Electrocardiographic QT interval prolongation and risk of primary cardiac arrest in diabetic patients

Sudden cardiac death due to ventricular arrhythmia in diabetes mellitus: A bench to bedside review

Diabetes mellitus (DM) confers an increased risk of sudden cardiac death (SCD) independent of its associated cardiovascular comorbidities. DM induces adverse structural, electrophysiologic, and autonomic cardiac remodeling that can increase one's risk of ventricular arrhythmias and SCD. Although glycemic control and prevention of microvascular and macrovascular complications are cornerstones in the management of DM, they are not adequate for the prevention of SCD. In this narrative review, we describe the contribution of DM to the pathophysiologic mechanism of SCD beyond its role in atherosclerotic cardiovascular disease and heart failure. On the basis of this pathophysiologic framework, we outline potential preventive and therapeutic strategies to mitigate the risk of SCD in this population of high-risk patients.

Type 2 diabetes and in-hospital sudden cardiac arrest in ST-elevation myocardial infarction in the US

Aims

We aimed to assess the impact of diabetes on sudden cardiac arrest (SCA) in US patients hospitalized for ST-elevation myocardial infarction (STEMI).

Methods

We used the National Inpatient Sample (2005-2017) data to identify adult patients with STEMI. The primary outcome was in-hospital SCA. Secondary outcomes included in-hospital mortality, ventricular tachycardia (VT), ventricular fibrillation (VF), cardiogenic shock (CS), acute renal failure (ARF), and the revascularization strategy in SCA patients.

Results

SCA significantly increased from 4% in 2005 to 7.6% in 2018 in diabetes patients and from 3% in 2005 to 4.6% in 2018 in non-diabetes ones (p < 0.001 for both). Further, diabetes was associated with an increased risk of SCA [aOR = 1.432 (1.336-1.707)]. In SCA patients with diabetes, the mean age (SD) decreased from 68 (13) to 66 (11) years old, and mortality decreased from 65.7% to 49.3% during the observation period (p < 0.001). Compared to non-diabetes patients, those with T2DM had a higher adjusted risk of mortality, ARF, and CS [aOR = 1.72 (1.62-1.83), 1.52 (1.43-1.63), 1.25 (1.17-1.33); respectively] but not VF or VT. Those patients were more likely to undergo revascularization with CABG [aOR = 1.197 (1.065-1.345)] but less likely to undergo PCI [aOR = 0.708 (0.664-0.754)].

Conclusion

Diabetes is associated with an increased risk of sudden cardiac arrest in ST-elevation myocardial infarction. It is also associated with a higher mortality risk in SCA patients. However, the recent temporal mortality trend in SCA patients shows a steady decline, irrespective of diabetes.

Prolongation of the heart rate-corrected QT interval is associated with cardiovascular diseases: Systematic review and meta-analysis

BACKGROUND

Conflicting findings have described the association between prolonged heart rate-corrected QT interval (QTc) and cardiovascular disease.

AIMS

To identify articles investigating the association between QTc and cardiovascular disease morbidity and mortality, and to summarize the available evidence for the general and type 2 diabetes populations.

METHODS

A systematic search was performed in PubMed and Embase in May 2022 to identify studies that investigated the association between QTc prolongation and cardiovascular disease in both the general and type 2 diabetes populations. Screening, full-text assessment, data extraction and risk of bias assessment were performed independently by two reviewers. Effect estimates were pooled across studies using random-effect models.

RESULTS

Of the 59 studies included, 36 qualified for meta-analysis. Meta-analysis of the general population studies showed a significant association for: overall cardiovascular disease (fatal and non-fatal) (hazard ratio [HR] 1.68, 95% confidence interval [CI] 1.33-2.12; I²=69%); coronary heart disease (fatal and non-fatal) in women (HR 1.27, 95% CI 1.08-1.50; I²=38%; coronary heart disease (fatal and non-fatal) in men (HR 2.07, 95% CI 1.26-3.39; I²=78%); stroke (HR 1.59, 95% CI 1.29-1.96; I²=45%); sudden cardiac death (HR 1.60, 95% CI 1.14-2.25; I²=68%); and atrial fibrillation (HR 1.55, 95% CI 1.31-1.83; I²=0.0%). No significant association was found for cardiovascular disease in the type 2 diabetes population.

CONCLUSION

QTc prolongation was associated with risk of cardiovascular disease in the general population, but not in the type 2 diabetes population.

Protein Kinases Mediate Anti-Inflammatory Effects of Cannabidiol and Estradiol Against High Glucose in Cardiac Sodium Channels

Background: Cardiovascular anomalies are predisposing factors for diabetes-induced morbidity and mortality. Recently, we showed that high glucose induces changes in the biophysical properties of the cardiac voltage-gated sodium channel (Nav1.5) that could be strongly correlated to diabetes-induced arrhythmia. However, the mechanisms underlying hyperglycemia-induced inflammation, and how inflammation provokes cardiac arrhythmia, are not well understood. We hypothesized that inflammation could mediate the high glucose-induced biophyscial changes on Nav1.5 through protein phosphorylation by protein kinases A and C. We also hypothesized that this signaling pathway is, at least partly, involved in the cardiprotective effects of cannabidiol (CBD) and 17β-estradiol (E₂).

Methods and Results: To test these ideas, we used Chinese hamster ovarian (CHO) cells transiently co-transfected with cDNA encoding human Nav1.5 α-subunit under control, a cocktail of inflammatory mediators or 100 mM glucose conditions (for 24 h). We used electrophysiological experiments and action potential modeling. Inflammatory mediators, similar to 100 mM glucose, right shifted the voltage dependence of conductance and steady-state fast inactivation and increased persistent current leading to computational prolongation of action potential (hyperexcitability) which could result in long QT3 arrhythmia. We also used human iCell cardiomyocytes derived from inducible pluripotent stem cells (iPSC-CMs) as a physiologically relevant system, and they replicated the effects produced by inflammatory mediators observed in CHO cells. In addition, activators of PK-A or PK-C replicated the inflammation-induced gating changes of Nav1.5. Inhibitors of PK-A or PK-C, CBD or E₂ mitigated all the potentially deleterious effects provoked by high glucose/inflammation.

