Sudden death, impaired glucose tolerance, and diabetes in Japanese American men

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.

The influence of different glucose tolerance on QTc interval: a population-based study

BACKGROUND

Corrected QT (QTc) interval has been reported to be associated with type 2 diabetes. This study aimed to explore the relationship between different glucose tolerance and QTc intervals among middle-aged and older Chinese individuals.

METHODS

We conducted a cross-sectional analysis that included 9898 subjects (3194 men and 6704 women) in a Chinese population. Glucose tolerance was studied during the oral glucose tolerance test (OGTT). Insulin, blood pressure, hemoglobin A1c (HbA1c), serum lipids, hepatic transaminases and waist-to-hip ratio were assessed. The QTc interval was derived from ECG recordings, and the subjects were stratified based on different glucose tolerance.

RESULTS

QTc interval levels were increased significantly in the subjects with abnormal glucose metabolism compared with the normal glucose regulation group. Multiple regression analyses showed that the QTc interval was significantly associated with fasting plasma glucose, 2-h OGTT plasma glucose and HbA1c. The odds ratio of prolonged QTc was 1.396 for impaired glucose regulation (IFG)/impaired fasting glucose (IGT) (95% CI 0.126-1.730), and 1.342 for type 2 diabetes (95% CI 0.142-1.577) after all potential confounders were adjusted.

CONCLUSIONS

Impaired glucose tolerance (IGR) and diabetes are associated with prolonged QTc intervals among middle-aged and older Chinese individuals. Abnormal glucose regulation can be used to monitor the QTc interval in the population.

Sudden Cardiac Death in Patients With Type 1 Versus Type 2 Diabetes

OBJECTIVE

To investigate the association between type 1 diabetes mellitus (T1D) and type 2 diabetes mellitus (T2D) with risk of sudden cardiac arrest (SCA).

METHODS

In a prospective community-based study of SCA from February 1, 2002, through November 30, 2019, we ascertained 2771 cases age 18 years of age or older and matched them to 8313 controls based on geography, age, sex, and race/ethnicity. We used logistic regression to evaluate the independent association between diabetes, T1D, T2D, and SCA.

RESULTS

Patients had a mean age of 64.5±15.9 years, were 33.3% female and 23.9% non-White race. Overall, 36.7% (n=1016) of cases and 23.8% (n=1981) of controls had diabetes. Among individuals with diabetes, the proportion of T1D was 6.5% (n=66) among cases and 2.0% among controls (n=40). Diabetes was associated with 1.5-times higher odds of SCA. Compared with those without diabetes, the odds ratio and 95% CI for SCA was 4.36 (95% CI, 2.81 to 6.75; P<.001) in T1D and 1.45 (95% CI, 1.30 to 1.63; P<.001) in T2D after multivariable adjustment. Among those with diabetes, the odds of having SCA were 2.41 times higher in T1D than in T2D (95% CI, 1.53 to 3.80; P<.001). Cases of SCA with T1D were more likely to have an unwitnessed arrest, less likely to receive resuscitation, and less likely to survive compared with those with T2D.

CONCLUSION

Type 1 diabetes was more strongly associated with SCA compared with T2D and had less favorable outcomes following resuscitation. Diabetes type could influence the approach to risk stratification and prevention of SCA.

Association Between Time in Range and Postprandial Glucose Contribution Rate in Non-Insulin-Treated Type 2 Diabetes Patients: Inverse Correlation of Time in Range with Postprandial Glucose Contribution Rate

Background: Whether time in range (TIR), a parameter derived from continuous glucose monitoring (CGM), is a marker of postprandial hyperglycemia remains to be determined. In this study, we examined the association between TIR and postprandial glucose in non-insulin-treated type 2 diabetic patients. Methods: Our cross-sectional study included 729 non-insulin-treated patients with type 2 diabetes who underwent CGM without any changes in drug therapy on admission. The 24-h CGM record was analyzed for average glucose, standard deviation, percentage coefficient of variation, time above range, TIR, time below range, area under the curve (AUC) of basal glucose, AUC of postprandial glucose, and postprandial glucose contribution rate (%). The primary endpoint was the association between TIR and the postprandial glucose contribution rate. Results: We made TIR groups divided into 10% increments for a 7-group and compared with <40% to >90%. The basal and postprandial glucose AUCs correlated negatively with TIR. The postprandial glucose contribution rate correlated with TIR. The cutoff value for TIR, where postprandial glucose contribution rate was lower than the basal glucose contribution rate, was 66.3%. Conclusions: In non-insulin-treated type 2 diabetic patients, postprandial glucose AUC was higher in the high TIR group, whereas the basal glucose AUC was higher in the low TIR group. Good glycemic control can be achieved with therapeutic interventions that target postprandial glucose and basal glucose in patients with TIR ≥66.3% and <66.3%, respectively. University Medical Information Network [UMIN] ID: UMIN0000254333.

Ca2+ mishandling and mitochondrial dysfunction: a converging road to prediabetic and diabetic cardiomyopathy

Diabetic cardiomyopathy is defined as the myocardial dysfunction that suffers patients with diabetes mellitus (DM) in the absence of hypertension and structural heart diseases such as valvular or coronary artery dysfunctions. Since the impact of DM on cardiac function is rather silent and slow, early stages of diabetic cardiomyopathy, known as prediabetes, are poorly recognized, and, on many occasions, cardiac illness is diagnosed only after a severe degree of dysfunction was reached. Therefore, exploration and recognition of the initial pathophysiological mechanisms that lead to cardiac dysfunction in diabetic cardiomyopathy are of vital importance for an on-time diagnosis and treatment of the malady. Among the complex and intricate mechanisms involved in diabetic cardiomyopathy, Ca²⁺ mishandling and mitochondrial dysfunction have been described as pivotal early processes. In the present review, we will focus on these two processes and the molecular pathway that relates these two alterations to the earlier stages and the development of diabetic cardiomyopathy.

Ischemic Heart Disease Related Sudden Cardiac Death in Autopsied Cases: An Egyptian perspective

ABSTRACT

Diagnosis of the underlying cause of sudden unexpected death in a previously healthy individual remains one of the important challenges in forensic practice. Ischemic heart disease is the most common cause of sudden death. The current study aims to investigate the incidence and pathology of sudden ischemic cardiac death in Egypt. All cases of sudden cardiac death (SCD) examined by different forensic departments throughout Egypt during the period of January 2010 through December 2014 were included. Cases underwent complete autopsy examination including a thorough gross and microscopic examination of the heart and great blood vessels. Of 535 cases of SCD diagnosed during the period of the study, coronary atherosclerosis was the principle finding in 420 (78.5%) cases. The highest numbers of deaths were reported in fifth and sixth decades with male preference. Other causes of SCD included myocarditis, cardiomyopathies, valvular heart disease, and hypertensive heart disease (7.8%, 4.1%, 4.1%, and 2.8%, respectively). There was severe stenosis (>75%) of at least 1 coronary artery in 74% of cases. Type VI atherosclerosis was found in 40.7% of cases. The left anterior descending branch was the most affected artery by atherosclerosis. Acute coronary pathological events were demonstrated in 27.6% of cases. Recent myocardial infarction was evident in 55.5% of cases, whereas old infarcts were demonstrated in 44.5% of cases. Features of hypertensive heart disease were present in 18.3% of cases. In conclusion, ischemic heart disease is the leading cause of SCD in Egypt.

