Cardiac function and coronary arteriography in asymptomatic type 1 (insulin-dependent) diabetic patients: evidence for a specific diabetic heart disease

Quantitative MRI in cardiometabolic disease: From conventional cardiac and liver tissue mapping techniques to multi-parametric approaches

Cardiometabolic disease refers to the spectrum of chronic conditions that include diabetes, hypertension, atheromatosis, non-alcoholic fatty liver disease, and their long-term impact on cardiovascular health. Histological studies have confirmed several modifications at the tissue level in cardiometabolic disease. Recently, quantitative MR methods have enabled non-invasive myocardial and liver tissue characterization. MR relaxation mapping techniques such as T₁, T_1ρ, T₂ and T₂* provide a pixel-by-pixel representation of the corresponding tissue specific relaxation times, which have been shown to correlate with fibrosis, altered tissue perfusion, oedema and iron levels. Proton density fat fraction mapping approaches allow measurement of lipid tissue in the organ of interest. Several studies have demonstrated their utility as early diagnostic biomarkers and their potential to bear prognostic implications. Conventionally, the quantification of these parameters by MRI relies on the acquisition of sequential scans, encoding and mapping only one parameter per scan. However, this methodology is time inefficient and suffers from the confounding effects of the relaxation parameters in each single map, limiting wider clinical and research applications. To address these limitations, several novel approaches have been proposed that encode multiple tissue parameters simultaneously, providing co-registered multiparametric information of the tissues of interest. This review aims to describe the multi-faceted myocardial and hepatic tissue alterations in cardiometabolic disease and to motivate the application of relaxometry and proton-density cardiac and liver tissue mapping techniques. Current approaches in myocardial and liver tissue characterization as well as latest technical developments in multiparametric quantitative MRI are included. Limitations and challenges of these novel approaches, and recommendations to facilitate clinical validation are also discussed.

Diastolic dysfunction is more apparent in STZ-induced diabetic female mice, despite less pronounced hyperglycemia

Diabetic cardiomyopathy is a distinct pathology characterized by early emergence of diastolic dysfunction. Increased cardiovascular risk associated with diabetes is more marked for women, but an understanding of the role of diastolic dysfunction in female susceptibility to diabetic cardiomyopathy is lacking. To investigate the sex-specific relationship between systemic diabetic status and in vivo occurrence of diastolic dysfunction, diabetes was induced in male and female mice by streptozotocin (5x daily i.p. 55 mg/kg). Echocardiography was performed at 7 weeks post-diabetes induction, cardiac collagen content assessed by picrosirius red staining, and gene expression measured using qPCR. The extent of diabetes-associated hyperglycemia was more marked in males than females (males: 25.8 ± 1.2 vs 9.1 ± 0.4 mM; females: 13.5 ± 1.5 vs 8.4 ± 0.4 mM, p < 0.05) yet in vivo diastolic dysfunction was evident in female (E/E' 54% increase, p < 0.05) but not male diabetic mice. Cardiac structural abnormalities (left ventricular wall thinning, collagen deposition) were similar in male and female diabetic mice. Female-specific gene expression changes in glucose metabolic and autophagy-related genes were evident. This study demonstrates that STZ-induced diabetic female mice exhibit a heightened susceptibility to diastolic dysfunction, despite exhibiting a lower extent of hyperglycemia than male mice. These findings highlight the importance of early echocardiographic screening of asymptomatic prediabetic at-risk patients.

Molecular mechanisms of cardiac pathology in diabetes - Experimental insights

Diabetic cardiomyopathy is a distinct pathology independent of co-morbidities such as coronary artery disease and hypertension. Diminished glucose uptake due to impaired insulin signaling and decreased expression of glucose transporters is associated with a shift towards increased reliance on fatty acid oxidation and reduced cardiac efficiency in diabetic hearts. The cardiac metabolic profile in diabetes is influenced by disturbances in circulating glucose, insulin and fatty acids, and alterations in cardiomyocyte signaling. In this review, we focus on recent preclinical advances in understanding the molecular mechanisms of diabetic cardiomyopathy. Genetic manipulation of cardiomyocyte insulin signaling intermediates has demonstrated that partial cardiac functional rescue can be achieved by upregulation of the insulin signaling pathway in diabetic hearts. Inconsistent findings have been reported relating to the role of cardiac AMPK and β-adrenergic signaling in diabetes, and systemic administration of agents targeting these pathways appear to elicit some cardiac benefit, but whether these effects are related to direct cardiac actions is uncertain. Overload of cardiomyocyte fuel storage is evident in the diabetic heart, with accumulation of glycogen and lipid droplets. Cardiac metabolic dysregulation in diabetes has been linked with oxidative stress and autophagy disturbance, which may lead to cell death induction, fibrotic 'backfill' and cardiac dysfunction. This review examines the weight of evidence relating to the molecular mechanisms of diabetic cardiomyopathy, with a particular focus on metabolic and signaling pathways. Areas of uncertainty in the field are highlighted and important knowledge gaps for further investigation are identified. This article is part of a Special issue entitled Cardiac adaptations to obesity, diabetes and insulin resistance, edited by Professors Jan F.C. Glatz, Jason R.B. Dyck and Christine Des Rosiers.

Carvedilol and antioxidant proteins in a type I diabetes animal model

BACKGROUND

Patients with diabetes are at a high risk of developing both micro- and macrovascular disease. Hyperglycaemia seems to be the main factor in the pathogenesis of diabetic cardiomyopathy, often based on increased oxidative stress. Carvedilol, a β-adrenergic blocker, has intrinsic antioxidant properties and was previously described to be effective in the protection of cardiac mitochondria against oxidative stress. The objective of this study was to evaluate the effect of carvedilol on hyperglycaemia-induced oxidative damage and mitochondrial abnormalities in cardiac and skeletal muscle in streptozotocin-treated rats.

MATERIALS AND METHODS

Body mass, blood glucose, the level of protein carbonylation, caspase-9- and caspase-3-like activities, mitochondrial proteins, the status of antioxidant defence system and stress-related proteins were evaluated in streptozotocin vs streptozotocin + carvedilol (1 mg/kg/day)-treated rats.

RESULTS

The results showed that carvedilol decreased blood glucose in streptozotocin-treated animals. Content of catalase in the heart and SOD2, SOD1 and catalase in skeletal muscle were increased by carvedilol treatment in streptozotocin-treated animals. At this particular time point, streptozotocin-induced hyperglycaemia did not cause caspase activation or increase in protein carbonylation status. The data showed that carvedilol increased the level of antioxidant enzymes, what may contribute to preserve cell redox balance during hyperglycaemia. We also showed here for the first time that carvedilol effects on streptozotocin-treated rats are tissue dependent, with a more predominant effect on skeletal muscle.

CONCLUSIONS

Based on data showing modulation of the antioxidant network in the heart, carvedilol may be beneficial in diabetic patients without advanced disease complications, delaying their progression.

Modulation of myocardial injury and collagen deposition following ischaemia-reperfusion by linagliptin and liraglutide, and both together

Studies have indicated that dipeptidyl peptidase-4 (DPP-4) inhibitors and glucagon-like peptide-1 (GLP-1) agonists reduce infarct size after myocardial ischaemia. Whether these agents modify cardiac remodelling after ischaemia is unclear. Furthermore, it is not known if combination of the two types of drugs is superior to either agent alone. We investigated the modulatory effect of the DPP-4 inhibitor linagliptin alone, the GLP-1 activator liraglutide alone, or the two agents together on myocardial infarct size, left ventricular contractile function and cardiac remodelling signals after a brief period of left coronary artery (LCA) occlusion. C57BL/6 mice were treated with vehicle, the DPP-4 inhibitor linagliptin, the GLP-1 activator liraglutide, or both agents together for 5 days, and then subjected to LCA occlusion (1 h) and reperfusion (3 h). Ischaemia-reperfusion increased reactive oxygen species (ROS) generation and expression of NADPH oxidase (p47(phox), p22(phox) and gp91(phox) subtypes), collagens, fibronectin and proinflammatory cytokines (interleukin 6, tumour necrosis factor α and monocyte chemoattractant protein-1) in the LCA-supplied regions. Pre-treatment with linagliptin or liraglutide reduced infarct size, protected cardiomyocytes from injury and preserved cardiac contractile function in a similar fashion. It is interesting that profibrotic (collagen deposition) signals were expressed soon after ischaemia-reperfusion. Both linagliptin and liraglutide suppressed ROS generation, NADPH oxidase and proinflammatory signals, and reduced collagen deposition. Addition of linagliptin or liraglutide had no significant additive effect above and beyond that of liraglutide and linagliptin given alone. In conclusion, linagliptin and liraglutide can improve cardiac contractile function and indices of cardiac remodelling, which may be related to their role in inhibition of ROS production and proinflammatory cytokines after ischaemia.