Conclusion: These findings suggest that PK-A and PK-C may mediate the anti-inflammatory effects of CBD and E₂ against high glucose-induced arrhythmia. CBD, via Nav1.5, may be a cardioprotective therapeutic approach in diabetic postmenopausal population.

Hormonal Signaling Actions on Kv7.1 (KCNQ1) Channels

Kv7 channels (Kv7.1-7.5) are voltage-gated K⁺ channels that can be modulated by five β-subunits (KCNE1-5). Kv7.1-KCNE1 channels produce the slow-delayed rectifying K⁺ current, I_Ks, which is important during the repolarization phase of the cardiac action potential. Kv7.2-7.5 are predominantly neuronally expressed and constitute the muscarinic M-current and control the resting membrane potential in neurons. Kv7.1 produces drastically different currents as a result of modulation by KCNE subunits. This flexibility allows the Kv7.1 channel to have many roles depending on location and assembly partners. The pharmacological sensitivity of Kv7.1 channels differs from that of Kv7.2-7.5 and is largely dependent upon the number of β-subunits present in the channel complex. As a result, the development of pharmaceuticals targeting Kv7.1 is problematic. This review discusses the roles and the mechanisms by which different signaling pathways affect Kv7.1 and KCNE channels and could potentially provide different ways of targeting the channel.

Metformin Shortens Prolonged QT Interval in Diabetic Mice by Inhibiting L-Type Calcium Current: A Possible Therapeutic Approach

The incidence and mortality of cardiovascular disease in diabetic patients are 2-3 times higher than those in non-diabetic patients. Abnormal function of the L-type calcium channel in myocardial tissue might result in multiple cardiac disorders such as a prolonged QT interval. Therefore, QT prolongation is an independent risk factor of cardiovascular disease in patients with diabetes mellitus. Metformin, a hypoglycemic agent, is widely known to effectively reduce the occurrence of macrovascular diseases. The aim of the present study was to evaluate the effect of metformin on prolonged QT interval and to explore potential ionic mechanisms induced by diabetes. Diabetic mouse models were established with streptozotocin and an electrocardiogram was used to monitor the QT interval after 4 weeks of metformin treatment in each group. Action potential duration (APD) and L-type calcium current (I_Ca-L) were detected by patch-clamp in isolated mice ventricular cardiomyocytes and neonatal cardiomyocytes of mice. The expression levels of CACNA1C mRNA and Cav1.2 were measured by real-time PCR, western blot and immunofluorescence. A shortened QT interval was observed after 4 weeks of metformin treatment in diabetic mice. Patch-clamp results revealed that both APD and I_Ca-L were shortened in mouse cardiomyocytes. Furthermore, the expression levels of CACNA1C mRNA and Cav1.2 were decreased in the metformin group. The same results were also obtained in cultured neonatal mice cardiomyocytes. Overall, these results verify that metformin could shorten a prolonged QT interval by inhibiting the calcium current, suggesting that metformin may play a role in the electrophysiology underlying diabetic cardiopathy.

Transgenic Rabbit Models in Proarrhythmia Research

Drug-induced proarrhythmia constitutes a potentially lethal side effect of various drugs. Most often, this proarrhythmia is mechanistically linked to the drug's potential to interact with repolarizing cardiac ion channels causing a prolongation of the QT interval in the ECG. Despite sophisticated screening approaches during drug development, reliable prediction of proarrhythmia remains very challenging. Although drug-induced long-QT-related proarrhythmia is often favored by conditions or diseases that impair the individual's repolarization reserve, most cellular, tissue, and whole animal model systems used for drug safety screening are based on normal, healthy models. In recent years, several transgenic rabbit models for different types of long QT syndromes (LQTS) with differences in the extent of impairment in repolarization reserve have been generated. These might be useful for screening/prediction of a drug's potential for long-QT-related proarrhythmia, particularly as different repolarizing cardiac ion channels are impaired in the different models. In this review, we summarize the electrophysiological characteristics of the available transgenic LQTS rabbit models, and the pharmacological proof-of-principle studies that have been performed with these models—highlighting the advantages and disadvantages of LQTS models for proarrhythmia research. In the end, we give an outlook on potential future directions and novel models.

Cannabidiol protects against high glucose-induced oxidative stress and cytotoxicity in cardiac voltage-gated sodium channels

BACKGROUND AND PURPOSE

Cardiovascular complications are the major cause of mortality in diabetic patients. However, the molecular mechanisms underlying diabetes-associated arrhythmias are unclear. We hypothesized that high glucose could adversely affect Na_v 1.5, the major cardiac sodium channel isoform of the heart, at least partially via oxidative stress. We further hypothesized that cannabidiol (CBD), one of the main constituents of Cannabis sativa, through its effects on Na_v 1.5, could protect against high glucose-elicited oxidative stress and cytotoxicity.

EXPERIMENTAL APPROACH

To test these ideas, we used CHO cells transiently co-transfected with cDNA encoding human Na_v 1.5 α-subunit under control and high glucose conditions (50 or 100 mM for 24 hr). Several experimental and computational techniques were used, including voltage clamp of heterologous expression systems, cell viability assays, fluorescence assays and action potential modelling.

KEY RESULTS

High glucose evoked cell death associated with elevation in reactive oxygen species (ROS) right shifted the voltage dependence of conductance and steady-state fast inactivation, and increased persistent current leading to computational prolongation of action potential (hyperexcitability) which could result in long QT3 arrhythmia. CBD mitigated all the deleterious effects provoked by high glucose. Perfusion with lidocaine (a well-known sodium channel inhibitor with antioxidant effects) or co-incubation of Tempol (a well-known antioxidant) elicited protection, comparable to CBD, against the deleterious effects of high glucose.

CONCLUSION AND IMPLICATIONS

These findings suggest that, through its favourable antioxidant and sodium channel inhibitory effects, CBD may protect against high glucose-induced arrhythmia and cytotoxicity.

Association of hypoglycaemia and risk of cardiac arrhythmia in patients with diabetes mellitus: A systematic review and meta-analysis

AIMS

Hypoglycaemia is associated with increased cardiovascular risk among individuals with diabetes mellitus. It has been hypothesized that hypoglycaemia may trigger autonomic changes leading to increased cardiac arrhythmia risk. We conducted a systematic review and meta-analysis to explore this association.

