Effect of glycaemic control on myocardial sympathetic innervation assessed by [123I]metaiodobenzylguanidine scintigraphy: a 4-year prospective study in IDDM patients

Impact of blood glucose control on sympathetic and vagus nerve functional status in patients with type 2 diabetes mellitus

AIMS

Present study observed the impact of blood glucose control on sympathetic and vagus functional status in type 2 diabetes mellitus (DM) patients through observing the association between glycosylated hemoglobin (HbA1c) level and sympathetic and vagus functional status detected by heart rate recovery (HRR) and heart rate variability (HRV) assessments.

METHODS

Consecutive hospitalized DM patients were divided into well glycemic control group (HbA1c < 7.0%, group WGC, n = 100) and poor glycemic control group (HbA1c ≥ 7.0%, group PGC, n = 100), 100 hospitalized patients without DM served as control group (group C). All subjects underwent blood biochemistry test, treadmill exercise testing and 24-h Holter monitoring.

RESULTS

HRR and HRV parameters were significantly lower in group WGC and PGC than in group C. Standard deviation of NN intervals (SDNN), standard deviation of all 5-min average NN intervals (SDANN), very low frequency (VLF) values were significantly lower in group PGC than in group WGC. HbA1c level was negatively correlated with HRR1, SDNN, SDANN, VLF, low frequency and high frequency. Logistic regression analysis showed that lower SDNN, SDANN and VLF values were risk factors for high HbA1c levels in DM patients after adjusting for gender, age and beta-blocker use in the model 1, and for gender, age, beta-blocker use, coronary artery disease and hypertension in the model 2.

CONCLUSIONS

Present results indicate that sympathetic and vagal functional status are impaired independent of HbA1c level, while poor glycemic control is related to more significant neurocardiac dysfunction in DM patients.

A Comparative Assessment of Cardiovascular Autonomic Reflex Testing and Cardiac 123I-Metaiodobenzylguanidine Imaging in Patients with Type 1 Diabetes Mellitus without Complications or Cardiovascular Risk Factors

AIM

To compare the cardiovascular autonomic reflex tests (CARTs) with cardiac sympathetic innervation imaging with ¹²³I-metaiodobenzylguanidine (MIBG) in patients with type 1 diabetes mellitus (T1DM).

PATIENTS AND METHODS

Forty-nine patients (29 males, mean age 36 ± 10 years, mean T1DM duration 19 ± 6 years) without cardiovascular risk factors were prospectively enrolled. Participants were evaluated for autonomic dysfunction by assessing the mean circular resultant (MCR), Valsalva maneuver (Vals), postural index (PI), and orthostatic hypotension (OH). Within one month from the performance of these tests, patients underwent cardiac MIBG imaging and the ratio of the heart to upper mediastinum count density (H/M) at 4 hours postinjection was calculated (abnormal values, H/M < 1.80).

RESULTS

Twenty-nine patients (59%) had abnormal CARTs, and 37 (76%) patients had an H/M_4 < 1.80 (p = 0.456). MCR, PI, Vals, and OH were abnormal in 29 (59%), 8 (16%), 5 (10%), and 11 (22%) patients, respectively. When using H/M_4 < 1.80 as the reference standard, a cutoff point of ≥2 abnormal CARTs had a sensitivity of 100% but a specificity of only 33% for determining CAN.

CONCLUSIONS

CARTs are not closely associated with ¹²³I-MIBG measurements, which can detect autonomic dysfunction more efficiently than the former. In comparison to semiquantitative cardiac MIBG assessment, the recommended threshold of ≥2 abnormal CARTs to define cardiovascular autonomic dysfunction is highly sensitive but of limited specificity and is independently determined by the duration of T1DM.

Review: Autonomic neuropathy: a marker of cardiovascular risk

Cardiac autonomic neuropathy (CAN) represents a serious complication as it carries an approximately five-fold risk of mortality in patients with diabetes just as in those with chronic liver diseases. The high mortality rate may be related to silent myocardial infarction, cardiac arrhythmias, cardiovascular and cardiorespiratory instability and to other causes not yet explained. Resting tachycardia due to parasympathetic damage may represent one of the earliest signs. Typical findings referring to autonomic dysfunction may include exercise intolerance, orthostatic hypotension and cardiac dysfunction to rest or exercise. Severe autonomic neuropathy may be responsible for spontaneous respiratory arrest and unexplained sudden death. A relationship between the presence and/or severity of CAN and corrected QT interval prolongation is well documented. Better understanding of the prognostic importance of autonomic neuropathy followed the use of simple non-invasive cardiovascular reflex tests. These most commonly include heart rate variation in response to deep breathing, standing, the Valsalva maneouvre and blood pressure response to standing and sustained handgrip. Near normoglycaemia is now generally accepted as the primary approach to the prevention of diabetic neuropathy, but is not achievable in most patients. Our experience of the use of the antioxidant alpha-lipoic acid in the treatment of cardiac autonomic neuropathy is described.

