Clinical determinants of increased QT dispersion in patients with diabetes mellitus

Exploring electrocardiographic alterations and the prolongation of QT interval in patients with diabetes mellitus

Background

Diabetes mellitus (DM) affects a substantial proportion of the world's population and is associated with an increased risk of sudden cardiac death (SCD) due to cardiac arrhythmias, specifically prolonged QT intervals. This study investigates the correlation between glycemic control and cardiac health in 77 diabetic patients.

Methods

Patients with both type 1 and type 2 DM aged 14 to 82 years were included. Various clinical and metabolic parameters were evaluated, including glycated hemoglobin (HbA1C). QT intervals were measured using electrocardiograms (ECGs), and patients were categorized based on their QTc intervals. SPSS was used for statistical analysis, including one-way ANOVA tests.

Results

The study revealed diverse age and gender representation among diabetic patients. Most patients had type 2 diabetes (87%) with varying illness durations. Patients ranged in age from 14 to 82 years, with a mean of 48.14 16.58 years. The gender distribution was even (49% male and 51% female). Most participants had diabetes for less than five years (57%) and varied treatment histories (71% managed with oral hypoglycemic agents, 17% with insulin, and 12% with a combination). The ECG revealed ST-T alterations (4%) as well as sinus tachycardia (13%) and left ventricular hypertrophy (19%).

Conclusion

This study sheds light on the intricate relationship between diabetes, glycemic control, and cardiac health. QTc interval variations were observed even though the clinical and metabolic profiles of the patients varied. The influence of glycemic control on QT intervals and cardiovascular outcomes in diabetic patients requires additional study.

Toluene Inhalant Addiction and Cardiac Functions in Young Adults: A Comparison of Electrocardiographic and Echocardiographic Parameters

BACKGROUND

Volatile substance (thinner) addiction can cause serious cardiac events, such as malignant ventricular arrhythmias, acute coronary syndromes, sudden death syndrome, and dilated cardiomyopathy, as reported in many case studies. We aimed to find echocardiographic and electrocardiographic parameters that could foresee these adverse outcomes in clinical settings.

METHODS

We enrolled 32 healthy young adult patients with at least 1 year of thinner addiction and no cardiac symptoms. We also recruited a control group of 30 healthy individuals without any medical problems. Both groups received standard echocardiography and ECG tests. We analyzed the following echocardiographic parameters: LVEDd (left ventricular end-diastolic diameter), LVESd (left ventricular end-systolic diameter), mitral valve EF slope, E/A ratio, and aortic and pulmonary valve VTI (velocity time integral). We also measured the corrected (QTc), uncorrected QT intervals, and widest P-wave values in the ECG. We used the SPSS 13 software for statistical analysis.

RESULTS

The echocardiographic findings did not differ significantly between the groups. However, the ECG results showed that the thinner addicts had higher values of corrected (QTc), uncorrected QT intervals, and widest P-wave values than the control group, according to Mann-Whitney U and Student's T test.

CONCLUSION

Corrected QT (QTc) and P-wave duration are increased in individuals with a thinner addiction. These findings may suggest a higher risk of sudden cardiac death, atrial, and ventricular dysrhythmias in the future.

Electrical Features of the Diabetic Myocardium. Arrhythmic and Cardiovascular Safety Considerations in Diabetes

Diabetes is a chronic metabolic disease characterized by hyperglycemia in the absence of treatment. Among the diabetes-associated complications, cardiovascular disease is the major cause of mortality and morbidity in diabetic patients. Diabetes causes a complex myocardial dysfunction, referred as diabetic cardiomyopathy, which even in the absence of other cardiac risk factors results in abnormal diastolic and systolic function. Besides mechanical abnormalities, altered electrical function is another major feature of the diabetic myocardium. Both type 1 and type 2 diabetic patients often show cardiac electrical remodeling, mainly a prolonged ventricular repolarization visible in the electrocardiogram as a lengthening of the QT interval duration. The underlying mechanisms at the cellular level involve alterations on the expression and activity of several cardiac ion channels and their associated regulatory proteins. Consequent changes in sodium, calcium and potassium currents collectively lead to a delay in repolarization that can increase the risk of developing life-threatening ventricular arrhythmias and sudden death. QT duration correlates strongly with the risk of developing torsade de pointes, a form of ventricular tachycardia that can degenerate into ventricular fibrillation. Therefore, QT prolongation is a qualitative marker of proarrhythmic risk, and analysis of ventricular repolarization is therefore required for the approval of new drugs. To that end, the Thorough QT/QTc analysis evaluates QT interval prolongation to assess potential proarrhythmic effects. In addition, since diabetic patients have a higher risk to die from cardiovascular causes than individuals without diabetes, cardiovascular safety of the new antidiabetic drugs must be carefully evaluated in type 2 diabetic patients. These cardiovascular outcome trials reveal that some glucose-lowering drugs actually reduce cardiovascular risk. The mechanism of cardioprotection might involve a reduction of the risk of developing arrhythmia.