MATERIALS AND METHODS

Ovid Medline, Embase, Scopus, Web of Science and Cochrane were searched from inception to October 10, 2017. We included studies of adults with diabetes (Type 1 or Type 2) that compared acute electrocardiogram (ECG) changes during episodes of hypoglycaemia and euglycaemia.

RESULTS

Our search resulted in 4625 citations, among which 20 studies met the predefined inclusion criteria. Finally, 12 studies were included in the descriptive analysis and 15 in the meta-analysis. Overall hypoglycaemia was associated with a reduction in heart rate variability and an increase in arrhythmia occurrence. QTc interval length was more significantly prolonged during hypoglycaemia compared to euglycaemia (pooled mean difference [95% confidence intervals] [0.64 (0.27-1.01], P = ·001). Subgroup analysis based on diabetes type showed that QTc prolongation occurred in individuals with Type 1 and Type 2 diabetes; however, the change between euglycaemia reached statistical significance only among individuals with Type 1 diabetes.

CONCLUSION

Our findings suggest that hypoglycaemia results in ECG alterations that are associated with increased risk of cardiac arrhythmia, which is associated with increased cardiovascular events and mortality. More clinical studies are needed to determine the cardiac risks of hypoglycaemia in individuals with diabetes, especially in Type 2 diabetes.

GWAS of the electrocardiographic QT interval in Hispanics/Latinos generalizes previously identified loci and identifies population-specific signals

QT interval prolongation is a heritable risk factor for ventricular arrhythmias and can predispose to sudden death. Most genome-wide association studies (GWAS) of QT were performed in European ancestral populations, leaving other groups uncharacterized. Herein we present the first QT GWAS of Hispanic/Latinos using data on 15,997 participants from four studies. Study-specific summary results of the association between 1000 Genomes Project (1000G) imputed SNPs and electrocardiographically measured QT were combined using fixed-effects meta-analysis. We identified 41 genome-wide significant SNPs that mapped to 13 previously identified QT loci. Conditional analyses distinguished six secondary signals at NOS1AP (n = 2), ATP1B1 (n = 2), SCN5A (n = 1), and KCNQ1 (n = 1). Comparison of linkage disequilibrium patterns between the 13 lead SNPs and six secondary signals with previously reported index SNPs in 1000G super populations suggested that the SCN5A and KCNE1 lead SNPs were potentially novel and population-specific. Finally, of the 42 suggestively associated loci, AJAP1 was suggestively associated with QT in a prior East Asian GWAS; in contrast BVES and CAP2 murine knockouts caused cardiac conduction defects. Our results indicate that whereas the same loci influence QT across populations, population-specific variation exists, motivating future trans-ethnic and ancestrally diverse QT GWAS.

Fine mapping of QT interval regions in global populations refines previously identified QT interval loci and identifies signals unique to African and Hispanic descent populations

BACKGROUND

The electrocardiographically measured QT interval (QT) is heritable and its prolongation is an established risk factor for several cardiovascular diseases. Yet, most QT genetic studies have been performed in European ancestral populations, possibly reducing their global relevance.

OBJECTIVE

To leverage diversity and improve biological insight, we fine mapped 16 of the 35 previously identified QT loci (46%) in populations of African American (n = 12,410) and Hispanic/Latino (n = 14,837) ancestry.

METHODS

Racial/ethnic-specific multiple linear regression analyses adjusted for heart rate and clinical covariates were examined separately and in combination after inverse-variance weighted trans-ethnic meta-analysis.

RESULTS

The 16 fine-mapped QT loci included on the Illumina Metabochip represented 21 independent signals, of which 16 (76%) were significantly (P-value≤9.1×10-5) associated with QT. Through sequential conditional analysis we also identified three trans-ethnic novel SNPs at ATP1B1, SCN5A-SCN10A, and KCNQ1 and three Hispanic/Latino-specific novel SNPs at NOS1AP and SCN5A-SCN10A (two novel SNPs) with evidence of associations with QT independent of previous identified GWAS lead SNPs. Linkage disequilibrium patterns helped to narrow the region likely to contain the functional variants at several loci, including NOS1AP, USP50-TRPM7, and PRKCA, although intervals surrounding SLC35F1-PLN and CNOT1 remained broad in size (>100 kb). Finally, bioinformatics-based functional characterization suggested a regulatory function in cardiac tissues for the majority of independent signals that generalized and the novel SNPs.

CONCLUSION

Our findings suggest that a majority of identified SNPs implicate gene regulatory dysfunction in QT prolongation, that the same loci influence variation in QT across global populations, and that additional, novel, population-specific QT signals exist.

Hyperglycemia induces defective Ca2+ homeostasis in cardiomyocytes

Diabetes and other metabolic conditions characterized by elevated blood glucose constitute important risk factors for cardiovascular disease. Hyperglycemia targets myocardial cells rendering ineffective mechanical properties of the heart, but cellular alterations dictating the progressive deterioration of cardiac function with metabolic disorders remain to be clarified. In the current study, we examined the effects of hyperglycemia on cardiac function and myocyte physiology by employing mice with high blood glucose induced by administration of streptozotocin, a compound toxic to insulin-producing β-cells. We found that hyperglycemia initially delayed the electrical recovery of the heart, whereas cardiac function became defective only after ~2 mo with this condition and gradually worsened with time. Prolonged hyperglycemia was associated with increased chamber dilation, thinning of the left ventricle (LV), and myocyte loss. Cardiomyocytes from hyperglycemic mice exhibited defective Ca²⁺ transients before the appearance of LV systolic defects. Alterations in Ca²⁺ transients involved enhanced spontaneous Ca²⁺ releases from the sarcoplasmic reticulum (SR), reduced cytoplasmic Ca²⁺ clearance, and declined SR Ca²⁺ load. These defects have important consequences on myocyte contraction, relaxation, and mechanisms of rate adaptation. Collectively, our data indicate that hyperglycemia alters intracellular Ca²⁺ homeostasis in cardiomyocytes, hindering contractile activity and contributing to the manifestation of the diabetic cardiomyopathy.

NEW & NOTEWORTHY

We have investigated the effects of hyperglycemia on cardiomyocyte physiology and ventricular function. Our results indicate that defective Ca²⁺ handling is a critical component of the progressive deterioration of cardiac performance of the diabetic heart.

