Pathogenesis of arrhythmias in a model of CKD

Indoxyl Sulfate Induces Ventricular Arrhythmias Attenuated by Secretoneurin in Right Ventricular Outflow Tract Cardiomyocytes

Ventricular arrhythmias (VAs) are major causes of sudden cardiac death in chronic kidney disease (CKD) patients. Indoxyl sulfate (IS) is one common uremic toxin found in CKD patients. This study investigated whether IS could induce VAs via increasing right ventricular outflow tract (RVOT) arrhythmogenesis. Using conventional microelectrodes and whole-cell patch clamps, we studied the action potentials (APs) and ionic currents of isolated rabbit RVOT tissue preparations and single cardiomyocytes before and after IS (0.1 and 1.0 μM). Calcium fluorescence imaging was performed in RVOT cardiomyocytes treated with and without IS (1.0 μM) to evaluate the calcium transient and the calcium leak. In rabbit RVOT tissues, IS (0.1 and 1.0 μM) attenuated the contractility and shortened the AP durations in a dose-dependent manner. In addition, IS (0.1 and 1.0 μM) enhanced the pro-arrhythmia effects of isoproterenol (ISO, 1.0 μM) and rapid ventricular pacing in RVOT (before versus after ISO, 25% versus 83%, N = 12). In RVOT cardiomyocytes, IS (1.0 μM) significantly decreased the L-type calcium currents but increased the sodium-calcium exchanger and sodium window currents. Cardiomyocytes treated with IS (1.0 μM) had lower calcium transients but higher diastolic calcium and calcium leak than those without IS treatment. Pretreatment with secretoneurin (SN, 30 nM, a potent neuropeptide, suppressing CaMKII) or KN-93 (0.1 μM, a CaMKII inhibitor) prevented IS-induced ionic current changes and arrhythmogenesis. In conclusion, IS modulates RVOT electrophysiology and arrhythmogenesis via enhanced CaMKII activity, which is attenuated by SN, leading to a novel therapeutic target for CKD arrhythmias.

Accelerated idioventricular rhythm as a manifestation of chronic renocardiac syndrome: A case report

In this case report, we describe a patient who presented with chronic symptoms and signs of uremia and persistent accelerated idioventricular rhythm (AIVR) on electrocardiogram. Findings from blood tests, echocardiography, renal ultrasound, and renal scan were suggestive of heart failure with reduced ejection fraction and chronic kidney disease, and attendance of daily hemodialysis sessions led to the restoration of sinus rhythm. Typically, AIVR has a favorable prognosis and, if necessary, medical intervention focuses on addressing the underlying responsible causes. Accumulation of uremic toxins has the potential to trigger the formation of AIVR and clearance of small solutes through conventional hemodialysis may contribute to sinus rhythm restoration.

New Insights on Cardiac Arrhythmias in Patients With Kidney Disease

The risk of arrhythmia and its management become increasingly complex as kidney disease progresses. This presents a multifaceted clinical challenge. Our discussion addresses these specific challenges relevant to patients as their kidney disease advances. We highlight numerous opportunities for enhancing the current standard of care within this realm. Additionally, this review delves into research concerning early detection, prevention, diagnosis, and treatment of various arrhythmias spanning the spectrum of kidney disease.

The Dietary Fiber Inulin Slows Progression of Chronic Kidney Disease-Mineral Bone Disorder (CKD-MBD) in a Rat Model of CKD

Chronic kidney disease (CKD)-mineral bone disorder (CKD-MBD) leads to fractures and cardiovascular disease. Observational studies suggest beneficial effects of dietary fiber on both bone and cardiovascular outcomes, but the effect of fiber on CKD-MBD is unknown. To determine the effect of fiber on CKD-MBD, we fed the Cy/+ rat with progressive CKD a casein-based diet of 0.7% phosphate with 10% inulin (fermentable fiber) or cellulose (non-fermentable fiber) from 22 weeks to either 30 or 32 weeks of age (~30% and ~15% of normal kidney function; CKD 4 and 5). We assessed CKD-MBD end points of biochemistry, bone quantity and quality, cardiovascular health, and cecal microbiota and serum gut-derived uremic toxins. Results were analyzed by two-way analysis of variance (ANOVA) to evaluate the main effects of CKD stage and inulin, and their interaction. The results showed that in CKD animals, inulin did not alter kidney function but reduced the increase from stage 4 to 5 in serum levels of phosphate and parathyroid hormone, but not fibroblast growth factor-23 (FGF23). Bone turnover and cortical bone parameters were similarly improved but mechanical properties were not altered. Inulin slowed progression of aorta and cardiac calcification, left ventricular mass index, and fibrosis. To understand the mechanism, we assessed intestinal microbiota and found changes in alpha and beta diversity and significant changes in several taxa with inulin, together with a reduction in circulating gut derived uremic toxins such as indoxyl sulfate and short-chain fatty acids. In conclusion, the addition of the fermentable fiber inulin to the diet of CKD rats led to a slowed progression of CKD-MBD without affecting kidney function, likely mediated by changes in the gut microbiota composition and lowered gut-derived uremic toxins. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Electrical and Structural Insights into Right Ventricular Outflow Tract Arrhythmogenesis

The right ventricular outflow tract (RVOT) is the major origin of ventricular arrhythmias, including premature ventricular contractions, idiopathic ventricular arrhythmias, Brugada syndrome, torsade de pointes, long QT syndrome, and arrhythmogenic right ventricular cardiomyopathy. The RVOT has distinct developmental origins and cellular characteristics and a complex myocardial architecture with high shear wall stress, which may lead to its high vulnerability to arrhythmogenesis. RVOT myocytes are vulnerable to intracellular sodium and calcium overload due to calcium handling protein modulation, enhanced CaMKII activity, ryanodine receptor phosphorylation, and a higher cAMP level activated by predisposing factors or pathological conditions. A reduction in Cx43 and Scn5a expression may lead to electrical uncoupling in RVOT. The purpose of this review is to update the current understanding of the cellular and molecular mechanisms of RVOT arrhythmogenesis.

The Dietary Fermentable Fiber Inulin Alters the Intestinal Microbiome and Improves Chronic Kidney Disease Mineral-Bone Disorder in a Rat Model of CKD

Background

Dietary fiber is important for a healthy diet, but intake is low in CKD patients and the impact this has on the manifestations of CKD-Mineral Bone Disorder (MBD) is unknown.

Methods

The Cy/+ rat with progressive CKD was fed a casein-based diet of 0.7% phosphate with 10% inulin (fermentable fiber) or cellulose (non-fermentable fiber) from 22 weeks to either 30 or 32 weeks of age (~30 and ~15 % of normal kidney function). We assessed CKD-MBD, cecal microbiota, and serum gut-derived uremic toxins. Two-way ANOVA was used to evaluate the effect of age and inulin diet, and their interaction.