Handling of Ventricular Fibrillation in the Emergency Setting

Ventricular fibrillation (VF) and sudden cardiac death (SCD) are predominantly caused by channelopathies and cardiomyopathies in youngsters and coronary heart disease in the elderly. Temporary factors, e.g., electrolyte imbalance, drug interactions, and substance abuses may play an additive role in arrhythmogenesis. Ectopic automaticity, triggered activity, and reentry mechanisms are known as important electrophysiological substrates for VF determining the antiarrhythmic therapies at the same time. Emergency need for electrical cardioversion is supported by the fact that every minute without defibrillation decreases survival rates by approximately 7%–10%. Thus, early defibrillation is an essential part of antiarrhythmic emergency management. Drug therapy has its relevance rather in the prevention of sudden cardiac death, where early recognition and treatment of the underlying disease has significant importance. Cardioprotective and antiarrhythmic effects of beta blockers in patients predisposed to sudden cardiac death were highlighted in numerous studies, hence nowadays these drugs are considered to be the cornerstones of the prevention and treatment of life-threatening ventricular arrhythmias. Nevertheless, other medical therapies have not been proven to be useful in the prevention of VF. Although amiodarone has shown positive results occasionally, this was not demonstrated to be consistent. Furthermore, the potential proarrhythmic effects of drugs may also limit their applicability. Based on these unfavorable observations we highlight the importance of arrhythmia prevention, where echocardiography, electrocardiography and laboratory testing play a significant role even in the emergency setting. In the following we provide a summary on the latest developments on cardiopulmonary resuscitation, and the evaluation and preventive treatment possibilities of patients with increased susceptibility to VF and SCD.

Evaluation of cardiac hypertrophy in the setting of sudden cardiac death

Ventricular hypertrophy is a common pathological finding at autopsy that can act as a substrate for arrhythmogenesis. Pathologists grapple with the significance of ventricular hypertrophy when assessing the sudden and unexpected deaths of young people and what it could mean for surviving family members. The pathological spectrum of left ventricular hypertrophy (LVH) is reviewed herein. This article is oriented to the practicing autopsy pathologist to help make sense of various patterns of increased heart muscle, particularly those that are not clearly cardiomyopathic, yet present in the setting of sudden cardiac death. The article also reviews factors influencing arrhythmogenesis as well as genetic mutations most commonly associated with ventricular hypertrophy, especially those associated with hypertrophic cardiomyopathy (HCM).

Marked exercise-induced T-wave heterogeneity in symptomatic diabetic patients with nonflow-limiting coronary artery stenosis

BACKGROUND

T-wave heterogeneity (TWH) independently predicted cardiovascular mortality in Health Survey 2000 based on 12-lead ECGs recorded at rest. We investigated whether TWH is elevated during exercise tolerance testing (ETT) in symptomatic diabetic patients with nonflow-limiting coronary artery stenosis compared to control subjects without diabetes.

METHODS

Cases were all patients (n = 20) with analyzable ECG recordings during both rest and ETT who were enrolled in the Effects of Ranolazine on Coronary Flow Reserve (CFR) in Symptomatic Patients with Diabetes and Suspected or Known Coronary Artery Disease (RAND-CFR) study (NCT01754259); median CFR was 1.44; 80% of cases had CFR <2. Control subjects (n = 9) were nondiabetic patients who had functional flow reserve (FFR) >0.8, a range not associated with inducible ischemia. TWH was analyzed from precordial leads V4 , V5 , and V6 by second central moment analysis, which assesses the interlead splay of T-waves about a mean waveform.

RESULTS

During exercise to similar rate-pressure products (p = .31), RAND-CFR patients exhibited a 49% increase in TWH during exercise (rest: 49 ± 5 μV; exercise: 73 ± 8 μV, p = .003). By comparison, in control subjects, TWH was not significantly altered (rest: 52 ± 11 μV; ETT: 38 ± 5 μV, p = .19). ETT-induced ST-segment depression >1 mm (p = .11) and Tpeak -Tend (p = .18) and QTc intervals (p = .80) failed to differentiate cases from controls.

CONCLUSIONS

TWH is capable of detecting latent repolarization abnormalities, which are present during ETT in diabetic patients with nonflow-limiting stenosis but not in control subjects. The technique developed in this study permits TWH analysis from archived ECGs and thereby enables mining of extensive databases for retrospective studies and hypothesis testing.

The association of long-term glycaemic variability versus sustained chronic hyperglycaemia with heart rate-corrected QT interval in patients with type 2 diabetes

Objectives

Prolonged heart rate-corrected QT(QTc) interval is related to ventricular arrhythmia and cardiovascular mortality, with considerably high prevalence of type 2 diabetes. Additionally, long-term glycaemic variability could be a significant risk factor for diabetic complications in addition to chronic hyperglycaemia. We compared the associations of long-term glycaemic variability versus sustained chronic hyperglycaemia with the QTc interval among type 2 diabetes patients.

Methods

In this cross-sectional study, 2904 type 2 diabetes patients were recruited who had undergone at least four fasting plasma glucose (FPG) and 2-hour postprandial plasma glucose (PPG) measurements (at least once for every 3 months, respectively) during the preceding year. Long-term glycaemic variabilities of FPG and 2-hour PPG were assessed by their standard deviations (SD-FPG and SD-PPG, respectively), and chronic fasting and postprandial hyperglycaemia were assessed by their means (M-FPG and M-PPG, respectively). HbA1c was also determined upon enrolment to assess current overall glycaemic control. QTc interval was estimated from resting 12-lead electrocardiograms, and more than 440 ms was considered abnormally prolonged.

