The value of QT interval dispersion for identification of total mortality risk in non-insulin-dependent diabetes mellitus

Prediction of sudden cardiac arrest in the general population: Review of traditional and emerging risk factors

Sudden cardiac death (SCD) is the most common and devastating outcome of sudden cardiac arrest (SCA), defined as an abrupt and unexpected cessation of cardiovascular function leading to circulatory collapse. The incidence of SCD is relatively infrequent for individuals in the general population, in the range of 0.03-0.10% per year. Yet, the absolute number of cases around the world is high due to the sheer size of the population at risk, making SCA/SCD a major global health issue. Based on conservative estimates, there are at least 2 million cases of SCA occurring worldwide on a yearly basis. As such, identification of risk factors associated with SCA in the general population is an important objective from a clinical and public health standpoint. This review will provide an in-depth discussion of established and emerging factors predictive of SCA/SCD in the general population beyond coronary artery disease and impaired left ventricular ejection fraction. Contemporary studies evaluating the association between age, sex, race, socioeconomic status and the emerging contribution of diabetes and obesity to SCD risk beyond their role as atherosclerotic risk factors will be reviewed. In addition, the role of biomarkers, particularly electrocardiographic ones, on SCA/SCD risk prediction in the general population will be discussed. Finally, the use of machine learning as a tool to facilitate SCA/SCD risk prediction will be examined.

Cardiac autonomic neuropathy and risk of cardiovascular disease and mortality in type 1 and type 2 diabetes: a meta-analysis

We aimed to determine the prognostic association between cardiac autonomic neuropathy (CAN) and cardiovascular disease events (CVE) and mortality in type 1 and type 2 diabetes through a systematic review and meta-analysis. This systematic review and meta-analysis was registered with PROSPERO (CRD42020216305) and was conducted with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) methodological criteria. CAN was defined on the basis of 1 (early/possible CAN) or ≥2 (definite CAN) positive autonomic function tests as per the Toronto Consensus guidelines. Studies included those with prospective CVE or mortality data. Methodological variables/risk of bias were assessed using ROBINS-I (Risk Of Bias In Non-randomized Studies - of Interventions) and RoB-2 (Risk-Of-Bias tool for randomized trials) appraisal tools. Electronic database searches yielded 18 467 articles; 84 articles were screened full-text, 26 articles fulfilled the inclusion criteria for quantitative synthesis. Sixteen studies from patients with (n=2875) and without (n=11 722) CAN demonstrated a pooled relative risk (RR) of 3.16 (95%CI 2.42 to 4.13; p<0.0001) of future CVE in favour of CAN. Nineteen studies provided all-cause mortality data from patients with (n=3679) and without (n=12 420) CAN, with a pooled RR of 3.17 (95%CI 2.11 to 4.78; p<0.0001) in favour of CAN. The risk of both future CVE and mortality was higher in type 1 compared with type 2 diabetes and with a definite CAN (vs possible CAN) diagnosis. Three studies were considered to have risk of serious bias. This study confirms the significant association between CAN and CVE and all-cause mortality. The implementation of population-based CAN screening will identify a subgroup with disproportionately higher cardiovascular and mortality risk that will allow for earlier targeted intervention.

Essential thrombocythaemia first presenting as myocardial infarction in a 36-year-old male

Essential thrombocythaemia (ET) is a myeloproliferative neoplasm where there is a clonal proliferation of thrombocytes. Whilst most often diagnosed incidentally, it can uncommonly present with arterial thrombosis. This is a case presentation of a 36-year-old male who was diagnosed with ET following myocardial infarction caused by multiple thrombotic emboli. The patient was initially misdiagnosed with viral myopericarditis based on an atypical history of chest pain with a viral prodrome. Reattendance a month later with further chest pain, dynamically raised troponin and ECG changes raised suspicions of ACS. Analysis of blood markers from both admissions showed consistently elevated platelet counts. A CMR scan revealed focal ischaemic scars in multiple cardiac segments consistent with an acute coronary event or coronary embolisation. A subsequent coronary angiography demonstrated minimal coronary artery disease. JAK2 gene V617F mutation was detected, confirming ET. The patient was commenced on pegylated interferon-alpha and dual antiplatelet therapy, and discharged with follow-up.

Effects of metformin on atrial and ventricular arrhythmias: evidence from cell to patient

Metformin has been shown to have various cardiovascular benefits beyond its antihyperglycemic effects, including a reduction in stroke, heart failure, myocardial infarction, cardiovascular death, and all-cause mortality. However, the roles of metformin in cardiac arrhythmias are still unclear. It has been shown that metformin was associated with decreased incidence of atrial fibrillation in diabetic patients with and without myocardial infarction. This could be due to the effects of metformin on preventing the structural and electrical remodeling of left atrium via attenuating intracellular reactive oxygen species, activating 5′ adenosine monophosphate-activated protein kinase, improving calcium homeostasis, attenuating inflammation, increasing connexin-43 gap junction expression, and restoring small conductance calcium-activated potassium channels current. For ventricular arrhythmias, in vivo reports demonstrated that activation of 5′ adenosine monophosphate-activated protein kinase and phosphorylated connexin-43 by metformin played a key role in ischemic ventricular arrhythmias reduction. However, metformin failed to show anti-ventricular arrhythmia benefits in clinical trials. In this review, in vitro and in vivo reports regarding the effects of metformin on both atrial arrhythmias and ventricular arrhythmias are comprehensively summarized and presented. Consistent and controversial findings from clinical trials are also summarized and discussed. Due to limited numbers of reports, further studies are needed to elucidate the mechanisms and effects of metformin on cardiac arrhythmias. Furthermore, randomized controlled trials are needed to clarify effects of metformin on cardiac arrhythmias in human.

Autonomic Nervous System Dysfunction: JACC Focus Seminar

Autonomic nervous system control of the heart is a dynamic process in both health and disease. A multilevel neural network is responsible for control of chronotropy, lusitropy, dromotropy, and inotropy. Intrinsic autonomic dysfunction arises from diseases that directly affect the autonomic nerves, such as diabetes mellitus and the syndromes of primary autonomic failure. Extrinsic autonomic dysfunction reflects the changes in autonomic function that are secondarily induced by cardiac or other disease. An array of tests interrogate various aspects of cardiac autonomic control in either resting conditions or with physiological perturbations from resting conditions. The prognostic significance of these assessments have been well established. Clinical usefulness has not been established, and the precise mechanistic link to mortality is less well established. Further efforts are required to develop optimal approaches to delineate cardiac autonomic dysfunction and its adverse effects to develop tools that can be used to guide clinical decision-making.

Insulin treatment augments KCNQ1/KCNE1 currents but not KCNQ1 currents, which is associated with an increase in KCNE1 expression

Diabetes mellitus affects ion channel physiology. We have previously reported that acute application of insulin suppresses the KCNQ1/KCNE1 currents that play an important role in terminating ventricular action potential. In this study, we investigated the effect of long-term insulin treatment on KCNQ1/KCNE1 currents using the Xenopus oocyte expression system. Insulin treatment with a duration longer than 6 h had an opposite effect to acute insulin application, that is, it augmented the KCNQ1/KCNE1 currents. Inhibitors of PI3K, wortmannin and LY294002, and a MEK inhibitor, U0126, abolished the potentiating effect of long-term insulin treatment. The long-term treatment with insulin had no effect on KCNQ1 currents indicating an essential role of KCNE1 in the insulin effect, which is similar to the acute insulin effect. Cycloheximide, an inhibitor of protein synthesis, and brefeldin A, an inhibitor of protein transport from endoplasmic reticulum, suppressed the long-term insulin effect. Western blotting analysis combined with these pharmacological data suggest that long-term insulin treatment augments KCNQ1/KCNE1 currents by increasing KCNE1 protein expression.