Results

In CKD animals, dietary inulin led to changes in microbiota alpha and beta diversity at 30 and 32 weeks, with higher relative abundance of several taxa, including Bifidobacterium and Bacteroides , and lower Lactobacillus . Inulin reduced serum levels of gut-derived uremic toxins, phosphate, and parathyroid hormone, but not fibroblast growth factor-23. Dietary inulin decreased aorta and cardiac calcification and reduced left ventricular mass index and cardiac fibrosis. Bone turnover and cortical bone parameters were improved with inulin; however, bone mechanical properties were not altered.

Conclusions

The addition of the fermentable fiber inulin to the diet of CKD rats led to changes in the gut microbiota composition, lowered gut-derived uremic toxins, and improved most parameters of CKD-MBD. Future studies should assess this fiber as an additive therapy to other pharmacologic and diet interventions in CKD.

Significance Statement

Dietary fiber has well established beneficial health effects. However, the impact of fermentable dietary fiber on the intestinal microbiome and CKD-MBD is poorly understood. We used an animal model of progressive CKD and demonstrated that the addition of 10% of the fermentable fiber inulin to the diet altered the intestinal microbiota and lowered circulating gut-derived uremic toxins, phosphorus, and parathyroid hormone. These changes were associated with improved cortical bone parameters, lower vascular calcification, and reduced cardiac hypertrophy, fibrosis and calcification. Taken together, dietary fermentable fiber may be a novel additive intervention to traditional therapies of CKD-MBD.

Chronic Kidney Disease Induces Proarrhythmic Remodeling

BACKGROUND

Patients with chronic kidney disease (CKD) are at increased risk of developing cardiac arrhythmogenesis and sudden cardiac death; however, the basis for this association is incompletely known.

METHODS

Here, using murine models of CKD, we examined interactions between kidney disease progression and structural, electrophysiological, and molecular cardiac remodeling.

RESULTS

C57BL/6 mice with adenine supplemented in their diet developed progressive CKD. Electrocardiographically, CKD mice developed significant QT prolongation and episodes of bradycardia. Optical mapping of isolated-perfused hearts using voltage-sensitive dyes revealed significant prolongation of action potential duration with no change in epicardial conduction velocity. Patch-clamp studies of isolated ventricular cardiomyocytes revealed changes in sodium and potassium currents consistent with action potential duration prolongation. Global transcriptional profiling identified dysregulated expression of cellular stress response proteins RBM3 (RNA-binding motif protein 3) and CIRP (cold-inducible RNA-binding protein) that may underlay the ion channel remodeling. Unexpectedly, we found that female sex is a protective factor in the progression of CKD and its cardiac sequelae.

CONCLUSIONS

Our data provide novel insights into the association between CKD and pathologic proarrhythmic cardiac remodeling. Cardiac cellular stress response pathways represent potential targets for pharmacologic intervention for CKD-induced heart rhythm disorders.

Uremic toxins in chronic kidney disease highlight a fundamental gap in understanding their detrimental effects on cardiac electrophysiology and arrhythmogenesis

Chronic kidney disease (CKD) and cardiovascular disease (CVD) have an estimated 700-800 and 523 million cases worldwide, respectively, with CVD being the leading cause of death in CKD patients. The pathophysiological interplay between the heart and kidneys is defined as the cardiorenal syndrome (CRS), in which worsening of kidney function is represented by increased plasma concentrations of uremic toxins (UTs), culminating in dialysis patients. As there is a high incidence of CVD in CKD patients, accompanied by arrhythmias and sudden cardiac death, knowledge on electrophysiological remodeling would be instrumental for understanding the CRS. While the interplay between both organs is clearly of importance in CRS, the involvement of UTs in pro-arrhythmic remodeling is only poorly investigated, especially regarding the mechanistic background. Currently, the clinical approach against potential arrhythmic events is mainly restricted to symptom treatment, stressing the need for fundamental research on UT in relation to electrophysiology. This review addresses the existing knowledge of UTs and cardiac electrophysiology, and the experimental research gap between fundamental research and clinical research of the CRS. Clinically, mainly absorbents like ibuprofen and AST-120 are studied, which show limited safe and efficient usability. Experimental research shows disturbances in cardiac electrical activation and conduction after inducing CKD or exposure to UTs, but are scarcely present or focus solely on already well-investigated UTs. Based on UTs data derived from CKD patient cohort studies, a clinically relevant overview of physiological and pathological UTs concentrations is created. Using this, future experimental research is stimulated to involve electrophysiologically translatable animals, such as rabbits, or in vitro engineered heart tissues.

Effects of ferric citrate and intravenous iron sucrose on markers of mineral, bone, and iron homeostasis in a rat model of CKD-MBD

BACKGROUND

Anemia and chronic kidney disease-mineral and bone disorder (CKD-MBD) are common and begin early in CKD. Limited studies have concurrently compared the effects of ferric citrate (FC) versus intravenous (IV) iron on CKD-MBD and iron homeostasis in moderate CKD.

METHODS

We tested the effects of 10 weeks of 2% FC versus IV iron sucrose in rats with moderate CKD (Cy/+ male rat) and untreated normal (NL) littermates. Outcomes included a comprehensive assessment of CKD-MBD, iron homeostasis and oxidative stress.

RESULTS

CKD rats had azotemia, elevated phosphorus, parathyroid hormone and fibroblast growth factor-23 (FGF23). Compared with untreated CKD rats, treatment with FC led to lower plasma phosphorus, intact FGF23 and a trend (P = 0.07) toward lower C-terminal FGF23. FC and IV iron equally reduced aorta and heart calcifications to levels similar to NL animals. Compared with NL animals, CKD animals had higher bone turnover, lower trabecular volume and no difference in mineralization; these were unaffected by either iron treatment. Rats treated with IV iron had cortical and bone mechanical properties similar to NL animals. FC increased the transferrin saturation rate compared with untreated CKD and NL rats. Neither iron treatment increased oxidative stress above that of untreated CKD.

CONCLUSIONS

Oral FC improved phosphorus homeostasis, some iron-related parameters and the production and cleavage of FGF23. The intermittent effect of low-dose IV iron sucrose on cardiovascular calcification and bone should be further explored in moderate-advanced CKD.

Clinical Phenotyping of Out-of-Hospital Cardiac Arrest Patients With Shockable Rhythm - Machine Learning-Based Unsupervised Cluster Analysis

BACKGROUND

The hypothesis of this study is that latent class analysis could identify the subphenotypes of out-of-hospital cardiac arrest (OHCA) patients associated with the outcomes and allow us to explore heterogeneity in the effects of extracorporeal cardiopulmonary resuscitation (ECPR).

