressed in mammalian cardiac and skeletal muscle, and aberrant expression is associated with cardiac disorders and electrophysiological changes in cardiomyocytes. Similarly, cardiac dysfunction has been observed in early life-stage mahi-mahi (Coryphaena hippurus) exposed to crude oil, a phenotype that has been associated with an upregulation of miR133b as well as subsequent downregulation of a delayed rectifier potassium channel (IKr) and calcium signaling genes that are important for proper heart development during embryogenesis. To examine the potential role of miR133b in oil-induced early life-stage cardiotoxicity in fish, cleavage-stage zebrafish (Danio rerio) embryos were either (1) microinjected with ∼3 nL of negative control miR (75 μM) or miR133b (75 μM) or (2) exposed to a treatment solution containing 5 μM benzo(a)pyrene (BaP), a model polycyclic aromatic hydrocarbon, as a positive control. At 72 h post fertilization (hpf), miR133b-injected fish exhibited BaP-like cardiovascular malformations, including a significantly increased pericardial area relative to negative control miR-injected embryos, as well as a significantly reduced eye area. qPCR revealed that miR133b microinjection decreased the abundance of cardiac-specific IKr kcnh6 at 5 hpf, which may contribute to action potential elongation in oil-exposed cardiomyocytes. Additionally, ryanodine receptor 2, a crucial calcium receptor in the sarcoplasmic reticulum, was also downregulated by miR133b. These results indicate that an oil-induced increase in miR133b may contribute to cardiac abnormalities in oil-exposed fish by targeting cardiac-specific genes essential for proper heart development.

Translational investigation of electrophysiology in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) patients are at increased risk of ventricular arrhythmias and sudden cardiac death, which can occur even in the absence of structural changes of the heart. HCM mouse models suggest mutations in myofilament components to affect Ca2+ homeostasis and thereby favor arrhythmia development. Additionally, some of them show indications of pro-arrhythmic changes in cardiac electrophysiology. In this study, we explored arrhythmia mechanisms in mice carrying a HCM mutation in Mybpc3 (Mybpc3-KI) and tested the translatability of our findings in human engineered heart tissues (EHTs) derived from CRISPR/Cas9-generated homozygous MYBPC3 mutant (MYBPC3hom) in induced pluripotent stem cells (iPSC) and to left ventricular septum samples obtained from HCM patients.We observed higher arrhythmia susceptibility in contractility measurements of field-stimulated intact cardiomyocytes and ventricular muscle strips as well as in electromyogram recordings of Langendorff-perfused hearts from adult Mybpc3-KI mice than in wild-type (WT) controls. The latter only occurred in homozygous (Hom-KI) but not in heterozygous (Het-KI) mouse hearts. Both Het- and Hom-KI are known to display pro-arrhythmic increased Ca2+ myofilament sensitivity as a direct consequence of the mutation. In the electrophysiological characterization of the model, we observed smaller repolarizing K+ currents in single cell patch clamp, longer ventricular action potentials in sharp microelectrode recordings and longer ventricular refractory periods in Langendorff-perfused hearts in Hom-KI, but not Het-KI. Interestingly, reduced K+ channel subunit transcript levels and prolonged action potentials were already detectable in newborn, pre-hypertrophic Hom-KI mice. Human iPSC-derived MYBPC3hom EHTs, which genetically mimicked the Hom-KI mice, did exhibit lower mutant mRNA and protein levels, lower force, beating frequency and relaxation time, but no significant alteration of the force-Ca2+ relation in skinned EHTs. Furthermore, MYBPC3hom EHTs did show higher spontaneous arrhythmic behavior, whereas action potentials measured by sharp microelectrode did not differ to isogenic controls. Action potentials measured in septal myectomy samples did not differ between patients with HCM and patients with aortic stenosis, except for the only sample with a MYBPC3 mutation.The data demonstrate that increased myofilament Ca2+ sensitivity is not sufficient to induce arrhythmias in the Mybpc3-KI mouse model and suggest that reduced K+ currents can be a pro-arrhythmic trigger in Hom-KI mice, probably already in early disease stages. However, neither data from EHTs nor from left ventricular samples indicate relevant reduction of K+ currents in human HCM. Therefore, our study highlights the species difference between mouse and human and emphasizes the importance of research in human samples and human-like models.