Downregulation in GATA4 and Downstream Structural and Contractile Genes in the db/db Mouse Heart

Reduced expression of GATA4, a transcriptional factor for structural and cardioprotective genes, has been proposed as a factor contributing to the development of cardiomyopathy. We investigated whether the reduction of cardiac GATA4 expression reported in diabetes alters the expression of downstream genes, namely, atrial natriuretic peptide (ANP), B-type natriuretic, peptide (BNP), and α- and β-myosin heavy chain (MHC). db/db mice, a model of type 2 diabetes, with lean littermates serving as controls, were studied. db/db mice exhibited obesity, hyperglycemia, and reduced protein expression of cardiac GLUT4 and IRAP (insulin-regulated aminopeptidase), the structural protein cosecreted with GLUT4. Hearts from db/db mice had reduced protein expression of GATA4 (~35%) with accompanying reductions in mRNA expression of ANP (~40%), BNP (~85%), and α-MHC mRNA (~50%) whereas expression of β-MHC mRNA was increased by ~60%. Low GATA4 was not explained by an increased ligase or atrogin1 expression. CHIP protein content was modestly downregulated (27%) in db/db mice whereas mRNA and protein expression of the CHIP cochaperone HSP70 was significantly decreased in db/db hearts. Our results indicate that low GATA4 in db/db mouse heart is accompanied by reduced expression of GATA4-regulated cardioprotective and structural genes, which may explain the development of cardiomyopathy in diabetes.

Therapeutic effects of neuregulin-1 in diabetic cardiomyopathy rats

Background

Diabetic cardiomyopathy (DCM) is a disorder of the heart muscle in people with diabetes, which is characterized by both systolic and diastolic dysfunction. The effective treatment strategy for DCM has not been developed.

Methods

Rats were divided into 3 groups with different treatment. The control group was only injected with citrate buffer (n = 8). The diabetes group and diabetes treated group were injected with streptozotocin to induce diabetes. After success of diabetes induction, the rats with diabetes were treated with (diabetes treated group, n = 8) or without (diabetes group, n = 8) recombinant human Neuregulin-1 (rhNRG-1). All studies were carried out 16 weeks after induction of diabetes. Cardiac catheterization was performed to evaluate the cardiac function. Apoptotic cells were determined by TUNEL staining. Left ventricular (LV) sections were stained with Masson to investigate myocardial collagen contents. Related gene expressions were analyzed by quantitative real-time PCR (qRT-PCR).

Results

Diabetes impaired cardiac function manifested by reduced LV systolic pressure (LVSP), maximum rate of LV pressure rise and fall (+dp/dt max and -dp/dt max) and increased LV end-diastolic pressure (LVEDP). The rhNRG-1 treatment could significantly alleviate these symptoms and improve heart function. More TUNEL staining positive cells were observed in the diabetic group than that in the control group, and the rhNRG-1 treatment decreased apoptotic cells number. Furthermore, qRT-PCR assay demonstrated that rhNRG-1 treatment could decrease the expression of bax and caspase-3 and increase that of bcl-2. Collagen volume fraction was higher in the diabetic group than in the control group. Fibrotic and fibrotic related mRNA (type I and type III collagen) levels in the myocardium were significantly reduced by administration of rhNRG-1.

Conclusion

rhNRG-1 could significantly improve the heart function and reverse the cardiac remodeling of DCM rats with chronic heart failure. These results support the clinical possibility of applying rhNRG-1 as an optional therapeutic strategy for DCM treatment in the future.

Diabetic cardiomyopathy: from the pathophysiology of the cardiac myocytes to current diagnosis and management strategies

Diabetic cardiomyopathy (DCM), although a distinct clinical entity, is also a part of the diabetic atherosclerosis process. It may be independent of the coexistence of ischemic heart disease, hypertension, or other macrovascular complications. Its pathological substrate is characterized by the presence of myocardial damage, reactive hypertrophy, and intermediary fibrosis, structural and functional changes of the small coronary vessels, disturbance of the management of the metabolic cardiovascular load, and cardiac autonomic neuropathy. These alterations make the diabetic heart susceptible to ischemia and less able to recover from an ischemic attack. Arterial hypertension frequently coexists with and exacerbates cardiac functioning, leading to the premature appearance of heart failure. Classical and newer echocardiographic methods are available for early diagnosis. Currently, there is no specific treatment for DCM; targeting its pathophysiological substrate by effective risk management protects the myocardium from further damage and has a recognized primary role in its prevention. Its pathophysiological substrate is also the objective for the new therapies and alternative remedies.

Factors contributing to left ventricular diastolic dysfunction in long-term type I diabetic subjects

Although non-invasive studies in type I diabetic subjects indicate left ventricular (LV) diastolic dysfunction, the contribution of borderline or mild hypertension to such changes is obscure. Thus, digitized M-mode echocardiograms were obtained in 32 (18 men) young (less than 50 years) normotensive controls and 32 (21 men) long-term (greater than or equal to 12 years) type I diabetics with blood pressures ranging from normal to hypertensive. All diabetics were without clinical heart disease, none were previously treated for hypertension or using cardioactive drugs. Heart rate, systolic and diastolic blood pressures were higher in diabetic than control subjects. Their LV end-diastolic dimension was smaller, whereas wall thickness, LV mass index and fractional shortening were similar to controls. In diabetics, however, the normalized peak filling rate was decreased and the rapid filling period fraction of diastole increased. In multivariate analysis, diabetes and LV mass independently and inversely influenced the normalized peak filling rate, while fractional shortening did so positively. Furthermore, diabetes and systolic blood pressure independently influenced the rapid filling period fraction of diastole. This study is the first to demonstrate systolic blood pressure and LV mass as independent contributors to subclinical LV diastolic abnormalities in diabetics. These findings may therefore indicate the need to treat even mild hypertension in diabetics in an effort to delay the development of cardiopathy.

Isolated and preclinical impairment of left ventricular filling in insulin-dependent and non-insulin-dependent diabetic patients

BACKGROUND

Diabetes mellitus can induce a pattern of myocardial pathology known as specific diabetic cardiomyopathy, even if this is not clearly specified.

HYPOTHESIS

The aim of our study was to evaluate the presence of preclinical myocardial damage in insulin- and non-insulin-dependent diabetic patients and controls by assessment with Doppler echocardiography.

METHODS

Twenty insulin-dependent diabetic (IDDM) patients, 10 non-insulin-dependent diabetic (NIDDM) patients, and 12 healthy individuals (C) as controls, matched for age, gender, and without overt cardiovascular disease, were assessed in this study.

RESULTS

Systolic function parameters presented normal values in the three groups, with the exception of a slight reduction in ventricular volume indices in the NIDDM group. Diastolic function was clearly impaired in both groups of patients versus that in healthy controls. In particular, ventricular filling was impaired in the NIDDM compared with the IDDM patients, especially the peak early filling rate E (p < 0.001). Moreover, in the IDDM group, the duration of diabetes (p < 0.01) and glycosilated hemoglobin value (HbA1C, p < 0.02) were higher than in the NIDDM group. Multiple regression analysis showed a significant inverse correlation between HbA1C and peak late filling rate A (R2 = 0.28) in both groups of patients and a direct correlation between velocity time integral E and age, duration of diabetes, and HbA1C (R2 = 0.46). The two groups presented a small, homogeneous number of cases with initial microangiopathy and borderline autonomic neuropathy, associated with microalbuminuria. Doppler echocardiography showed an early impairment of left ventricular filling, as well as an early preclinical alteration of myocardial function in diabetic patients, especially in the NIDDM group.