Prolonged Tp-e Interval, Tp-e/QT Ratio and Tp-e/QTc Ratio in Patients with Type 2 Diabetes Mellitus

BACKGROUND

Type 2 diabetes mellitus (T2DM) is associated with increased risk of malignant ventricular arrhythmias. Cardiac electrical inhomogeneity may be the leading cause of the increased arrhythmic risk in patients with T2DM. The peak and the end of the T wave (Tp-e) interval and associated Tp-e/QT ratio are promising measures of ventricular repolarization indicating transmural dispersion of repolarization. The aim of this study was to assess ventricular repolarization in patients with T2DM by using Tp-e interval, Tp-e/QT ratio and Tp-e/corrected QT interval (QTc) ratio.

METHODS

Forty-three patients with T2DM and 43 healthy control subjects, matched by gender and age, were studied. All participants underwent electrocardiography (ECG) recording. PR, RR and QT intervals represents the ECG intervals. These are not abbreviations. In all literature these ECG intervals are written like in this text. Tp-e intervals were measured from 12-lead ECG. Rate QTc was calculated by using the Bazett's formula. Tp-e/QT ratio and Tp-e/QTc ratio were also calculated.

RESULTS

Mean Tp-e interval was significantly prolonged in patients with T2DM compared to controls (79.4±10.3, 66.4±8.1 ms, respectively; P<0.001). We also found significantly higher values of Tp-e/QT ratio and Tp-e/QTc ratio in patients with diabetes than controls (0.21±0.03, 0.17±0.02 and 0.19±0.02, 0.16±0.02, respectively; P<0.001). There was no difference in terms of the other ECG parameters between the groups.

CONCLUSION

Tp-e interval, Tp-e/QT ratio and Tp-e/QTc ratio were prolonged in patients with T2DM. We concluded that T2DM leads to augmentation of transmural dispersion of repolarization suggesting increased risk for ventricular arrhythmogenesis.

Cardiac Involvement in Peripheral Neuropathies

Cardiac autonomic neuropathy (CAN) is the least recognized and understood complication of peripheral neuropathy. However, because of its potential adverse effects including sudden death, CAN is one of the most important forms of autonomic neuropathies. CAN presents with different clinical manifestations including postural hypotension, exercise intolerance, fluctuation of blood pressure and heart rate, arrhythmia, and increased risk of myocardial infarction. In this article, the prevalence, clinical presentations, and management of cardiac involvement in certain peripheral neuropathies, including diabetic neuropathy, Guillain-Barré syndrome, chronic inflammatory polyneuropathy, human immunodeficiency virus-associated neuropathy, hereditary neuropathies, and amyloid neuropathy are examined in detail.

Electrocardiological features in obesity: the benefits of body surface potential mapping

BACKGROUND

Various ECG abnormalities are commonly observed in obesity and in metabolic syndrome.

SUMMARY

Some of these abnormalities are caused by the pushed-up position of the diaphragm due to obesity and others occur as a result of the complications of the condition. The position of the R wave may change, various arrhythmias may develop or the QT interval may be prolonged, which increases the tendency to malignant arrhythmias. In obesity, the ECG signs of ventricular hypertrophy are less informative due to the accumulation of epicardial and subcutaneous adipose tissue. In general, it can be concluded that a microcirculation disorder is present in metabolic syndrome that may primarily be associated with ST-T wave abnormalities.

KEY MESSAGES

Body surface potential mapping is a more sensitive method than traditional ECG with potentially greater use for diagnosis mainly in the early phase of non-ST elevation myocardial infarctions.

Insulin suppresses IKs (KCNQ1/KCNE1) currents, which require β-subunit KCNE1

Abnormal QT prolongation in diabetic patients has become a clinical problem because it increases the risk of lethal ventricular arrhythmia. In an animal model of type 1 diabetes mellitus, several ion currents, including the slowly activating delayed rectifier potassium current (IKs), are altered. The IKs channel is composed of KCNQ1 and KCNE1 subunits, whose genetic mutations are well known to cause long QT syndrome. Although insulin is known to affect many physiological and pathophysiological events in the heart, acute effects of insulin on cardiac ion channels are poorly understood at present. This study was designed to investigate direct electrophysiological effects of insulin on IKs (KCNQ1/KCNE1) currents. KCNQ1 and KCNE1 were co-expressed in Xenopus oocytes, and whole cell currents were measured by a two-microelectrode voltage-clamp method. Acute application of insulin suppressed the KCNQ1/KCNE1 currents and phosphorylated Akt and extracellular signal-regulated kinase (ERK), the two major downstream effectors, in a concentration-dependent manner. Wortmannin (10(-6) M), a phosphoinositide 3-kinase (PI3K) inhibitor, attenuated the suppression of the currents and phosphorylation of Akt by insulin, whereas U0126 (10(-5) M), a mitogen-activated protein kinase kinase (MEK) inhibitor, had no effect on insulin-induced suppression of the currents. In addition, insulin had little effect on KCNQ1 currents without KCNE1, which indicated an essential role of KCNE1 in the acute suppressive effects of insulin. Mutagenesis studies revealed amino acid residues 111-118 within the distal third C-terminus of KCNE1 as an important region. Insulin has direct electrophysiological effects on IKs currents, which may affect cardiac excitability.

Mortality in type 2 diabetes mellitus: magnitude of the evidence from a systematic review and meta-analysis

Background:

Type 2 diabetes is associated with an increase in age-related mortality. A systematic review and meta-analysis were performed to define the relative risks (RR) of all-cause or cause-specific mortality in type 2 diabetes and to determine gaps in current research.

Methods:

A comprehensive literature search was undertaken for studies (published 1990–2010) on mortality in type 2 diabetes. The study reports on the measure of mortality as defined by RR for all-cause and cause-specific mortality, heterogeneity, sensitivity analyses and biases.

Results:

In total 35 studies (220,689 patients; mean follow-up of 10.7 years) were eligible for inclusion: 33 studies reported increased mortality risks; 24 had full data on 95% confidence intervals (CIs), one study reported no excess mortality in men diagnosed after 65 years whereas three reported increased mortality in similar age groups in both sexes. Meta-analysis showed RR = 1.85 (95% CI 1.79–1.92) for all-cause mortality [men RR=1.57 (95% CI 1.46–1.68); women RR=2.0 (95% CI 1.89–2.12)], RR=1.76 (95% CI 1.66–1.88) for cardiovascular mortality and RR=2.26 (95% CI: 1.7-3.02) for stroke. There was no statistically significant evidence of publication bias.

Conclusion:

Type 2 diabetes increases mortality approximately two-fold increase and macrovascular disease is the principal cause of death.