METHODS AND RESULTS

This study was a retrospective analysis of a multicenter prospective observational study (CRITICAL study) of OHCA patients. It included adult OHCA patients with initial shockable rhythm. Patients from 2012 to 2016 (development dataset) were included in the latent class analysis, and those from 2017 (validation dataset) were included for evaluation. The association between subphenotypes and outcomes was investigated. Further, the heterogeneity of the association between ECPR implementation and outcomes was explored. In the study results, a total of 920 patients were included for latent class analysis. Three subphenotypes (Groups 1, 2, and 3) were identified, mainly characterized by the distribution of partial pressure of O2(PO2), partial pressure of CO2(PCO2) value of blood gas assessment, cardiac rhythm on hospital arrival, and estimated glomerular filtration rate. The 30-day survival outcomes were varied across the groups: 15.7% in Group 1; 30.7% in Group 2; and 85.9% in Group 3. Further, the association between ECPR and 30-day survival outcomes by subphenotype groups in the development dataset was as varied. These results were validated using the validation dataset.

CONCLUSIONS

The latent class analysis identified 3 subphenotypes with different survival outcomes and potential heterogeneity in the effects of ECPR.

Calcium dysregulation increases right ventricular outflow tract arrhythmogenesis in rabbit model of chronic kidney disease

Chronic kidney disease (CKD) increases the risk of arrhythmia. The right ventricular outflow tract (RVOT) is a crucial site of ventricular tachycardia (VT) origination. We hypothesize that CKD increases RVOT arrhythmogenesis through its effects on calcium dysregulation. We analysed measurements obtained using conventional microelectrodes, patch clamp, confocal microscopy, western blotting, immunohistochemical examination and lipid peroxidation for both control and CKD (induced by 150 mg/kg neomycin and 500 mg/kg cefazolin daily) rabbit RVOT tissues or cardiomyocytes. The RVOT of CKD rabbits exhibited a short action potential duration, high incidence of tachypacing (20 Hz)‐induced sustained VT, and long duration of isoproterenol and tachypacing‐induced sustained and non‐sustained VT. Tachypacing‐induced sustained and non‐sustained VT in isoproterenol‐treated CKD RVOT tissues were attenuated by KB‐R7943 and partially inhibited by KN93 and H89. The CKD RVOT myocytes had high levels of phosphorylated CaMKII and PKA, and an increased expression of tyrosine hydroxylase‐positive neural density. The CKD RVOT myocytes exhibited large levels of I_to, I_Kr, NCX and L‐type calcium currents, calcium leak and malondialdehyde but low sodium current, SERCA2a activity and SR calcium content. The RVOT in CKD with oxidative stress and autonomic neuron hyperactivity exhibited calcium handling abnormalities, which contributed to the induction of VT.

Ventricular arrhythmias in mouse models of diabetic kidney disease

Chronic kidney disease (CKD) affects more than 20 million people in the US, and it is associated with a significantly increased risk of sudden cardiac death (SCD). Despite the significance, the mechanistic relationship between SCD and CKD is not clear and there are few effective therapies. Using optical mapping techniques, we tested the hypothesis that mouse models of progressive diabetic kidney disease (DKD) exhibit enhanced ventricular arrhythmia incidence and underlying arrhythmia substrates. Compared to wild-type mice, both Lepr^db/db eNOS^−/− (2KO) and high fat diet plus low dose streptozotocin (HFD + STZ) mouse models of DKD experienced sudden death and greater arrhythmia inducibility, which was more common with isoproterenol than programmed electrical stimulation. 2KO mice demonstrated slowed conduction velocity, prolonged action potential duration (APD), and myocardial fibrosis; both 2KO and HFD + STZ mice exhibited arrhythmias and calcium dysregulation with isoproterenol challenge. Finally, circulating concentrations of the uremic toxin asymmetric dimethylarginine (ADMA) were elevated in 2KO mice. Incubation of human cardiac myocytes with ADMA prolonged APD, as also observed in 2KO mice hearts ex vivo. The present study elucidates an arrhythmia-associated mechanism of sudden death associated with DKD, which may lead to more effective treatments in the vulnerable DKD patient population.

Fibroblast growth factor 23 (FGF23) induces ventricular arrhythmias and prolongs QTc interval in mice in an FGF receptor 4-dependent manner

Fibroblast growth factor 23 (FGF23) is a phosphate regulating protein hormone released by osteocytes. FGF23 becomes markedly elevated in chronic kidney disease (CKD), for which the leading cause of death is cardiovascular disease, particularly sudden cardiac death. Previously, we found that FGF23 increases intracellular Ca²⁺ in cardiomyocytes and alters contractility in mouse ventricles ex vivo via FGF receptor 4 (FGFR4). In the present study, we demonstrate that FGF23 induces cardiac arrhythmias and prolongs QTc interval in mice, and we tested whether these effects are mediated through FGFR4. In isolated Langendorff perfused hearts, FGF23 perfusion increased mechanical arrhythmias in the form of premature ventricular beats (PVBs), and induced runs of ventricular tachycardia in 6 of 11 animals, which were attenuated with pretreatment of an anti-FGFR4 blocking antibody. Ex vivo ECG analysis of isolated intact hearts showed increased ventricular arrhythmias and QTc prolongation after FGF23 infusion compared with vehicle. In vivo, injection of FGF23 into the jugular vein led to the emergence of premature ventricular contractions (PVCs) in 5 out of 11 experiments. FGF23 also produced a significant lengthening effect upon QTc interval in vivo. In vivo FGFR4 blockade ameliorated the arrhythmogenic and QTc prolonging effects of FGF23. Finally, FGF23 increased cardiomyocyte Ca²⁺ levels in intact left ventricular muscle which was inhibited by FGR4 blockade. We conclude that FGF23/FGFR4 signaling in the heart may contribute to ventricular arrhythmogenesis and repolarization disturbances commonly observed in patients with CKD via Ca²⁺ overload and may be an important therapeutic target to reduce cardiac mortality in CKD.NEW & NOTEWORTHY Here we provide direct evidence that fibroblast growth factor 23 (FGF23), a phosphaturic hormone elevated in chronic kidney disease, is proarrhythmic. FGF23 acutely triggered ventricular arrhythmias and prolonged corrected QT interval (QTc) in isolated mouse hearts and in vivo. FGF23 also increased Ca²⁺ levels in ventricular muscle tissue. Blockade of the FGF receptor 4 signaling pathway using a monoclonal antibody ameliorated ventricular arrhythmias, QTc prolongation, and elevated ventricular Ca²⁺ induced by FGF23, and may represent a potential therapeutic target in chronic kidney disease.