Insulin resistance is associated with impaired cardiac sympathetic innervation in patients with heart failure

AIMS

Insulin resistance (IR) represents, at the same time, cause and consequence of heart failure (HF) and affects prognosis in HF patients, but pathophysiological mechanisms remain unclear. Hyperinsulinemia, which characterizes IR, enhances sympathetic drive, and it can be hypothesized that IR is associated with impaired cardiac sympathetic innervation in HF. Yet, this hypothesis has never been investigated. Aim of the present observational study was to assess the relationship between IR and cardiac sympathetic innervation in non-diabetic HF patients.

METHODS AND RESULTS

One hundred and fifteen patients (87% males; 65 ± 11.3 years) with severe-to-moderate HF (ejection fraction 32.5 ± 9.1%) underwent iodine-123 meta-iodobenzylguanidine ((123)I-MIBG) myocardial scintigraphy to assess sympathetic innervation and Homeostasis Model Assessment Insulin Resistance (HOMA-IR) evaluation to determine the presence of IR. From (123)I-MIBG imaging, early and late heart to mediastinum (H/M) ratios and washout rate were calculated. Seventy-two (63%) patients showed IR and 43 (37%) were non-IR. Early [1.68 (IQR 1.53-1.85) vs. 1.79 (IQR 1.66-1.95); P = 0.05] and late H/M ratio [1.50 (IQR 1.35-1.69) vs. 1.65 (IQR 1.40-1.85); P = 0.020] were significantly reduced in IR compared with non-IR patients. Early and late H/M ratio showed significant inverse correlation with fasting insulinemia and HOMA-IR.

CONCLUSION

Cardiac sympathetic innervation is more impaired in patients with IR and HF compared with matched non-IR patients. These findings shed light on the relationship among IR, HF, and cardiac sympathetic nervous system. Additional studies are needed to clarify the pathogenetic relationship between IR and HF.

Metabolic syndrome: a sympathetic disease?

Metabolic syndrome is associated with adverse health outcomes and is a growing problem worldwide. Although efforts to harmonise the definition of metabolic syndrome have helped to better understand the prevalence and the adverse outcomes associated with the disorder on a global scale, the mechanisms underpinning the metabolic changes that define it are incompletely understood. Accumulating evidence from laboratory and human studies suggests that activation of the sympathetic nervous system has an important role in metabolic syndrome. Indeed, treatment strategies commonly recommended for patients with metabolic syndrome, such as diet and exercise to induce weight loss, are associated with sympathetic inhibition. Pharmacological and device-based approaches to target activation of the sympathetic nervous system directly are available and have provided evidence to support the important part played by sympathetic regulation, particularly for blood pressure and glucose control. Preliminary evidence is encouraging, but whether therapeutically targeting sympathetic overactivity could help to prevent metabolic syndrome and attenuate its adverse outcomes remains to be determined.

Concepts of scientific integrative medicine applied to the physiology and pathophysiology of catecholamine systems

This review presents concepts of scientific integrative medicine and relates them to the physiology of catecholamine systems and to the pathophysiology of catecholamine-related disorders. The applications to catecholamine systems exemplify how scientific integrative medicine links systems biology with integrative physiology. Concepts of scientific integrative medicine include (i) negative feedback regulation, maintaining stability of the body's monitored variables; (ii) homeostats, which compare information about monitored variables with algorithms for responding; (iii) multiple effectors, enabling compensatory activation of alternative effectors and primitive specificity of stress response patterns; (iv) effector sharing, accounting for interactions among homeostats and phenomena such as hyperglycemia attending gastrointestinal bleeding and hyponatremia attending congestive heart failure; (v) stress, applying a definition as a state rather than as an environmental stimulus or stereotyped response; (vi) distress, using a noncircular definition that does not presume pathology; (vii) allostasis, corresponding to adaptive plasticity of feedback-regulated systems; and (viii) allostatic load, explaining chronic degenerative diseases in terms of effects of cumulative wear and tear. From computer models one can predict mathematically the effects of stress and allostatic load on the transition from wellness to symptomatic disease. The review describes acute and chronic clinical disorders involving catecholamine systems-especially Parkinson disease-and how these concepts relate to pathophysiology, early detection, and treatment and prevention strategies in the post-genome era.

Microvascular dysfunction in the context of diabetic neuropathy

Microvascular dysfunction in diabetes plays a crucial role in the development of diabetic complications. The skin, as one of the most accessible organs, serves as a model for the investigation of microvascular dysfunction. Several non-invasive, mostly laser-Doppler-based methods have been developed lately to assess microvascular function in the skin. Microvascular functional changes occur even in the prediabetic state and become more complex with overt diabetes, being exacerbated by the presence of peripheral and/or autonomic diabetic neuropathy. The present article aims at shedding light on the implication of endothelial and neurovascular dysfunction in microvascular changes in diabetes, highlighting the contribution of different forms of diabetic neuropathy.