CONCLUSION

These early signs of cardiomyopathy could constitute a predisposing condition toward the high cardiac morbidity and mortality rate in diabetic patients.

ATP production and TCA activity are stimulated by propionyl-L-carnitine in the diabetic rat heart

BACKGROUND AND OBJECTIVE

The beneficial effect of propionyl-L-carnitine (PLC) on cardiac function in diabetes mellitus is well documented. This study was designed to determine whether the improvement in cardiac function mediated by PLC in the diabetic rat heart is associated with an increase in ATP production and tricarboxylic acid (TCA) cycle activity.

METHODS

Diabetes was induced by an intravenous injection of streptozotocin (60 mg/kg). Following diagnosis of diabetes, treatment was initiated by supplementing the drinking water with PLC at a concentration of 1 g/L for a period of 6 weeks. ATP production and TCA cycle activity were determined from oxidative rates of glucose and palmitate measured in isolated working hearts from control and diabetic animals.

RESULTS

The effect of diabetes was associated with a decrease in heart function, expressed as rate-pressure product (RPP), and in rates of myocardial glucose oxidation. Rates of palmitate oxidation in diabetic hearts were similar to those of control hearts. In PLC-treated diabetic hearts, rates of both glucose and palmitate oxidation were increased and a significant improvement in RPP was observed. As a result, overall ATP production and TCA cycle activity from glucose and palmitate oxidation were increased in diabetic hearts.

CONCLUSION

Our results indicate that the depression in RPP in the diabetic rat heart can be prevented with chronic PLC treatment. Increases in glucose and palmitate utilization with resultant increases in ATP production and TCA cycle activity may explain the benefit of PLC on diabetic rat heart function.

Insulin resistance increases PAI-1 in the heart

To determine whether insulin resistance increases expression of plasminogen activator inhibitor type-1 (PAI-1) in the heart, studies were performed in 22 mice with and 38 without myocardial infarction. Insulin resistance in transgenic animals genetically rendered insulin resistant was confirmed with the use of intraperitoneal glucose tolerance tests. Myocardial infarction was induced by coronary ligation, verified echocardiographically, and quantified by assay of depletion of creatine kinase (CK) from the left ventricle 2 weeks later. PAI-1 increased markedly in zones of infarction to 10.4+/-2.1 (SF) and significantly more to 27.3+/-3.6 in normal and insulin resistant mice compared with 0.45+/-0.04 and 0.50+/-0.03 in normal myocardium. Thus, insulin resistance induced accumulation of PAI-1 in the heart, particularly in zones of infarction. Such increases may contribute to fibrosis and diastolic dysfunction typical late after infarction in patients with insulin resistance.

Abnormal myocardial perfusion and contractile recruitment during exercise in type 1 diabetic patients

BACKGROUND

No data are available on the relationship between myocardial perfusion and left ventricular (LV) function in type 1 diabetes mellitus (T1DM), which may constitute a factor explaining the progressive contractile dysfunction to the overt phase of diabetic cardiomyopathy.

HYPOTHESIS

This study was undertaken to test whether myocardial perfusion abnormalities are present at rest and during exercise and whether they are related to contractile dysfunction in T1DM.

METHODS

Twenty-two patients with T1DM, aged 32 +/- 8.3 years, without macro- or microvascular complications, and 10 controls, aged 31 +/- 3 years, were studied. Left ventricular function and myocardial perfusion were assessed by two-dimensional and myocardial contrast echocardiography at rest and during handgrip (HG).

RESULTS

Fourteen patients with T1DM showed a decline in LV ejection fraction (LVEF) during HG (Group 1) while 8 had a normal response (Group 2). Both basal myocardial blood volume (MBV) and velocity (beta) were normal in T1DM. During exercise, MBV and beta increased and were associated with an increase in myocardial blood flow (MBF) in controls. In T1DM, beta did not change and MBV increased only in Group 2, while this increase was not observed in Group 1 (controls: 14.9 +/- 2.3 vs. Group 1: 7.6 +/- 1.6, p < 0.001; and vs. Group 2: 10.2 +/- 2.8, p < 0.001), beta (0.86 +/- 0.12 vs. 0.68 +/- 0.14, p < 0.001; and vs. 0.67 +/- 0.15, p < 0.001). A correlation between the ratio exercise MBF/resting MBF and LVEF at peak exercise in T1DM was observed (r = 0.805, p < 0.001).

CONCLUSIONS

A large proportion of patients with T1DM exhibit abnormalities in myocardial adaptable capacity to match an acute overload, which are related to a defective increase in myocardial perfusion.

Female children and adolescents with type 1 diabetes have more pronounced early echocardiographic signs of diabetic cardiomyopathy

OBJECTIVE

This study was designed to assess whether children and adolescents with type 1 diabetes have early echocardiographic signs of subclinical cardiac dysfunction and whether sex, state of metabolic control, and diabetes duration are of influence.

RESEARCH DESIGN AND METHODS

Systolic and diastolic blood pressure in supine and upright positions and echocardiographic parameters, including tissue Doppler measurements of the septal mitral annulus, were evaluated in 80 children and adolescents with stable type 1 diabetes and 52 age- and sex-matched control subjects. A possible correlation was examined for age, sex, HbA(1c), and diabetes duration with univariate and multivariate regression analysis.

RESULTS

Female diabetic patients showed significantly larger left ventricular wall dimensions (left ventricular posterior wall in diastole 0.54 +/- 0.08 vs. 0.48 +/- 0.11 cm) and signs of significant diastolic filling abnormalities on conventional and tissue Doppler echocardiography (mitral valve-atrial contraction velocity 0.47 +/- 0.12 vs. 0.40 +/- 0.09 m/s; tricuspid valve-atrial contraction velocity 0.35 +/- 0.09 vs. 0.30 +/- 0.07 m/s; early filling velocity/myocardial velocity during early filling 7.15 +/- 1.47 vs. 6.17 +/- 1.07; isovolumetric relaxation time [IVRT] 66 +/- 8 vs. 58 +/- 8 ms) compared with female control subjects, suggesting delayed myocardial relaxation. Male diabetic patients only differed significantly from their control subjects for IVRT (66 +/- 9 vs. 59 +/- 8 ms). The measured parameters showed an expected correlation with age and BMI standard deviation scores in the control group. This correlation was significantly weaker in the diabetic population; only a weak influence was found for diabetes duration and glycosylated hemoglobin levels.

CONCLUSIONS

Young diabetic patients already have significant changes in left ventricular dimensions and myocardial relaxation, with the girls clearly being more affected. Tissue Doppler proved to have additional value in the evaluation of ventricular filling in this population. Almost no correlation was found for diabetes duration and HbA(1c) with the cardiovascular changes.

Cardiovascular risk factors in ethnic minority women aged < or =30 years

Men and women of African and South Asian ancestry in the United States are increasingly recognized as being at greater risk for coronary heart disease (CHD) than Caucasians of European ancestry. Relatively little data on the genetic and lifestyle risk factors that predispose women to CHD in these ethnic minorities are available. We compared coronary risk factors in a volunteer sample of African-American, Asian Indian American, and Caucasian American women of college age. Life style, dietary, hemodynamic and anthropometric parameters, and laboratory data were sought from 70 subjects in each ethnic group. African-American women were found to have lower triglyceride levels and higher apolipoproten A-1, high-density lipoprotein (HDL), lipoprotein (a) (Lp(a)), fibrinogen, and fasting insulin levels. They also consumed more fat and cholesterol than their peers, had a higher percentage of body fat, body weight, and body mass indexes, and reported less physical activity than Caucasians. Asian Indian American women had higher Lp(a), HDL, and fibrinogen levels than Caucasian American women, and also reported less physical activity. Thus, young African- American and Asian Indian American women have several modifiable risk factors as well as some nontraditional lipid risk factors that warrant consideration for explaining the increased prevalence of CHD in these ethnic groups. The tendency toward peripheral insulin insensitivity and increased body fat in this age group of African-American women suggests diet and exercise may reduce the risk of subsequent CHD.