Exercise based assessment of cardiac autonomic function in type 1 versus type 2 diabetes mellitus

Background

Cardiac autonomic neuropathy (CAN) is a complication of diabetes mellitus (DM) that is associated with increased mortality. Exercise-based assessment of autonomic function has identified diminished parasympathetic reactivation after exercise in type 2 DM. It is postulated herein, that this would be more prominent among those with type 1 DM.

Methods

Sixteen subjects with type 1 DM (age 32.9 ± 10.1 years), 18 subjects with type 2 DM (55.4 ± 8.0 years) and 30 controls (44.0 ± 11.6 years) underwent exercise-based assessment of autonomic function. Two 16-min submaximal bicycle tests were performed followed by 45 min of recovery. On the second test, atropine (0.04 mg/kg) was administered near end-exercise so that all of the recovery occurred under parasympathetic blockade. Plasma epinephrine and norepinephrine levels were measured at rest, during exercise, and during recovery.

Results

There were no differences in resting or end-exercise heart rates in the three groups. Parasympathetic effect on RR-intervals during recovery (p < 0.03) and heart rate recovery (p = 0.02) were blunted in type 2 DM. Type 1 DM had higher baseline epinephrine and norepinephrine levels (p < 0.03), and exhibited persistent sympathoexcitation during recovery.

Conclusions

Despite a longer duration of DM in the study patients with type 1 versus type 2 DM, diminished parasympathetic reactivation was not noted in type 1 DM. Instead, elevation in resting plasma catecholamines was noted compared to type 2 DM and controls. The variable pathophysiology for exercise-induced autonomic abnormalities in type 1 versus type 2 DM may impact prognosis.

Targeted disruption of glycogen synthase kinase-3β in cardiomyocytes attenuates cardiac parasympathetic dysfunction in type 1 diabetic Akita mice

Type 1 diabetic Akita mice develop severe cardiac parasympathetic dysfunction that we have previously demonstrated is due at least in part to an abnormality in the response of the end organ to parasympathetic stimulation. Specifically, we had shown that hypoinsulinemia in the diabetic heart results in attenuation of the G-protein coupled inward rectifying K channel (GIRK) which mediates the negative chronotropic response to parasympathetic stimulation due at least in part to decreased expression of the GIRK1 and GIRK4 subunits of the channel. We further demonstrated that the expression of GIRK1 and GIRK4 is under the control of the Sterol Regulatory element Binding Protein (SREBP-1), which is also decreased in response to hypoinsulinemia. Finally, given that hyperactivity of Glycogen Synthase Kinase (GSK)3β, had been demonstrated in the diabetic heart, we demonstrated that treatment of Akita mice with Li⁺, an inhibitor of GSK3β, increased parasympathetic responsiveness and SREBP-1 levels consistent with the conclusion that GSK3β might regulate IKACh via an effect on SREBP-1. However, inhibitor studies were complicated by lack of specificity for GSK3β. Here we generated an Akita mouse with cardiac specific inducible knockout of GSK3β. Using this mouse, we demonstrate that attenuation of GSK3β expression is associated with an increase in parasympathetic responsiveness measured as an increase in the heart rate response to atropine from 17.3 ± 3.5% (n = 8) prior to 41.2 ± 5.4% (n = 8, P = 0.017), an increase in the duration of carbamylcholine mediated bradycardia from 8.43 ± 1.60 min (n = 7) to 12.71 ± 2.26 min (n = 7, P = 0.028) and an increase in HRV as measured by an increase in the high frequency fraction from 40.78 ± 3.86% to 65.04 ± 5.64 (n = 10, P = 0.005). Furthermore, patch clamp measurements demonstrated a 3-fold increase in acetylcholine stimulated peak IKACh in atrial myocytes from GSK3β deficiency mice compared with control. Finally, western blot analysis of atrial extracts from knockout mice demonstrated increased levels of SREBP-1, GIRK1 and GIRK4 compared with control. Taken together with our prior observations, these data establish a role of increased GSK3β activity in the pathogenesis of parasympathetic dysfunction in type 1 diabetes via the regulation of IKACh and GIRK1/4 expression.

The Association of Fasting Glucose, Insulin, and C-Peptide, with 19-Year Incidence of Coronary Heart Disease in Older Japanese-American Men; the Honolulu Heart Program

The role of fasting glucose, insulin levels, and C-peptide in coronary heart disease (CHD) in non-diabetic individuals remains uncertain. We examined the association between fasting glucose, insulin and C-peptide with the long-term incidence of CHD in Japanese-American men. In 1980–1982, from a random sample of the Honolulu Heart Program men (n = 1378), aged 61–81 years, data on several CHD and metabolic risk factors were obtained to examine the relation of fasting glucose, insulin and C-peptide to 19-year CHD incidence. Age-adjusted incidence of CHD increased with increasing quintiles of glucose, insulin and C-peptide. Age-adjusted CHD rates in the glucose quintiles were 11.9, 11.6, 14.4, 18.1 and 24.1 per 1000 person-years (trend p < 0.001). In individual Cox models (lowest quintiles of glucose, insulin and C-peptide as reference) the relative risks (95% confidence interval) of CHD incidence for the glucose quintiles adjusting for age, smoking, hypertension, cholesterol, physical activity, and body mass index, were 0.9 (0.6–1.4), 1.2 (0.8–1.8), 1.4 (0.9–2.2), and 1.7 (1.1–2.6), respectively (trend p = 0.004). Insulin and C-peptide were not significantly associated with CHD on multivariate analysis. Fasting glucose remained the only significant predictor of increased CHD risk (p = 0.003) in a model combining all 3 metabolic variables. In this cohort, only fasting glucose independently predicts long-term incidence of CHD. Age-adjusted insulin and C-peptide levels were associated with CHD incidence, but after adjustment for other risk factors, do not independently predict CHD.

Comparison of Survival After In-Hospital Cardiac Arrest in Patients With Versus Without Diabetes Mellitus

Diabetes mellitus (DM) increases the risk of sudden cardiac death, but the extent to which it influences survival after an in-hospital cardiac arrest (IHCA) remains unclear. We assessed the association of DM and survival after IHCA. The study included 1,009,073 patients aged ≥18 years who underwent cardiopulmonary resuscitation for IHCA between January 2003 and December 2013, recorded in the Nationwide Inpatient Sample database. The outcomes were survival to hospital discharge and discharge disposition assessed using multivariable logistic regression accounting for relevant covariates and clustering. Of the patients with IHCA, 30.8% (310,825) had DM and were more likely to be older and to have a higher prevalence of co-morbidities including hypertension, dyslipidemia, chronic kidney disease, and previous cardiovascular disease (all p <0.001). The rates of survival to hospital discharge after IHCA were 27.0% and 25.1% in patients with and without DM, respectively. After multivariable adjustment, DM was associated with a modestly lower risk-adjusted survival to hospital discharge (adjusted OR [aOR] 0.96, 95% confidence interval [95% CI] 0.95 to 0.97, p <0.001). This association was influenced by a number of factors (all interaction p <0.001), including a lower risk of survival among patients with DM who were younger (aOR 0.93, 95% CI 0.92 to 0.94 among those aged <75 years), those with a primary cardiovascular diagnosis (aOR 0.88, 95% CI 0.86 to 0.89), and those with ventricular fibrillation/ventricular tachycardia as the cardiac arrest rhythm (aOR 0.88, 95% CI 0.79 to 0.82). Patients with DM had lower odds of being discharged home with self-care after surviving an IHCA (p <0.001). In conclusion, preexisting DM was associated with a modestly lower risk-adjusted chance of survival after an IHCA.