Results

Patients with prolonged QTc interval (≥440 ms) had greater M-FPG, M-PPG, SD-PPG and HbA1c than those with normal QTc interval but comparable SD-FPG. QTc interval was correlated with M-FPG, M-PPG, SD-PPG and HbA1c (r = 0.133, 0.153, 0.245 and 0.207, respectively, p = 0.000) but not with SD-FPG (r = 0.024, p = 0.189). After adjusting for metabolic risk factors via multiple linear regression analysis, SD-PPG, M-PPG and HbA1c (t = 12.16, 2.69 and 10.16, respectively, p = 0.000) were the major independent contributors to the increased QTc interval. The proportion of prolonged QTc interval increased significantly from 10.9% to 14.2% to 26.6% for the first (T1) to second (T2) to third (T3) tertiles of SD-PPG. After adjusting via multiple logistic regression analysis, the odd ratios of prolonged QTc interval of the T2 and T3 versus the T1 of SD-PPG were 1.15 (95% CI, 0.82–1.60) and 2.62 (1.92–3.57), respectively.

Conclusions

Increased long-term variability of PPG is a strong independent risk factor for prolonged QTc interval in type 2 diabetes patients, in addition to long-term postprandial hyperglycaemia and current HbA1c.

Reduced functional connectivity between ventromedial prefrontal cortex and insula relates to longer corrected QT interval in HIV+ and HIV- individuals

OBJECTIVE

Prolongation of the QT interval, i.e., measure of the time between the start of the Q wave and the end of the T wave, is a precursor to fatal cardiac arrhythmias commonly observed in individuals infected with the Human Immunodeficiency Virus (HIV), and is related to dysregulation of the autonomic nervous system. We investigated the relationship between QT interval length and resting state functional connectivity (rsFC) of the ventromedial prefrontal cortex (VMPFC), a core region of the brain that is involved with cardio-autonomic regulation.

METHOD

Eighteen HIV+ men on antiretroviral therapy and with no history of heart disease were compared with 26 HIV-negative control subjects who had similar demographic and cardio-metabolic characteristics. A seed-based rsFC analysis of the right and left VMPFC was performed at the individual subject level, and 2nd-level analyses were conducted to identify the following: group differences in connectivity, brain regions correlating with corrected (QTc) interval length before and after controlling for those group differences, and regions where seed-based rsFC correlates with CD4 count and QTc interval within HIV+ individuals.

RESULTS

HIV-negative adults showed greater rsFC between the VMPFC seed regions and several default mode network structures. Across groups greater rsFC with the left anterior insula was associated with shorter QTc intervals, whereas right posterior insula connectivity with the VMPFC correlated with greater QTc intervals. HIV patients with lower CD4 counts and higher QTc intervals showed greater rsFC between the right VMPFC and the right posterior insula and dorsal cingulate gyrus.

CONCLUSIONS

This study demonstrates that QTc interval lengths are associated with distinct patterns of VMPFC rsFC with posterior and anterior insula. In HIV patients, longer QTc interval and lower CD4 count corresponded to weaker VMPFC connectivity with the dorsal striatrum.

SIGNIFICANCE

A forebrain control mechanism may be implicated in the suppression of cardiovagal influence that confers risk for ventricular arrhythmias and sudden cardiac death in HIV+ individuals.

Ranolazine reduces repolarization heterogeneity in symptomatic patients with diabetes and non-flow-limiting coronary artery stenosis

BACKGROUND

Experimental evidence suggests that ranolazine decreases susceptibility to ischemia-induced arrhythmias independent of effects on coronary artery blood flow.

OBJECTIVE

In symptomatic diabetic patients with non-flow-limiting coronary artery stenosis with diffuse atherosclerosis and/or microvascular dysfunction, we explored whether ranolazine reduces T-wave heterogeneity (TWH), an electrocardiographic (ECG) marker of arrhythmogenic repolarization abnormalities shown to predict sudden cardiac death.

METHODS

We studied all 16 patients with analyzable ECG recordings during rest and exercise tolerance testing before and after 4 weeks of ranolazine in the double-blind, crossover, placebo-controlled RAND-CFR trial (NCT01754259). TWH was quantified without knowledge of treatment assignment by second central moment analysis, which assesses the interlead splay of T waves in precordial leads about a mean waveform. Myocardial blood flow (MBF) was measured by positron emission tomography.

RESULTS

At baseline, prior to randomization, TWH during rest was 54 ± 7 μV and was not altered following placebo (47 ± 6 μV, p = .47) but was reduced by 28% (to 39 ± 5 μV, p = .002) after ranolazine. Ranolazine did not increase MBF at rest. Exercise increased TWH after placebo by 49% (to 70 ± 8 μV, p = .03). Ranolazine did not reduce TWH during exercise (to 75 ± 16 μV), and there were no differences among the groups (p = .95, ANOVA). TWH was not correlated with MBF at rest before (r²  = .07, p = .36) or after ranolazine (r²  = .23, p = .06).

CONCLUSIONS

In symptomatic diabetic patients with non-flow-limiting coronary artery stenosis with diffuse atherosclerosis and/or microvascular dysfunction, ranolazine reduced TWH at rest but not during exercise. Reduction in repolarization abnormalities appears to be independent of alterations in MBF.

The relationship between insulin sensitivity and heart rate-corrected QT interval in patients with type 2 diabetes

BACKGROUND

Reduced insulin sensitivity not only contributes to the pathogenesis of type 2 diabetes but is also linked to multiple metabolic risk factors and cardiovascular diseases (CVD). A prolonged heart rate-corrected QT interval (QTc interval) is related to ventricular arrhythmias and CVD mortality and exhibits a high prevalence among type 2 diabetes patients. The aim of the study was to investigate the relationship between insulin sensitivity and the QTc interval in patients with type 2 diabetes.