Magnetic resonance imaging analysis of cardiac cycle events in diabetic rats: the effect of angiotensin-converting enzyme inhibition

Non-invasive magnetic resonance imaging (MRI) was used to characterize changes in left and right ventricular cardiac cycles following induction of experimental, streptozotocin (STZ)-induced, diabetes in male Wistar rats at different ages. The effects of the angiotensin-converting enzyme (ACE) inhibitor captopril upon such chronic physiological changes were then evaluated, also for the first time. Diabetes was induced at the age of 7 weeks in two experimental groups, of which one group was subsequently maintained on captopril (2 g l(-1))-containing drinking water, and at 10 and 13 weeks in two further groups. The fifth group provided age-matched controls. All groups (each n = 4 animals) were scanned consistently at 16 weeks, in parallel with timings used in earlier studies that employed this experimental model. Cine magnetic resonance (MR) image acquisition provided transverse sections through both ventricles at twelve time points covering systole and most of diastole. These yielded reconstructions of cardiac anatomy used to derive critical functional indices and their dependence upon time following the triggering electrocardiographic R waves. The left and right ventricular end-diastolic (EDV), end-systolic (ESV) and stroke volumes (SV), and ejection fractions (EF) calculated from each, control and experimental, group showed matching values. This confirmed a necessary condition requiring balanced right and left ventricular outputs and further suggested that STZ-induced diabetes produced physiological changes in both ventricles. Absolute left and right ventricular SVs were significantly altered in all diabetic animals; EDVs and EFs significantly altered in animals diabetic from 7 and 10 but not 13 weeks. When normalized to body weight, left and right ventricular SVs had significantly altered in animals diabetic from 7 and 10 weeks but not 13 weeks. Normalized left ventricular EDVs were also significantly altered in animals diabetic from 7 and 10 weeks. However, normalized right ventricular EDVs were significantly altered only in animals made diabetic from 7 weeks. Diabetic hearts showed major kinetic changes in left and right ventricular contraction (ejection) and relaxation (filling). Both the initial rates of volume change (dV/dt) in both ventricles and the plots of dV/dt values through the cardiac cycle demonstrated more gradual developments of tension during systole and relaxation during diastole. Estimates of the derived left ventricular performance parameters of cardiac output, cardiac power output and stroke work in control animals were comparable with human values when normalized to both body (or cardiac) weight and heart rate. All deteriorated with diabetes. Comparisons of experimental groups diabetic from 7 weeks demonstrated that captopril treatment relieved the alterations in critical volumes, dependence of SV upon EDV, kinetics of systolic contraction and diastolic relaxation and in the derived indicators of ventricular performance. This study represents the first demonstration using non-invasive MRI of early, chronic changes in diastolic filling and systolic ejection in both the left and the right ventricles and of their amelioration by ACE inhibition following STZ-induction of diabetes in intact experimental animals.

Effects of acute hyperglycaemia on cardiac function: an echocardiographic study of monozygotic twins

BACKGROUND

A major cause of morbidity in type I diabetes is congestive heart failure due predominantly to left ventricular diastolic dysfunction. The mechanism of diastolic dysfunction remains unknown and does not relate to blood pressure, microvascular complications and glycated haemoglobin. Hyperglycaemia is the hallmark of diabetes and is a potential determinant of left ventricular diastolic dysfunction.

OBJECTIVE

To determine whether acute hyperglycaemia can induce changes in left ventricular diastolic function in normal subjects similar to those observed in insulin-dependent diabetes mellitus (IDDM).

DESIGN

Cross-sectional study.

SETTING

London teaching hospital.

SUBJECTS

Sixteen twins from eight identical twin pairs discordant for IDDM (age 18-38 years, five male) were studied; none had a history or evidence of myocardial ischaemia, valvular or primary heart muscle disease, systemic hypertension or nephropathy.

INTERVENTIONS

Non-diabetic twins underwent a hyperglycaemic clamp at 10 mmol/l.

MAIN OUTCOME MEASURES

Doppler echocardiography was performed in basal condition in identical twin pairs discordant for IDDM and repeated in the non-diabetic twins during hyperglycaemia. Blood glucose, insulin and catecholamines were measured at baseline and during hyperglycaemia.

RESULTS

Transmitral Doppler E/A velocity ratio was significantly lower in diabetic than non-diabetic twins at baseline (1.44 (0.38) vs. 1.51 (0.19), P<0.05). Glucose infusion in the non-diabetic twins resulted in an increase in their E/A ratio (1.51 (0.19) vs. 1.82 (0. 47), P<0.05) due to an increase in E velocity (68 (12) to 64.7 (10. 7), P<0.05) and a decrease in the peak A velocity (42.7 (3.85) to 38. 0 (4.1), P<0.05). No significant changes were observed in peak E velocity or isovolumic relaxation time in the non-diabetic twins between baseline and hyperglycaemia.

CONCLUSIONS

The alterations in left ventricular diastolic function induced by acute hyperglycaemia and consequent increase in plasma catecholamines do not mimic those demonstrated in IDDM patients.

Epidemiology of Diabetes Interventions and Complications (EDIC). Design, implementation, and preliminary results of a long-term follow-up of the Diabetes Control and Complications Trial cohort

OBJECTIVE

The Diabetes Control and Complications Trial (DCCT) demonstrated the powerful impact of glycemic control on the early manifestations of microvascular complications. Contemporary prospective data on the evolution of macrovascular and late microvascular complications of type 1 diabetes are limited. The Epidemiology of Diabetes Interventions and Complications (EDIC) study is a multicenter, longitudinal, observational study designed to use the well-characterized DCCT cohort of > 1,400 patients to determine the long-term effects of prior separation of glycemic levels on micro- and macrovascular outcomes.

RESEARCH DESIGN AND METHODS

Using a standardized annual history and physical examination, 28 EDIC clinical centers that were DCCT clinics will follow the EDIC cohort for 10 years. Annual evaluation also includes resting electrocardiogram. Doppler ultrasound measurements of ankle/arm blood pressure, and screening for nephropathy. At regular intervals, a timed 4-h urine is collected, lipid profiles are obtained, and stereoscopic fundus photographs are taken. In addition, dual B-mode Doppler ultrasound scans of the common and internal carotid arteries will be performed at years 1 and 6 and at study end.

RESULTS

Written informed consent was obtained from 96% of the DCCT subjects. The participants, compared with nonparticipants, tended to have better glycemic control at the completion of the DCCT and were more likely to have their diabetes care provided by DCCT personnel. The EDIC baseline measurement stratified by sex delineates multiple cardiovascular disease risk factor differences such as age (older in men), waist-to-hip ratio (higher in men). HDL cholesterol (lower in men), hypertension (more prevalent in men), and maximum intimal-medial thickness of common and internal carotid arteries (thicker in men). Of the original conventional treatment group, 69% have changed to continuous subcutaneous insulin infusion or multiple daily injections. Although the mean HbA1c difference between the intensive and conventional treatment groups narrowed at EDIC years 1 and 2, HbA1c remained significantly lower in the intensive group. Of all expected clinic visits, 95% were completed, and the quality of EDIC data is very similar to that observed in the DCCT.

CONCLUSIONS

Although obvious problems exist in extended follow-up studies of completed clinical trials, these are balanced by the value of continued systematic observation of the DCCT cohort. In contrast to other epidemiologic studies, EDIC will provide 1) definitive data on type 1 as distinct from type 2 diabetes; 2) reliance on prospective rather than on cross-sectional analysis; 3) long-term follow-up in a large population; 4) consistent use of objective, reliable measures of outcomes and glycemia; and 5) observation of patients from before the onset of complications.