Cardioprotective effects of rutin via alteration in TNF-α, CRP, and BNP levels coupled with antioxidant effect in STZ-induced diabetic rats

Diabetic cardiomyopathy (DCM) is a dreadful complication of diabetes responsible for 80 % mortality in diabetic patients, but unfortunately its pharmacotherapy is still incomplete. Rutin is a naturally occurring flavonoid having a long history of use in nutritional supplements for its action against oxidative stress, inflammation, and hyperglycemia, the key players involved in the progression of DCM, but remains unexplored for its role in DCM. This study was conducted to address this lacuna. It was performed in 4-week-old Streptozotocin-induced (45 mg/kg) diabetic rats for a period of 24 weeks to mimic the cardiotoxic effect of chronic hyperglycemia in diabetic patient's heart and to investigate the effect of rutin (50 mg/kg/day) in ameliorating these effects. Heart of the diabetic rats showed altered ECG parameters, reduced total antioxidant capacity, increased inflammatory assault, and degenerative changes. Interestingly, rutin treatment significantly ameliorated these changes with decrease in blood glucose level (p > 0.001), % HbA1c (p > 0.001) and reduced expression of TNF-α (p < 0.001), CRP (p < 0.001), and BNP (p < 0.01) compared to diabetic control rats. In addition, rutin provided significant protection against diabetes associated oxidative stress (p < 0.05), prevented degenerative changes in heart, and improved ECG parameters compared to diabetic control rats. The heart-to-body weight ratio was significantly reduced in rutin treatment group compared to diabetic control rats (p < 0.001). In conclusion, this study implicates that oxidative stress and inflammation are the central players involved in the progression of DCM and rutin ameliorates DCM through its antioxidant and anti-inflammatory actions on heart.

Rabbit models as tools for preclinical cardiac electrophysiological safety testing: Importance of repolarization reserve

It is essential to more reliably assess the pro-arrhythmic liability of compounds in development. Current guidelines for pre-clinical and clinical testing of drug candidates advocate the use of healthy animals/tissues and healthy individuals and focus on the test compound's ability to block the hERG current and prolong cardiac ventricular repolarization. Also, pre-clinical safety tests utilize several species commonly used in cardiac electrophysiological studies. In this review, important species differences in cardiac ventricular repolarizing ion currents are considered, followed by the discussion on electrical remodeling associated with chronic cardiovascular diseases that leads to altered ion channel and transporter expression and densities in pathological settings. We argue that the choice of species strongly influences experimental outcome and extrapolation of results to human clinical settings. We suggest that based on cardiac cellular electrophysiology, the rabbit is a useful species for pharmacological pro-arrhythmic investigations. In addition to healthy animals and tissues, the use of animal models (e.g. those with impaired repolarization reserve) is suggested that more closely resemble subsets of patients exhibiting increased vulnerability towards the development of ventricular arrhythmias and sudden cardiac death.

Diabetes, glucose tolerance, and the risk of sudden cardiac death

BACKGROUND

Diabetes predisposes to sudden cardiac death (SCD). However, it is uncertain whether greater proportion of cardiac deaths are sudden among diabetes patients than other subjects. It is also unclear whether the risk of SCD is pronounced already early in the course of the disease. The relationship of impaired glucose tolerance (IGT) and SCD is scarcely documented.

METHODS

A general population cohort of 10594 middle-aged subjects (mean age 44 years, 52.6 % male, follow-up duration 35-41 years) was divided into diabetes patients (n = 82), subjects with IGT (n = 3806, plasma glucose ≥9.58 mmol/l in one-hour glucose tolerance test), and controls (n = 6706).

RESULTS

Diabetes patients had an increased risk of SCD after adjustment confounders (hazard ratio 2.62, 95 % confidence interval 1.46-4.70, p = 0.001) but risk for non-sudden cardiac death was similarly increased and the proportion of SCD of cardiac deaths was not increased. The SCD risk persisted after exclusion of subjects with baseline cardiac disease or non-fatal cardiac events during the follow-up. Subjects with IGT were at increased risk for SCD (univariate hazard ratio 1.51; 95 % confidence interval 1.31-1.74; p < 0.001) and also for non-sudden cardiac deaths and non-fatal cardiac events but adjustments for other risk factors attenuated these effects.

CONCLUSIONS

Diabetes was associated with increased risk of SCD but also the risk of non-sudden cardiac death was similarly increased. The proportion of cardiac deaths being sudden in subjects with diabetes was not increased. The higher SCD risk in diabetes patients was independent of known cardiac disease at baseline or occurrence of non-fatal cardiac event during the follow-up.

Reduction in Kv Current Enhances the Temporal Dispersion of the Action Potential in Diabetic Myocytes: Insights From a Novel Repolarization Algorithm

BACKGROUND

Diabetes is associated with prolongation of the QT interval of the electrocardiogram and enhanced dispersion of ventricular repolarization, factors that, together with atherosclerosis and myocardial ischemia, may promote the occurrence of electrical disorders. Thus, we tested the possibility that alterations in transmembrane ionic currents reduce the repolarization reserve of myocytes, leading to action potential (AP) prolongation and enhanced beat-to-beat variability of repolarization.

METHODS AND RESULTS

Diabetes was induced in mice with streptozotocin (STZ), and effects of hyperglycemia on electrical properties of whole heart and myocytes were studied with respect to an untreated control group (Ctrl) using electrocardiographic recordings in vivo, ex vivo perfused hearts, and single-cell patch-clamp analysis. Additionally, a newly developed algorithm was introduced to obtain detailed information of the impact of high glucose on AP profile. Compared to Ctrl, hyperglycemia in STZ-treated animals was coupled with prolongation of the QT interval, enhanced temporal dispersion of electrical recovery, and susceptibility to ventricular arrhythmias, defects observed, in part, in the Akita mutant mouse model of type I diabetes. AP was prolonged and beat-to-beat variability of repolarization was enhanced in diabetic myocytes, with respect to Ctrl cells. Density of Kv K(+) and L-type Ca(2+) currents were decreased in STZ myocytes, in comparison to cells from normoglycemic mice. Pharmacological reduction of Kv currents in Ctrl cells lengthened AP duration and increased temporal dispersion of repolarization, reiterating features identified in diabetic myocytes.