METHODS

This cross-sectional observational study recruited 2927 patients with type 2 diabetes who visited the Affiliated Haian Hospital and Second Affiliated Hospital of Nantong University. The insulin sensitivity index (Matsuda index, ISI_Matsuda) derived from 75-g OGTT and other metabolic risk factors were examined in all patients. The QTc interval was estimated using a resting 12-lead electrocardiogram, and an interval longer than 440 ms was considered abnormally prolonged.

RESULTS

The QTc interval was significantly and negatively correlated with the ISI_Matsuda (r = -0.296, p < 0.001), and when the multiple linear regression analysis was adjusted for anthropometric parameters, metabolic risk factors, and current antidiabetic treatments, the QTc interval remained significantly correlated with the ISI_Matsuda (β = -0.23, t = -12.63, p < 0.001). The proportion of patients with prolonged QTc interval significantly increased from 12.1% to 17.9%, 25.6% and 37.9% from the fourth to third, second and first quartile of the ISI_Matsuda, respectively. After adjusting for anthropometric parameters by multiple logistic regression analysis, the corresponding odd ratios (ORs) for prolonged QTc interval of the first, second and third quartiles versus the fourth quartile of ISI_Matsuda were 3.11 (95% CI 2.23-4.34), 2.09 (1.51-2.88) and 1.53 (1.09-2.14), respectively, and p for trend was <0.001.

CONCLUSIONS

Reduced insulin sensitivity is associated with an increase in the QTc interval in patients with type 2 diabetes.

Prevalence and risk factors for prolonged QT interval and QT dispersion in patients with type 2 diabetes

AIMS

Prolonged QT interval is associated with cardiac arrhythmias and sudden death. The present study determined the prevalence of prolonged QT interval and QT dispersion and defined their clinical and metabolic predictors in patients with type 2 diabetes.

METHODS

Cross-sectional study included 501 patients with type 2 diabetes. A standard 12-lead electrocardiogram was recorded. QT corrected for heart rate (QTc) >440 ms and QT dispersion (QTd) >80 ms were considered abnormally prolonged. QTc ≥ 500 ms was considered a high-risk QTc prolongation. Demographic, clinical and laboratory data were collected. Independent risk factors for prolonged QTc and QTd were assessed using logistic regression analysis.

RESULTS

Prevalence of QTc > 440 ms and QTd > 80 ms were 44.1 and 3.6 %, respectively. Prevalence of high-risk QTc (≥500 ms) was 2 % only. Independent risk factors for QTc prolongation >440 ms were mean blood glucose (β = 2.192, p < 0.001), treatment with sulphonylurea (β = 5.198, p = 0.027), female gender (β = 8.844, p < 0.001), and coronary heart disease (β = 8.636, p = 0.001). Independent risk factors for QTc ≥ 500 ms were coronary heart disease (β = 4.134, p < 0.001) and mean blood glucose level (β = 1.735, p < 0.001). The independent risk factor for prolonged QTd was only coronary heart disease (β = 5.354, p < 0.001).

CONCLUSIONS

Although the prevalence of prolonged QTc > 440 ms is significant, the prevalence of high-risk QTc (≥500 ms) and QTd > 80 ms is very low in patients with type 2 diabetes. Hyperglycaemia and coronary heart disease are strong predictors of high-risk QTc.

Review: Diabetes and the QT interval: time for debate

The electrocardiographic QT interval has been extensively studied in ischaemic heart disease. Recently, there has been increasing interest in the relationship between diabetes and QT abnormalities. QT prolongation and increased QTd have been shown to predict cardiac death in both type 1 and type 2 diabetes mellitus. Although there is general agreement that QT interval is affected by cardiac ischaemia, the effect of hyperglycaemia on QT measures is controversial. There are also problems surrounding QTd. First, there is controversy as to whether the measure has any physiological meaning; secondly, there is no universally accepted method of measurement and hence no consensus about the upper limit of normal. Nevertheless, several studies have shown increased QTd in diabetic patients suggesting that assessment of the QT interval could be a cost effective way of stratifying aggressive treatment could be directed appropriately to such patients according to cardiovascular risk so that improve outcome.

Increased serum gamma-glutamyltransferase levels are associated with ventricular instability in type 2 diabetes

The purpose of our study is to examine the association between serum GGT levels and ventricular instability in Chinese patients with T2DM. We conducted a cross-sectional, community-based study in Nanjing, China from June to November 2011. Among 10,050 patients aged 40-79 years, we enrolled 2444 with pre-diabetes, 2496 with T2DM, and 4521 without diabetes (non-diabetes). Electrocardiograms were performed to measure the QT interval corrected for heart rate (QTc) and QT interval dispersion (QTd). Serum GGT levels, metabolic parameters, body mass index, and blood pressure were also measured. We found that there were no significant associations of increased QTc/QTd with serum GGT levels in participants with pre-existing T2DM and non-diabetes, after adjusting for age, duration of diabetes, and metabolic parameters. Even after adjustment, higher risks of QTc ≥ 440 ms/√s and QTd ≥ 58 ms were found in participants with serum GGT levels ≥49 U/L compared with those with <15 U/L in the pre-diabetes (QTc: OR 1.96, 95 % CI 1.23-2.47; QTd: OR 1.34, 95 % CI 1.07-1.94) and newly diagnosed T2DM (QTc: OR 2.01, 95 % CI 1.39-2.51; QTd: OR 1.53, 95 % CI 1.03-1.99) groups. We conclude that Increased serum GGT levels are associated with some markers of ventricular repolarization abnormalities in the early stage of T2DM.