Scintigraphic assessment of regionalized defects in myocardial sympathetic innervation and blood flow regulation in diabetic patients with autonomic neuropathy

OBJECTIVES

This study sought to evaluate whether regional sympathetic myocardial denervation in diabetes is associated with abnormal myocardial blood flow under rest and adenosine-stimulated conditions.

BACKGROUND

Diabetic autonomic neuropathy (DAN) has been invoked as a cause of unexplained sudden cardiac death, potentially by altering electrical stability or impairing myocardial blood flow, or both. The effects of denervation on cardiac blood flow in diabetes are unknown.

METHODS

We studied 14 diabetic subjects (7 without DAN, 7 with advanced DAN) and 13 nondiabetic control subjects without known coronary artery disease. Positron emission tomography using carbon-11 hydroxyephedrine was used to characterize left ventricular cardiac sympathetic innervation and nitrogen-13 ammonia to measure myocardial blood flow at rest and after intravenous administration of adenosine (140 microg/kg body weight per min).

RESULTS

Persistent sympathetic left ventricular proximal wall innervation was observed, even in advanced neuropathy. Rest myocardial blood flow was higher in the neuropathic subjects (109 +/- 29 ml/100 g per min) than in either the nondiabetic (69 +/- 8 ml/100 g per min, p < 0.01) or the nonneuropathic diabetic subjects (79 +/- 23 ml/100 g per min, p < 0.05). During adenosine infusion, global left ventricular myocardial blood flow was significantly less in the neuropathic subjects (204 +/- 73 ml/100 g per min) than in the nonneuropathic diabetic group (324 +/- 135 ml/100 g per min, p < 0.05). Coronary flow reserve was also decreased in the neuropathic subjects, who achieved only 46% (p < 0.01) and 44% (p < 0.01) of the values measured in nondiabetic and nonneuropathic diabetic subjects, respectively. Assessment of the myocardial innervation/blood flow relation during adenosine infusion showed that myocardial blood flow in neuropathic subjects was virtually identical to that in nonneuropathic diabetic subjects in the distal denervated myocardium but was 43% (p < 0.05) lower than that in the nonneuropathic diabetic subjects in the proximal innervated segments.

CONCLUSIONS

DAN is associated with altered myocardial blood flow, with regions of persistent sympathetic innervation exhibiting the greatest deficits of vasodilator reserve. Future studies are required to evaluate the etiology of these abnormalities and to evaluate the contribution of the persistent islands of innervation to sudden cardiac death complicating diabetes.

Myocardial dysfunction and adrenergic cardiac innervation in patients with insulin-dependent diabetes mellitus

BACKGROUND

Insulin-dependent diabetes mellitus (IDDM) is associated with an increased incidence of heart failure due to several factors, and in some cases a specific cardiomyopathy has been suggested.

OBJECTIVES

This study sought to assess the mechanisms of exercise-induced left ventricular (LV) dysfunction in asymptomatic patients with IDDM in the absence of hypertensive or coronary artery disease.

METHODS

Fourteen consecutive patients with IDDM were enrolled (10 men, 4 women; mean [+/- SD] age 28.5 +/- 6 years); 10 healthy subjects matched for gender (7 men, 3 women) and age (28.5 +/- 3 years) constituted the control group. LV volume, LV ejection fraction (LVEF) and end-systolic wall stress were calculated by two-dimensional echocardiography at rest and during isometric exercise. LV contractile reserve was assessed by post-extrasystolic potentiation (PESP) obtained by transesophageal cardiac electrical stimulation and dobutamine infusion. Myocardial iodine-123 metaiodobenzylguanidine (MIBG) scintigraphy was performed to assess adrenergic cardiac innervation.

RESULTS

Diabetic patients were classified into group A (n = 7), with an abnormal LVEF response to handgrip (42 +/- 7%), and group B (n = 7), with a normal response (72 +/- 8%). Baseline LVEF was normal in both group A and B patients (60 +/- 6% vs. 61 +/- 7%, p = NS). In group A patients, the LV circumferential wall stress-LVEF relation showed an impairment in LVEF disproportionate to the level of LV afterload. No significant changes in LVEF occurred during dobutamine (60 +/- 6% vs. 64 +/- 10%, p = NS), whereas PESP significantly increased LVEF (60 +/- 6% vs. 74 +/- 6%, p < 0.001); PESP at peak handgrip normalized the abnormal LVEF (42 +/- 7% vs. 72 +/- 5%, p < 0.001); and MIBG uptake normalized for body weight or for LV mass was lower than that in normal subjects (1.69 +/- 0.30 vs. 2.98 +/- 0.82 cpm/MBq per g, p = 0.01) and group B diabetic patients (vs. 2.79 +/- 0.94 cpm/MBq per g, p = 0.01). Finally, a strong linear correlation between LVEF at peak handgrip and myocardial MIBG uptake normalized for LV mass was demonstrated in the study patients.

CONCLUSIONS

Despite normal contractile reserve, a defective blunted recruitment of myocardial contractility plays an important role in determining exercise LV dysfunction in the early phase of diabetic cardiomyopathy. This abnormal response to exercise is strongly related to an impairment of cardiac sympathetic innervation.

[Anatomopathological bases of latent ventricular dysfunction in insulin-dependent diabetics]

INTRODUCTION AND OBJECTIVES

The natural history of diabetic cardiomyopathy remains unclear, mainly due to concurrent coronary disease or hypertension. Since the presence of confounding factors is less likely in youngsters, they constitute a suitable study model to analyze early stages of diabetic cardiomyopathy.

PATIENTS AND METHODS

We screened 33 young normotensive asymptomatic patients with type I diabetes mellitus. Mean age was 28 +/- 8 y (range 18 to 46 y) and there were 14 men.

RESULTS

2-D Echo showed normal left ventricular size and wall motion in all patients but one. Radionuclide basal ejection fraction was 56.5 +/- 6.6% and increased to 63 +/- 7.4% (p < 0.02) on exercise. According to Rozansky criteria, 16 patients had an abnormal response. Abnormal stress sestamibi was detected in 18 patients and only 3 had reversible defects. Coronary angiography was performed in 11 patients with at least one abnormal non-invasive study response. Coronary angiography revealed normal vessels in all patients and left anterior descending blood flow velocity (Doppler) increased 4 fold after papaverine infusion. Left ventricular biopsies showed hypertrophy (either nuclear or cellular) in 11, myocytolysis in 6, interstitial fibrosis in 9 and lipid deposits in 4. Morphometric analysis of cardiac samples comparing the diabetic group and a control group showed that the volume fraction of fibrosis (0.19 +/- 0.06 vs 0.10 +/- 0.06; p < 0.01), fiber area -mu2- (1,062 +/- 547 vs 600 +/- 167; p < 0.02) and fiber diameter -mu- (24.2 +/- 3.3 vs 15.1 +/- 3.4; p < 0.001) were higher in the former; and volume fraction of the myocytes was higher in the latter (0.71 +/- 0.006 vs 0.89 +/- 0.07; p < 0.001).

CONCLUSIONS

Left ventricular dysfunction, not related to coronary atherosclerosis or small vessel disease, is frequent in asymptomatic young diabetic patients. Abnormal pathologic findings are common in the type of cell hypertrophy, interstitial fibrosis, myocytolysis and lipid deposits.