Severity and multiplicity of microvascular complications are associated with QT interval prolongation in patients with type 2 diabetes

Aims/Introduction

A prolonged QT interval plays a causal role in life‐threatening arrhythmia, and becomes a risk factor for sudden cardiac death. Here, we assessed the association between microvascular complications and the QT interval in patients with type 2 diabetes.

Materials and Methods

Patients with type 2 diabetes (n = 219) admitted to Nippon Medical School Hospital (Tokyo, Japan) for glycemic control were enrolled. QT interval was measured manually in lead II on the electrocardiogram, and corrected for heart rate using Bazett's formula (QTc). Diabetic neuropathy, retinopathy and nephropathy were assessed by neuropathic symptoms or Achilles tendon reflex, ophthalmoscopy and urinary albumin excretion, respectively.

Results

In univariate analyses, female sex (P = 0.025), duration of type 2 diabetes (P = 0.041), body mass index (P = 0.0008), systolic blood pressure (P = 0.0011) and receiving insulin therapy (P < 0.0001) were positively associated with QTc. Patients with each of the three microvascular complications had longer QTc than those without: neuropathy (P = 0.0005), retinopathy (P = 0.0019) and nephropathy (P = 0.0001). As retinopathy or nephropathy progressed, QTc became longer (P < 0.001 and P < 0.001 for trend in retinopathy and nephropathy, respectively). Furthermore, QTc was prolonged with the multiplicity of the microvascular complications (P < 0.001 for trend). Multiple regression analyses showed that neuropathy, nephropathy and the multiplicity of the microvascular complications were independently associated with QTc.

Conclusions

Patients with type 2 diabetes with severe microvascular complications might be at high risk for life‐threatening arrhythmia associated with QT interval prolongation.

Increased Short-Term Beat-to-Beat QT Interval Variability in Patients with Impaired Glucose Tolerance

Prediabetic states and diabetes are important risk factors for cardiovascular morbidity and mortality. Determination of short-term QT interval variability (STVQT) is a non-invasive method for assessment of proarrhythmic risk. The aim of the study was to evaluate the STVQT in patients with impaired glucose tolerance (IGT). 18 IGT patients [age: 63 ± 11 years, body mass index (BMI): 31 ± 6 kg/m2, fasting glucose: 6.0 ± 0.4 mmol/l, 120 min postload glucose: 9.0 ± 1.0 mmol/l, hemoglobin A1c (HbA1c): 5.9 ± 0.4%; mean ± SD] and 18 healthy controls (age: 56 ± 9 years, BMI: 27 ± 5 kg/m2, fasting glucose: 5.2 ± 0.4 mmol/l, 120 min postload glucose: 5.5 ± 1.3 mmol/l, HbA1c: 5.4 ± 0.3%) were enrolled into the study. ECGs were recorded, processed, and analyzed off-line. The RR and QT intervals were expressed as the average of 30 consecutive beats, the temporal instability of beat-to-beat repolarization was characterized by calculating STVQT as follows: STVQT = Σ|QTn + 1 - QTn| (30x√2)-1. Autonomic function was assessed by means of standard cardiovascular reflex tests. There were no differences between IGT and control groups in QT (411 ± 43 vs 402 ± 39 ms) and QTc (431 ± 25 vs 424 ± 19 ms) intervals or QT dispersion (44 ± 13 vs 42 ± 17 ms). However, STVQT was significantly higher in IGT patients (5.0 ± 0.7 vs 3.7 ± 0.7, P < 0.0001). The elevated temporal STVQT in patients with IGT may be an early indicator of increased instability of cardiac repolarization during prediabetic conditions.

Characteristics and outcomes of diabetic patients with an implantable cardioverter defibrillator in a real world setting: results from the Israeli ICD registry

Aims

There are limited data regarding the effect of diabetes mellitus (DM) on the risks of both appropriate and inappropriate implantable cardioverter defibrillator (ICD) therapy. The present study was designed to compare the outcome of appropriate and inappropriate ICD therapy in patients with or without DM.

Methods and results

The risk of a first appropriate ICD therapy for ventricular tachyarrhythmias (including anti tachycardia pacing and shock) was compared between 764 DM and 1346 non-DM patients enrolled in the national Israeli ICD registry. We also compared the risks of inappropriate ICD therapy, and death or cardiac hospitalization between diabetic and non-diabetic patients. Diabetic patients were older, were more likely to have ischemic cardiomyopathy, lower ejection fraction, atrial fibrillation, and other co-morbidities. The 3-year cumulative incidence of appropriate ICD therapy was similar in the DM and non-DM groups (12 and 13%, respectively, p = 0.983). Multivariate analysis showed that DM did not affect the risk of appropriate ICD therapy (HR = 1.07, 95% CI 0.78–1.47, p = 0.694) or inappropriate therapy (HR = 0.72, 95% CI 0.42–1.23, p = 0.232). However, DM was associated with a 31% increased risk for death or cardiac hospitalization (p = 0.005). Results were similar in subgroup analyses including ICD and defibrillators with cardiac resynchronization therapy function recipients, primary or secondary prevention indication for an ICD.

Conclusions

Despite a significant excess of cardiac hospitalizations and mortality in the diabetic population, there was no difference in the rate of ICD treatments, suggesting that the outcome difference is not related to arrhythmias.

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.

Ryanodine receptor phosphorylation by CaMKII promotes spontaneous Ca(2+) release events in a rodent model of early stage diabetes: The arrhythmogenic substrate

BACKGROUND

Heart failure and arrhythmias occur more frequently in patients with type 2 diabetes (T2DM) than in the general population. T2DM is preceded by a prediabetic condition marked by elevated reactive oxygen species (ROS) and subclinical cardiovascular defects. Although multifunctional Ca2+ calmodulin-dependent protein kinase II (CaMKII) is ROS-activated and CaMKII hyperactivity promotes cardiac diseases, a link between prediabetes and CaMKII in the heart is unprecedented.

OBJECTIVES

To prove the hypothesis that increased ROS and CaMKII activity contribute to heart failure and arrhythmogenic mechanisms in early stage diabetes.

METHODS-RESULTS

Echocardiography, electrocardiography, biochemical and intracellular Ca2+ (Ca2+i) determinations were performed in fructose-rich diet-induced impaired glucose tolerance, a prediabetes model, in rodents. Fructose-rich diet rats showed decreased contractility and hypertrophy associated with increased CaMKII activity, ROS production, oxidized CaMKII and enhanced CaMKII-dependent ryanodine receptor (RyR2) phosphorylation compared to rats fed with control diet. Isolated cardiomyocytes from fructose-rich diet showed increased spontaneous Ca2+i release events associated with spontaneous contractions, which were prevented by KN-93, a CaMKII inhibitor, or addition of Tempol, a ROS scavenger, to the diet. Moreover, fructose-rich diet myocytes showed increased diastolic Ca2+ during the burst of spontaneous Ca2+i release events. Mice treated with Tempol or with sarcoplasmic reticulum-targeted CaMKII-inhibition by transgenic expression of the CaMKII inhibitory peptide AIP, were protected from fructose-rich diet-induced spontaneous Ca2+i release events, spontaneous contractions and arrhythmogenesis in vivo, despite ROS increases.

CONCLUSIONS

RyR2 phosphorylation by ROS-activated CaMKII, contributes to impaired glucose tolerance-induced arrhythmogenic mechanisms, suggesting that CaMKII inhibition could prevent prediabetic cardiovascular complications and/or evolution.