Perioperative doses of ondansetron or dolasetron do not lengthen the QT interval

OBJECTIVE

To test the primary hypothesis that ondansetron or dolasetron extends the rate-corrected QT electrocardiographic interval (QTc) greater than 60 milliseconds or increases the fraction of patients with QTc greater than 500 milliseconds in patients having noncardiac surgery, and the secondary hypothesis that QTc prolongation is worse in diabetic patients.

PATIENTS AND METHODS

We extracted data from the Cleveland Clinic's Perioperative Health Documentation System between March 25, 2006, and September 30, 2010, and additional perioperative medications from Cleveland Clinic pharmacy's Epic Cost of Goods Sold (COGS) system. We searched for patients who had a preoperative electrocardiogram within 1 month of surgery and postoperatively within 2 hours. We excluded patients given an antiemetic drug other than ondansetron or dolasetron perioperatively, and those given amiodarone.

RESULTS

A total of 1429 patients given serotonin-3 receptor (5HT3R) antagonists and 1022 controls met the enrollment criteria. Seventeen percent of patients given 5HT3R antagonists (n=242) and 22% of controls (n=220) had postoperative QTc exceeding 500 milliseconds. Mean ± SD presurgical and postsurgical QTc, respectively, were 438±37 milliseconds and 464±41 milliseconds for 5HT3R antagonist patients and 443±40 milliseconds and 469±47 milliseconds for control patients. Univariable mean ± SD perioperative increases in QTc were 26±39 and 26±48 milliseconds in the 2 groups. After adjusting for confounding variables, there were no differences in the mean increase in QTc in patients who were and were not given 5HT3R antagonists: -0.1 milliseconds (97.5% CI, -5.2 to 5.0 milliseconds; multivariable P=.97). The QTc was prolonged, but not significantly, in diabetic patients given 5HT3R antagonists (P=.16).

CONCLUSIONS

The average QTc prolongation from baseline was only 6%. Perioperative use of ondansetron or dolasetron was not associated with extended QT prolongation, and these results did not vary by diabetic status. Perioperative use of 5HT3R antagonists does not produce potentially dangerous perioperative electrocardiographic changes and does not seem to warrant a drug safety warning from the Food and Drug Administration.

Predictors of development and progression of microvascular complications in a cohort of Brazilian type 2 diabetic patients

AIMS

Microvascular complications are associated with increased mortality in diabetes. The objective of this study was to investigate the predictors of microvascular complication development and progression in a prospective study of Brazilian type 2 diabetic patients.

METHODS

A prospective follow-up study was carried out with 471 type 2 diabetic outpatients. Primary end points were the development or progression of retinopathy, peripheral neuropathy, and clinical nephropathy. Predictors were assessed for each individual microvascular complication and also as a composite outcome by Kaplan-Meier estimation of survival curves and by uni- and multivariate Cox analysis.

RESULTS

During a median follow-up of 57 months (range 2-84 months), 196 patients (41.6%) developed or had a progression in microvascular disease. Retinopathy occurred in 22.5%, nephropathy in 19.1%, and neuropathy in 15.5% of the patients. In Cox multivariate analysis, increased echocardiographic left ventricular mass (LVM) and longer diabetes duration were selected as predictors for all end points. Higher mean fasting glycemia was a predictor for retinopathy and neuropathy, lower serum high-density lipoprotein (HDL) cholesterol for neuropathy, and higher total cholesterol for nephropathy. Increased LVM [hazard ratio (HR): 1.39, 95% CI: 1.23-1.56], higher fasting glycemia (HR: 1.19, 95% CI: 1.04-1.36), and longer diabetes duration (HR: 1.28, 95% CI: 1.11-1.47) were the predictors of the composite end point.

CONCLUSIONS

Development and progression of microvascular complications in Brazilian type 2 diabetic patients are associated with worse hypertension and metabolic control. Additional studies are necessary to show if modification of these risk factors can reduce the burden of morbidity and mortality related to microvascular disease in type 2 diabetes.

miRNAs at the heart of the matter

Cardiovascular disease is among the main causes of morbidity and mortality in developed countries. The pathological process of the heart is associated with altered expression profile of genes that are important for cardiac function. MicroRNAs (miRNAs) have emerged as one of the central players of gene expression regulation. The implications of miRNAs in the pathological process of cardiovascular system have recently been recognized, representing the most rapidly evolving research field. Here, we summarize and analyze the currently available data from our own laboratory and other groups, providing a comprehensive overview of miRNA function in the heart, including a brief introduction of miRNA biology, expression profile of miRNAs in cardiac tissue, role of miRNAs in cardiac hypertrophy and heart failure, the arrhythmogenic potential of miRNAs, the involvement of miRNAs in vascular angiogenesis, and regulation of cardiomyocyte apoptosis by miRNAs. The target genes and signaling pathways linking the miRNAs to cardiovascular disease are highlighted. The applications of miRNA interference technologies for manipulating miRNA expression, stability, and function as new strategies for molecular therapy of human disease are evaluated. Finally, some specific issues related to future directions of the research on miRNAs relevant to cardiovascular disease are pinpointed and speculated.

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.

Macro and microvascular complications are determinants of increased infection-related mortality in Brazilian type 2 diabetes mellitus patients

OBJECTIVE

To investigate infection-related mortality and its predictors in Brazilian type 2 diabetic patients.