Inhibition of the prothrombinase complex on red blood cells by heparin and covalent antithrombin-heparin complex

The role of red blood cells (RBCs) in coagulation is not well understood. Overt exposure of phosphatidylserine on surfaces of RBCs provide docking sites for formation of the prothrombinase complex, which further aids in amplification of coagulation leading to subsequent thrombosis. No studies to date have evaluated heparin inhibition of the RBC-prothrombinase system. Therefore, this study examines the ability of heparin and a covalent antithrombin-heparin complex (ATH) to inhibit the RBC-prothrombinase system. Discontinuous inhibition assays were performed to obtain k₂ values for inhibition of free or prothrombinase-bound Xa by antithrombin and unfractionated heparin (AT + UFH) versus ATH. In addition, components of the complex (prothrombin, RBCs or Va) were excluded prior to reaction with inhibitors to investigate potential mechanisms involved. Inhibition of thrombin generation, fibrinogen conversion and plasma clotting by the RBC-prothrombinase system was also examined. Protection of Xa was observed for AT + UFH and not for ATH reactions. Inhibition rates for ATH were significantly faster when compared with AT + UFH results. The greatest impact on Xa inhibition was observed from factor Va omission for both inhibitors. ATH inhibited thrombin generation, fibrinogen conversion and plasma clotting better compared with AT + UFH. This study determined potential control of coagulation contributed by RBCs. Moreover, greater control of coagulation is achieved by covalently linking heparin to AT.

Increased QT interval dispersion predicts 15-year cardiovascular mortality in type 2 diabetic subjects: the population-based Casale Monferrato Study

OBJECTIVE

To evaluate the predictive role of increased corrected QT (QTc) and QT interval dispersion (QTd) on all-cause and cardiovascular mortality in a large, unselected type 2 diabetic population.

RESEARCH DESIGN AND METHODS

The prospective study included 1,357 type 2 diabetic patients from the Casale Monferrato Study. At baseline, QTc intervals >0.44 s and QTd intervals >0.08 s were considered abnormally prolonged. Both all-cause and cardiovascular mortality were assessed 15 years after the baseline examination.

RESULTS

During the follow-up period, 862 subjects per 12,450 person-years died. Multivariate analysis showed that the hazard ratio (HR) of cardiovascular mortality was significantly increased in subjects with prolonged QTd (1.26 [95% CI 1.02-1.55]) and was only slightly reduced after multiple adjustments. Conversely, prolonged QTc did not increase the HRs for all-cause or cardiovascular mortality.

CONCLUSIONS

Increased QTd predicts cardiovascular mortality after a long-term follow-up period in a large, unselected population of type 2 diabetic subjects.

The ECG vertigo in diabetes and cardiac autonomic neuropathy

The importance of diabetes in the epidemiology of cardiovascular diseases cannot be overemphasized. About one third of acute myocardial infarction patients have diabetes, and its prevalence is steadily increasing. The decrease in cardiac mortality in people with diabetes is lagging behind that of the general population. Cardiovascular disease is a broad term which includes any condition causing pathological changes in blood vessels, cardiac muscle or valves, and cardiac rhythm. The ECG offers a quick, noninvasive clinical and research screen for the early detection of cardiovascular disease in diabetes. In this paper, the clinical and research value of the ECG is readdressed in diabetes and in the presence of cardiac autonomic neuropathy.

Diabetes does not affect ventricular repolarization and sudden cardiac death risk in patients with dilated cardiomyopathy

BACKGROUND

We studied the effects of diabetes on ventricular repolarization parameters and sudden cardiac death in patients with dilated cardiomyopathy (DCM).

METHODS

We enrolled 132 consecutive patients in New York Heart Association (NYHA) heart failure functional classes II or III and left ventricular ejection fraction <40% without evidence of coronary artery disease. In 45 patients (34%), diabetes was diagnosed according to standard criteria (study group), and the remaining 87 (66%) had no diabetes (controls). All patients underwent a 5-minute high-resolution electrocardiogram recording for determination of QT variability (QTV) index and were followed for 1 year thereafter.

RESULTS

At baseline, the two groups did not differ in age, gender, left ventricular ejection fraction, NYHA functional class, or plasma brain natriuretic peptide levels. Similarly, QTV index did not differ between the study group (-0.51 +/- 0.55) and controls (-0.48 +/- 0.51; P = 0.48). During follow-up, 18 patients (14%) died of cardiac causes. Of the 18 deaths, eight were attributed to heart failure, and 10 to sudden cardiac death. Mortality was higher in the study group (10/45, 20%) than in controls (8/87, 10%) (P = 0.03). The same was true of the heart failure mortality (6/45 [13%] vs 2/87 [2%], P = 0.01), but not of the sudden cardiac death rate (3/45 [7%] vs 7/87 [8%], P = 0.78). By multiple variable analyses, diabetes predicted total and heart failure mortality, and a high QTV predicted sudden cardiac death.

CONCLUSIONS

Diabetes appears to increase the risk of heart failure in patients with DCM without affecting ventricular repolarization parameters and sudden cardiac death risk.

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.

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

OBJECTIVES

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

RESEARCH DESIGN AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Possible cardioprotective effect of angiotensin-converting enzyme inhibitors during treatment of American tegumentary leishmaniasis with meglumine antimoniate

We conducted an observational retrospective study to identify factors associated with prolongation of corrected QT (QTc) interval during treatment of American tegumentary leishmaniasis with meglumine antimoniate. A group of 108 patients with normal ECG before treatment were included. Thirty-one patients (29%) developed increase of QTc interval beyond 0.44s in the second ECG performed after an average of (mean+/-S.D.) 12.6+/-4.9 days. After univariate and multivariate analysis, the age was associated with prolonged QTc interval, and the use of angiotensin-converting enzyme (ACE) inhibitors demonstrated a protective factor. These results identify elderly as a risk factor to develop prolonged QTc due to antimonial therapy (odds ratio: 1.1; 95% confidence interval: 1.01-1.12), and suggest that use of ACE inhibitors is a possible cardioprotective agent (odds ratio: 0.3; 95% confidence interval: 0.003-0.34). Further studies using prospective methodology are necessary to define the role of ACE inhibitors as prophylactic agent in high-risk patients.

Disfunção autonômica cardiovascular no diabetes mellitus experimental

Muitas informações novas têm sido publicadas nos últimos anos a respeito da fisiopatologia da disfunção autonômica cardiovascular em ratos e camundongos diabéticos. Nosso grupo tem estudado o curso temporal das alterações cardiovasculares associadas ao diabetes experimental há alguns anos, obtendo evidências consistentes de grave disautonomia em modelos animais de diabetes. O objetivo deste trabalho foi revisar a contribuição que estudos envolvendo diferentes modelos de deficiência e resistência à insulina têm fornecido para o entendimento, tratamento e prevenção da disfunção autonômica cardiovascular do diabetes.

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

AIMS/HYPOTHESIS

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

METHODS

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

RESULTS

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

CONCLUSIONS/INTERPRETATION

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

Cardiovascular autonomic neuropathy: diagnosis and management

Cardiovascular autonomic neuropathy increases morbidity and mortality, and reduces quality of life and activities of daily living of the patients with diabetes. The reduced cardiovascular autonomic function as measured by heart rate variability is strongly associated with an increased risk of silent myocardial ischemia and mortality. Currently, no specific therapeutic strategies can be recommended for cardiac autonomic neuropathy, but management of hyperglycemia and the use of angiotensin-converting enzyme inhibitors and beta blockers should be instituted.

