Atrial natriuretic peptide (ANP), via its vasodilating and diuretic effects, has an important physiological role in the maintenance of arterial blood pressure and volume. Its guanylyl cyclase-A ...(GC-A) receptor is highly expressed in vascular endothelium, but the functional relevance of this is controversial. To dissect the endothelium-mediated actions of ANP in vivo, we inactivated the GC-A gene selectively in endothelial cells by homologous loxP/Tie2-Cre-mediated recombination. Notably, despite full preservation of the direct vasodilating effects of ANP, mice with endothelium-restricted deletion of the GC-A gene (EC GC-A KO) exhibited significant arterial hypertension and cardiac hypertrophy. Echocardiographic and Doppler flow evaluations together with the Evan's blue dilution technique showed that the total plasma volume of EC GC-A KO mice was increased by 11-13%, even under conditions of normal dietary salt intake. Infusion of ANP caused immediate increases in hematocrit in control but not in EC GC-A KO mice, which indicated that ablation of endothelial GC-A completely prevented the acute contraction of intravascular volume produced by ANP. Furthermore, intravenous ANP acutely enhanced the rate of clearance of radio-iodinated albumin from the circulatory system in control but not in EC GC-A KO mice. We conclude that GC-A-mediated increases in endothelial permeability are critically involved in the hypovolemic, hypotensive actions of ANP.
Atrial fibrillation (AF) is the arrhythmia most commonly diagnosed in clinical practice. It is associated with significant morbidity and mortality. Prevalence of AF and complications of AF, estimated ...by hospitalisations, have increased dramatically in the last decade. Being able to predict AF would allow tailoring of management strategies and a focus on primary or secondary prevention. Models predicting recurrent AF would have particular clinical use for the selection of rhythm control therapy. There are existing prognostic models which combine several predictors or risk factors to generate an individualised estimate of risk of AF. The aim of this systematic review is to summarise and compare model performance measures and predictive accuracy across different models and populations at risk of developing incident or recurrent AF.
Methods tailored to systematic reviews of prognostic models will be used for study identification, risk of bias assessment and synthesis. Studies will be eligible for inclusion where they report an internally or externally validated model. The quality of studies reporting a prognostic model will be assessed using the Prediction Study Risk Of Bias Assessment Tool (PROBAST). Studies will be narratively described and included variables and predictive accuracy compared across different models and populations. Meta-analysis of model performance measures for models validated in similar populations will be considered where possible.
To the best of our knowledge, this will be the first systematic review to collate evidence from all studies reporting on validated prognostic models, or on the impact of such models, in any population at risk of incident or recurrent AF. The review may identify models which are suitable for impact assessment in clinical practice. Should gaps in the evidence be identified, research recommendations relating to model development, validation or impact assessment will be made. Findings will be considered in the context of any models already used in clinical practice, and the extent to which these have been validated.
PROSPERO ( CRD42018111649 ).
Patients with long QT syndrome (LQTS) are at increased risk not only for ventricular arrhythmias but also for atrial pathology including atrial fibrillation (AF). Some patients with "lone" AF carry ...Na(+)-channel mutations.
The purpose of this study was to determine the mechanisms underlying atrial pathology in LQTS.
In mice with a heterozygous knock-in long QT syndrome type 3 (LQT3) mutant of the cardiac Na(+) channel (ΔKPQ-SCN5A) and wild-type (WT) littermates, atrial size, function, and electrophysiologic parameters were measured in intact Langendorff-perfused hearts, and histologic analysis was performed.
Atrial action potential duration, effective refractory period, cycle length, and PQ interval were prolonged in ΔKPQ-SCN5A hearts (all P < .05). Flecainide (1 μM) reversed atrial action potential duration prolongation and induced postrepolarization refractoriness (P < .05). Arrhythmias were infrequent during regular rapid atrial rate in both WT and ΔKPQ-SCN5A but were inducible in 15 (38%) of 40 ΔKPQ-SCN5A and 8 (29%) of 28 WT mice upon extrastimulation. Pacing protocols generating rapid alterations in rate provoked atrial extrasystoles and arrhythmias in 6 (66%) of 9 ΔKPQ-SCN5A but in 0 (0%) of 6 WT mice (P < .05). Atrial diameter was increased by nearly 10% in ΔKPQ-SCN5A mice > 5 months old without increase in fibrotic tissue.
Murine hearts bearing an LQT3 mutation show abnormalities in atrial electrophysiology and subtle changes in atrial dimension, including an atrial arrhythmogenic phenotype on provocation. These results support clinical data suggesting that LQTS mutations can cause atrial pathology and arrhythmogenesis and indicate that murine sodium channel LQTS models may be useful for exploring underlying mechanisms.