METHODS

It was carried out a long-term prospective study with 471 type 2 diabetic outpatients. Several clinical, laboratory and electrocardiographic variables were recorded at baseline. Predictive factors for infection-related mortality were evaluated by Kaplan-Meyer estimation of survival curves, univariate and multivariate Cox survival analysis. Excess infection-related mortality in this cohort was evaluated by comparing its rate with that of the Rio de Janeiro background population and calculating standardized mortality rates (SMR).

RESULTS

During a median follow up of 57 months (range: 1-86 months), 40 (33.1%) patients died from infection-related causes. After adjusting for age and sex, the infection-related SMR was 6.6 (95% confidence interval [95% CI]: 4.8-9.0). In Cox multivariate analysis the predictors of infection-related mortality were older age (hazard ratio [HR]: 1.91; 95% CI: 1.35-2.70), pre-existing peripheral arterial disease (HR: 3.86; 95% CI: 1.80-8.28) and cerebrovascular disease (HR: 3.28; 95% CI: 1.24-8.70), lower HDL-cholesterol (HR: 2.50; 95% CI: 1.32-4.74) and increased 24h-proteinuria (HR: 1.22; 95% CI: 1.08-1.37). After excluding patients with peripheral and cerebrovascular disease at baseline, neuropathy and coronary heart disease were selected as predictors of mortality, besides older age and proteinuria.

CONCLUSIONS

Brazilian type 2 diabetic patients have a six-fold excess infection-related mortality than the general population. This increased mortality is mainly determined by the presence of micro and macrovascular complications. Multifactorial risk interventions are needed in order to decrease this burden of infection-related mortality.

Increased risk of cardiac death in primary hyperparathyroidism: what is a role of electrical instability?

BACKGROUND

Increased risk of death in patients with primary hyperparathyroidism (PHPT) is referred to cardiovascular complications induced by hypercalcemia. At the moment the role of bioelectrical risk and of enhanced sympathetic activity, not related to cardiovascular complications, is unknown in PHPT patients.

METHODS

The study was designed to evaluate the QT parameters and sympathovagal balance in 28 PHPT uncomplicated patients compared to 29 healthy subjects (HS). Nine of 28 patients were restudied after parathyroidectomy. Standard ECG, short and 24-h ECG monitoring were performed to calculate QT parameters and Heart Rate Variability (HRV).

RESULTS

QTc interval resulted shorter in PHPT patients than in HS and QTc dispersion resulted higher in PHPT patients than HS. The physiological adaptation of QT length to R-R interval was lacking in PHPT patients. Enhanced sympathetic tone was found in PTHP patients than controls. These data were confirmed after parathyroidectomy.

CONCLUSION

Our findings revealed an increased risk to develop life-threatening arrhythmias in PHPT patients due to bioelectrical instability induced by hypercalcemia. Parathyroidectomy doesn't seem to reverse this abnormality.

Restoring depressed HERG K+ channel function as a mechanism for insulin treatment of abnormal QT prolongation and associated arrhythmias in diabetic rabbits

Abnormal QT prolongation (QT-P) in diabetic patients has become a nonnegligible clinical problem and has attracted increasing attention from basic scientists, because it increases the risk of lethal ventricular arrhythmias. Correction of QT-P may be an important measure in minimizing sudden cardiac death in diabetic patients. Here we report the efficacy of insulin in preventing QT-P and the associated arrhythmias and the mechanisms underlying the effects in a rabbit model of type 1 insulin-dependent diabetes mellitus (IDDM). The heart rate-corrected QT (QTc) interval and action potential duration were considerably prolonged, with frequent ventricular tachycardias. The rapid delayed rectifier K+ current (IKr) was markedly reduced in IDDM hearts, and hyperglycemia depressed the function of the human ether-a-go-go-related gene (HERG), which conducts IKr. The impairment was primarily ascribed to the enhanced oxidative damage to the myocardium, as indicated by the increased intracellular level of reactive oxygen species and simultaneously decreased endogenous antioxidant reserve and by the increased lipid peroxidation and protein oxidation. Moreover, IDDM or hyperglycemia resulted in downregulation of HERG protein level. Insulin restored the depressed IKr/HERG and prevented QTc/action potential duration prolongation and the associated arrhythmias, and the beneficial actions of insulin are partially due to its antioxidant ability. Our study represents the first documentation of oxidative stress as the major metabolic mechanism for HERG K+ dysfunction, which causes diabetic QT-P, and suggests IKr/HERG as a potential therapeutic target for treatment of the disorder.

Usefulness of QT-interval parameters for cardiovascular risk stratification in type 2 diabetic patients with arterial hypertension