Implantable cardioverter defibrillators in diabetics: efficacy and safety in patients at risk of sudden cardiac death

Diabetes mellitus is a major risk factor for arrhythmogenesis and is associated with a two-fold increase in all-cause mortality and a four-fold increase in cardiovascular mortality including sudden cardiac death when compared with nondiabetics. Implantable cardioverter defibrillators (ICD) have been shown to effectively reduce arrhythmic death and all-cause mortality in patients with severe myocardial dysfunction. With a high competing risk of nonarrhythmic cardiac and noncardiac death, survival benefit of ICD in patients with diabetes mellitus could be reduced, but the subanalysis of diabetic patients in randomized clinical trials provides reassurance regarding a similar beneficial survival effect of ICD and cardiac resynchronization therapy in diabetics, as observed in the overall population with advanced heart disease. In this article, the authors highlight some of the clinical issues related to diabetes, summarize the data on the efficacy of ICD in diabetics when compared with nondiabetics and discuss concerns related to ICD implantation in patients with diabetes.

Increased inducibility of ventricular tachycardia and decreased heart rate variability in a mouse model for type 1 diabetes: effect of pravastatin

Although a reduction in the high-frequency (HF) component of heart rate variability (HRV) is a major complication of diabetes and a risk factor for sudden death, its relationship to ventricular tachycardia (VT) is unknown. We developed a mouse model for the study of VT and its relationship to changes in HRV in the Akita type 1 diabetic mouse. Programmed ventricular stimulation of anesthetized mice demonstrated that Akita mice were more inducible for VT compared with wild-type mice: 78.6% versus 28.6% (P = 0.007). Optical mapping of perfused hearts demonstrated multifocal breakthroughs that occasionally gave rise to short-lived rotors consistent with focal initiation and maintenance of VT. Treatment of Akita mice with pravastatin, which had been previously shown clinically to decrease ventricular ectopy and to increase HRV, decreased the inducibility of VT: 36.8% compared with 75.0% with placebo treatment (P = 0.022). The HF fraction of HRV was reduced in Akita mice (48.6 ± 5.2% vs. 70.9 ± 4.8% in wild-type mice, P = 0.005) and was increased compared with placebo treatment in pravastatin-treated mice. Pretreatment of Akita mice with the muscarinic agonist carbamylcholine or the β-adrenergic receptor blocker propranolol decreased the inducibility of VT (P = 0.001). In conclusion, the increased inducibility of focally initiated VT and reduced HF fraction in Akita mice were partially reversed by both pravastatin treatment and pharmacologic reversal of parasympathetic dysfunction. In this new animal model for the study of the pathogenesis of VT in type 1 diabetes, pravastatin may play a role in the prevention of VT by attenuating parasympathetic dysfunction.

Impaired fasting plasma glucose and type 2 diabetes are related to the risk of out-of-hospital sudden cardiac death and all-cause mortality

OBJECTIVE

The aim of the study was to determine whether impaired fasting plasma glucose (FPG) and type 2 diabetes may be risk factors for sudden cardiac death (SCD).

RESEARCH DESIGN AND METHODS

This prospective study was based on 2,641 middle-aged men 42-60 years of age at baseline. Impaired FPG level (≥5.6 mmol/L) among nondiabetic subjects (501 men) was defined according to the established guidelines, and the group with type 2 diabetes included subjects (159 men) who were treated with oral hypoglycemic agents, insulin therapy, and/or diet.

RESULTS

During the 19-year follow-up, a total of 190 SCDs occurred. The relative risk (RR) for SCD was 1.51-fold (95% CI 1.07-2.14, P = 0.020) for nondiabetic men with impaired FPG and 2.86-fold (1.87-4.38, P < 0.001) for men with type 2 diabetes as compared with men with normal FPG levels, after adjustment for age, BMI, systolic blood pressure, serum LDL cholesterol, smoking, prevalent coronary heart disease (CHD), and family history of CHD. The respective RRs for out-of-hospital SCDs (157 deaths) were 1.79-fold (1.24-2.58, P = 0.001) for nondiabetic men with impaired FPG and 2.26-fold (1.34-3.77, P < 0.001) for men with type 2 diabetes. Impaired FPG and type 2 diabetes were associated with the risk of all-cause death. As a continuous variable, a 1 mmol/L increment in FPG was related to an increase of 10% in the risk of SCD (1.10 [1.04-1.20], P = 0.001).

CONCLUSIONS

Impaired FPG and type 2 diabetes represent risk factors for SCD.

Diabetes increases mortality after myocardial infarction by oxidizing CaMKII

Diabetes increases oxidant stress and doubles the risk of dying after myocardial infarction, but the mechanisms underlying increased mortality are unknown. Mice with streptozotocin-induced diabetes developed profound heart rate slowing and doubled mortality compared with controls after myocardial infarction. Oxidized Ca(2+)/calmodulin-dependent protein kinase II (ox-CaMKII) was significantly increased in pacemaker tissues from diabetic patients compared with that in nondiabetic patients after myocardial infarction. Streptozotocin-treated mice had increased pacemaker cell ox-CaMKII and apoptosis, which were further enhanced by myocardial infarction. We developed a knockin mouse model of oxidation-resistant CaMKIIδ (MM-VV), the isoform associated with cardiovascular disease. Streptozotocin-treated MM-VV mice and WT mice infused with MitoTEMPO, a mitochondrial targeted antioxidant, expressed significantly less ox-CaMKII, exhibited increased pacemaker cell survival, maintained normal heart rates, and were resistant to diabetes-attributable mortality after myocardial infarction. Our findings suggest that activation of a mitochondrial/ox-CaMKII pathway contributes to increased sudden death in diabetic patients after myocardial infarction.

Sudden cardiac death after myocardial infarction in type 2 diabetic patients with no residual myocardial ischemia

OBJECTIVE

Diabetes mellitus (DM) is a well-established risk factor for coronary artery disease. Nonetheless, it remains unclear whether DM contributes to sudden cardiac death in patients who survive myocardial infarction (MI). The objective of this study was to compare the incidence of sudden cardiac death post-MI in diabetic and nondiabetic patients with no residual myocardial ischemia.

RESEARCH DESIGN AND METHODS

A total of 610 consecutive post-MI patients referred to a cardiac rehabilitation program with negative exercise stress test were studied.

RESULTS

Of these, 236 patients had DM at baseline. Over a mean follow-up of 5 years, 67 patients with DM (28.4%) and 76 of 374 patients without DM (20.2%) had died with a hazard ratio (HR) of 1.74 (95% CI: 1.28-2.56; P < 0.001). Patients with DM also had a higher incidence of cardiac death (1.84 [1.16-3.21]; P = 0.01), principally due to a higher incidence of sudden cardiac death (2.14 [1.22-4.23]; P < 0.001). Multiple Cox regression analysis revealed that only DM (adjusted HR: 1.9 [95% CI: 1.04-3.40]; P = 0.04), left ventricular ejection fraction (LVEF) ≤30% (3.6 [1.46-8.75]; P < 0.01), and New York Heart Association functional class >II (4.2 [1.87-9.45]; P < 0.01) were independent predictors for sudden cardiac death. Among patients with DM, the 5-year sudden cardiac death rate did not differ significantly among those with LVEF ≤30%, LVEF 31-50%, or LVEF >50% (8.8 vs. 7.8 vs. 6.8%, respectively; P = 0.83).

CONCLUSIONS

Post-MI patients with DM, even in the absence of residual myocardial ischemia clinically, were at higher risk of sudden cardiac death than their non-DM counterparts.