CONCLUSIONS

Reductions in the repolarizing K(+) currents may contribute to electrical disturbances of the diabetic heart.

Hypoglycaemia and QT interval prolongation in type 1 diabetes--bridging the gap between clamp studies and spontaneous episodes

AIMS

We propose a study design with controlled hypoglycaemia induced by subcutaneous injection of insulin and matched control episodes to bridge the gap between clamp studies and studies of spontaneous hypoglycaemia. The observed prolongation of the heart rate corrected QT interval (QTc) during hypoglycaemia varies greatly between studies.

METHODS

We studied ten adults with type 1 diabetes (age 41±15years) without cardiovascular disease or neuropathy. Single-blinded hypoglycaemia was induced by a subcutaneous insulin bolus followed by a control episode on two occasions separated by 4weeks. QT intervals were measured using the semi-automatic tangent approach, and QTc was derived by Bazett's (QTcB) and Fridericia's (QTcF) formulas.

RESULTS

QTcB increased from baseline to hypoglycaemia (403±20 vs. 433±39ms, p<0.001). On the euglycaemia day, QTcB also increased (398±20 vs. 410±27ms, p<0.01), but the increase was less than during hypoglycaemia (p<0.001). The same pattern was seen for QTcF. Plasma adrenaline levels increased significantly during hypoglycaemia compared to euglycaemia (p<0.01). Serum potassium levels decreased similarly after insulin injection during both hypoglycaemia and euglycaemia.

CONCLUSIONS

Hypoglycaemia as experienced after a subcutaneous injection of insulin may cause QTc prolongation in type 1 diabetes. However, the magnitude of prolongation is less than typically reported during glucose clamp studies, possible because of the study design with focus on minimizing unwanted study effects.

Hypoglycemia from a cardiologist's perspective

Hypoglycemia in people with diabetes mellitus (DM) has been potentially linked to cardiovascular morbidity and mortality. Pathophysiologically, hypoglycemia triggers activation of the sympathoadrenal system, leading to an increase in counter-regulatory hormones and, consequently, increased myocardial workload and oxygen demand. Additionally, hypoglycemia triggers proinflammatory and hematologic changes that provide the substrate for possible myocardial ischemia in the already-diseased diabetic cardiovascular system. Hypoglycemia creates electrophysiologic alterations causing P-R-interval shortening, ST-segment depression, T-wave flattening, reduction of T-wave area, and QTc-interval prolongation. Patients who experience hypoglycemia are at an increased risk of silent ischemia as well as QTc prolongation and consequent arrhythmias. The Action to Control Cardiovascular Risk in Diabetes (ACCORD) trial showed an increase in all-cause mortality with intensive glycemic control, whereas the Action in Diabetes and Vascular Disease: Preterax and Diamicron Modified Release Controlled Evaluation (ADVANCE) study and Veteran's Affairs Diabetes Trial (VADT) showed no benefit with aggressive glycemic control. Women, elderly patients, and those with renal insufficiency are more vulnerable to hypoglycemic events. In fact, hypoglycemia is the most common metabolic complication experienced by older patients with DM in the United States. The concurrent use of medications like β-blockers warrants caution in DM because they can mask warning signs of hypoglycemia. Here we aim to elucidate the pathophysiology, review the electrocardiographic changes, analyze the current clinical literature, and consider the safety considerations of hypoglycemia as it relates to the cardiovascular system. In conclusion, in the current era of DM and its vascular ramifications, hypoglycemia from a cardiologist's perspective deserves due attention.

Type 2 diabetes induces subendocardium-predominant reduction in transient outward K+ current with downregulation of Kv4.2 and KChIP2

In the present study, we examined if and how cardiac ion channels are modified by type 2 diabetes mellitus (T2DM). Subendocardial (Endo) myocytes and subepicardial (Epi) myocytes were isolated from left ventricles of Otsuka-Long-Evans-Tokushima Fatty rats (OLETF) rats, a rat model of T2DM, and Otsuka-Long-Evans-Tokushima (LETO) rats (nondiabetic control rats). Endo and Epi myocytes were used for whole cell patch-clamp recordings and for protein and mRNA analyses. Action potential durations in Endo and Epi myocytes were longer in OLETF rats than in LETO rats, and the difference was larger in Endo myocytes. Steady-state transient outward K+ current ( Ito) density was reduced in Endo but not Epi myocytes of OLETF rats compared with LETO rats, although the contribution of the fast component of Ito recovery from inactivation was smaller in both Endo and Epi myocytes of OLETF rats than in LETO rats. Kv4.2 protein was reduced only in Endo myocytes in OLETF rats, although voltage-gated K+ channel-interacting protein 2 (KChIP2) protein levels in both Endo and Epi myocytes were lower in OLETF rats than in LETO rats. Corresponding regional differences in mRNA levels of KChIP2 and Kv4.2 were observed between OLETF and LETO rats. mRNA levels of Iroquois homeobox 5 in Endo myocytes were 53% higher in OLETF rats than in LETO rats. Densities of inward rectifier K+ current and L-type Ca2+ current and mRNA levels of Kv4.3 and Kv1.4 were similar in OLETF and LETO rats. In conclusion, T2DM induces Endo-predominant prolongation of the action potential duration via a reduction of the fast component of Ito recovery from inactivation and reduced steady-state Ito, in which downregulation of Kv4.2 and KChIP2 may be involved. Increased Iroquois homeobox 5 expression may underlie Kv4.2 downregulation in T2DM.

Lack of the QTc physiologic decrease during cardiac stress test in patients with type 2 diabetes treated with secretagogues

Patients with type 2 diabetes are at increased susceptibility to a prolonged QT interval. Furthermore, insulin secretagogues, drugs used to treat diabetes, may prolong QT interval and provoke arrhythmias. We evaluated whether secretagogues can affect QTc interval during cardiac stress test in 20 patients with type 2 diabetes treated with secretagogues. ECG stress test was performed in all patients. QTc interval was calculated both before cardiac stress test (BCST) and at acme of cardiac stress test (ACST). Diabetic patients treated with secretagogues showed longer QTc-ACST values than those treated with metformin only. QTc-ACST values resulted shorter than QTc-BCST values in control group. Diabetic patients treated with secretagogues showed QTc-ACST values significantly longer than QTc-BCST values. In our study, diabetic patients treated with secretagogues did not show the QTc physiologic decrease that is a protective against arrhythmias. These results suggest to evaluate, in these patients, QT length, even during routine cardiac stress test.