QT dispersion: comparison between participants with Type 1 and 2 diabetes and association with microalbuminuria in diabetes

BACKGROUND AND AIMS

The interlead variation of QT duration in surface electrocardiogram [ECG; QT dispersion (QTd)] has been shown to predict mortality in both diabetic and general population. Diabetic cardiac autonomic neuropathy (CAN) is a common complication of diabetes, and it is also associated with worse prognosis among the diabetic population. In this study, we investigated the association between QTd duration and CAN, as well as other complications of diabetes in participants with Types 1 and 2 diabetes.

METHODS

A total of 184 patients with either Type 1 (n=63) or 2 (n=121) diabetes, as well as 100 control participants, matched for age and sex with the diabetic individuals, were studied. QT and RR intervals were measured on 12 leads of resting ECG tracing. QTd was calculated semiautomatically using a computer program as the difference between the maximum and the minimum QT in any of the 12 leads. CAN was diagnosed when two out of the four classical tests were abnormal.

RESULTS

QTd was not significantly different between controls and patients with either Type 1 or 2 diabetes. Age-adjusted QTd intervals were not significantly different between patients with Types 1 and 2 diabetes (P=.86). For both types of diabetes, no significant differences were found in QTd between patients with and without CAN. Multivariable linear regression analysis, after adjustment for a number of confounding factors, demonstrated a positive association between QTd and duration of diabetes (P=.02) in the group of the patients with Type 1 diabetes. In those with Type 2 diabetes, QTd was associated with age (P=.006) and presence of microalbuminuria (P=.001). In addition, no significant association was found with retinopathy or blood pressure levels.

CONCLUSIONS

Age-adjusted QTd interval was not different between patients with Types 1 and 2 diabetes. CAN is not associated with QTd interval in both types of diabetes. Furthermore, microalbuminuria was found to be the strongest predictor of QTd in patients with Type 2 diabetes. Because long QTd interval predicts cardiac mortality in participants with diabetes, it is suggested that it may be a useful adjuvant index in the evaluation of cardiovascular risk in participants with Type 2 diabetes and microalbuminuria.

QT dispersion in type 2 diabetic patients with altered diurnal blood pressure rhythm

BACKGROUND

QT dispersion (QTd) is a good prognostic marker in type 2 diabetic patients without previous cardiovascular disease. Diabetic patients with an attenuated decline in nocturnal blood pressure (non-dippers) have been shown to have increased risk of diabetic complications, vascular events and mortality.

AIM

The aim of this study was to evaluate the relationship between diurnal blood pressure rhythm, QTd and microvascular complications in type 2 diabetic patients.

METHODS

Cardiovascular autonomic function tests, 24-h ambulatory blood pressure monitoring and urinary albumin excretion measurements were performed in healthy controls (n = 25), normoalbuminuric (n = 34) and microalbuminuric (n = 23) type 2 diabetic patients. QTd was assessed manually from 12-lead surface electrocardiograms.

RESULTS

Compared with the controls, both normoalbuminuric and microalbuminuric diabetic patients had increased QTd (59.11 +/- 15.86; 60.27 +/- 17.95 vs. 40.48 +/- 10.92, p < 0.001 and p < 0.001, respectively). Similarly, diabetic patients had increased QTd regardless of the presence of autonomic neuropathy. On the other hand, non-dipper diabetic patients had increased QTd compared with the controls and dipper diabetic patients (69.73 +/- 14.50 vs. 40.48 +/- 10.92; 47.84 +/- 9.62 ms, p < 0.001). There was a negative correlation between QTd and diurnal diastolic blood pressure change (r = -0.48, p < 0.0005).

CONCLUSION

Patients with type 2 diabetes mellitus were found to have increased QT dispersion irrespective of the presence of diabetic autonomic neuropathy. However, QT dispersion in dipper diabetic patients was similar to the controls. This finding might point out that attenuated decline of nocturnal blood pressure could be a more sensitive marker for autonomic neuropathy.

QT interval abnormalities are often present at diagnosis in diabetes and are better predictors of cardiac death than ankle brachial pressure index and autonomic function tests

OBJECTIVES

To study serial measures of maximum QT interval corrected for heart rate (QTc) and QT dispersion (QTD) and their association with cardiac mortality patients with non-insulin dependent diabetes and to compare QT abnormalities with other mortality predictors (ankle brachial pressure index (ABPI) and autonomic function tests) in their ability to predict cardiac death.

SETTING

Teaching hospital.

METHODS AND PATIENTS

QT interval analysis, heart rate (RR) variation in response to deep breathing and standing, and ABPI were analysed in 192 patients with non-insulin dependent diabetes. Cardiac death was the primary end point.

RESULTS

Mean (SD) follow up was 12.7 (3.2) years (range 1.2-17.1 years). There were 48 deaths, of which 26 were cardiac. QTc and QTD were individually significant predictors of cardiac mortality throughout the follow up period (p < 0.001). The predictability of QT parameters was superior to the predictability of ABPI and RR interval analysis. Temporal changes in QT parameters showed that the mean absolute QT parameter was a significant predictor of cardiac death (p < 0.001), whereas an intraindividual change in QT parameter over time was not predictive.

CONCLUSION

QT abnormalities seem to exist at the point of diagnosis of diabetes and do not appear to change between then and the subsequent cardiac death. Furthermore, the analysis of QT interval is superior to ABPI and the RR interval in identifying diabetic patients at high risk of cardiac death.

Regulation of QT indices mediated by autonomic nervous function in patients with type 2 diabetes

Both the QT interval and QT dispersion in diabetic patients have been reported to increase with the progression of cardiac autonomic neuropathy and to have a prognostic value. We assessed the cardiac autonomic influences on QT indices using the measurements of baroreflex sensitivity, heart rate variability, and cardiac (123)I-metaiodobenzylguanidine scintigraphic findings in patients with type 2 diabetes mellitus. Forty-two consecutive patients with type 2 diabetes (mean+/-SD: 54+/-10 years, 22 women and 20 men) were studied. Baroreflex sensitivity negatively correlated with the maximum and minimum QTc intervals as well as QT/QTc dispersion. However, the high-frequency power and the ratio of low-frequency power to high-frequency power of heart rate variability did not correlate with any QT indices. The percent washout rate of (123)I-metaiodobenzylguanidine positively correlated with QT/QTc dispersion, but not with maximum and minimum QTc intervals. Our findings suggest that cardiac vagal dysfunction is related to QT interval prolongation while both sympathetic and vagal dysfunctions are related to increased QT dispersion in type 2 diabetic patients. Baroreflex sensitivity and percent washout rate of (123)I-metaiodobenzylguanidine may be useful parameters indicating the abnormalities of the cardiac ventricular repolarization in this population.

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.