Structural and Electrophysiological Changes in a Model of Cardiotoxicity Induced by Anthracycline Combined With Trastuzumab.

BackgroundCombined treatment with anthracyclines (e.g., doxorubicin; Dox) and trastuzumab (Trz), a humanized anti-human epidermal growth factor receptor 2 (HER2; ErbB2) antibody, in patients with HER2-positive cancer is limited by cardiotoxicity, as manifested by contractile dysfunction and arrhythmia. The respective roles of the two agents in the cardiotoxicity of the combined therapy are incompletely understood.ObjectiveTo assess cardiac performance, T-tubule organization, electrophysiological changes and intracellular Ca2+ handling in cardiac myocytes (CMs) using an in vivo rat model of Dox/Trz-related cardiotoxicity.Methods and ResultsAdult rats received 6 doses of either Dox or Trz, or the two agents sequentially. Dox-mediated left ventricular (LV) dysfunction was aggravated by Trz administration. Dox treatment, but not Trz, induced T-tubule disarray. Moreover, Dox, but not Trz monotherapy, induced prolonged action potential duration (APD), increased incidence of delayed afterdepolarizations (DADs) and beat-to-beat variability of repolarization (BVR), and slower Ca2+ transient decay. Although APD, DADs, BVR and Ca2+ transient decay recovered over time after the cessation of Dox treatment, subsequent Trz administration exacerbated these abnormalities. Trz, but not Dox, reduced Ca2+ transient amplitude and SR Ca2+ content, although only Dox treatment was associated with SERCA downregulation. Finally, Dox treatment increased Ca2+ spark frequency, resting Ca2+ waves, sarcoplasmic reticulum (SR) Ca2+ leak, and long-lasting Ca2+ release events (so-called Ca2+ “embers”), partially reproduced by Trz treatment.ConclusionThese results suggest that in vivo Dox but not Trz administration causes T-tubule disarray and pronounced changes in electrical activity of CMs. While adaptive changes may account for normal AP shape and reduced DADs late after Dox administration, subsequent Trz administration interferes with such adaptive changes. Intracellular Ca2+ handling was differently affected by Dox and Trz treatment, leading to SR instability in both cases. These findings illustrate the specific roles of Dox and Trz, and their interactions in cardiotoxicity and arrhythmogenicity.

Statistical and entropy-based features can efficiently detect the short-term effect of caffeinated coffee on the cardiac physiology

An electrocardiograph (ECG) is the most effective way to find the changes in cardiac physiology. It is the representation of the electrical activities of the heart and can be understood using different waves, peaks, and intervals. Several factors affect the functionality of the heart that includes lifestyle, stress, daily diet, etc. Coffee, the most widely consumed beverage in the world, is an integral part of everyday life. Caffeine, the prime constituent of coffee, is believed to affect the heart physiology. However, the effect of consumption of caffeinated coffee on the cardiac electrophysiological changes, estimated from the morphological features (e.g., peaks, waves, intervals), is controversial. This has led to the exploration of other feature extraction methods to detect the changes accurately. In recent years, the statistical and entropy-based features have emerged as an efficient method to extract hidden patterns from the ECG signal. These features have been successfully explored in arrhythmia detection, noise removal, biometric identification, etc. Hence, we hypothesized that the statistical and entropy-based features could be efficiently used in detecting the changes in the ECG signal after coffee consumption. For the evaluation of our hypothesis, 5-sec ECG segments were extracted from the recorded ECG signals from 14 volunteers in pre- and post-coffee consumption conditions. From each segment, the statistical and entropy-based features were computed. Then, the statistically significant features were extracted using Wilcoxon's signed-rank test. The results showed a significant difference in the statistical parameters post-consumption of coffee. Further, to validate our findings, several machine learning models were used for the automatic detection of these changes, and the results show the highest classification accuracy of 75%. The results support our hypothesis that the statistical and entropy-based features can efficiently detect the changes in the ECG signals, which is induced by coffee consumption. The findings of the proposed hypothesis may open up a new research arena of detecting the presence of different drugs and alcohol in the human body by analyzing the ECG signals.