QT-interval parameters are potential indicators of increased cardiovascular risk. We evaluated prospectively their prognostic value, in relation to other risk markers, for cardiovascular fatal and nonfatal events in a cohort of 271 hypertensive type 2 diabetic outpatients. QT intervals were measured from 12-lead standard ECGs obtained on admission and maximum rate-corrected QT-interval duration and QT-interval dispersion (QTd) calculated. Clinical and laboratory data and 2-D echocardiograms (available in 126 patients) were recorded. Survival analyses included Kaplan-Meier survival curves, uni and multivariate Cox proportional-hazards models. After a median follow-up of 55 months (range 2-84), 68 total fatal or nonfatal cardiovascular events and 34 cardiovascular deaths (24 of them from cardiac causes) were observed. In multivariate Cox analysis, QTd was an independent predictor for total cardiovascular events (HR: 1.16, 95% CI: 1.01-1.34, for each 10 ms increments) and for cardiac deaths (HR: 1.28, 95% CI: 1.01-1.60). Other independent risk indicators for cardiovascular morbidity and mortality were echocardiographic left ventricular hypertrophy (Echo-LVH), serum triglycerides, presence of pre-existing cardiac and peripheral arterial disease, age, diabetes duration, heart rate and the presence of frequent ventricular premature contractions on ECG. The combination of QTd and Echo-LVH improved cardiovascular risk stratification compared with either alone, the presence of both prolonged QTd (>65 ms) and Echo-LVH was associated with a 3.2-fold (95% CI: 1.7-6.1) increased risk of a first cardiovascular event and a 5.9-fold (95% CI: 2.1-16.4) increased risk of cardiovascular death. Thus, QT provided additive prognostic information for cardiovascular morbidity and mortality beyond that obtained from conventional risk markers, including Echo-LVH, in type 2 diabetic patients with arterial hypertension.

Mortality and predictors of mortality in a cohort of Brazilian type 2 diabetic patients

OBJECTIVE

To investigate mortality rates and predictors of mortality in Brazilian type 2 diabetic patients.

RESEARCH DESIGN AND METHODS

A prospective follow-up study was carried out with 471 type 2 diabetic outpatients. Primary end points were all-cause, diabetes-related, and cardiovascular deaths. Excess mortality in this cohort was evaluated by calculating standardized mortality ratios (SMRs) in relation to those of the Rio de Janeiro population. Predictors of mortality were assessed by Kaplan-Meier survival curves and by uni- and multivariate Cox survival analyses.

RESULTS

During a median follow-up of 57 months (range 2-84 months), 121 (25.7%) patients died, 91 (75.2%) from diabetes-related causes and 44 (36.4%) from cardiovascular diseases. After adjusting for age and sex, the all-cause SMR was 3.36 (95% confidence interval [CI] 2.81-4.02) and the cardiovascular SMR was 3.28 (CI 2.44-4.41). In the Cox multivariate analysis, the predictors of mortality were older age, increased 24-h proteinuria, preexisting vascular disease, presence of frequent ventricular premature contractions and prolonged maximum heart rate-corrected QT interval on baseline electrocardiogram, and decreased serum HDL cholesterol. The use of beta-blockers was a protective factor. In Kaplan-Meier curves, these variables were capable of distinguishing subgroups of patients with significantly different prognoses.

CONCLUSIONS

Brazilian type 2 diabetic patients had a more than threefold excess mortality than the general population, largely because of increased cardiovascular mortality risk. Several clinical, laboratory, and electrocardiographic predictors of mortality were identified that could possibly be modified to decrease the mortality burden of type 2 diabetes in Brazil.

QT interval, cardiovascular risk factors and risk of death in diabetes

A prolonged QT interval is considered an indicator of increased risk of malignant ventricular arrhythmias and/or sudden death. It has been proposed that autonomic neuropathy in diabetes is related to QT interval prolongation and increased mortality rates. Several studies in Type 1 and Type 2 diabetic patients have confirmed the independent relation between prolonged QT interval duration or increased QT interval dispersion and chronic ischemic heart disease. It has been consistently shown that autonomic neuropathy is related to QT interval duration while more controversies exist on the association with QT interval dispersion. In recent years, studies have confirmed the value of QT interval as a predictor of total mortality in both diabetic and non-diabetic subjects. Moreover, several studies have shown a significant relation between QT interval prolongation and cardiovascular disease risk factors. QT interval could be used to stratify the cardiovascular risk in diabetic patients. We still do not know why QT interval is prolonged and how this abnormality leads to death. Nevertheless, QT interval is a simple, low-cost measure, easily obtainable without the need of the patient's compliance and which could help to select patients who need second level diagnostic procedures and strict observation.

QTc interval prolongation is a predictor of future strokes in patients with type 2 diabetes mellitus

BACKGROUND AND PURPOSE

QTc interval prolongation is a predictor of cardiovascular morbidity and mortality in general populations and in patients with diabetes. The aim of this study was to investigate the predictors of stroke in patients with type 2 diabetes, with particular emphasis on the independent role of QT interval parameters.

METHODS

We carried out a long-term follow-up study with 471 type 2 diabetics. Several clinical, laboratory, ECG, and echocardiographic variables were recorded at baseline. Predictive factors for stroke were evaluated by Kaplan-Meier estimation of survival curves and by univariate and multivariate Cox survival analyses.

RESULTS

After a median follow-up of 57 months (range, 2 to 84 months), 40 incident strokes were observed. QTc interval prolongation (>or=470 ms1/2) was an independent predictor of stroke, with adjusted hazard ratios ranging from 2.2 to 2.9 (95% confidence intervals, 1.1 to 6.0). Other independent factors associated with stroke were older age; the presence of cerebrovascular disease at baseline; increased 24-hour proteinuria, serum triglycerides, and left ventricular mass; and decreased high-density lipoprotein cholesterol. Excluding patients with previous cerebrovascular disease from the analysis did not change the results significantly.

CONCLUSIONS

QTc interval prolongation is a predictor of future stroke in patients with type 2 diabetes. Intervention studies are needed to assess whether this factor could be modified.