Electrocardiographic repolarization complexity and abnormality predict all-cause and cardiovascular mortality in diabetes: the strong heart study

Type 2 diabetes is associated with increased risk of cardiovascular (CV) and all-cause mortality. Although electrocardiographic measures of repolarization abnormality and complexity stratify risk in the general population, their prognostic value in diabetes has not been well characterized. Digital electrocardiogram (ECG) readings were acquired for 994 American Indians with type 2 diabetes. ST segment depression (STD) >/=50 micro V and rate-corrected QT interval (QTc) >460 ms were examined as measures of repolarization abnormality. The principal component analysis (PCA) of the ratio of the second to first eigenvalues of the T-wave vector (PCA ratio) (>32.0% in women and >24.6% in men) was examined as a measure of repolarization complexity on the ECG. After a mean follow-up of 4.7 +/- 1.0 years, there were 56 CV deaths and 155 deaths from all causes. In univariate analyses, STD, QTc, and the PCA ratio predicted CV and all-cause mortality. After multivariate adjustment for age, sex, and other risk factors, STD (hazard ratio 3.68, 95% CI 1.70-7.96) and PCA ratio (2.61, 1.33-5.13) remained predictive of CV mortality and both STD (2.36, 1.38-4.02) and QTc (2.03, 1.32-3.12) predicted all-cause mortality. Computerized ECG measures of repolarization abnormality and complexity predict CV and all-cause mortality in type 2 diabetes, supporting their use to identify high-risk individuals with diabetes.

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.

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.

The association between cardiovascular autonomic neuropathy and mortality in individuals with diabetes: a meta-analysis

OBJECTIVE

To examine by meta-analysis the relationship between cardiovascular autonomic neuropathy (CAN) and risk of mortality in individuals with diabetes.

RESEARCH DESIGN AND METHODS

We searched Medline for English-language articles published from 1966 to 2001. Fifteen studies having a baseline assessment of cardiovascular autonomic function and mortality follow-up were identified. The analyses were stratified according to whether a single abnormality or two or more measures of cardiovascular autonomic function were used to define CAN. A global measure of association (i.e., relative risk) was generated for each group by pooling estimates across the studies using the Mantel-Haenszel procedure.

RESULTS

CAN was significantly associated with subsequent mortality in both groups, although the magnitude of the association was stronger for those studies for which two or more measures were used to define CAN. The pooled relative risk for studies that defined CAN with the presence of two or more abnormalities was 3.45 (95% CI 2.66-4.47; P < 0.001) compared with 1.20 (1.02-1.41; P = 0.03) for studies that used one measure.

CONCLUSIONS

These results support an association between CAN and increased risk of mortality. The stronger association observed in studies defining CAN by the presence of two or more abnormalities may be due to more severe autonomic dysfunction in these subjects or a higher frequency of other comorbid complications that contributed to their higher mortality risk. Future studies should evaluate whether early identification of subjects with CAN can lead to a reduction in mortality.

Circadian variation in the onset of myocardial infarction: effect of duration of diabetes

There are conflicting reports regarding circadian variation in the onset of acute myocardial infarction (MI) among patients with diabetes. We therefore, studied the circadian pattern of the incidence of acute MI in patients (n = 3,882) who were enrolled in the Onset Study stratified by the presence, type, and duration of diabetes. The Onset Study was conducted at 64 U.S. medical centers between August 1989 and September 1996. We used harmonic regression model to evaluate the circadian variation of MI symptom onset in patients with and without diabetes. Subgroup analysis was performed according to the presence, type, and duration of diabetes by the chi(2) test (dividing the day into four 6-h intervals). Patients without diabetes exhibited a prominent morning peak in the incidence of acute MI symptom onset (P < 0.001). In contrast, patients with type 1 diabetes and type 2 diabetes > or =5 years had a marked attenuation of the morning peak. Patients who had type 2 diabetes diagnosed within the previous 5 years had a pattern of onset of acute MI similar to patients without diabetes. Patients with type 1 diabetes and those with type 2 diabetes > or =5 years have an attenuation of the morning peak in acute MI. Inconsistency in observation of such an effect in patients with diabetes in the past may well have been due to difference in the duration of diabetes and thus the variable extent of underlying autonomic dysfunction.

Diabetic autonomic neuropathy

Diabetic autonomic neuropathy (DAN) is a serious and common complication of diabetes. Despite its relationship to an increased risk of cardiovascular mortality and its association with multiple symptoms and impairments, the significance of DAN has not been fully appreciated. The reported prevalence of DAN varies widely depending on the cohort studied and the methods of assessment. In randomly selected cohorts of asymptomatic individuals with diabetes, approximately 20% had abnormal cardiovascular autonomic function. DAN frequently coexists with other peripheral neuropathies and other diabetic complications, but DAN may be isolated, frequently preceding the detection of other complications. Major clinical manifestations of DAN include resting tachycardia, exercise intolerance, orthostatic hypotension, constipation, gastroparesis, erectile dysfunction, sudomotor dysfunction, impaired neurovascular function, "brittle diabetes," and hypoglycemic autonomic failure. DAN may affect many organ systems throughout the body (e.g., gastrointestinal [GI], genitourinary, and cardiovascular). GI disturbances (e.g., esophageal enteropathy, gastroparesis, constipation, diarrhea, and fecal incontinence) are common, and any section of the GI tract may be affected. Gastroparesis should be suspected in individuals with erratic glucose control. Upper-GI symptoms should lead to consideration of all possible causes, including autonomic dysfunction. Whereas a radiographic gastric emptying study can definitively establish the diagnosis of gastroparesis, a reasonable approach is to exclude autonomic dysfunction and other known causes of these upper-GI symptoms. Constipation is the most common lower-GI symptom but can alternate with episodes of diarrhea. Diagnostic approaches should rule out autonomic dysfunction and the well-known causes such as neoplasia. Occasionally, anorectal manometry and other specialized tests typically performed by the gastroenterologist may be helpful. DAN is also associated with genitourinary tract disturbances including bladder and/or sexual dysfunction. Evaluation of bladder dysfunction should be performed for individuals with diabetes who have recurrent urinary tract infections, pyelonephritis, incontinence, or a palpable bladder. Specialized assessment of bladder dysfunction will typically be performed by a urologist. In men, DAN may cause loss of penile erection and/or retrograde ejaculation. A complete workup for erectile dysfunction in men should include history (medical and sexual); psychological evaluation; hormone levels; measurement of nocturnal penile tumescence; tests to assess penile, pelvic, and spinal nerve function; cardiovascular autonomic function tests; and measurement of penile and brachial blood pressure. Neurovascular dysfunction resulting from DAN contributes to a wide spectrum of clinical disorders including erectile dysfunction, loss of skin integrity, and abnormal vascular reflexes. Disruption of microvascular skin blood flow and sudomotor function may be among the earliest manifestations of DAN and lead to dry skin, loss of sweating, and the development of fissures and cracks that allow microorganisms to enter. These changes ultimately contribute to the development of ulcers, gangrene, and limb loss. Various aspects of neurovascular function can be evaluated with specialized tests, but generally these have not been well standardized and have limited clinical utility. Cardiovascular autonomic neuropathy (CAN) is the most studied and clinically important form of DAN. Meta-analyses of published data demonstrate that reduced cardiovascular autonomic function as measured by heart rate variability (HRV) is strongly (i.e., relative risk is doubled) associated with an increased risk of silent myocardial ischemia and mortality. The determination of the presence of CAN is usually based on a battery of autonomic function tests rather than just on one test. Proceedings from a consensus conference in 1992 recommended that three tests (R-R variation, Valsalva maneuver, and postural blood pressure testing)or longitudinal testing of the cardiovascular autonomic system. Other forms of autonomic neuropathy can be evaluated with specialized tests, but these are less standardized and less available than commonly used tests of cardiovascular autonomic function, which quantify loss of HRV. Interpretability of serial HRV testing requires accurate, precise, and reproducible procedures that use established physiological maneuvers. The battery of three recommended tests for assessing CAN is readily performed in the average clinic, hospital, or diagnostic center with the use of available technology. Measurement of HRV at the time of diagnosis of type 2 diabetes and within 5 years after diagnosis of type 1 diabetes (unless an individual has symptoms suggestive of autonomic dysfunction earlier) serves to establish a baseline, with which 1-year interval tests can be compared. Regular HRV testing provides early detection and thereby promotes timely diagnostic and therapeutic interventions. HRV testing may also facilitate differential diagnosis and the attribution of symptoms (e.g., erectile dysfunction, dyspepsia, and dizziness) to autonomic dysfunction. Finally, knowledge of early autonomic dysfunction can encourage patient and physician to improve metabolic control and to use therapies such as ACE inhibitors and beta-blockers, proven to be effective for patients with CAN.