Association between KCNQ1 genetic variants and QT interval in a Chinese population

AIM

There is a close link between electrocardiographic ventricular repolarization QT parameters and Type 2 diabetes. The aim of the present study was to assess the effects of QT-related and diabetes-related variants in KCNQ1 on QT interval in a Chinese population.

METHODS

We recruited 2415 patients with Type 2 diabetes and 1163 subjects with normal glucose regulation in the present study. QT interval was obtained and the heart rate-corrected QT interval (QTc) was calculated using Bazett's formula. Four single nucleotide polymorphisms in KCNQ1 were selected (rs12296050, rs12576239, rs2237892 and rs2237895) and genotyped.

RESULTS

In participants with normal glucose regulation, the minor allele T of rs12296050 was associated with a 3.46-ms QTc prolongation under an additive model (P = 0.0109, empirical P = 0.0498). In patients with Type 2 diabetes, we did not find any association for the single nucleotide polymorphisms.

CONCLUSIONS

Our findings indicate that KCNQ1 is associated with QT interval in a Chinese population with normal glucose regulation.

A common variant of NOS1AP is associated with QT interval duration in a Chinese population with Type 2 diabetes

AIMS

Electrocardiographic ventricular repolarization QT parameters are independent risk factors for cardiovascular events and sudden cardiac death in diabetic patients. The aim of the study was to investigate the association of polymorphisms of the nitric oxide synthase 1 adaptor protein (NOS1AP) gene with QT interval in Chinese subjects with or without Type 2 diabetes.

METHODS

Three single nucleotide polymorphisms (SNPs) (rs10494366, rs12143842 and rs12029454) were genotyped in 1240 Type 2 diabetic patients (631 men and 609 women) and 1196 normal controls (433 men and 763 women). Individuals with overt diseases other than diabetes were excluded. Heart-rate corrected QT interval (QTc) was determined by standard 12-lead ECG and Bazett formula. Sex-pooled analysis and sex-specific analysis for genotype-phenotype association were both conducted.

RESULTS

In the diabetic group, the rs12143842 T allele was associated with a 3.87-ms (P = 0.014, empirical P = 0.039) increase in QTc duration for each additional allele copy, while rs10494366 and rs12029454 exhibited no significant association with QTc. We found no evidence of association for the three SNPs in subjects with normal glucose regulation. No significant SNP-gender and -diabetes affection interaction was observed.

CONCLUSIONS

The genetic variant rs12143842 in NOS1AP is associated with QT interval duration in a Chinese population with Type 2 diabetes. Future studies in different populations are needed to validate this finding and to evaluate the impact of NOS1AP variants on cardiovascular events and sudden cardiac death in diabetic patients.

Type 2 diabetes mellitus and the risk of sudden cardiac arrest in the community

The reduction of mortality from sudden cardiac arrest (SCA) in the setting of coronary heart disease (CHD) remains a major challenge, especially among patients with type 2 diabetes. Diabetes is associated with an increased risk of SCA, at least in part, from an increased presence and extent of coronary atherosclerosis (macrovascular disease). Diabetes also is associated with microvascular disease and autonomic neuropathy; and, these non-coronary atherosclerotic pathophysiologic processes also have the potential to increase the risk of SCA. In this report, we review the absolute and relative risk of SCA associated with diabetes. We summarize recent evidence that suggests that the increase in risk in patients with diabetes is not specific for SCA, as diabetes also is associated with a similar increase in risk for non-SCA CHD death and non-fatal myocardial infarction. These data are consistent with prior observations that coronary atherosclerosis is a major contributor to the increased SCA risk associated with diabetes. We also present previously published and unpublished data that demonstrates that both clinically-recognized microvascular and autonomic neuropathy also are associated with the risk of SCA among treated patients with diabetes, after taking into account prior clinically-recognized heart disease and other risk factors for SCA. We then discuss how these data might inform research and clinical efforts to prevent SCA. Although the prediction of SCA in this "high" risk population is likely to remain a challenge, as it is in other "high" risk clinical populations, we suggest that current recommendations for the prevention of SCA in the community, related to both lifestyle prescriptions and risk factor reduction, are likely to reduce mortality from SCA among patients with diabetes.

A combined abnormality in heart rate variation and QT corrected interval is a strong predictor of cardiovascular death in type 1 diabetes

OBJECTIVE

Long-term diabetes is associated with excess morbidity and mortality, and cardiovascular autonomic neuropathy and QTc interval abnormalities are both predictive of early cardiovascular death in diabetes. We aimed to investigate the effect of these risk factors in a large cohort of type 1 diabetic patients followed prospectively for 10 years.

MATERIAL AND METHODS

Three-hundred-and-ninety-one type 1 diabetic mellitus patients (240 M and 151 F, age 41.8 years +/- 9.9 (mean +/-SD), duration of DM 27.3 years +/- 8.2) were followed in an outpatient setting.

RESULTS

Patients with decreased heart rate variability had an excess overall mortality that diminished after adjusting for conventional cardiovascular risk factors; hazard ratio 2.5 (0.9-6.8; p = 0.071) compared to patients with normal heart rate variability. Likewise, prolonged QTc interval was associated with premature death with an adjusted hazard ratio of 2.3 (1.3-4.0; p = 0.005). In a combined analysis, patients with abnormal values for heart rate variability and QTc had a poorer prognosis compared to patients with normal test values for both parameters (adjusted hazard ratio 6.7 (1.8-25; p = 0.005)). Of the 34 patients with both test values abnormal, 15 died and 14 of these from cardiovascular causes.

CONCLUSIONS

We conclude that combined abnormality in heart rate variability and QTc is a strong predictor of mortality in type 1 diabetes independently of conventional risk factors. These results have implications for future screening and treatment programmes for cardiovascular disease in type 1 diabetes.

Cardiac autonomic neuropathy in diabetes mellitus: prevalence, risk factors and utility of corrected QT interval in the ECG for its diagnosis

OBJECTIVES

To study the prevalence and risk factors for cardiac autonomic neuropathy (CAN) and the utility of prolongation of corrected QT interval (QTc) in the ECG to diagnose CAN in patients with diabetes mellitus.