Clinical Potential of Targeting Fibroblast Growth Factor-23 and αKlotho in the Treatment of Uremic Cardiomyopathy

Chronic kidney disease is highly prevalent, affecting 10% to 15% of the adult population worldwide and is associated with increased cardiovascular morbidity and mortality. As chronic kidney disease worsens, a unique cardiovascular phenotype develops characterized by heart muscle disease, increased arterial stiffness, atherosclerosis, and hypertension. Cardiovascular risk is multifaceted, but most cardiovascular deaths in patients with advanced chronic kidney disease are caused by heart failure and sudden cardiac death. While the exact drivers of these deaths are unknown, they are believed to be caused by uremic cardiomyopathy: a specific pattern of myocardial hypertrophy, fibrosis, with both diastolic and systolic dysfunction. Although the pathogenesis of uremic cardiomyopathy is likely to be multifactorial, accumulating evidence suggests increased production of fibroblast growth factor-23 and αKlotho deficiency as potential major drivers of cardiac remodeling in patients with uremic cardiomyopathy. In this article we review the increasing understanding of the physiology and clinical aspects of uremic cardiomyopathy and the rapidly increasing knowledge of the biology of both fibroblast growth factor-23 and αKlotho. Finally, we discuss how dissection of these pathological processes is aiding the development of therapeutic options, including small molecules and antibodies, directly aimed at improving the cardiovascular outcomes of patients with chronic kidney disease and end-stage renal disease.

Cardiac calcium dysregulation in mice with chronic kidney disease

Cardiovascular complications are leading causes of morbidity and mortality in patients with chronic kidney disease (CKD). CKD significantly affects cardiac calcium (Ca²⁺) regulation, but the underlying mechanisms are not clear. The present study investigated the modulation of Ca²⁺ homeostasis in CKD mice. Echocardiography revealed impaired fractional shortening (FS) and stroke volume (SV) in CKD mice. Electrocardiography showed that CKD mice exhibited longer QT interval, corrected QT (QTc) prolongation, faster spontaneous activities, shorter action potential duration (APD) and increased ventricle arrhythmogenesis, and ranolazine (10 µmol/L) blocked these effects. Conventional microelectrodes and the Fluo‐3 fluorometric ratio techniques indicated that CKD ventricular cardiomyocytes exhibited higher Ca²⁺ decay time, Ca²⁺ sparks, and Ca²⁺ leakage but lower [Ca²⁺]_i transients and sarcoplasmic reticulum Ca²⁺ contents. The CaMKII inhibitor KN93 and ranolazine (RAN; late sodium current inhibitor) reversed the deterioration in Ca²⁺ handling. Western blots revealed that CKD ventricles exhibited higher phosphorylated RyR2 and CaMKII and reduced phosphorylated SERCA2 and SERCA2 and the ratio of PLB‐Thr17 to PLB. In conclusions, the modulation of CaMKII, PLB and late Na⁺ current in CKD significantly altered cardiac Ca²⁺ regulation and electrophysiological characteristics. These findings may apply on future clinical therapies.

Atrial fibrillation and its arrhythmogenesis associated with insulin resistance

Background

Insulin resistance (IR) is considered as a risk factor for atrial fibrillation (AF) even before diabetes develops. The pathophysiology and underlying mechanism are largely unclear.

Methods

We investigated the corresponding mechanism in two IR models of rats fed 15-week high-fat (HFa) and high-fructose/cholesterol (HFr) diets. AF was evaluated and induced by burst atrial pacing. Isolated atrial myocytes were used for whole-cell patch clamp and calcium assessment. Ex vivo whole heart was used for optical mapping. Western blot and immunofluorescence were used for quantitative protein evaluation.

Results

Both HFa and HFr rat atria were vulnerable to AF evaluated by burst atrial pacing. Isolated atrial myocytes from HFa and HFr rats revealed significantly increased sarcoplasmic reticulum calcium content and diastolic calcium sparks. Whole-heart mapping showed prolonged calcium transient duration, conduction velocity reduction, and repetitive ectopic focal discharge in HFa and HFr atria. Protein analysis revealed increased TGF-β1 and collagen expression; increased superoxide production; abnormal upregulation of calcium-homeostasis-related proteins, including oxidized CaMKIIδ, phosphorylated-phospholamban, phosphorylated-RyR-2, and sodium-calcium exchanger; and increased Rac1 activity in both HFa and HFr atria. We observed that inhibition of CaMKII suppressed AF in both HF and HFr diet-fed rats. In vitro palmitate-induced IR neonatal cardiomyocytes and atrial fibroblasts expressed significantly more TGF-β1 than did controls, suggesting paracrine and autocrine effects on both myocytes and fibroblasts.

Conclusions

IR engenders both atrial structural remodeling and abnormal intracellular calcium homeostasis, contributing to increased AF susceptibility. The inhibition of CaMKII may be a potential therapeutic target for AF in insulin resistance.

microRNA-206 overexpression inhibits epithelial-mesenchymal transition and glomerulosclerosis in rats with chronic kidney disease by inhibiting JAK/STAT signaling pathway

Chronic kidney disease (CKD) is a traumatic disease with significant psychic consequences to the patient's overall physical condition. microRNA-206 (miR-206) has been reported to play an essential role in the development of various diseases. The purpose of the present study is to investigate the effect of miR-206 through the JAK/STAT signaling pathway on epithelial-mesenchymal transition (EMT) of renal tubular epithelial cells and glomerulosclerosis in rats with CKD. The targeting relationship between miR-206 and ANXA1 was verified. To explore the role of miR-206 in CKD, the model of CKD rats was established to detect glomerular sclerosis index (GSI), contents of interleukin-6 (IL-6) and transforming growth factor-beta1 (TGF-β1), and expression of type IV collagen. Moreover, to further determine the roles of both miR-206 and the JAK/STAT signaling pathway in CKD, the gain- and loss-of function approaches were performed with the expression of ANXA1, α-SMA, E-cadherin, vimentin, N-cadherin, and the JAK/STAT signaling pathway-related genes detected. miR-206 negatively targeted ANXA1. Overexpressed miR-206 inhibited the degeneration and interstitial fibrosis of renal tubular epithelial cells, decreased GSI of rats, and the expression of type IV collagen, TGF-β1 and IL-6. Overexpressed miR-206 inhibited the degeneration of renal tubular epithelial cells, the expression of ANXA1, α-SMA, TGF-β1, p-STAT3, STAT3, p-STAT1, STAT1, p-JAK2, and JAK2, while promoted the expression of E-cadherin. Taken together the results, miR-206 inhibits EMT of renal tubular epithelial cells and glomerulosclerosis by inactivating the JAK/STAT signaling pathway via ANXA1 in CKD.