Myocardial alterations in diabetes and hypertension

Diabetes mellitus is a complex group of diseases that has hyperglycemia as a common metabolic abnormality. Although it is well-known that diabetic patients are susceptible to the effects of large vessel atherosclerosis with specific cardiac and cerebral complications, the association of diabetes mellitus with cardiac dysfunction caused by cardiomyopathy in the absence of significant coronary artery disease has been recognized for many years. However, the pathogenesis of diabetic cardiomyopathy remains unknown and has been somewhat controversial. Specifically, whether diabetes mellitus with its metabolic effects is sufficient to account for cardiomyopathy remains to be proven. This paper reviews the evidence for and against a metabolic etiology. In addition, we review the clinical and experimental evidence that supports the view that diabetes mellitus acts together with hypertension to produce structural damage in the heart that manifests as ventricular dysfunction and ultimately congestive heart failure. The concomitant effects of the metabolic derangements of diabetes and the vascular abnormalities associated with hypertension may lead to microvascular-induced tissue injury. Findings supporting this hypothesis are presented, along with observations suggesting that treatment with vasodilating calcium channel blockers or angiotensin converting enzyme inhibitors may be beneficial in regard to tissue pathology and mortality in experimental models. Recent clinical studies also support a role for the microcirculation in diabetics. Finally, it is suggested that if the microcirculation is pathogenetically involved in diabetic cardiomyopathy, then agents that improve microcirculatory flow along with tight control of hypertension may be as beneficial in the treatment or prevention of diabetic cardiomyopathy as strict metabolic control of hyperglycemia.

Effects of type 1 diabetes mellitus on cardiac function: a study of monozygotic twins

OBJECTIVE

To investigate left ventricular size and function in type 1 diabetes and their relation with diabetes duration, glycaemic control, autonomic dysfunction, and complications of diabetes.

DESIGN

Cross sectional study using a pulsed wave Doppler echocardiogram to assess left ventricular dimensions, wall thickness, and transmitral blood flow velocity signals.

PATIENTS

40 monozygotic twin pairs (23 male, mean age 26 years) discordant for type 1 diabetes and 40 non-diabetic singleton controls with no clinical evidence of cardiac ischaemia.

RESULTS

For all Doppler echocardiographic measurements there were strong correlations between monozygotic twins but not between twins and control subjects. Left ventricular dimensions, wall thickness and systolic function, peak E velocity, and the velocity integrals of early left ventricular filling were similar in all three groups. Peak A velocity and the velocity integrals of late ventricular filling (mean (SD)) were greater in diabetic twins (45 (12) v 38 (8) cm/s, P = 0.002; and 32 (11) v 26 (6), P = 0.0002). Diabetic twins had lower E/A ratio (1.59 (0.39) v 1.83 (0.39), P < 0.001), greater atrial filling fraction to total diastolic filling (28 (6) v 25 (5)%, P = 0.002), and prolonged isovolumic relaxation time (72 (12) v 63 (9) ms, P < 0.001). The differences in Doppler findings between diabetic and non-diabetic twins were related to disease duration whereas the prolongation of the isovolumic relaxation time was related to cardiac autonomic dysfunction.

CONCLUSIONS

These results show that twins with type 1 diabetes have left ventricular diastolic dysfunction related to diabetes duration and cardiac autonomic dysfunction but not to glycaemic control or microvascular complications. In addition, genetic factors contribute to left ventricular dimension and function.

Myocardial dysfunction and abnormal left ventricular exercise response in autonomic diabetic patients

In diabetic patients, the pathophysiologic mechanisms of exercise-induced left ventricular (LV) dysfunction remain controversial. In this study, the role of myocardial contractility recruitment in determining an abnormal LV response to isometric or dynamic exercise has been investigated in 14 diabetic patients with autonomic dysfunction. Ischemic heart disease was excluded by the absence of LV wall motion abnormalities induced by isotonic and isometric exercise and by coronary angiography. Left ventricular and myocardial function were studied at rest, and during isometric and isotonic exercise, by two-dimensional echocardiography; moreover, recruitment of an inotropic reserve was assessed by postextrasystolic potentiation at rest and at peak handgrip. An abnormal response of LV ejection fraction to isometric (9/14) or to dynamic (8/14) exercise was frequent in study patients. In these patients, baseline myocardial contractility was normal, and the significant increase in ejection fraction by postextrasystolic potentiation indicated a normal contractile reserve (65 +/- 7% vs. 74 +/- 6%, p = 0.001). Nevertheless, the downward displacement of LV ejection fraction-systolic wall stress relationships during exercise suggests an inadequate increase in myocardial contractility. However, the abnormal ejection fraction at peak handgrip was completely reversed by postextrasystolic potentiation (67 +/- 6% vs. 58.1 +/- 10%, p = 0.008), a potent inotropic stimulation independent of the integrity of adrenergic cardiac receptors. A defective inotropic recruitment, despite the presence of a normal LV contractile reserve, plays an important role in deexercise LV dysfunction in diabetic patients with autonomic neuropathy.

Left ventricular systolic function in middle-aged patients with diabetes mellitus

In cross-sectional studies of asymptomatic diabetic patients, multiple abnormalities in left ventricular (LV) function have been found. Long-term significance of these abnormalities is unknown because follow-up studies have not been previously performed. LV ejection fraction (EF) by radionuclide angiocardiography was examined in middle-aged control subjects (n = 44), in patients with insulin-dependent (IDDM) (n = 32) and non-insulin-dependent (NIDDM) (n = 32) diabetes mellitus at baseline and after 4-year follow-up. At baseline, all study subjects were free from cardiovascular disease. LVEF at rest did not differ between the groups at baseline. The decrease in LVEF at rest during follow-up was 1.1 +/- 1.1% (mean +/- SEM) in control subjects, 3.1 +/- 1.3% (p = NS, compared with control subjects) in patients with IDDM, and 7.2 +/- 1.4% (p < 0.01) in patients with NIDDM. At follow-up examination, abnormally low LVEF at rest (< 50%) was found in 7% of control subjects, 13% of patients with IDDM (p = NS), and in 31% of patients with NIDDM (p < 0.05). Compared with control subjects, the prevalence of an abnormal LVEF response to exercise (an increase by < 5%, or a decrease) was higher in diabetic groups at both examinations. This prevalence increased in control subjects from 10% at baseline to 26% at follow-up examination.(ABSTRACT TRUNCATED AT 250 WORDS)

Diabetic cardiomyopathy

Diabetic cardiomyopathy as a distinct entity was first recognized by Rubler et al. in diabetics with congestive heart failure (CHF), who had no evidence of coronary atherosclerosis. The Framingham study showed a 2.4-fold increased incidence of CHF in diabetic men and a 5.1-fold increase in diabetic women over 18 years. Pathological studies show left ventricular hypertrophy and fibrosis with varying degrees of small vessel disease, the functional significance of which is uncertain. Hypertension was recognized as an important cofactor in the development of fatal congestive heart failure in diabetics. On cardiac catheterization, in patients symptomatic of heart failure, either congestive or restrictive patterns have been observed. In contrast, asymptomatic diabetics had decreased left ventricular compliance but normal systolic function on hemodynamic study. Noninvasive studies show alterations in systolic and especially diastolic function, particularly in diabetics with microvascular complications and/or coexistent hypertension. Using load-independent measures of contractility, however, systolic function was generally found to be normal in asymptomatic normotensive diabetics. Experimental studies have focused on the mildly diabetic dog and the severely diabetic rat. Decreased left ventricular compliance and increased interstitial connective tissue were observed in chronically diabetic dogs. In contrast, ventricular myocardium from diabetic rats exhibits a reversible decrease in the speed of contraction, prolongation of contraction, and a delay in relaxation. These mechanical changes are associated with a decreased myosin ATPase, a shift in myosin isoenzyme distribution, alterations in a variety of Ca2+ fluxes, and changes in responses to alpha- and beta-adrenergic and cholinergic stimulation. These biochemical changes may be secondary to alterations in carbohydrate, lipid, and adenine nucleotide metabolism in the diabetic heart.(ABSTRACT TRUNCATED AT 250 WORDS)

Information on type 1 diabetes mellitus and QT interval from identical twins

To determine whether QT interval is influenced by genetic factors and whether QT-interval prolongation occurs in type 1 diabetes or is related to diabetic autonomic neuropathy, QT intervals were measured, and autonomic function was assessed in 44 pairs of identical twins who were discordant for type 1 diabetes. Twins were compared with 44 normal control subjects of similar age and sex. QT intervals were corrected for heart rate (QTc). QTc in diabetic twins correlated with that in their nondiabetic co-twins (r = 0.41; p = 0.006). Diabetic twins had significantly longer QTc than did their nondiabetic co-twins and control subjects (416 +/- 18 vs 407 +/- 16 and 403 +/- 19 ms, respectively; p < 0.005). A greater number of abnormal autonomic function tests were detected in diabetic twins than in their nondiabetic co-twins and control subjects (8 vs 2 and 0%, respectively; p < 0.01). Diabetic twins with disease duration > 14 years (n = 22) had longer QTc than did their nondiabetic co-twins (420 +/- 17 vs 402 +/- 14 ms; p < 0.0005). Twins with diabetes for > 14 years had a greater frequency of abnormal autonomic function tests than did those with diabetes < 14 years (15 vs 2%; p < 0.001). QTc did not correlate with autonomic function in diabetic twins. It is concluded that QT interval is influenced by genetic factors, and in type 1 diabetes, QTc can be prolonged independently of autonomic neuropathy.