Absence of glucose transporter 4 diminishes electrical activity of mouse hearts during hypoxia

Insulin resistance, which characterizes type 2 diabetes, is associated with reduced translocation of glucose transporter 4 (GLUT4) to the plasma membrane following insulin stimulation, and diabetic patients with insulin resistance show a higher incidence of ischaemia, arrhythmias and sudden cardiac death. The aim of this study was to examine whether GLUT4 deficiency leads to more severe alterations in cardiac electrical activity during cardiac stress due to hypoxia. To fulfil this aim, we compared cardiac electrical activity from cardiac-selective GLUT4-ablated (G4H-/-) mouse hearts and corresponding control (CTL) littermates. A custom-made cylindrical 'cage' electrode array measured potentials (Ves) from the epicardium of isolated, perfused mouse hearts. The normalized average of the maximal downstroke of Ves ( (|d Ves/dt(min)|na), which we previously introduced as an index of electrical activity in normal, ischaemic and hypoxic hearts, was used to assess the effects of GLUT4 deficiency on electrical activity. The |d Ves/dt(min)|na of G4H −/− and CTL hearts decreased by 75 and 47%, respectively (P < 0.05), 30 min after the onset of hypoxia. Administration of insulin attenuated decreases in values of |d Ves/dt(min)|na in G4H −/− hearts as well as in CTL hearts, during hypoxia. In general, however, G4H −/− hearts showed a severe alteration of the propagation sequence and a prolonged total activation time. Results of this study demonstrate that reduced glucose availability associated with insulin resistance and a reduction in GLUT4-mediated glucose transport impairs electrical activity during hypoxia, and may contribute to cardiac vulnerability to arrhythmias in diabetic patients.

QT variability index changes with severity of cardiovascular autonomic neuropathy

Cardiovascular autonomic neuropathy (CAN) has been frequently postulated to increase susceptibility to ventricular arrhythmias and sudden cardiac death in diabetic patients. The relation between the progression of CAN in diabetes and ventricular repolarization remains to be fully described. Therefore, this study examined QT interval variability and heart rate interbeat variability to identify any alterations of cardiac repolarization in diabetic patients in relation to severity of CAN. Seventy control participants without (CAN-) and 74 patients with CAN (CAN+) were enrolled in this study. Among 74 CAN + patients, 62 are early CAN + (eCAN +) , and 12 are definite CAN + (dCAN +) according to autonomic nervous system function tests as described by Ewing. The results showed that the QT variability index (QTVI) was significantly higher and positive in the dCAN + (0.51 ±1.32) group than in the eCAN + (-0.39 ±0.91) and CAN - (-0.54 ±0.72) groups. The QT variability to heart-rate variability ratio provides a measure of the balance between QT and heart interbeat variability. QTVI was more sensitive in identifying disease progression at all stages. Our study supports the hypothesis that QTVI could be used as a clinical test to identify early CAN and as a marker of CAN progression in diabetic patients and may help physicians in determining the best therapeutic strategy for these patients.

Functional neuroanatomy and sleep-disordered breathing: implications for autonomic regulation

A major concern with sleep-disordered breathing conditions, which include obstructive sleep apnea (OSA), central apnea, and congenital central hypoventilation syndrome (CCHS), is the high incidence of accompanying autonomic dysfunction and metabolic disorders. Patients with OSA show exaggerated sympathetic tone, leading to hypertension, cardiac arrhythmia, profuse sweating, impaired cerebral perfusion, and stroke. In addition, OSA appears in 86% of obese Type II diabetic patients, suggesting common deleterious processes. Autonomic deficiencies also appear in CCHS patients, who are often hypoglycemic. The impaired autonomic control may stem from injury to central sympathetic and parasympathetic regulatory areas resulting from apnea-related inflammation, hypoxia, or perfusion-related consequences in OSA, and genetic mutation repercussions in CCHS. Disturbed sleep organization from apnea arousals may also disrupt hormonal release. Brain areas affected in both OSA and CCHS include cortical and limbic regions that influence hypothalamic-regulated sympathetic control and hormone release, essential for glycemic regulation, as well as parasympathetic nuclei influencing the pancreas and other viscera, and raphé serotonergic sites, important for thermal and vascular regulation. Brain injury and altered functional responses appear in OSA and CCHS, assessed with magnetic resonance imaging techniques, in areas which show regional gray matter loss, alterations of free water within tissue, loss of axonal integrity, and disruption of functional responses to autonomic and ventilatory challenges. Evaluation of neural injury and distortion in functional signals to autonomic challenges in localized brain areas can provide insights into common pathological mechanisms for dysregulation of hormonal release and autonomic processes in sleep-disordered breathing and metabolic disorders.

Common genetic variants associated with sudden cardiac death: the FinSCDgen study

Background

Sudden cardiac death (SCD) accounts for up to half of cardiac mortality. The risk of SCD is heritable but the underlying genetic variants are largely unknown. We investigated whether common genetic variants predisposing to arrhythmia or related electrocardiographic phenotypes, including QT-interval prolongation, are associated with increased risk of SCD.

Methodology/Principal Findings

We studied the association between 28 candidate SNPs and SCD in a meta-analysis of four population cohorts (FINRISK 1992, 1997, 2002 and Health 2000, n = 27,629) and two forensic autopsy series (The Helsinki Sudden Death Study and The Tampere Autopsy Study, n = 694). We also studied the association between established cardiovascular risk factors and SCD. Causes of death were reviewed using registry-based health and autopsy data. Cox regression and logistic regression models were adjusted for age, sex, and geographic region. The total number of SCDs was 716. Two novel SNPs were associated with SCD: SCN5A rs41312391 (relative risk [RR] 1.27 per minor T allele, 95% CI 1.11–1.45, P = 3.4×10⁻⁴) and rs2200733 in 4q25 (RR 1.28 per minor T allele, 95% CI 1.11–1.48, P = 7.9×10⁻⁴). We also replicated the associations for 9p21 (rs2383207, RR 1.13 per G allele, 95% CI 1.01–1.26, P = 0.036), as well as for male sex, systolic blood pressure, diabetes, cigarette smoking, low physical activity, coronary heart disease, and digoxin use (P<0.05).

Conclusions/Significance

Two novel genetic variants, one in the cardiac sodium channel gene SCN5A and another at 4q25 previously associated with atrial fibrillation, are associated with SCD.

Use of the dietary supplement 5-aminiolevulinic acid (5-ALA) and its relationship with glucose levels and hemoglobin A1C among individuals with prediabetes

OBJECTIVE

This study examined the association between 5-aminolevulinic acid (5-ALA) and glucose tolerance.

DESIGN

A double blinded, randomized prospective parallel-group comparison study.

SETTING

Participants were recruited from the community in Honolulu, Hawaii, using radio and TV ads, and at community events.

PARTICIPANTS

One hundred fifty-four males and females ages 40-70 years, with evidence of prediabetes: hemoglobin A1c (HbA1c) 5.8%-7.0% at the screening visit.

INTERVENTION

Participants were randomized equally to one of three study groups: (1) low dose 5-ALA supplement (15 mg capsule); (2) high dose 5-ALA (50 mg capsule); and (3) control (placebo capsule of identical size and color).

MAIN OUTCOME MEASURES

HbA1c and 2 hours post-oral glucose tolerance test (OGTT) glucose levels.

RESULTS

Among individuals taking 5-ALA supplements for 12 weeks, 2 hours post-OGTT glucose levels declined significantly compared to those not taking the supplement (p= 0.02). The relationships were stronger among those with baseline glucose intolerance, or 2 hours post-OGTT glucose measurements greater than 140 mg/dL (p= 0.005 and p= 0.02 for the low and high dose group, respectively). Similar trends were observed for HbA1c but results were of borderline significance (p= 0.07). No untoward effects were reported.