High Fibroblast Growth Factor 23 concentrations in experimental renal failure impair calcium handling in cardiomyocytes

The overwhelming majority of patients with chronic kidney disease (CKD) die prematurely before reaching end‐stage renal disease, mainly due to cardiovascular causes, of which heart failure is the predominant clinical presentation. We hypothesized that CKD‐induced increases of plasma FGF23 impair cardiac diastolic and systolic function. To test this, mice were subjected to 5/6 nephrectomy (5/6Nx) or were injected with FGF23 for seven consecutive days. Six weeks after surgery, plasma FGF23 was higher in 5/6Nx mice compared to sham mice (720 ± 31 vs. 256 ± 3 pg/mL, respectively, P = 0.034). In cardiomyocytes isolated from both 5/6Nx and FGF23 injected animals the rise of cytosolic calcium during systole was slowed (−13% and −19%, respectively) as was the decay of cytosolic calcium during diastole (−15% and −21%, respectively) compared to controls. Furthermore, both groups had similarly decreased peak cytosolic calcium content during systole. Despite lower cytosolic calcium contents in CKD or FGF23 pretreated animals, no changes were observed in contractile parameters of cardiomyocytes between the groups. Expression of calcium handling proteins and cardiac troponin I phosphorylation were similar between groups. Blood pressure, the heart weight:tibia length ratio, α‐MHC/β‐MHC ratio and ANF mRNA expression, and systolic and diastolic function as measured by MRI did not differ between groups. In conclusion, the rapid, CKD‐induced rise in plasma FGF23 and the similar decrease in cardiomyocyte calcium transients in modeled kidney disease and following 1‐week treatment with FGF23 indicate that FGF23 partly mediates cardiomyocyte dysfunction in CKD.

Sudden Cardiac Death in Dialysis: Arrhythmic Mechanisms and the Value of Non-invasive Electrophysiology

Sudden Cardiac Death (SCD) is the leading cause of cardiovascular death in dialysis patients. This review discusses potential underlying arrhythmic mechanisms of SCD in the dialysis population. It examines recent evidence from studies using implantable loop recorders and from electrophysiological studies in experimental animal models of chronic kidney disease. The review summarizes advances in the field of non-invasive electrophysiology for risk prediction in dialysis patients focusing on the predictive value of the QRS-T angle and of the assessments of autonomic imbalance by means of heart rate variability analysis. Future research directions in non-invasive electrophysiology are identified to advance the understanding of the arrhythmic mechanisms. A suggestion is made of incorporation of non-invasive electrophysiology procedures into clinical practice. Key Concepts: - Large prospective studies in dialysis patients with continuous ECG monitoring are required to clarify the underlying arrhythmic mechanisms of SCD in dialysis patients. - Obstructive sleep apnoea may be associated with brady-arrhythmias in dialysis patients. Studies are needed to elucidate the burden and impact of sleeping disorders on arrhythmic complications in dialysis patients. - The QRS-T angle has the potential to be used as a descriptor of uremic cardiomyopathy. - The QRS-T angle can be calculated from routine collected surface ECGs. Multicenter collaboration is required to establish best methodological approach and normal values. - Heart Rate Variability provides indirect assessment of cardiac modulation that may be relevant for cardiac risk prediction in dialysis patients. Short-term recordings with autonomic provocations are likely to overcome the limitations of out of hospital 24-h recordings and should be prospectively assessed.

QRS-T Angle Predicts Cardiac Risk and Correlates With Global Longitudinal Strain in Prevalent Hemodialysis Patients

Background: Cardiovascular disease is the commonest cause of death in hemodialysis (HD) patients but accurate risk prediction is lacking. The spatial QRS – T angle is a promising electrophysiological marker for sudden cardiac death risk stratification. The aim of this study was to assess the prognostic value of spatial QRS-T angle derived from standard 12 lead electrocardiograms (ECG) and its association with echocardiographic parameters in HD patients.

Methods: This prospective study of 178 prevalent HD patients (aged 67 ± 14 years, 72% men) collected ECG and echocardiographic data on an annual basis. Baseline echocardiograms at study entry were used for cross-sectional comparisons with ECGs. Study endpoints were all-cause mortality, cardiovascular mortality, and major adverse cardiac events (MACE). The QRS – T angle was calculated from standard 10-s ECG as the total cosine R to T (TCRT) using singular value decomposition and expressed in degrees. TCRT above 100° was defined as abnormal.

Results: During a follow-up period of 36 ± 19 months, 74 patients died, including 17 cardiac deaths, and 54 suffered from MACE. In multivariate Cox regression analysis, QRS-T angle by TCRT at baseline was associated with increased cardiovascular mortality both as a continuous value and dichotomized below or above 100° (HR 1.016, p = 0.029, CI: 1.002–1.030 and HR 3.506, CI: 1.118–10.995, p = 0.031 respectively) and with MACE dichotomized at 100° (HR 1.902, CI: 1.046–3.459; p = 0.035). In multivariate regression analysis including baseline parameters, echocardiographic global longitudinal strain (GLS) was significantly correlated with TCRT (F 9.648, r² = 0.192, standardized β = 0.331, unstandardized β = 3.567, t = 4.4429, CI: 1.976–5.157, p < 0.001).

Conclusion: TCRT correlates with GLS and is independently associated with cardiac deaths and MACE in HD patients.

Clinical significance of J wave in prediction of ventricular arrhythmia in patients with acute myocardial infarction

BACKGROUND

J wave syndrome and myocardial ischemia are related with malignant ventricular arrhythmia (VA). The characteristics of dynamic J wave in patients with early phase of acute myocardial infarction (AMI) and subsequent VA or electrical storm (ES) have not been well evaluated.

OBJECTIVE

We investigated the utility of J wave in the prediction of VA and ES in patients within the early phase of AMI.

METHODS

This study retrospectively enrolled 208 patients (mean age 69±15 years, 171 males) with AMI. Of them, 50 patients had experienced VA during hospitalization and 24 had ES. The clinical and electrocardiographic characteristics of these patients with and without VA were compared.

RESULTS

Patients with VA had a higher incidence of chronic kidney disease (CKD) and J wave compared with those without VA. The hazard ratio (HR) of J wave for VA was 4.31 (p<0.01) and CKD was 2.64 (p<0.01). In the VA group, ES patients had a higher incidence of diabetes mellitus (DM) (HR 2.73, p=0.02) and J wave (HR 4.21, p<0.01). If the AMI patients had J wave, the OR for mortality was 2.14 (p=0.03), VA events was 6.23 (p<0.01), and ES events was 12.15 (p<0.01). If VA patients had J wave, the mortality rate will significantly increase (OR 68.62, p=0.01).

CONCLUSION

The AMI patients who develop VA in the early phase of AMI had a higher incidence of J wave and CKD, and those who develop ES had a higher incidence of J wave and DM. It seems that J wave in AMI patients is a poor prognostic factor, and we found that J wave will increase mortality, VA events, and ES events. The majority locations of J wave were inferior leads although there was no relationship between the locations and VA incidence. If the VA patients had inferior or lateral J wave, it would further increase the risk of mortality.