Insulin resistance in microvascular angina (syndrome X)

Patients with microvascular angina (syndrome X) may be insulin resistant. We designed a study to establish whether this is the case. 11 patients with microvascular angina were compared with 9 matched subjects with noncardiac chest pain. Patients and controls were evaluated by coronary sinus catheterisation, and by isotopic measurement of glucose turnover, indirect calorimetry, and forearm technique during a 3 h baseline period after overnight fast and during a 2 h hyperinsulinaemic euglycaemic clamp. Pace-induced increase in coronary sinus blood flow was less in patients than in controls, whereas forearm blood flow did not differ between groups. Baseline measures of glucose metabolism were normal. During the clamp, glucose production and lipolysis were equally suppressed in both groups. Mean (SE) total insulin-induced glucose uptake was significantly impaired in patients compared with controls (3.9 [0.7] vs 6.4 [0.7] mg/kg per min; p < 0.01), and insulin-stimulated glucose uptake in the forearm was significantly reduced in patients (0.88 [0.10] vs 1.6 [0.30] mmol/L; p < 0.001). Reduced oxidative and nonoxidative metabolism accounted for the defect in overall glucose uptake in patients. No correlation between changes in coronary sinus blood flow and total body glucose uptake was seen. We found that microvascular angina was associated with substantial insulin resistance. Whether this relation is causal or coincidental is as yet unsettled.

Comments on the clinical impact of hypertension in type I diabetes

In type I diabetes, the quality of life and, in essence, the long-term prognosis or life expectancy of the patient are invariably related to the manifestation of untoward complications. Increased arterial blood pressure (hypertension) has a great influence in these complications. Cumulative evidence has shown that proteinuric type I diabetic patients are easily susceptible to hypertension and its accompanying sequelae. The debilitating effects of hypertension on the progressive development of diabetic nephropathy leading to renal dysfunction and mortality in renal transplant patients have been documented. Proliferative retinopathy and cardiovascular lesions are also frequent devastating complications in hypertensive-diabetic patients. The mechanism of sodium/lithium countertransport activity and the genetic predisposition to hypertension require further elucidation.

Autonomic nervous function and its relationship to cardiac performance in middle-aged diabetic patients without clinically evident cardiovascular disease

Autonomic nervous function was evaluated in 36 patients with insulin-dependent diabetes mellitus (IDDM), 39 patients with non-insulin-dependent diabetes mellitus (NIDDM) and 48 control subjects, all without clinically evident cardiovascular disease. Valsalva ratio and heart rate variation during deep breathing were lower in both diabetic groups than in the control group. Autonomic nervous function score (ANFS) was more abnormal in patients with IDDM than in control subjects, but was not significantly increased in patients with NIDDM. There was a negative correlation between ANFS and left ventricular diastolic filling evaluated by echocardiography or peak heart rate during exercise in both diabetic groups. There were no correlations between ANFS and left ventricular systolic function at rest or during exercise in any of the groups. In conclusion, autonomic nervous function was abnormal in middle-aged diabetic patients, and it was associated with impaired left ventricular diastolic filling at rest and decreased heart rate response to exercise, but not with left ventricular systolic function.

The effect of posture and environmental temperature on cardiovascular reflexes in normal subjects and diabetes mellitus

This study was undertaken to determine the effects of environmental temperature (17 degrees C or 27 degrees C) and posture on heart rate variability during forced sinus arrhythmia (deep breathing), and of environmental temperature on the heart rate and blood pressure responses to standing, and to the cold pressor test. A group of non-diabetic young subjects (23 +/- 5 years) and a group of older diabetic patients (54 +/- 15 years) were studied. At 27 degrees C, supine resting heart rate and systolic blood pressure were lower than at 17 degrees C in both diabetic and non-diabetic subjects, and heart rate variability was lower than at 17 degrees C in the non-diabetic subjects (p less than 0.01) with seven of 17 abnormal or borderline results (all seven subjects had normal values at 17 degrees C). Room temperature had no effect on supine heart rate variability in the diabetic patients. At 27 degrees C heart rate variability in the upright posture was significantly greater than supine (p less than 0.001) in the non-diabetic subjects. In the diabetic subjects, heart rate variability when standing at 17 degrees C increased such that five patients classified as abnormal when supine had normal values when upright. A similar pattern was observed at 27 degrees C, although only those with normal heart rate variability showed an increase on standing. Room temperature had no effect on the responses to the cold pressor test, or the blood pressure responses to standing, although the heart rate response was greater in both groups at 27 degrees C. This study shows that care should be taken to standardize the conditions under which heart rate variability is determined.

Diabetic heart muscle disease

Diabetic patients may have various abnormalities in left ventricular systolic and diastolic function not attributable to coronary heart disease, hypertension or other known cardiac disease. Although the exact causes of this diabetic heart muscle disease or "diabetic cardiomyopathy" are still incompletely understood, several mechanisms may contribute to it including disturbed myocardial energy metabolism, microvascular changes, structural changes in collagen, increased myocardial fibrosis, and cardiac autonomic neuropathy. Perhaps the most typical feature of diabetic heart muscle disease is an abnormal filling pattern of the left ventricle, suggesting reduced compliance or prolonged relaxation. Left ventricular systolic function is commonly normal at rest in asymptomatic diabetic patients, but it frequently becomes abnormal during exercise. The abnormalities in left ventricular systolic function may be partly reversible along with an improvement of metabolic control of diabetes. It is not known how frequently subclinical abnormalities in left ventricular function in diabetic patients result in clinically manifest heart failure.

A comparison of the pathological spectrum of hypertensive, diabetic, and hypertensive-diabetic heart disease

The hearts obtained at autopsy of 67 patients with hypertension, diabetes mellitus, or both were examined microscopically and histochemically, and the amount of fibrosis was determined. Significant differences in heart weight, interstitial fibrosis, replacement fibrosis, and perivascular fibrosis were found among the groups. The mean heart weight of the hypertensive-diabetic patients was significantly greater than that of the hypertensive patients and the diabetic patients. The amount of microscopic fibrosis increased between the groups, the lowest in hypertensive hearts, midrange in diabetic hearts, and highest in hypertensive-diabetic hearts. Total fibrosis correlated with heart weight among diabetic and hypertensive-diabetic patients and was significantly greater among patients with congestive heart failure, most of whom had histories of both hypertension and diabetes. The microscopic grade of fibrosis correlated significantly (p less than 0.01) with a quantitative, histochemical determination of the amount of collagen per milligram of total noncollagenous protein in the heart tissue. Myocardial fibrosis may contribute to the diastolic dysfunction typical of hypertensive-diabetic cardiomyopathy, in which congestive heart failure is a common sequela. The importance of hypertension in the pathogenesis of severe diabetic heart disease is discussed.