CONCLUSIONS

Further studies are indicated. The potential benefits of 5-ALA dietary supplementation are affirmed by this investigation.

Coronary artery calcification by computed tomography in epidemiologic research and cardiovascular disease prevention

Both American and European guidelines recommend coronary artery calcification (CAC) as a tool for screening asymptomatic individuals at intermediate risk for coronary heart disease (CHD). These recommendations are based on epidemiologic studies mostly in the United States. We review (1) the use of CAC in primary prevention of CHD in the United States, (2) epidemiologic studies of CAC in asymptomatic adults outside of the United States, and (3) international epidemiologic studies of CAC. This review will not consider clinical studies of CAC among patients or symptomatic individuals. US studies have shown that CAC is a strong independent predictor of CHD in both sexes among middle-aged and old age groups, various ethnic groups, and individuals with and without diabetes and that CAC plays an important role in reclassifying individuals from intermediate to high risk. Studies in Europe support these conclusions. The Electron-Beam Tomography, Risk Factor Assessment Among Japanese and US Men in the Post-World-War-II birth cohort (ERA JUMP) Study is the first international study to compare subclinical atherosclerosis, including CAC among Japanese, Japanese Americans, Koreans, and whites. It showed that as compared with whites, Japanese had lower levels of atherosclerosis, whereas Japanese Americans had similar or higher levels. CAC is being increasingly used as a screening tool for asymptomatic individuals in Europe and the United States. CAC is a powerful research tool, because it enables us to describe differences in atherosclerotic burden across populations. Such research could identify factors responsible for differences among populations, which may improve CHD prevention.

T-wave alternans and heart rate variability: a comparison in patients with myocardial infarction with or without diabetes mellitus

BACKGROUND

The aim of this study was to investigate the differences in T-wave alternans (TWA) and heart rate variability (HRV) among patients with myocardial infarction with or without diabetes mellitus and the relationship between TWA and HRV.

METHODS

The study population included 133 patients: 59 patients with myocardial infarction (MI) (group post-MI without diabetes); 40 myocardial infarction with diabetes (group post-MI with diabetes); and 34 controls (group control). Cardiac autonomic neuropathy assessment was made using frequency domain (low-frequency [LF] power, high-frequency [HF] power, LF/HF) and time domain (SDNN, standard deviation of the averaged normal sinus RR intervals for all 5-minute segments [SDANN]) of HRV indexes. Both TWA and HRV were measured on the Holter monitor, and TWA was calculated automatically using the time-domain modified moving average method.

RESULTS

TWA values differed significantly between controls (40 ± 16 μV) and group post-MI with (62 ± 17 μV, P < 0.05) or without (60 ± 15 μV, P < 0.05) diabetes. In addition, group post-MI with diabetes had lower standard deviation of all normal sinus RR intervals (SDNN), standard deviation of the averaged normal sinus RR intervals for all 5-minute segments (SDANN), and HF, indicating depressed vagus nerve activity, and higher LF/HF ratio, indicating elevated sympathetic nerve activity, than controls and group post-MI without diabetes (P < 0.05). TWA correlated with SDNN and SDANN (r = 0.29, 0.31; P < 0.001).

CONCLUSIONS

TWA was elevated in patients following myocardial infarction, both in those with or without diabetes. Myocardial infarction patients had a lower time domain, HF, and a higher LF/HF ratio HRV, especially in those with diabetes. The analysis of modified moving agerage (MMA)-based TWA and HRV can be a useful tool for identifying post-myocardial infarction patients at high risk of arrhythmic events.

Risk factor and prediction modeling for sudden cardiac death in women with coronary artery disease

BACKGROUND

To our knowledge, the risk of sudden cardiac death (SCD) and the assessment of risk factors in prediction models have not been evaluated in women with coronary artery disease (CAD). We sought to evaluate the incidence of SCD as well as its risk factors and their predictive accuracy among a population of women with CAD.

METHODS

The Heart and Estrogen/progestin Replacement Study evaluated the effects of hormone replacement therapy on cardiovascular events among 2763 postmenopausal women with CAD. Sudden cardiac death was defined as death resulting from a cardiac origin that occurred within 1 hour of symptom onset. The associations between candidate predictor variables and SCD were evaluated in a Cox proportional hazards model. The C-index was used to compare the predictive value of the clinical risk factors with left ventricular ejection fraction (LVEF) alone and in combination. The net reclassification improvement was also computed.

RESULTS

Over a mean follow-up of 6.8 years, SCD comprised 136 of the 254 cardiac deaths. The annual SCD event rate was 0.79% (95% confidence interval, 0.67-0.94). The following variables were independently associated with SCD in the multivariate model: myocardial infarction, heart failure, an estimated glomerular filtration rate of less than 40 mL/min/1.73 m(2), atrial fibrillation, physical inactivity, and diabetes. The incidences of SCD among women with 0 (n = 683), 1 (n = 1224), 2 (n = 610), and 3 plus (n = 246) risk factors at baseline were 0.3%, 0.5%, 1.2%, and 2.9% per year, respectively. The combination of clinical risk factors and LVEF (C-index, 0.681) were better predictors of SCD than LVEF alone (C-index, 0.600) and resulted in a net reclassification improvement of 0.20 (P < .001).

CONCLUSIONS

Sudden cardiac death comprised the majority of cardiac deaths among postmenopausal women with CAD. Independent predictors of SCD, including myocardial infarction, congestive heart failure, an estimated glomerular filtration rate of less than 40 mL/min/1.73 m(2), atrial fibrillation, physical inactivity, and diabetes, improved SCD prediction when they were considered in addition to LVEF.

Sudden cardiac death among people with diabetes: preventive measures documented in their medical records

AIMS

The purpose of this study was to examine how prevention of complications for people with diabetes mellitus had been conducted, as described in their medical records, focusing particularly on sudden cardiac death. A further aim was to compare the documentation with guidelines for diabetes care.

BACKGROUND

Diabetes mellitus is associated with an increased risk of cardiovascular disease, death and sudden cardiac death. About half of those affected by sudden cardiac death are assumed to have had one or more risk factors for cardiovascular disease that could have been treated effectively resulting in a reduced risk of sudden death.

DESIGN

Survey.

METHOD

Fifty-six people diagnosed with diabetes mellitus, who had died of a sudden cardiac arrest between the years 2003-2005, from the Northern Sweden MONICA myocardial registry were included. These people's medical records were examined with regard to documentation of the care given during the year prior to the person's sudden cardiac death.

RESULTS

The qualitative content analysis resulted in four categories: individualised goals for diabetes care; prevention of complications; self-care; and factors which may affect ability to adhere to treatment. The quantitative analysis showed that few people with diabetes mellitus achieved goals for metabolic control, compared with those set in guidelines for diabetes mellitus care.

CONCLUSION

To prevent complications for people with diabetes mellitus, it is a challenge for nurses and physicians to involve people with diabetes mellitus in their own care to improve the prognosis.

RELEVANCE TO CLINICAL PRACTICE

Examination of medical records of people with diabetes mellitus showed that documentation could be more informative and systematic. It is important to achieve better adherence to treatment and to increase people's understanding of their illness.