Blood pressure and cardiac autonomic function in relation to risk factors and treatment perspectives in Type 1 diabetes

The cumulative incidence of diabetic nephropathy in Type 1 diabetes mellitus is in the order of 25 30%. The recognition that elevated blood pressure (BP) is a major factor in the progression of these patients to end-stage renal failure has led to the widespread use of antihypertensive therapy in order to preserve glomerular filtration rate and ultimately to reduce mortality. The routine measurement of microalbuminuria allows early identification of the subgroup of patients at increased risk of developing clinical nephropathy. Microalbuminuric Type 1 diabetic patients show a number of characteristic pathological abnormalities. In addition to elevated BP and abnormal circadian rhythm, there are also associated abnormalities of vagal function, lipid profile and endothelial function, as well as an increased prevalence of retinopathy. The first section of this two-part review focusses on the early changes associated with renal involvement in Type 1 diabetes. It addresses the associations between urinary albumin excretion, glycaemic control, smoking, BP, circadian BP variation, QT interval abnormalities and autonomic function in three groups of patients; those with normoalbuminuria, those progressing towards microalbuminuria and those with established low-grade microalbuminuria.

Relation of QT interval dispersion to the number of different cardiac abnormalities in diabetes mellitus

Three studies have clearly shown that a prolonged QT dispersion (QTD) is the best predictor of cardiac death in patients with type 2 diabetes mellitus (DM). This was originally believed to be because QTD identified electrical inhomogeneity, but recent data suggests that this is unlikely. The alternative possibility is that QTD is a convenient identifier of hidden but lethal cardiac abnormalities. We explored whether the latter possibility is true by examining exactly what spectrum of cardiac abnormalities, if any, are over-represented in diabetics with a prolonged QTD. Two hundred nineteen patients with type 2 DM who had been first diagnosed with DM 3 to 6 years previously underwent intensive cardiac examinations. Patients with prolonged QTD had a significantly increased incidence of myocardial ischemia and left ventricular (LV) hypertrophy, and to a lesser extent, autonomic dysfunction. The main independent determinant of a prolonged QTD was ischemia, as seen on both ambulatory ST-segment monitoring (p <0.001) and Duke score on treadmill testing (p <0.001). It was also observed that QTD increased progressively as the number of different cardiac abnormalities increased (p <0.001). These studies suggest that QTD is a useful, general prescreening test to select diabetics for more detailed cardiac examinations (especially for ischemia and LV hypertrophy), and that if cardiac examinations were targeted by way of QTD screening, then a high incidence of hidden but treatable cardiac abnormalities could be found.

Influence of cardiac autonomic neuropathy on heart rate dependence of ventricular repolarization in diabetic patients

OBJECTIVE

Prolongation of the QT interval and increased QT dispersion are associated with a poor cardiac prognosis. The goal of this study was to assess the long-term influence of the autonomic nervous system on the heart rate dependence of ventricular repolarization in patients with diabetic autonomic neuropathy (DAN).

RESEARCH DESIGN AND METHODS

We studied 27 subjects (mean age 51.8 years) divided into three age- and sex-matched groups: nine control subjects, nine diabetic subjects with DAN (mostly at a mild stage; DAN+), and nine diabetic subjects without DAN (DAN-). DAN was assessed on heart rate variations during standard maneuvers (Valsalva, deep-breathing, and lying-to-standing maneuvers). No subject had coronary artery disease or left ventricular dysfunction or hypertrophy, and no subject was taking any drugs known to prolong the QT interval. All subjects underwent electrocardiogram and 24-h Holter recordings for heart rate variations (time and frequency domain) and QT analysis (selective beat averaging QT/RR relation, nocturnal QT lengthening).

RESULTS

Rate-corrected QT intervals (Bazett formula) did not differ significantly between the three groups. The diurnal and nocturnal levels of low frequency/high frequency, an index of sympathovagal balance, were significantly reduced in DAN+ subjects. Using the selective beat-averaging technique, a day-night modulation of the QT/RR relation was evidenced in control and DAN- subjects. This long-term modulation was significantly different in DAN+ subjects, with a reversed day-night pattern and an increased nocturnal QT rate dependence.

CONCLUSIONS

In diabetic patients with mild parasympathetic denervation, QT heart rate dependence was found to be impaired, as determined by noninvasive assessment using Holter data. Analysis of ventricular repolarization could represent a sensitive index of the progression of neuropathy. The potential prognostic impact of a reversed day-night pattern with steep nocturnal QT/RR relation still remains to be defined.

Prevalence of increased QT interval duration and dispersion in type 2 diabetic patients and its relationship with coronary heart disease: a population-based cohort

OBJECTIVE

To evaluate the prevalence of prolonged QT interval and dispersion in a population-based cohort of type 2 diabetic patients and their relationship with clinical and metabolic variables.

DESIGN

Cross-sectional population-based cohort.

SETTING

Diabetes clinics and general practitioners in Casale Monferrato (Northern Italy).

SUBJECTS

A total of 1357 patients with known type 2 diabetes (70% of the cohort).

MAIN OUTCOMES MEASURES

Albumin excretion rate and coronary heart disease (CHD); a standard supine 12-lead electrocardiogram (ECG) was recorded and coded according to the Minnesota code criteria. QT interval corrected for heart rate (QTc) > 0.44 s and QTc dispersion > 0.080 s were considered abnormally prolonged.

RESULTS

Prevalence of increased QTc duration and QTc dispersion were 25.8% (95% CI 23.5-28.3) and 33.1% (95% CI 30.6-35.7), with no sex differences. No metabolic differences were found, apart from fibrinogen and creatinine levels, which were higher in patients with increased QTc dispersion. Patients with CHD had higher mean adjusted values of QTc and QTc dispersion, whereas no association was found with albumin excretion rate (AER) and diabetes treatment. QTc duration and QTc dispersion were significantly correlated (0.17, P < 0.001). In multiple regression analysis, only CHD was independently associated with QTc, after adjustment for age and sex (beta=0.010, P < 0.001, R2=2.5%); as regards QTc dispersion, a similar association with CHD was found (beta=0.20, P < 0.001, R2=4.8%).

CONCLUSIONS

This population-based study shows a considerably high prevalence of increased QTc and QTc dispersion in type 2 diabetic patients and their association with CHD. These findings have both epidemiological and clinical relevance, as they might be implicated in the excess mortality risk of type 2 diabetic patients.