Effect of phase of menstrual cycle on insulin sensitivity, peripheral blood flow and cardiovascular responses to hyperinsulinaemia in young women with type 1 diabetes

Disturbances of blood glucose control around the time of menstruation are often reported by women with Type 1 diabetes. To investigate the possibility that such changes may be due to alterations in insulin sensitivity or peripheral blood flow we have studied 9 women with Type 1 diabetes during the follicular and luteal phases of the menstrual cycle. Insulin sensitivity was assessed by the glucose clamp technique with insulin doses of 40 (low dose) and 100 (high dose) mU m-2 min-1. Glucose disposal rates were 2.5 +/- 0.3 (mean +/- SE) mg kg-1 min-1 during the follicular phase and 3.2 +/- 0.3 mg kg-1 min-1 in the luteal phase with low dose insulin, and 5.9 +/- 0.4 and 6.4 +/- 0.6 mg kg-1 min-1, respectively, with high dose insulin. These differences were not statistically significant. Forearm blood flow, heart rate, and blood pressure were similar during both phases.

Prevalence and significance of left ventricular filling abnormalities determined by Doppler echocardiography in young type I (insulin-dependent) diabetic patients

In 16 insulin-dependent diabetic patients, 36 +/- 8 years old with no microangiopathy, hypertension or coronary artery disease, and 16 healthy control subjects matched for sex, age and body surface area, the following parameters were obtained by Doppler-echocardiography: (1) end-diastolic left ventricular thickness and radius; (2) aortic pulse wave velocity; (3) mitral flow with measurement of early and late (atrial) peak velocities (E and A), pressure half-time and the velocity time integrals of the entire mitral curve and of the atrial wave; and (4) isovolumic relaxation time (i.e., the time between aortic closure and the mitral opening signals recorded simultaneously by continuous-wave Doppler). Heart rate and systolic blood pressure were not different in the 2 groups. Aortic pulse wave velocity and the wall thickness to radius ratio were significantly increased in the diabetic patients compared to the controls. E was significantly reduced whereas A/E, pressure half-time, the atrial contribution to the left ventricular filling (i.e., the ratio of the atrial velocity time integral to the mitral velocity time integral) and the isovolumic relaxation time were significantly increased in the diabetic group versus the control subjects. Lastly, 11 of 16 diabetic patients (69%) had at least 2 of the following abnormalities: A/E greater than 0.71, an atrial contribution to the left ventricular filling greater than 0.25, a pressure half-time greater than 50 ms and an isovolumic relaxation time greater than 88 ms. No correlations were found between the wall thickness to radius ratio, aortic pulse wave velocity and the filling indexes.(ABSTRACT TRUNCATED AT 250 WORDS)

Non-invasive evaluation of cardiac function in young patients with type 1 diabetes

Cardiac function was evaluated in 40 Type 1 diabetic patients aged less than 30 years and compared with 20 age- and sex-matched control subjects using resting and exercise electrocardiography, and echocardiography. The duration of diabetes was from 0.25 to 25 years (mean 10 years), and few patients had microvascular complications. Left ventricular end-diastolic and end-systolic diameters were similar in both groups, with no significant differences between the groups in mean thickness of the intraventricular septum and the posterior wall of the left ventricle. Fractional shortening and mean velocity of circumferential fibre shortening as indices of ventricular function were similar in both groups. Left ventricular hypertrophy (Minnesota Code 3,1) was observed in the resting electrocardiogram of 22 patients and 12 control subjects (NS), but no other significant abnormalities were observed. One diabetic patient developed asymptomatic ST segment depression during exercise electrocardiography. In conclusion, the chamber size, wall thickness, and systolic function of the left ventricle are normal in most young Type 1 diabetic patients who have few microvascular complications.

Diabetic heart disease--Part II: The clinical and pathological spectrum

Diabetes mellitus is a significant condition, affecting major segments of all population groups studied. With the introduction of insulin and oral hypoglycemic therapy, together with better understanding of diet and weight control gained over the past half century, the primary causes of diabetic morbidity and mortality have shifted in varying proportions from metabolic derangements, infection, and renal insufficiency to different types of cardiovascular disease. Despite extensive clinical and laboratory research on the etiology, pathogenesis, and even the existence of cardiovascular disease associated with diabetes mellitus, however, considerable debate is still apparent in this field. Our purpose is to present an overview of the subject of diabetic heart disease, with a critical analysis of epidemiologic, clinical, and pathological data. Some of this material will be addressed from the perspective of research in this area over the past decade by one of us (SMF), particularly in experimental hypertensive and diabetic cardiomyopathy. However, overall, an attempt will be made to provide an objective and balanced analysis in order to answer the question: does diabetic heart disease exist?

Endomyocardial biopsy pathology in insulin-dependent diabetic patients with abnormal ventricular function

We have previously shown impaired ventricular function in asymptomatic middle-aged type 1 (insulin-dependent) diabetic patients who had no evidence of coronary artery disease. The diabetic patients had normal coronary angiograms but reduced ventricular ejection fraction on exercise. To examine the possible contribution of small vessel disease to this functional abnormality, we compared endomyocardial biopsies from seven symptom-free type 1 diabetic patients with biopsies from seven age- and sex-matched non-diabetic subjects. Interstitial fibrosis was present in three diabetic patients, arteriolar hyalinization in three patients and arteriolar thickening was observed in five patients. Morphometry performed on electron micrographs showed no significant difference in the thickness of the capillary basal lamina between diabetics and controls. While the functional significance of the abnormalities on light microscopy is unclear, our findings indicate that the abnormality of cardiac function described in diabetes is not associated with thickening of the myocardial capillary basal lamina.

[Stress testing of long-term type I diabetic patients with radionuclide ventriculography]

Left ventricular function was assessed by means of radionuclide ventriculography in 42 patients with long-standing (13 +/- 5 yrs) insulin-dependent diabetes mellitus and in eleven healthy age matched control subjects. Only diabetics were included in the study without diabetes related cardiac risk factors such as hypertension and CAD in order to evaluate diabetes specific changes of cardiac function. No differences were seen between diabetics and controls concerning heart rate and functional parameters of left ventricle in systole and diastole. The rapid filling period was not prolonged. According to our radionuclide data there is no evidence of diabetes related impairment of ventricular function in young patients with long-standing type-1-diabetes mellitus.

Cardiac disease in diabetes

The current approach to cardiac disease recognizes that the cardiovascular problems of diabetic patients have both a coronary artery atherosclerotic component and an independent myocardial component. The presence of the myocardial component has become more apparent in recent years, and a full understanding of the balance between the two components is necessary for proper treatment of the cardiac problems of patients with diabetes.

Impaired left ventricular systolic function during exercise in middle-aged insulin-dependent and noninsulin-dependent diabetic subjects without clinically evident cardiovascular disease

Equilibrium radionuclide angiocardiography was performed on 19 men and 17 women with insulin-dependent diabetes mellitus (IDDM) and on 24 men and 15 women with noninsulin-dependent diabetes mellitus (NIDDM) and on 24 male and 24 female control subjects aged 46 to 67 years. All were without clinically evident cardiovascular disease. No significant differences were found in left ventricular (LV) ejection fraction at rest between men with IDDM (56 +/- 1%; mean +/- standard error of the mean) or NIDDM (58 +/- 1%) and control men (58 +/- 1%), whereas LV ejection fraction was higher in women with IDDM (63 +/- 1%; p less than 0.01) and NIDDM (64 +/- 2%; p less than 0.01) than in control women (58 +/- 1%). An abnormal LV ejection fraction response to dynamic exercise (an increase of less than 5% units or a decrease) was observed in 1 control man (4%), in 8 men with IDDM (42%, p less than 0.01) and in 10 men with NIDDM (42%, p less than 0.01). The respective figures were 4 (17%) for control women, 7 (44%, difference not significant) for women with IDDM and 10 (71%, p less than 0.01) for women with NIDDM. Abnormal LV ejection fraction response to exercise in diabetic patients was not related to the metabolic control of diabetes, presence of microangiopathy or abnormalities in the autonomic nervous function. Myocardial perfusion scintigraphy performed in 18 diabetic patients in whom LV ejection fraction decreased during exercise showed a reversible perfusion defect in only 5 (28%).(ABSTRACT TRUNCATED AT 250 WORDS)