DESIGN AND SETTING

Cross-sectional study conducted among patients attending the diabetic clinic of a teaching hospital.

METHODS

The prevalence of CAN among 100 patients with type 1 and type 2 diabetes mellitus was assessed by the five autonomic function tests by Eving's methodology. The CAN score in each patient and its relationship to the QTc interval were analysed. Possible influences of age, duration of diabetes and coexistent peripheral neuropathy on the occurrence of CAN also were studied.

RESULTS

The prevalence of CAN was 60%. Univariate analysis showed a significant association between CAN and higher age (odds ratio (OR) 15.75), prolongation of QTc (OR 5.55), duration of disease over 10 years (OR 2) and peripheral neuropathy (p<0.001) in patients with type 1 diabetes. Significant risks for CAN among patients with type 2 diabetes were coexistent peripheral neuropathy (OR 14), prolonged QTc (OR 9.75), higher age (OR 7.2) and disease duration over 10 years (OR 1.92) in univariate analysis, but none of them showed independent risk in multivariate analysis. Disease duration over 10 years resulted in QTc prolongation in a significant numbers of cases with type 1 (p<0.001) and type 2 (p = 0.006) diabetes. The sensitivity, specificity and positive predictive value of QTc prolongation for the diagnosis of CAN were 77%, 62.5% and 77% in type 1 and 76.5%, 75% and 81.3% in type 2, respectively. Higher CAN scores correlated with longer QTc intervals (coefficient of correlation 0.73; p<0.001).

CONCLUSIONS

The prevalence of CAN in diabetes mellitus is high. Higher age, longer duration of diabetes and peripheral neuropathy are significant risk factors. QTc interval in the ECG can be used to diagnose CAN with reasonable sensitivity, specificity and positive predictive value.

Association of NOS1AP genetic variants with QT interval duration in families from the Diabetes Heart Study

OBJECTIVES

Prolongation of the electrocardiographic QT interval is a risk factor for sudden cardiac death (SCD). Diabetic individuals are at increased risk for prolonged QT interval and SCD. We sought to replicate the finding that genetic variants in the nitric oxide synthase 1 adaptor protein (NOS1AP) gene are associated with QT interval duration in a type 2 diabetes-enriched sample of European ancestry.

RESEARCH DESIGN AND METHODS

Two single nucleotide polymorphisms (SNPs) in NOS1AP were genotyped in 624 European Americans and 127 African Americans from 400 pedigrees enriched for type 2 diabetes. An additive genetic model was tested for each SNP in ancestry-specific analyses in the total sample and the diabetic subset (European Americans, n = 514; African Americans, n = 115), excluding from the analyses individuals taking QT-altering medications.

RESULTS

In European Americans, rs10494366 minor homozygotes had a 9.3-ms-longer QT interval compared with major homozygotes (P = 5.7 x 10(-5)); rs10918594 minor homozygotes had a 12.5-ms-longer QT interval compared with major homozygotes (P = 1.5 x 10(-6)). Restricting analyses to the diabetic European Americans strengthened the effect despite the reduction in sample size (11.3-ms difference, P = 5.1 x 10(-5); 13.9-ms difference, P = 1.6 x 10(-6), respectively). No association between the NOS1AP SNPs and QT interval duration was observed in the limited number of African Americans.

CONCLUSIONS

Two NOS1AP SNPs are strongly associated with QT interval duration in a predominately diabetic European-American sample. Stronger effects of NOS1AP variants in diabetic individuals suggest that this patient subset may be particularly susceptible to genetic variants that influence myocardial depolarization and repolarization as manifest in the QT interval.

Role of slow delayed rectifier K+-current in QT prolongation in the alloxan-induced diabetic rabbit heart

AIM

In diabetes mellitus, several cardiac electrophysiological parameters are known to be affected. In rodent experimental diabetes models, changes in these parameters were reported, but only limited relevant information is available in other species, having cardiac electrophysiological properties more resembling the human, including the rabbit. The present study was designed to analyse the effects of experimental type 1 diabetes on ventricular repolarization and the underlying transmembrane potassium currents in rabbit hearts.

METHODS

Diabetes was induced by a single injection of alloxan (145 mg kg(-1) i.v.). After the development of diabetes (3 weeks), electrophysiological studies were performed using whole cell voltage clamp and ECG measurements.

RESULTS

The QT(c) interval in diabetic rabbits was moderately but statistically significantly longer than measured in the control animals (155 +/- 1.8 ms vs. 145 +/- 2.8 ms, respectively, n = 9-10, P < 0.05). This QT(c)-lengthening effect of diabetes was accompanied by a significant reduction in the density of the slow delayed rectifier K(+) current, I(Ks) (from 1.48 +/- 0.35 to 0.86 +/- 0.17 pA pF(-1) at +50 mV, n = 19-21, P < 0.05) without changes in current kinetics. No differences were observed either in the density or in the kinetics of the inward rectifier K(+) current (I(K1)), the rapid delayed rectifier K(+) current (I(Kr)), the transient outward current (I(to)) and the L-type calcium current (I(CaL)) between the control and alloxan-treated rabbits.

CONCLUSION

It is concluded that type 1 diabetes mellitus, although only moderately, lengthens ventricular repolarization. Diabetes attenuates the repolarization reserve by decreasing the density of I(Ks) current, and thereby may enhance the risk of sudden cardiac death.

Neuropad indicator test for diagnosis of sudomotor dysfunction in type 2 diabetes

Neuropad is a new indicator test used to diagnose sudomotor dysfunction, a component of autonomic neuropathy. In this cross-sectional study, Neuropad is evaluated and compared with corrected QT (QT c), another test used in the diagnosis of autonomic neuropathy. The indicator test measures sweat production on the basis of a color change of cobalt (II) chloride solution from blue to pink upon absorption of water. This study involved 105 patients (43 men, 62 women) with type 2 diabetes with a mean age of 56.2+/-11.5 y and a mean disease duration of 10.0+/-6.3 y. Age, sex, disease duration, glycosylated hemoglobin, and QT c were compared between patients with normal and abnormal test results. The QT c interval was measured and the new indicator test was applied in all patients. The 2 tests were compared, and the sensitivity, specificity, positive predictive value, and negative predictive value for the indicator test were calculated. Autonomic neuropathy was diagnosed in 40 patients (38.1%) with QT c interval measurement and in 72 patients (68.6%) with the new indicator test (P=.001). The sensitivity, specificity, positive predictive value, and negative predictive value for the indicator test were 87.5%, 43.1%, 48.6%, and 84.8%, respectively. Patients with abnormal test outcomes had longer QT c than those whose test results were normal (0.433 vs 0.398 s; P=.002). Study results suggest that the new indicator test has an acceptable sensitivity but a low specificity and is not superior to other tests in the diagnosis of sudomotor dysfunction.