Uremia increases QRS duration after β-adrenergic stimulation in mice

Chronic kidney disease (CKD) and uremia increase the risk of heart disease and sudden cardiac death. Coronary artery disease can only partly account for this. The remaining mechanistic links between CKD and sudden death are elusive, but may involve cardiac arrhythmias. For the present study, we hypothesized that a thorough electrophysiological study in mice with CKD would provide us valuable information that could aid in the identification of additional underlying causes of sudden cardiac death in patients with kidney disease. Partial (5/6) nephrectomy (NX) in mice induced mild CKD: plasma urea in NX was 24 ± 1 mmol/L (n = 23) versus 12 ± 1 mmol/L (n = 22) in sham-operated control mice (P < 0.05). Echocardiography did not identify structural or mechanical remodeling in NX mice. Baseline ECG parameters were comparable in conscious NX and control mice; however, the normal 24-h diurnal rhythm in QRS duration was lost in NX mice. Moreover, β-adrenergic stimulation (isoprenaline, 200 μg/kg intraperitoneally) prolonged QRS duration in conscious NX mice (from 12 ± 1 to 15 ± 2 msec, P < 0.05), but not in sham-operated controls (from 13 ± 1 to 13 ± 2 msec, P > 0.05). No spontaneous arrhythmias were observed in conscious NX mice, and intracardiac pacing in anesthetized mice showed a comparable arrhythmia vulnerability in NX and sham-operated mice. Isoprenaline (2 mg/kg intraperitoneally) changed the duration of the QRS complex from 11.2 ± 0.4 to 11.9 ± 0.5 (P = 0.06) in NX mice and from 10.7 ± 0.6 to 10.6 ± 0.6 (P = 0.50) in sham-operated mice. Ex vivo measurements of cardiac ventricular conduction velocity were comparable in NX and sham mice. Transcriptional activity of Scn5a, Gja1 and several profibrotic genes was similar in NX and sham mice. We conclude that proper kidney function is necessary to maintain diurnal variation in QRS duration and that sympathetic regulation of the QRS duration is altered in kidney disease.

Skeletal vascular perfusion is altered in chronic kidney disease

Patients with chronic kidney disease (CKD) are at an alarming risk of cardiovascular disease and fracture-associated mortality. CKD has been shown to have negative effects on vascular reactivity and organ perfusion. Although alterations in bone blood flow are linked to dysregulation of bone remodeling and mass in multiple conditions, changes to skeletal perfusion in the setting of CKD have not been explored. The goal of this study was to establish the effect of CKD on skeletal perfusion in a rat model of CKD. In two experiments with endpoints at 30 and 35 weeks of age, respectively, normal (NL) and Cy/+ (CKD) animals (n = 6/group) underwent in vivo intra-cardiac fluorescent microsphere injection to assess bone tissue perfusion. These two separate time points aimed to describe skeletal perfusion at 30 and 35 weeks based on previous studies demonstrating significant progression of hyperparthyroid bone disease during this timeframe. CKD animals had blood urea nitrogen (BUN) levels significantly higher than NL at both 30 and 35 weeks. At 30 weeks, perfusion was significantly higher in the femoral cortex (+259%, p < 0.05) but not in the tibial cortex (+140%, p = 0.11) of CKD animals relative to NL littermates. Isolated tibial marrow perfusion at 30 weeks showed a trend toward being higher (+183%, p = 0.08) in CKD. At 35 weeks, perfusion was significantly higher in both the femoral cortex (+173%, p < 0.05) and the tibial cortex (+241%, p < 0.05) in CKD animals when compared to their normal littermates. Isolated tibial marrow perfusion (-57%, p <0.05) and vertebral body perfusion (-71%, p <0.05) were lower in CKD animals. The current study demonstrates two novel findings regarding bone perfusion in an animal model of high turnover CKD. First, cortical bone perfusion in CKD animals is higher than in normal animals. Second, alterations in bone marrow perfision differed among the stages of CKD and were distinct from perfusion to the cortical bone. Determining whether these changes in bone perfusion are drivers, propagators, or consequences of skeletal deterioration in CKD will necessitate further work.

Calcium as a cardiovascular toxin in CKD-MBD

Disordered calcium balance and homeostasis are common in patients with chronic kidney disease. Such alterations are commonly associated with abnormal bone remodeling, directly and indirectly. Similarly, positive calcium balance may also be a factor in the pathogenesis of extra skeletal soft tissue and arterial calcification. Calcium may directly affect cardiac structure and function through direct effects to alter cell signaling due to abnormal intracellular calcium homeostasis 2) extra-skeletal deposition of calcium and phosphate in the myocardium and small cardiac arterioles, 3) inducing cardiomyocyte hypertrophy through calcium and hormone activation of NFAT signaling mechanisms, and 4) increased aorta calcification resulting in chronic increased afterload leading to hypertrophy. Similarly, calcium may alter vascular smooth muscle cell function and affect cell signaling which may predispose to a proliferative phenotype important in arteriosclerosis and arterial calcification. Thus, disorders of calcium balance and homeostasis due to CKD-MBD may play a role in the high cardiovascular burden observed in patients with CKD.

Do Implantable Cardioverter Defibrillators Reduce Mortality in Patients With Chronic Kidney Disease at All Stages?

The benefits of implantable cardioverter defibrillator (ICD) implantation in chronic kidney disease (CKD) patients with high sudden cardiac death (SCD) risk are uncertain. To clarify the effects of receiving an ICD in CKD patients, we conducted this meta-analysis to identify the effects of ICDs on patients with CKD, including those on dialysis. We searched the Cochrane library, EMBASE, PubMed, and clinical trials for studies published before July 2016. Eleven studies including 20,196 CKD patients were considered for inclusion. The pooled analysis suggested that patients with an estimated glomerular filtration rate (eGFR) < 60 mL/minute/1.73 m2 would benefit from receiving treatments with ICDs compared with patients without an ICD device (aHR = 0.74; 95% confidence interval [CI], 0.63 to 0.86). [corrected]. This is the first report of a subgroup analysis on the survival rate of ICD implantation in CKD patients according to an eGFR group. The subgroup analysis indicated a similar protective association of ICDs in stage 3 (aHR = 0.71; 95% CI, 0.61 to 0.82) and 5 (aHR = 0.71; 95% CI, 0.54 to 0.92) CKD patients [corrected] compared with the control group. However, there was no significant improvement in all-cause mortality in stage 4 CKD patients (aHR = 1.02; 95%CI, 0.75 to 1.37) [corrected]. This is the first meta-analysis reporting that ICD implantation reduces all-cause mortality in stage 3 and 5 [corrected] CKD patients. However, the data do not indicate there is any benefit to ICD implantation in stage 4 [corrected] CKD patients.

QRS/T-wave and calcium alternans in a type I diabetic mouse model for spontaneous postmyocardial infarction ventricular tachycardia: A mechanism for the antiarrhythmic effect of statins

BACKGROUND

The incidence of sudden arrhythmic death is markedly increased in diabetics.