Diabetes, heart rate, and mortality

A large body of evidence indicates that a persistently high heart rate is associated with a significant risk for higher mortality and sudden death in individuals with a variety cardiovascular disorders, as well as in the general population. Heart rates elevated beyond a certain threshold have been found to be a risk factor for mortality in patients with hypertension, in survivors of myocardial infarction, and in patients with impaired cardiac function. Conversely, a naturally slow heart rate, or one that is slow by virtue of sympathetic blockade induced by pharmacologic agents, may result in longer survival. This is particularly evident in the case of beta-adrenergic blocking drugs, especially in patients after myocardial infarction and in those with acute as well as chronic cardiac failure, a syndrome in which there is a complex neurohormonal disturbance with elevated heart rate. Persistently elevated heart rate is also a feature of diabetes mellitus associated with autonomic neuropathy. Whether this also constitutes an independent risk factor for sudden and augmented mortality is not well defined. In this review, the data on the role of increased heart rate as a risk factor for mortality are examined in the context of other factors that may have therapeutic implications.

Prevalence of Q-T interval dispersion in type 1 diabetes and its relation with cardiac ischemia : the EURODIAB IDDM Complications Study Group

OBJECTIVE

The interlead variation in duration of the Q-T interval on the surface electrocardiogram (Q-T interval dispersion [QTd]) has been shown to predict mortality in type 2 diabetic patients. We evaluated the prevalence of QTd prolongation in the EURODIAB population and its relation to corrected Q-T interval (QTc), sex, age, duration of diabetes, blood glucose control, and complications. RESEARCH DESIGN AND METHODS; A total of 3,042 type 1 diabetic patients were studied. QTc was calculated according to the Bazett's formula; QTc > 0.44 s was considered abnormally prolonged. QTd was calculated using the difference between the maximum and the minimum QTc in any thoracic lead. QTd >0.080 s was considered abnormally prolonged.

RESULTS

The prevalence of an increased QTd was 7%. A significant relation was observed between QTd prolongation and diastolic blood pressure (P < 0.05). A higher prevalence of QTd prolongation was observed in patients with ischemic heart disease (P = 0.004), whereas no relationship was observed with retinopathy, albumin excretion rate, or measures of somatic and autonomic neuropathy. QTc and QTd were significantly related (P = 0.001); however, a proportion of patients with normal QTd showed a prolonged QTc (>0.44 s).

CONCLUSIONS

In patients with type 1 diabetes, QTd is associated with ischemic heart disease and diastolic blood pressure but not neuropathy. Although QTd is statistically related to duration of QTc, increased QTd and increased QTc identify different patients, and their predictive value deserves prospective evaluation.

Value of corrected QT interval dispersion in identifying patients initiating dialysis at increased risk of total and cardiovascular mortality

Cardiovascular disease remains the most common cause of premature death in end-stage renal disease (ESRD). Although several predictors of cardiac death have been reported, identifying individuals most at risk remains difficult. Previous studies in nonuremic populations have associated cardiac mortality, in particular sudden death, with increased QT dispersion (QTd); defined as the difference between the maximal and minimal QT interval on a standard electrocardiogram. The present study aimed to determine the prognostic value of QTd and corrected QTd (QTdc) in predicting total, cardiovascular, and arrhythmia-related mortality in ESRD patients initiating dialysis. The study was a retrospective cohort of adult ESRD patients starting peritoneal dialysis or hemodialysis between 1990 and 1994. Statistical analysis was by Cox proportional hazard modeling and Kaplan-Meier analysis. Primary study endpoints were total, cardiovascular, and arrhythmia-related mortality. Nonfatal cardiovascular events were a secondary endpoint. A total of 147 patients were studied for a period of 5 to 9 years. In Cox modeling, QTdc was an independent predictor of total (relative risk [RR] = 1.53; difference for RR = 50 msec; P = 0.0001) and cardiovascular mortality (RR = 1.57; difference for RR = 50 msec; P = 0.028) and trended toward arrhythmia-related mortality (P = 0.061). Total mortality also was predicted independently by lack of renal transplantation, radiographic cardiomegaly, and predialysis serum albumin. In multivariate analysis, QTdc was associated weakly with serum calcium, mean QT interval, and presence of diabetes mellitus. QTdc may be a useful marker for identifying dialysis patients at an increased risk for overall and cardiovascular mortality.

Low prevalence of cardiac autonomic neuropathy in Type 1 diabetic patients without nephropathy

AIM

To assess the prevalence of cardiac autonomic neuropathy (CAN) in Type 1 diabetic patients with and without nephropathy.

METHODS

Sixty-six consecutive patients without nephropathy (n = 24), with incipient (n = 26) or overt nephropathy (n = 16) and a diabetes duration between 21 and 31 years were examined. Heart rate variability (HRV) as measure for CAN was investigated with short-term spectral analysis in the low-frequency (LF) band (0.06-0.15 Hz), reflecting sympathetic and vagal activity, and high-frequency (HF) band (0.15-0.50 Hz), reflecting vagal activity. HRV was expressed as spectral power (ms2, log-transformed). Normal, age-corresponding reference values were established in 184 controls. QTc intervals and dispersion were measured.

RESULTS

After adjustment for age, there was no significant difference between healthy controls and patients without nephropathy. After further adjustment for diabetes duration, HbA1c, hypertension and treatment with beta-blockers, HRV in both frequency bands decreased with evidence of nephropathy. LF band (supine): patients without nephropathy 5.56 (4.89-6.21) (least squares means and 95% confidence interval (CI)), incipient nephropathy 5.72 (5.15-6.29) and overt nephropathy 4.11 (3.27-4.96). HF band (supine): without nephropathy 5.93 (5.26-6.60), incipient nephropathy 5.99 (5.41-6.57) and overt nephropathy 4.84 (4.00-5.68). Significant differences were found for patients without and with incipient nephropathy compared with those with overt nephropathy in the LF band and between patients with incipient nephropathy compared with those with overt nephropathy in the HF band. QTc intervals and QTc dispersion increased significantly with increasing nephropathy.

CONCLUSIONS

Long-term Type 1 diabetes without nephropathy was not associated with impaired cardiac autonomic function in our study. However, in those with nephropathy, a loss of both vagal and sympathetic activity was present, and the severity of CAN correlated positively with more advanced nephropathy.

Qt dispersion and mortality in the elderly

BACKGROUND

The prognostic value of QT interval dispersion measured from a standard 12-lead electrocardiogram (ECG) in the general population is not well established. The purpose of the present study was primarily to assess the value of QT interval dispersion obtained from 12-lead ECG in the prediction of total, cardiac, stroke, and cancer mortality in the elderly.

METHODS

A random population sample of community-living elderly people (n = 330, age > or = 65 years, mean 74 +/- 6 years) underwent a comprehensive clinical evaluation, laboratory tests, and 12-lead ECG recordings.