QTc interval and resting heart rate as long-term predictors of mortality in type 1 and type 2 diabetes mellitus: a 23-year follow-up

AIMS/HYPOTHESIS

We evaluated the association of QT interval corrected for heart rate (QT(c)) and resting heart rate (rHR) with mortality (all-causes, cardiovascular, cardiac, and ischaemic heart disease) in subjects with type 1 and type 2 diabetes.

METHODS

We followed 523 diabetic patients (221 with type 1 diabetes, 302 with type 2 diabetes) who were recruited between 1974 and 1977 in Switzerland for the WHO Multinational Study of Vascular Disease in Diabetes. Duration of follow-up was 22.6 +/- 0.6 years. Causes of death were obtained from death certificates, hospital records, post-mortem reports, and additional information given by treating physicians.

RESULTS

In subjects with type 1 diabetes QT(c), but not rHR, was associated with an increased risk of: (1) all-cause mortality (hazard ratio [HR] 1.10 per 10 ms increase in QT(c), 95% CI 1.02-1.20, p = 0.011); (2) mortality due to cardiovascular (HR 1.15, 1.02-1.31, p = 0.024); and (3) mortality due to cardiac disease (HR 1.19, 1.03-1.36, p = 0.016). Findings for subjects with type 2 diabetes were different: rHR, but not QT(c) was associated with mortality due to: (1) all causes (HR 1.31 per 10 beats per min, 95% CI 1.15-1.50, p < 0.001); (2) cardiovascular disease (HR 1.43, 1.18-1.73, p < 0.001); (3) cardiac disease (HR 1.45, 1.19-1.76, p < 0.001); and (4) ischaemic heart disease (HR 1.52, 1.21-1.90, p < 0.001). Effect modification of QT(c) by type 1 and rHR by type 2 diabetes was statistically significant (p < 0.05 for all terms of interaction).

CONCLUSIONS/INTERPRETATION

QT(c) is associated with long-term mortality in subjects with type 1 diabetes, whereas rHR is related to increased mortality risk in subjects with type 2 diabetes.

Impaired cell communication in the diabetic heart. The role of the renin angiotensin system

The influence of diabetes mellitus on the process of cell communication and impulse propagation was investigated in trabeculae isolated from the ventricle of diabetic rat hearts. Diabetes was produced by a single intraperitoneal injection of streptozotocin (60 mg/Kg). Cell-to-cell spread of Lucifer yellow CH was studied with the cut-end method. Measurements of the diffusion coefficient of Lucifer Yellow CH (D) was made by fitting the experimental results to theoretical points using an interactive computer program for non-linear regression. The results indicated an average value of D of 3 +/- 0.8x10(-7 )cm(2)/s for the controls (n = 5) and 3.8 +/- 0.5x10(-8 )cm(2)/s (n = 7) (p < 0.05) for diabetic hearts. No change of efflux of the dye through the surface cell membrane was found in diabetic rat compared to controls (p > 0.05). Moreover, the dye binding in the cytosol of diabetic heart was not significantly different from controls. The calculated values of junctional permeability for the dye was found to be p (j) = 1.5x10(-3 )cm/s for control and 1.5x10(-5 )cm/s for diabetic heart. To investigate the possible role of the activation of the renin-angiotensin system (RAS) on the change in cell communication, diabetic rats were treated with enalapril (25 mg/Kg/day) for a period of 14 days. Measurements of the diffusion coefficient (D) of the dye indicated a significant increase of D (6.7 +/- 1.1x10(-7 )cm(2)/s) (n = 4) (p < 0.05) compared with diabetic rats not exposed to enalapril. No change on efflux of the dye or cytoplasmic binding was found in animals treated with enalapril. The calculated value of junctional permeability showed a significant increase (p (j) = 3.9x10(-4 )cm/s) in presence of enalapril compared with controls. In addition, angiotensin II (10(-8 )M) added to the bath caused a significant decrease of conduction velocity in cardiac muscle of diabetic heart. In conclusion, Cell communication and impulse propagation are significantly impaired in the ventricle from diabetic rats, a phenomenon partly related to the activation of the RAS.

Electrocardiographic Predictors of Incident Congestive Heart Failure and All-Cause Mortality in Postmenopausal Women

Background— Information is limited about ECG predictors of the risk of incident congestive heart failure (CHF), particularly in women without overt manifestations of cardiovascular disease (CVD).

Methods and Results— We evaluated hazard ratios for incident CHF and all-cause mortality using Cox regression in 38 283 participants of the Women’s Health Initiative (WHI) during a 9-year follow-up. All risk models were adjusted for demographic and available clinical and therapeutic variables (multivariable-adjusted models). A backward selection procedure was used to identify dominant predictors among those that were significant as individual ECG predictors. Eleven ECG variables were significant predictors of incident CHF, with none of them having a significant interaction with baseline CVD status. From 6 dominant ECG predictors, wide QRS/T angle had a nearly 3-fold increased risk in multivariable-adjusted single ECG variable models. Two other repolarization variables, STV 5 depression and high TV 1 amplitude, and 2 QRS-related variables, QRS non-dipolar voltage and myocardial infarction (MI) by ECG, were all associated with &2-fold increase of incident CHF risk. Overall, 11 of the 12 ECG variables were significant predictors of all-cause mortality. Four variables had a significant interaction with CVD status requiring stratification. Three among these 4 were strong, dominant predictors in the CVD group: ECG MI, wide QRS/T angle, and low TV 5 amplitude had risk increase from >2-fold to 3-fold, with considerably lower risks in the CVD-free group.

Conclusions— Several repolarization variables in postmenopausal women are predictors of the risk of incident CHF and all-cause mortality as important as old ECG MI.