Popeye domain containing (POPDC) proteins are predominantly expressed in the heart and skeletal muscle, modulating the K2P potassium channel TREK-1 in a cAMP-dependent manner. POPDC1 and POPDC2 ...variants cause cardiac conduction disorders with or without muscular dystrophy. Searching for POPDC2-modulated ion channels using a functional co-expression screen in Xenopus oocytes, we found POPDC proteins to modulate the cardiac sodium channel Nav1.5. POPDC proteins downregulate Nav1.5 currents in a cAMP-dependent manner by reducing the surface expression of the channel. POPDC2 and Nav1.5 are both expressed in different regions of the murine heart and consistently POPDC2 co-immunoprecipitates with Nav1.5 from native cardiac tissue. Strikingly, the knock-down of popdc2 in embryonic zebrafish caused an increased upstroke velocity and overshoot of cardiac action potentials. The POPDC modulation of Nav1.5 provides a new mechanism to regulate cardiac sodium channel densities under sympathetic stimulation, which is likely to have a functional impact on cardiac physiology and inherited arrhythmias.
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•Popeye-domain-containing proteins (POPDC) modulate the cardiac sodium channel Nav1.5•POPDC2 modulates Nav1.5 surface expression and currents in a cAMP-dependent manner•Knock-down of popdc2 in embryonic zebrafish indicate altered sodium channel densities•Nav1.5 modulation might be relevant for sympathetic stimulation and arrhythmias
Biochemistry; Molecular biology; Physiology
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
ObjectivesProlonged ECG monitoring is clinically useful to detect unknown atrial fibrillation (AF) in stroke survivors. The diagnostic yield of prolonged ECG monitoring in other patient populations ...is less well characterised. We therefore studied the diagnostic yield of prolonged Holter ECG monitoring for AF in an unselected patient cohort referred from primary care or seen in a teaching hospital.MethodsWe analysed consecutive 7-day ECG recordings in unselected patients referred from different medical specialities and assessed AF detection rates by indication, age and comorbidities.ResultsSeven-day Holter ECGs (median monitoring 127.5 hours, IQR 116 to 152) were recorded in 476 patients (mean age 54.6 (SD 17.0) years, 55.9% female) without previously known AF, requested to evaluate palpitations (n=241), syncope (n=99), stroke or transient ischaemic attack (n=75), dizziness (n=29) or episodic chest pain (n=32). AF was newly detected in 42/476 (8.8%) patients. Oral anticoagulation was initiated in 40/42 (95.2%) patients with newly detected AF. Multivariate logistic regression, adjusted for age, sex and monitoring duration found four clinical parameters to be associated with newly detected AF: hypertension OR=2.54, (1.08 to 8.61) (adjusted OR (95% CI)), p=0.034; previous stroke or TIA OR=4.14 (1.81 to 13.01), p=0.001; left-sided valvular heart disease OR=5.07 (2.48 to 18.70), p<0.001 and palpitations OR=2.86, (1.33 to 10.44), p=0.015.ConclusionsOpen multispeciality access to prolonged ECG monitoring, for example, as part of integrated, cross-sector AF care, can accelerate diagnosis of AF and increase adequate use of oral anticoagulation, especially in older and symptomatic patients with comorbidities.
Macrolide antibiotics are known to have a different proarrhythmic potential in the presence of comparable QT prolongation in the surface ECG. Because the extent of QT prolongation has been used as a ...surrogate marker for cardiotoxicity, we aimed to study the different electrophysiological effects of the macrolide antibiotics erythromycin, clarithromycin, and azithromycin in a previously developed experimental model of proarrhythmia. In 37 Langendorff-perfused rabbit hearts, erythromycin (150-300 microM, n = 13) clarithromycin (150-300 microM, n = 13), and azithromycin (150-300 microM, n = 11) led to similar increases in QT interval and monophasic action potential (MAP) duration. In bradycardic (atrioventricular-blocked) hearts, eight simultaneously recorded epi- and endocardial MAPs demonstrated increased dispersion of repolarization in the presence of all three antibiotics. Erythromycin and clarithromycin led to early afterdepolarizations (EADs) and torsade de pointes (TdP) after lowering of potassium concentration. In the presence of azithromycin, no EAD or TdP occurred. Erythromycin and clarithromycin changed the MAP configuration to a triangular pattern, whereas azithromycin caused a rectangular pattern of MAP prolongation. In 13 additional hearts, 150 microM azithromycin was administered after previous treatment with 300 microM erythromycin and suppressed TdP provoked by erythromycin. In conclusion, macrolide antibiotics lead to similar prolongation of repolarization but show a different proarrhythmic potential (erythromycin > clarithromycin > azithromycin). In the presence of azithromycin, neither EAD nor TdP occur. This effect may be related to a rectangular pattern of action potential prolongation, whereas erythromycin and clarithromycin cause triangular action potential prolongation and induce TdP.