OBJECTIVE

The purpose of this study was to develop a mouse model for postmyocardial infarction (post-MI) ventricular tachycardia (VT) in the diabetic heart and determine the mechanism of an antiarrhythmic effect of statins.

METHODS

ECG transmitters were implanted in wild-type (WT), placebo, and pravastatin-treated type I diabetic Akita mice. MIs were induced by coronary ligation, and Ca²⁺ transients were studied by optical mapping, and Ca²⁺ transients and sparks in left ventricular myocytes (VM) by the Ionoptix system and confocal microscopy.

RESULTS

Burst pacing of Akita mouse hearts resulted in rate-related QRS/T-wave alternans, which was attenuated in pravastatin-treated mice. Post-MI Akita mice developed QRS/T-wave alternans and VT at 2820 ± 879 beats per mouse, which decreased to 343 ± 115 in pravastatin-treated mice (n = 13, P <.05). Optical mapping demonstrated pacing-induced VT originating in the peri-infarction zone and Ca²⁺ alternans, both attenuated in hearts of statin-treated mice. Akita VM displayed Ca²⁺ alternans, and triggered activity as well as increased Ca²⁺ transient decay time (Tau), Ca²⁺ sparks, and cytosolic Ca²⁺ and decreased SR Ca²⁺ stores all of which were in part reversed in cells from statin treated mice. Homogenates of Akita ventricles demonstrated decreased SERCA2a/PLB ratio and increased ratio of protein phosphatase (PP-1) to the PP-1 inhibitor PPI-1 which were reversed in homogenates of pravastatin-treated Akita mice.

CONCLUSION

Pravastatin decreased the incidence of post-MI VT and Ca²⁺ alternans in Akita mouse hearts in part by revering abnormalities of Ca²⁺ handling via the PP-1/PPI-1 pathway.

Electronegative LDL-mediated cardiac electrical remodeling in a rat model of chronic kidney disease

The mechanisms underlying chronic kidney disease (CKD)–associated higher risks for life-threatening ventricular tachyarrhythmias remain poorly understood. In rats subjected to unilateral nephrectomy (UNx), we examined cardiac electrophysiological remodeling and relevant mechanisms predisposing to ventricular arrhythmias. Adult male Sprague-Dawley rats underwent UNx (n = 6) or sham (n = 6) operations. Eight weeks later, the UNx group had higher serum blood urea nitrogen and creatinine levels and a longer electrocardiographic QTc interval than did the sham group. Patch-clamp studies revealed epicardial (EPI)-predominant prolongation of the action potential duration (APD) at 50% and 90% repolarization in UNx EPI cardiomyocytes compared to sham EPI cardiomyocytes. A significant reduction of the transient outward potassium current (I_to) in EPI but not in endocardial (ENDO) cardiomyocytes of UNx rats led to a decreased transmural gradient of I_to. The reduction of I_to currents in UNx EPI cardiomyocytes was secondary to downregulation of KChIP2 but not Kv4.2, Kv4.3, and Kv1.4 protein expression. Incubation of plasma electronegative low-density lipoprotein (LDL) from UNx rats with normal EPI and ENDO cardiomyocytes recapitulated the electrophysiological phenotype of UNx rats. In conclusion, CKD disrupts the physiological transmural gradient of I_to via downregulation of KChIP2 proteins in the EPI region, which may promote susceptibility to ventricular tachyarrhythmias. Electronegative LDL may underlie downregulation of KChIP2 in CKD.

Racial Differences in Association of Serum Calcium with Mortality and Incident Cardio- and Cerebrovascular Events

CONTEXT

Abnormalities in calcium metabolism may potentially contribute to the development of vascular disease. Calcium metabolism may be different in African American (AA) vs white individuals, but the effect of race on the association of serum calcium with clinical outcomes remains unclear.

OBJECTIVE

This study sought to examine race-specific associations of serum calcium levels with mortality and with major incident cardiovascular events.

DESIGN AND SETTING

This was a historical cohort study in the U.S. Department of Veterans Affairs health care facilities.

PARTICIPANTS

Participants included veterans (n = 1 967 622) with estimated glomerular filtration rate ≥ 60 mL/min/1.73 m².

MAIN OUTCOME MEASURES

The association between serum calcium levels with all-cause mortality, incident coronary heart disease (CHD), and ischemic stroke incidence was examined in multivariable adjusted Cox proportional hazards models, including an interaction term for calcium and race.

RESULTS

The association of calcium with all-cause mortality was U-shaped in both AA and white patients, but race modified the association of calcium with all-cause mortality. Compared with white patients, AA patients experienced lower risk of mortality when calcium was ≥ 8.8 mg/dL, with a statistically significant interaction (P < .001). Conversely, AA vs white race was associated with higher mortality when calcium was < 8.8 mg/dL. Calcium showed no significant association with ischemic stroke or CHD in both races; and race did not modify these associations (P = .37 and 0.11, respectively for interaction term).

CONCLUSIONS

Race modified the U-shaped association between calcium and all-cause mortality. Serum calcium is not associated with incident stroke or CHD in either AA or white patients. The race-specific difference in the association of calcium levels with mortality warrants further examination.

Defining myocardial tissue abnormalities in end-stage renal failure with cardiac magnetic resonance imaging using native T1 mapping

Noninvasive quantification of myocardial fibrosis in end-stage renal disease is challenging. Gadolinium contrast agents previously used for cardiac magnetic resonance imaging (MRI) are contraindicated because of an association with nephrogenic systemic fibrosis. In other populations, increased myocardial native T1 times on cardiac MRI have been shown to be a surrogate marker of myocardial fibrosis. We applied this method to 33 incident hemodialysis patients and 28 age- and sex-matched healthy volunteers who underwent MRI at 3.0T. Native T1 relaxation times and feature tracking–derived global longitudinal strain as potential markers of fibrosis were compared and associated with cardiac biomarkers. Left ventricular mass indices were higher in the hemodialysis than the control group. Global, Septal and midseptal T1 times were all significantly higher in the hemodialysis group (global T1 hemodialysis 1171 ± 27 ms vs. 1154 ± 32 ms; septal T1 hemodialysis 1184 ± 29 ms vs. 1163 ± 30 ms; and midseptal T1 hemodialysis 1184 ± 34 ms vs. 1161 ± 29 ms). In the hemodialysis group, T1 times correlated with left ventricular mass indices. Septal T1 times correlated with troponin and electrocardiogram-corrected QT interval. The peak global longitudinal strain was significantly reduced in the hemodialysis group (hemodialysis -17.7±5.3% vs. -21.8±6.2%). For hemodialysis patients, the peak global longitudinal strain significantly correlated with left ventricular mass indices (R = 0.426), and a trend was seen for correlation with galectin-3, a biomarker of cardiac fibrosis. Thus, cardiac tissue properties of hemodialysis patients consistent with myocardial fibrosis can be determined noninvasively and associated with multiple structural and functional abnormalities.