RESULTS

By the end of the 10-year follow-up, 180 subjects (55%) had died and 150 (45%) were still alive. Heart rate corrected QT (QTc) dispersion had been longer in those who had died than in the survivors (75 +/- 32 ms vs 63 +/- 35 ms, P = 0.01). After adjustment for age and sex in the Cox proportional hazards model, prolonged QTc dispersion (> or = 70 msec) predicted all-cause mortality (relative risk [RR] 1.38, 95% confidence interval [CI] 1.02-1.86) and particularly stroke mortality (RR 2.7, 95% CI 1.29-5.73), but not cardiac (RR 1.38, 95% CI 0.87-2.18) or cancer (RR 1.51, 95% CI 0.91-2.50) mortality. After adjustment for age, sex, body mass index, blood pressure, blood glucose and cholesterol concentrations, functional class, history of cerebrovascular disease, diabetes, smoking, previous myocardial infarction, angina pectoris, congestive heart failure, medication, left ventricular hypertrophy on ECG, presence of atrial fibrillation and R-R interval, increased QTc dispersion still predicted stroke mortality (RR 3.21, 95% CI 1.09-9.47), but not total mortality or mortality from other causes. The combination of increased QTc dispersion and left ventricular hypertrophy on ECG was a powerful independent predictor of stroke mortality in the present elderly population (RR 16.52, 95% CI 3.37-80.89). QTcmin (the shortest QTc interval among the 12 leads of ECG) independently predicted total mortality (RR 1.0082, 95% CI 1.0028-1.0136, P = 0.003), cardiac mortality (RR 1.0191, 95% CI 1.0102-1.0281, P < 0.0001) and cancer mortality (RR 1.0162, 95% CI 1.0049-1.0277, P = 0.005).

CONCLUSIONS

Increased QTc dispersion yields independent information on the risk of dying from stroke among the elderly and its component, QTcmin, from the other causes of death.

Betablocker treatment in diabetes mellitus

OBJECTIVES

Betablockers have been convincingly shown to reduce total and cardiovascular morbidity and mortality of hypertensive diabetic patients. In diabetic patients, after myocardial infarction, these agents confer a twice as high protective effect when compared to non-diabetic patients. However, most paradoxically, betablocking agents are used less frequently in diabetes. Control of hypertension is insufficient in most of the diabetic patients, probably because a combination of antihypertensive agents including betablockers is frequently needed to sufficiently control blood pressure but is not used in these patients. The fear of betablocker-associated side effects in diabetes may be partly responsible for the frequent antihypertensive mono-therapy and the resulting poor quality of blood pressure control among diabetic patients.

DESIGN

We have performed an analysis of the literature to assess whether possible adverse metabolic effects, a higher risk of hypoglycaemia or less nephroprotective effects of beta1-selective betablocking agents could justify the reticence in prescribing these antihypertensive agents to diabetic patients.

RESULTS

A thorough review of the literature does not indicate that beta1-selective betablocking agents have important adverse effects on glucose metabolism, prolong hypoglycaemia or mask hypoglycaemic symptoms. In diabetic nephropathy, betablockers are as nephroprotective as angiotensin converting enzyme inhibitors.

CONCLUSIONS

The unnecessary less frequent prescription of beta1-selective betablockers in diabetes mellitus may contribute to the higher cardiovascular mortality among these patients.

Clinical determinants of increased QT dispersion in patients with diabetes mellitus

AIMS

To compare QT dispersion measurements in diabetic patients to control subjects and assess any associations between QT dispersion and diabetic clinical characteristics.

METHODS

A total of 512 diabetics and 50 age and gender matched controls were studied. QT interval was measured manually in 12-lead conventional electrocardiograms, and QT dispersion (QTd), heart rate-corrected QT dispersion (QTcd), number of leads-adjusted QT dispersion (adjuQTd) and adjacent QT dispersion (adjaQTd) were calculated. Demographic, clinical, laboratory and electrocardiographic data were recorded.

RESULTS

Diabetics showed increased QT dispersion compared to controls (QTd: P<0.001, QTcd: P<0.001, adjuQTd: P<0.001), even those with recent diagnosis (less than 2 years) and without arterial hypertension, ECG abnormalities or chronic degenerative complications (QTd: P=0.01, QTcd: P<0.001, adjuQTd: P=0.04). Left ventricular hypertrophy (QTd: P<0.001, QTcd: P<0.001, adjuQTd: P<0.001, adjaQTd: P<0.001) and conduction disturbances (QTd: P=0.002, QTcd: P=0.003, adjuQTd: P=0.003) were the electrocardiographic findings associated with increased QT dispersion in bivariate analysis. Clinical variables were the presence of arterial hypertension (QTd: P=0.004, QTcd: P=0.01, adjuQTd: P<0.001), even without left ventricular hypertrophy (QTd: P=0.01, QTcd: P=0.03, adjuQTd: P=0.003), and the presence of diabetic cardiovascular complications (QTd: P=0.02, QTcd: P=0.01, adjuQTd: P=0.008, adjaQTd: P=0.03). No association between QT dispersion and the presence of diabetic microvascular complications, glycaemic control, age and gender, or cardiovascular drugs was observed. Multivariate regressive statistical analysis confirmed the associations noted in bivariate analysis.

CONCLUSIONS

Diabetic patients have increased QT dispersion compared to non-diabetics even those without arterial hypertension and cardiovascular complications and with recent diagnosis. The presence of arterial hypertension, diabetic cardiovascular complications and electrocardiographic abnormalities of left ventricular hypertrophy and conduction disturbances were associated to increased QT dispersion in diabetes mellitus.

Increased QTc dispersion is related to blunted circadian blood pressure variation in normoalbuminuric type 1 diabetic patients

A reduced nocturnal fall in blood pressure (BP) and increased QT dispersion both predict an increased risk of cardiovascular events in diabetic as well as nondiabetic subjects. The relationship between these two parameters remains unclear. The role of diabetic autonomic neuropathy in both QT dispersion and circadian BP variation has been proposed, but data have been conflicting. The aim of the present study was to describe associations between QT dispersion and circadian BP variation as well as autonomic function in type 1 diabetic patients. In 106 normoalbuminuric (urinary albumin excretion <20 microg/min) normotensive patients, we performed 24-h ambulatory BP (Spacelabs 90207) and short-term (three times in 5 min) power spectral analysis of RR interval oscillations, as well as cardiovascular reflex tests (deep breathing test, postural heart rate, and BP response). No patient had received (or had earlier received) antihypertensive or other medical treatment apart from insulin. In a resting 12-lead electrocardiogram, the QT interval was measured by the tangent method in all leads with well-defined T-waves. The measurement was made by one observer blinded to other data. The QT interval was corrected for heart rate using Bazett's formula. The QTc dispersion was defined as the difference between the maximum and the minimum QTc interval in any of the 12 leads. When comparing patients with QTc dispersion below and above the median (43 ms), the latter had significantly higher night BP (114/67 vs. 109/62 mmHg, P < 0.003/P < 0.001), whereas day BP was comparable (129/81 vs. 127/79 mmHg). Diurnal BP variation was blunted in the group with QTc dispersion >43 ms with significantly higher night/day ratio, both for systolic (88.8 vs. 86.2%, P < 0.01) and diastolic (83.1 vs. 79.5%, P < 0.01) BP. The association between QTc dispersion and diastolic night BP persisted after controlling for potential confounders such as sex, age, duration of diabetes, urinary albumin excretion, and HbA1c. Power spectral analysis suggested an altered sympathovagal balance in patients with QTc dispersion above the median (ratio of low-frequency/high-frequency power: 1.0 vs. 0.85, P < 0.01). In normoalbuminuric type 1 diabetic patients, increased QTc dispersion is associated with reduced nocturnal fall in BP and an altered sympathovagal balance. This coexistence may be operative in the ability of these parameters to predict cardiovascular events.