The case for hypoglycaemia as a proarrhythmic event: basic and clinical evidence

Recent clinical studies show that hypoglycaemia is associated with increased risk of death, especially in patients with coronary artery disease or acute myocardial infarction. This paper reviews data from cellular and clinical research supporting the hypothesis that acute hypoglycaemia increases the risk of malignant ventricular arrhythmias and death in patients with diabetes by generating the two classic abnormalities responsible for the proarrhythmic effect of medications, i.e. QT prolongation and Ca(2+) overload. Acute hypoglycaemia causes QT prolongation and the risk of ventricular tachycardia by directly suppressing K(+) currents activated during repolarisation, a proarrhythmic effect of many medications. Since diabetes itself, myocardial infarction, hypertrophy, autonomic neuropathy and congestive heart failure also cause QT prolongation, the arrhythmogenic effect of hypoglycaemia is likely to be greatest in patients with pre-existent cardiac disease and diabetes. Furthermore, the catecholamine surge during hypoglycaemia raises intracellular Ca(2+), thereby increasing the risk of ventricular tachycardia and fibrillation by the same mechanism as that activated by sympathomimetic inotropic agents and digoxin. Diabetes itself may sensitise myocardium to the arrhythmogenic effect of Ca(2+) overload. In humans, noradrenaline (norepinephrine) also lengthens action potential duration and causes further QT prolongation. Finally, both hypoglycaemia and the catecholamine response acutely lower serum K(+), which leads to QT prolongation and Ca(2+) loading. Thus, hypoglycaemia and the subsequent catecholamine surge provoke multiple, interactive, synergistic responses that are known to be proarrhythmic when associated with medications and other electrolyte abnormalities. Patients with diabetes and pre-existing cardiac disease may therefore have increased risk of ventricular tachycardia and fibrillation during hypoglycaemic episodes.

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.

Influence of diabetes and/or myocardial infarction on prevalence of abnormal T-wave alternans

BACKGROUND

Subjects with microvolt-level T-wave alternans (TWA) in association with structural heart disease have an increased risk for sudden cardiac death. The presence of diabetes (DM) is associated with an increased risk of sudden death but there is limited data on the impact of DM and previous myocardial infarction (MI) on TWA prevalence.

METHODS

We performed a case-control cross-sectional study in 140 patients referred for routine exercise testing within a large multispecialty clinic. All patients with a history of DM and MI status within the past year were eligible: group 1 (no DM or MI), group 2 (DM only), group 3 (MI only), group 4 (DM and MI). Patients performed a symptom-limited Bruce protocol exercise test with assessment of TWA by the spectral method using commercially available equipment. We used published criteria for the blinded interpretation of TWA; all tests not unequivocally negative were considered abnormal.

RESULTS

Age and gender were similar in all groups. The prevalence of abnormal TWA in groups 1-4 was 24%, 20%, 48%, and 62%, respectively (between group P = 0.002). Logistic regression analysis in all patients showed that abnormal TWA was related to prior MI [OR (95% CI): 4.0 (1.8-8.9), P < 0.001] but not to prevalent DM [0.9 (0.4-1.8), P = 0.72]. In patients with DM, the prevalence of abnormal TWA was related to reduced ejection fraction (P = 0.034) but not to BMI, DM duration, glycemic control, insulin use, or the presence of microvascular complications.

CONCLUSION

The presence of DM alone does not increase risk of abnormal TWA. Prospective studies are required to establish the prognostic value of TWA in patients with DM.

Characteristics of undiagnosed diabetes mellitus in a population undergoing health screening in Japan: target populations for efficient screening

AIMS

To estimate the prevalence of undiagnosed diabetes mellitus and its relationship with various risk factors in a population undergoing health screening in Japan.

METHODS

Oral glucose tolerance tests were carried out in a total sample of 14,674 Japanese subjects undergoing health screening, aged 20-83 years and without known diabetes. The prevalence of glucose tolerance categories (1999 WHO criteria) was adjusted for sample probabilities. The optimal FPG cut-off point for screening diabetes was estimated using ROC curve analysis for the continuous value of FPG corresponding to a 2-h PG of 200 mg/dl. The number needed to screen (NNTS) to identify one person with undiagnosed diabetes with various risk factors was estimated using the following equation: the number of undiagnosed diabetic plus nondiabetic subjects/the number of undiagnosed diabetic subjects.

RESULTS

The prevalence of undiagnosed diabetes among men and women was 6.4% (NNTS 15.7) and 3.2% (NNTS 31.7), respectively. The optimal FPG cut-off point for screening diabetes among men and women was 105 and 106 mg/dl, respectively. NNTS was lower in individuals with more risk factors, e.g. aging (> or =50), BMI (> or =25), hypertension (SBP> or =140 mmHg and/or DBP> or =90 mmHg) and dyslipidemia (TC> or =220 and/or HDL-C<40 and/or TG> or =150 mg/dl), resulting in the lowest NNTS in individuals having all four risk factors among men (6.1) and women (6.7), respectively.

CONCLUSIONS

In Japan, screening for diabetes may be more efficient among individuals having an FPG of more than 105-106 mg/dl and with more risk factors, especially in men.

Systematic review: comparative effectiveness and safety of premixed insulin analogues in type 2 diabetes

BACKGROUND

Evidence comparing premixed insulin analogues (a mixture of rapid-acting and intermediate-acting insulin analogues) with other antidiabetic agents is urgently required to guide appropriate therapy.

PURPOSE

To summarize the English-language literature on the effectiveness and safety of premixed insulin analogues compared with other antidiabetic agents in adults with type 2 diabetes.

DATA SOURCES

The authors searched MEDLINE, EMBASE, CINAHL, and the Cochrane Central Register of Controlled Trials from inception to February 2008 and sought unpublished data from the U.S. Food and Drug Administration, European Medicines Agency, and industry.

STUDY SELECTION

Studies with control groups that compared premixed insulin analogues with another antidiabetic medication in adults with type 2 diabetes.

DATA EXTRACTION

2 reviewers using standardized protocols performed serial abstraction.

DATA SYNTHESIS

Evidence from clinical trials was inconclusive for clinical outcomes, such as mortality. Therefore, the review focused on intermediate outcomes. Premixed insulin analogues were similar to premixed human insulin in decreasing fasting glucose levels, hemoglobin A(1c) levels, and the incidence of hypoglycemia but were more effective in decreasing postprandial glucose levels (mean difference, -1.1 mmol/L; 95% CI, -1.4 to -0.7 mmol/L [-19.2 mg/dL; 95% CI, -25.9 to -12.5 mg/dL]). Compared with long-acting insulin analogues, premixed insulin analogues were superior in decreasing postprandial glucose levels (mean difference, -1.5 mmol/L; CI, -1.9 to -1.2 mmol/L [-27.9 mg/dL; CI, -34.3 to -21.5 mg/dL]) and hemoglobin A(1c) levels (mean difference, -0.39% [CI, -0.50% to -0.28%]) but were inferior in decreasing fasting glucose levels (mean difference, 0.7 mmol/L; CI, 0.3 to 1.0 mmol/L [12.0 mg/dL; CI, 6.0 to 18.1 mg/dL]) and were associated with a higher incidence of hypoglycemia. Compared with noninsulin antidiabetic agents, premixed insulin analogues were more effective in decreasing fasting glucose levels (mean difference, -1.1 mmol/L; CI, -1.7 to -0.6 mmol/L [-20.5 mg/dL; CI, -29.9 to -11.2 mg/dL]), postprandial glucose levels (mean difference, -2.1 mmol/L; CI, -3.4 to -0.8 mmol/L [-37.4 mg/dL; CI, -61.0 to -13.7 mg/dL]), and hemoglobin A(1c) levels (mean difference, -0.49% [CI, -0.86% to -0.12%]) but were associated with a higher incidence of hypoglycemia.

LIMITATIONS

The literature search was restricted to studies published in English. Data on clinical outcomes were limited. The small number of studies for each comparison limited assessment of between-study heterogeneity.