Subcutaneous nerve activity and mechanisms of sudden death in a rat model of chronic kidney disease

BACKGROUND

The mechanisms of sudden death in chronic kidney disease (CKD) remain unclear.

OBJECTIVE

The purpose of this study was to test the hypotheses that subcutaneous nerve activity (SCNA) can be used to estimate sympathetic tone in ambulatory rats and that abrupt reduction of SCNA precedes the spontaneous arrhythmic death of Cy/+ rats.

METHODS

Radiotransmitters were implanted in ambulatory normal (N = 6) and Cy/+ (CKD; N = 6) rats to record electrocardiogram and SCNA. Two additional rats were studied before and after chemical sympathectomy with 6-hydroxydopamine.

RESULTS

In normal rats, the baseline heart rate (HR) and SCNA were 351 ± 29 bpm and 5.12 ± 2.97 mV·s, respectively. SCNA abruptly increased HR by 4.31% (95% confidence interval 4.15%-4.47%). In comparison, the CKD rats had reduced baseline HR (336 ± 21 bpm, P < .01) and SCNA (4.27 ± 3.19 mV·s, P < .01). When SCNA was observed, HR increased by only 2.48% (confidence interval 2.29%-2.67%, P < .01). All Cy/+ rats died suddenly, preceded by sinus bradycardia, advanced (second- and third-degree) AV block (N = 6), and/or ventricular tachycardia or fibrillation (N = 3). Sudden death was preceded by a further reduction of SCNA (3.22 ± 2.86 mV·s, P < .01) and sinus bradycardia (243 ± 55 bpm, P < .01). Histologic studies in CKD rats showed myocardial calcification that involved the conduction system. Chemical sympathectomy resulted in progressive reduction of SCNA over 7 days.

CONCLUSION

SCNA can be used to estimate sympathetic tone in ambulatory rats. CKD is associated with reduced HR response to SCNA and conduction system diseases. Abrupt reduction of sympathetic tone precedes AV block, ventricular arrhythmia, and sudden death of CKD rats.

Reduced skeletal muscle function is associated with decreased fiber cross-sectional area in the Cy/+ rat model of progressive kidney disease

BACKGROUND

The combination of skeletal muscle wasting and compromised function plays a role in the health decline commonly observed in chronic kidney disease (CKD) patients, but the pathophysiology of muscle mass/strength changes remains unclear. The purpose of this study was to characterize muscle properties in the Cy/+ rat model of spontaneously progressive CKD.

METHODS

Leg muscle function and serum biochemistry of male Cy/+ (CKD) rats and their nonaffected littermates (NLs) were assessed in vivo at 25, 30 and 35 weeks of age. Architecture and histology of extensor digitorum longus (EDL) and soleus (SOL) muscles were assessed ex vivo at the conclusion of the experiment. We tested the hypothesis that animals with CKD have progressive loss of muscle function, and that this functional deficit is associated with loss of muscle mass and quality.

RESULTS

Thirty-five-week-old CKD rats produced significantly lower maximum torque in ankle dorsiflexion and shorter time to maximum torque, and longer half relaxation time in dorsiflexion and plantarflexion compared with NL rats. Peak dorsiflexion torque (but not plantarflexion torque) in CKD remained steady from 25 to 35 weeks, while in NL rats, peak torque increased. Mass, physiologic cross-sectional area (CSA) and fiber-type (myosin heavy chain isoform) proportions of EDL and SOL were not different between CKD and NL. However, the EDL of CKD rats showed reduced CSAs in all fiber types, while only MyHC-1 fibers were decreased in area in the SOL.

CONCLUSIONS

The results of this study demonstrate that muscle function progressively declines in the Cy/+ rat model of CKD. Because whole muscle mass and architecture do not vary between CKD and NL, but CKD muscles show reduction in individual fiber CSA, our data suggest that the functional decline is related to increased muscle fiber atrophy.

Arrhythmogenic Remodeling in Murine Models of Deoxycorticosterone Acetate-Salt-Induced and 5/6-Subtotal Nephrectomy-Salt-Induced Cardiorenal Disease

BACKGROUND

Renal failure is associated with adverse cardiac remodeling and sudden cardiac death. The mechanism leading to enhanced arrhythmogenicity in the cardiorenal syndrome is unclear. The aim of this study was to characterize electrophysiological and tissue alterations correlated with enhanced arrhythmogenicity in two distinct mouse models of renal failure.

METHODS

Thirty-week-old 129Sv mice received a high-salt diet and deoxycorticosterone acetate (DOCA) for 8 weeks, followed by an additional period of high-salt diet for 27 weeks (DOCA-salt aged model). Adult CD-1 mice were submitted to 5/6-subtotal nephrectomy (SNx) and treated for 11 weeks with a high-salt diet (SNx-salt adult model). Vulnerability to arrhythmia as well as conduction velocities (CVs) of the hearts were determined ex vivo with epicardial mapping. Subsequently, the hearts were characterized for connexin 43 (Cx43) and fibrosis.

RESULTS

DOCA-salt and SNx-salt mice developed renal dysfunction characterized by albuminuria. Heart, lung and kidney weights were increased in DOCA-salt mice. Both DOCA-salt and SNx-salt mice were highly susceptible to ventricular arrhythmias. DOCA-salt mice had a significant decrease in both longitudinal and transversal CV in the left ventricle. Histological analysis revealed a significant reduction in Cx43 expression as well as an increase in interstitial fibrosis in both DOCA-salt and SNx-salt mice.

CONCLUSION

DOCA-salt and SNx-salt treatment induced renal dysfunction, which resulted in structural and electrical cardiac remodeling and enhanced arrhythmogenicity. The reduced Cx43 expression and increased fibrosis levels in these hearts are likely candidates for the formation of the arrhythmogenic substrate.

Sudden cardiac death in end stage renal disease: unlocking the mystery

Sudden cardiac death (SCD) is a major cause of concern in end stage renal disease (ESRD), contributing to 70% of cardiovascular mortality and 27% of all-cause mortality in dialysis patients. Yet its mechanisms and pathogenesis remain largely obscure. This review discusses the potential reasons for an exaggerated risk of SCD in ESRD populations taking into account recent studies and registry data and additionally explores the reasons for the reported recent decline in SCD. The types of arrhythmias typical of the hemodialysis population are yet to be fully characterised and in this paper, we introduce an ongoing implantable loop recorder (ILR) based study in hemodialysis patients--CRASH ILR (Cardio Renal Arrhythmia Study in Haemodialysis patients using Implantable Loop Recorders). The findings of this study will hopefully guide the design and implementation of larger ILR based studies before undertaking larger scale interventional therapeutic trials in this high risk population.