Atrial fibrillation (AF) is caused by different mechanisms but current treatment strategies do not target these mechanisms. Stratified therapy based on mechanistic drivers and biomarkers of AF have ...the potential to improve AF prevention and management outcomes. We will integrate mechanistic insights with known pathophysiological drivers of AF in models predicting recurrent AF and prevalent AF to test hypotheses related to AF mechanisms and response to rhythm control therapy.
We will harmonise and combine baseline and outcome data from 12 studies collected by six centres from the United Kingdom, Germany, France, Spain, and the Netherlands which assess prevalent AF or recurrent AF. A Delphi process and statistical selection will be used to identify candidate clinical predictors. Prediction models will be developed in patients with AF for AF recurrence and AF-related outcomes, and in patients with or without AF at baseline for prevalent AF. Models will be used to test mechanistic hypotheses and investigate the predictive value of plasma biomarkers.
This retrospective, harmonised, individual patient data analysis will use information from 12 datasets collected in five European countries. It is envisioned that the outcome of this analysis would provide a greater understanding of the factors associated with recurrent and prevalent AF, potentially allowing development of stratified approaches to prevention and therapy management.
Atrial fibrillation (AF) is a common arrhythmia. Better prevention and treatment of AF are needed to reduce AF‐associated morbidity and mortality. There are several major mechanisms that cause AF in ...patients, including a genetic predisposition to develop AF. Genome‐wide association studies have identified genetic variants associated with AF populations, with the strongest hits clustering on chromosome 4q25, close to the gene for the homeobox transcription factor PITX2. The effect of these common gene variants on cardiac PITX2 mRNA is currently under study. PITX2 protein regulates right–left differentiation of the embryonic heart, thorax and aorta. PITX2 is expressed in the adult left atrium, but much less so in other heart chambers. Pitx2 deficiency results in electrical and structural remodelling, and impaired repair of the heart in murine models, all of which may influence AF through divergent mechanisms. PITX2 levels and single nucleotide polymorphisms on chromosome 4q25 may also be a predictor of the effectiveness of anti‐arrhythmic drug therapy.
Reduced Pitx2 expression leads to proarrhythmic cardiac electrical atrial remodelling. Several different murine models of Pitx2 downregulation have shown atrial action potential shortening and a depolarised atrial resting membrane, two established causes of arrhythmia. Alterations in calcium and potassium handling genes and TASK‐like background currents have been postulated to contribute in different models. The type of electrical remodelling may be a predictor of the anti‐arrhythmic effectiveness of rhythm control therapy. Sodium currents may also contribute. IRK, Inwardly rectifying potassium channels; K2P, Two‐pore domain potassium channels; TASK, TWIK‐related acid‐sensitive K+ channel.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Granulocyte colony-stimulating factor (G-CSF), alone or in combination with stem cell factor (SCF), can improve hemodynamic cardiac function after myocardial infarction. Apart from impairing the pump ...function, myocardial infarction causes an enhanced vulnerability to ventricular arrhythmias. Therefore, we investigated the electrophysiological effects of G-CSF/SCF and the underlying cellular events in a murine infarction model. G-CSF/SCF improved cardiac output after myocardial infarction. Although G-CSF/SCF led to a twofold increased, potentially proarrhythmic homing of bone marrow (BM)-derived cells to the area of infarction, <1% of these cells adopted a cardial phenotype. Inducibility of ventricular tachycardias during programmed stimulation was reduced 5 wk after G-CSF/SCF treatment. G-CSF/SCF increased cardiomyocyte diameter, arteriogenesis, and expression of connexin43 in the border zone of the infarction. An enhanced expression of the G-CSF receptor demonstrated in cardiomyocytes and other cell types of the infarcted myocardium indicates a sensitization of the heart to direct influences of this cytokine. In addition to paracrine effects potentially caused by the increased homing of BM-derived cells, these might contribute to the therapeutic effects of G-CSF.
Reversible protein phosphorylation is an essential regulatory mechanism in many cellular functions. In contrast to protein kinases, the role and regulation of protein phosphatases has remained ...ambiguous. To address this issue, we generated transgenic mice that overexpress the catalytic subunit α of protein phosphatase 2A (PP2A) (PP2Acα) in the heart driven by the α-myosin heavy chain promoter. Overexpression of the PP2Acα gene in the heart led to increased levels of the transgene both at RNA and protein levels. This was accompanied by a significant increase of PP2A enzyme activity in the myocardium. Morphological analysis revealed isles of necrosis and fibrosis. The phosphorylation state of phospholamban, troponin inhibitor, and eukaryotic elongation factor 2 was reduced significantly. The expression of junctional (calsequestrin) and free SR proteins (SERCA and phospholamban) was not altered. Whereas no increase in morbidity or mortality was noted, transgenic mice developed cardiac hypertrophy and reduced contractility of the heart, as well as cardiac dilatation as shown by biplane echocardiography. Taken together, these findings are indicative of the fundamental role of PP2A in cardiac function and imply that disturbances in protein phosphatases expression and activity may cause or aggravate the course of cardiac diseases.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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