Multivariate associates of QT interval parameters in diabetic patients with arterial hypertension: importance of left ventricular mass and geometric patterns

The aim of the study was to assess the determinants of increased QT interval parameters in diabetic patients with arterial hypertension and, in particular, the strength of their relationships to echocardiographically derived left ventricular mass (LVM) and geometric patterns. In a cross-sectional study with 289 hypertensive type 2 diabetic outpatients, maximal QT and QTc (heart rate-corrected) intervals, and QT, QTc, and number-of-leads-adjusted QT interval dispersions were manually measured from standard baseline 12-lead ECGs. Electrocardiographic criteria for left ventricular hypertrophy (LVH) were either Sokolow-Lyon or Cornell sex-specific voltages. LVM and geometric patterns were determined by 2D echocardiography. Statistical analyses involved bivariate tests (Mann-Whitney, chi2, Spearman's correlation coefficients, ANOVA and receiver-operating-characteristic (ROC) curve analyses) and multivariate tests (multiple linear and logistic regressions). QT dispersion measurements showed significant correlations with echocardiographic LVM (r=0.26-0.27). ROC curves demonstrated a poor isolated predictive performance of all QT parameters for detection of LVH (areas under curve: 0.58-0.59), comparable to that of electrocardiographic voltage criteria. Only patients with concentric hypertrophy had significantly increased QT dispersion (QTd) when compared to those with normal geometries (64.24+/-21.09 vs 53.20+/-15.35, P<0.05). In multivariate analyses, both electrocardiographic and echocardiographic LVH were independent predictors of increased QTd, as well as only QTd and gender were determinants of LVM. In conclusion, increased QT interval dispersion is associated with LVM and concentric hypertrophy geometric pattern in diabetic hypertensive patients, although in isolation neither QTd nor any QT parameter presents enough predictive performance to be recommended as screening procedures for detection of LVH.

Prognostic value of QT interval parameters in type 2 diabetes mellitus: results of a long-term follow-up prospective study

The prognostic importance of electrocardiographic ventricular repolarization QT parameters (maximum rate-corrected QT interval-QTcmax, QT interval dispersion-QTd, and QTcd), in relation to other risk markers, on cardiovascular and cardiac mortality, and on total fatal or nonfatal cardiovascular events, was evaluated prospectively in 471 type 2 diabetic outpatients. During a median follow-up of 57 months (range: 2-84), 121 (25.7%), patients died, 44 (36.3% of them) from cardiovascular causes and 106 (22.5%) fatal or nonfatal cardiovascular events were observed. In Cox proportional hazards multivariate analysis, both QTd and QTcmax were independent predictors of cardiovascular and cardiac mortality (hazard ratio [HR]: 1.34, 95% confidence interval [95% CI]: 1.12-1.59, for each 10-ms increments in QTd and HR: 1.17, 95% CI: 1.03-1.21 for 10-ms increments in QTcmax, for cardiovascular mortality). They were also predictors of total fatal or nonfatal cardiac and cardiovascular events (HR: 1.18, 95% CI: 1.05-1.33 for QTd and HR: 1.09, 95% CI: 1.04-1.15 for QTcmax). Additional independent prognostic markers for total cardiovascular events were the presence of previous cardiac disease, cerebral or peripheral vascular disease, age, male gender, known diabetes duration, heart rate, and serum triglycerides. Excluding patients with prior cardiac disease did not change significantly the prognostic performance of QTd but decreased that of QTcmax. In conclusion, QT interval parameters give additional prognostic information in patients with type 2 diabetes mellitus, beyond that obtained from traditional risk factors. QT interval dispersion seems a better prognostic marker than maximum QT interval, particularly in patients without previous cardiac diseases.

Electrocardiographic ventricular repolarization parameters in chronic Chagas' disease as predictors of asymptomatic left ventricular systolic dysfunction

Electrocardiographic repolarization parameters are potential markers of arrhythmogenic risk and have not been evaluated in Chagas' disease. The aim of this report was to investigate their associations with LV systolic function assessed by two-dimensional echocardiography. In a cross-sectional study involving 738 adult outpatients in the chronic phase of Chagas' disease, maximal QTc and T wave peak-to-end (TpTe) intervals, and QT, QTapex (QTa), IT and TpTe interval dispersions, and variation coefficients were measured and calculated from 12-lead standard ECGs. Clinical, radiological, ECG, and echocardiographic data were recorded. In bivariate statistical analysis, all repolarization parameters were significantly increased in patients with moderate or severe LV systolic dysfunction, and these patients showed more clinical, radiologic, and ECG abnormalities. Receiver operating characteristic curve analysis demonstrated that isolatedly QTd had the best predictive performance for LV dysfunction, with an 80% specificity and 67% sensitivity for values >60 ms in the subgroup of chagasic patients with abnormal ECGs and no heart failure. Multivariate logistic regression selected, as the best predictive model for LV dysfunction in this subgroup of patients, the presence of cardiomegaly on chest X ray (OR 14.06, 95% CI, 5.54-35.71), QTd >60 ms (OR 9.35, 95% CI, 4.01-21.81), male gender (OR 7.70, 95% CI, 2.98-19.91) and the presence of frequent premature ventricular contractions (PVCs) on ECG (OR 4.06, 95% CI, 1.65-9.97). This model showed 90% specificity and 71% sensitivity. In conclusion, QTd was associated to LV systolic function and could be used to predict asymptomatic dysfunction in chronic Chagas' disease. The presence of cardiomegaly, frequent PVCs, and male sex refined LV function stratification in these patients.