CONCLUSION

Premixed insulin analogues provide glycemic control similar to that of premixed human insulin and may provide tighter glycemic control than long-acting insulin analogues and noninsulin antidiabetic agents.

Parasympathetic response in chick myocytes and mouse heart is controlled by SREBP

Parasympathetic stimulation of the heart, which provides protection from arrhythmias and sudden death, involves activation of the G protein-coupled inward rectifying K+ channel GIRK1/4 and results in an acetylcholine-sensitive K+ current, I KACh. We describe a unique relationship between lipid homeostasis, the lipid-sensitive transcription factor SREBP-1, regulation of the cardiac parasympathetic response, and the development of ventricular arrhythmia. In embryonic chick atrial myocytes, lipid lowering by culture in lipoprotein-depleted serum increased SREBP-1 levels, GIRK1 expression, and I KACh activation. Regulation of the GIRK1 promoter by SREBP-1 and lipid lowering was dependent on interaction with 2 tandem sterol response elements and an upstream E-box motif. Expression of dominant negative SREBP-1 (DN-SREBP-1) reversed the effect of lipid lowering on I KACh and GIRK1. In SREBP-1 knockout mice, both the response of the heart to parasympathetic stimulation and the expression of GIRK1 were reduced compared with WT. I KACh, attenuated in atrial myocytes from SREBP-1 knockout mice, was stimulated by SREBP-1 expression. Following myocardial infarction, SREBP-1 knockout mice were twice as likely as WT mice to develop ventricular tachycardia in response to programmed ventricular stimulation. These results demonstrate a relationship between lipid metabolism and parasympathetic response that may play a role in arrhythmogenesis.

Short- and long-term effect of simvastatin therapy on the heterogeneity of cardiac repolarization in diabetic patients

The interlead variability of QT interval in the 12-lead electrocardiogram, QT dispersion (QTd), has been shown to reflect dispersion of ventricular refractoriness and may provide a measure of arrhythmogenic potential in diabetic patients. QTd and heart rate corrected QTd (QTcd) were also proposed to be accurate predictors of cardiac death in patients with diabetes. In recent years, experimental and clinical evidence demonstrates that statins exert antiarrhythmic properties. Therefore, in the present study, we have examined whether simvastatin treatment has any effect on the QTd and QTcd in patients with diabetes mellitus. Sixty type 2 diabetic patients without known coronary artery disease and low-density lipoprotein cholesterol >100mg/dl and 30 age and sex-matched non-diabetic controls were included in a prospective study. Out of 60 diabetic patients, 30 were treated with simvastatin 40 mg/day for 1 year and the remaining 30 subjects were served as diabetic controls. No lipid lowering therapy was administered to the diabetic and the non-diabetic controls. QTd and QTcd of treated diabetics and the non-diabetic controls were measured at baseline, 6, 12 weeks and at 1 year. QTd and QTcd of the diabetic controls were obtained at baseline, 6 and 12 weeks. Both QTd and QTcd were significantly greater in patients with the diabetes than in the non-diabetic controls at baseline (52+/-13 ms vs. 41+/-12 ms, p<0.001 and 62+/-17 ms vs. 42+/-11 ms, p<0.001, respectively). Simvastatin therapy significantly decreased both QTd and QTcd at the end of first year compared to baseline (51+/-15 ms vs. 33+/-11 ms, p<0.001 and 60+/-18 ms vs. 38+/-12 ms, p<0.001, respectively). No significant change were found in QTd and QTcd in the non-diabetic (p=0.29 and p=0.87 by ANOVA, respectively) and in the diabetic controls (p=0.72 and p=0.57, by ANOVA, respectively). This study suggests for the first time that simvastatin treatment in diabetic patients with hyperlipidemia is associated with an improvement in the heterogeneity of cardiac repolarization. This may be one of the mechanisms for the reduction in clinical events reported in the survival studies with statins. Further prospective randomized studies are warranted to confirm our findings.

Postprandial dysmetabolism: the missing link between diabetes and cardiovascular events?

OBJECTIVE

To investigate the association of postprandial dysmetabolism, ie, hyperglycemia, and hyperlipidemia with myocardial disease in diabetic, glucose-intolerant, and glucose-tolerant patients.

METHODS

We performed a MEDLINE search of the English-language literature published between January 1979 and April 2007 for studies regarding postprandial dysmetabolism and heart disease.

RESULTS

Postprandial dysmetabolism is associated with increased inflammation, endothelial dysfunction, decreased fibrinolysis, plaque instability, and cardiac events.

CONCLUSION

There is a direct and proportional association between postprandial dysmetabolism and both coronary artery disease and cardiac events.

Patients with a history of diabetes have a lower survival rate after in-hospital cardiac arrest

AIM

To describe the association between a history of diabetes and outcome among patients suffering an in-hospital cardiac arrest.

METHOD

All patients suffering an in-hospital cardiac arrest in whom cardiopulmonary resuscitation (CPR) was attempted at Sahlgrenska University Hospital in Göteborg between 1994 and 2006 and at nine further hospitals in Sweden between 2005 and 2006.

RESULTS

In all, 1810 patients were included in the survey, 395 (22%) of whom had a previous history of diabetes. Patients with a history of diabetes differed from those without such a history by having a higher prevalence of previous myocardial infarction, stroke, heart failure and renal disease. They were more frequently treated with anti-arrhythmic drugs during resuscitation. Whereas immediate survival did not differ between groups (51.7% and 53.1%, respectively), patients with diabetes were discharged alive from hospital (29.3%) less frequently compared with those without diabetes (37.6%). When correcting for dissimilarities at baseline, the adjusted odds ratio for being discharged alive (diabetes/no diabetes) was 0.57 (95% CL 0.40-0.79).

CONCLUSION

Among patients suffering an in-hospital cardiac arrest in Sweden in whom CPR was attempted, 22% had a history of diabetes. These patients had a lower survival rate, which cannot simply be explained by different co-morbidity.

Acute hyperglycaemia disturbs cardiac repolarization in Type 1 diabetes

AIMS

Patients with Type 1 diabetes have an increased risk of cardiovascular mortality. Notably, a prolonged heart rate adjusted QT interval (QTc) is a predictor of sudden cardiovascular death. Therefore, the objectives of this study were to investigate whether acute hyperglycaemia affects the QTc duration and the QTc dispersion in patients with Type 1 diabetes and in healthy volunteers.

METHODS

Acute hyperglycaemia (15 mmol/l) for 120 min was induced in 35 males (22 men with Type 1 diabetes and 13 age-matched non-diabetic volunteers). All participants were non-smokers without any diabetic complications. Electrocardiogram recordings were performed at normoglycaemia and at 0, 60 and 120 min of hyperglycaemia.

RESULTS

Compared with normoglycaemia, acute hyperglycaemia increased the QTc interval in both patients with Type 1 diabetes (390 +/- 6 vs. 415 +/- 5 ms, P < 0.001) and in healthy volunteers (378 +/- 5 vs. 412 +/- 8 ms, P < 0.01). During hyperglycaemia, the QTc dispersion was prolonged in healthy volunteers (36 +/- 4 ms vs. 54 +/- 7 ms, P < 0.05) but not in patients with Type 1 diabetes (45 +/- 3 ms at baseline vs. 48 +/- 5 ms, NS).

CONCLUSIONS

Acute hyperglycaemia alters myocardial ventricular repolarization in patients with Type 1 diabetes and in healthy volunteers and might consequently be an additional risk factor for cardiovascular events.