Impact of diabetes on cardiac sympathetic innervation in patients with heart failure: a 123I meta-iodobenzylguanidine (123I MIBG) scintigraphic study

OBJECTIVE

Impaired parasympathetic and sympathetic nervous system activity have been demonstrated in patients with diabetes mellitus (DM) and correlated with worse prognosis. Few data are available on the effect of DM on cardiac neuropathy in heart failure (HF). The aim of the current study was to assess cardiac sympathetic activity in HF patients with and without DM.

RESEARCH DESIGN AND METHODS

Patients with severe HF (n = 75), with (n = 37) and without DM (n = 38), and 14 diabetic patients with normal cardiac function underwent (123)I meta-iodobenzylguanidine scintigraphy from which early and late heart-to-mediastinum (H/M) ratios were calculated. Clinical, echocardiographic, and biochemical data were measured.

RESULTS

DM compared with non-DM patients showed significantly lower early (1.65 ± 0.21 vs. 1.75 ± 0.21; P < 0.05) and late H/M ratios (1.46 ± 0.22 vs. 1.58 ± 0.24; P < 0.03). Early and late H/M were significantly higher in DM patients without HF (2.22 ± 0.35 and 1.99 ± 0.24, respectively) than HF patients with (P < 0.0001) and without (P < 0.0001) DM. In HF patients, an inverse correlation between early or late H/M ratio and hemoglobin A1c (HbA1c) (Pearson = -0.473, P = 0.001; Pearson = -0.382, P = 0.001, respectively) was observed. In DM, in multivariate analysis, HbA1c and ejection fraction remained significant predictors of early H/M; HbA1c remained the only significant predictor of late H/M. No correlation between early or late H/M and HbA1c was found in non-DM patients.

CONCLUSIONS

Diabetic patients with HF show lower cardiac sympathetic activity than HF patients not having DM or than DM patients with a similar degree of autonomic dysfunction not having HF. HbA1c correlated with the degree of reduction in cardiac sympathetic activity.

Diabetic cardiomyopathy: ongoing controversies in 2012

Diabetic cardiomyopathy is a controversial clinical entity that in its initial state is usually characterized by left ventricular diastolic dysfunction in patients with diabetes mellitus that cannot be explained by coronary artery disease, hypertension, or any other known cardiac disease. It was reported in up to 52-60% of well-controlled type-II diabetic subjects, but more recent studies, using standardized tissue Doppler criteria and more strict patient selection, revealed a much lower prevalence. The pathological substrate is myocardial damage, left ventricular hypertrophy, interstitial fibrosis, structural and functional changes of the small coronary vessels, metabolic disturbance, and autonomic cardiac neuropathy. Hyperglycemia causes myocardial necrosis and fibrosis, as well as the increase of myocardial free radicals and oxidants, which decrease nitric oxide levels, worsen the endothelial function, and induce myocardial inflammation. Insulin resistance with hyperinsulinemia and decreased insulin sensitivity may also contribute to the left ventricular hypertrophy. Clinical manifestations of diabetic cardiomyopathy may include dyspnea, arrhythmias, atypical chest pain, and dizziness. Currently, there is no specific treatment of diabetic cardiomyopathy that targets its pathophysiological substrate, but various therapeutic options are discussed that include improving diabetic control with both diet and drugs (metformin and thiazolidinediones), the use of ACE inhibitors, beta blockers, and calcium channel blockers. Daily physical activity and a reduction in body mass index may improve glucose homeostasis by reducing the glucose/insulin ratio and the increase of both insulin sensitivity and glucose oxidation by the skeletal and cardiac muscles.

Obesity, diabetes and atrial fibrillation; epidemiology, mechanisms and interventions

The last few decades have witnessed a global rise in adult obesity of epidemic proportions. The potential impact of this is emphasized when one considers that body mass index (BMI) is a powerful predictor of death, type 2 diabetes (T2DM) and cardiovascular (CV) morbidity and mortality [1, 2]. Similarly we have witnessed a parallel rise in the incidence of atrial fibrillation (AF), the commonest sustained cardiac arrhythmia, which is also a significant cause of cardiovascular morbidity and mortality. Part of this increase is attributable to advances in the treatment of coronary heart disease (CHD) and heart failure (HF) improving life expectancy and consequently the prevalence of AF. However, epidemiological studies have demonstrated an independent association between obesity and AF, possibly reflecting common pathophysiology and risk factors for both conditions. Indeed, weight gain and obesity are associated with structural and functional changes of the cardiovascular system including left atrial and ventricular remodeling, haemodynamic alterations, autonomic dysfunction, and diastolic dysfunction. Moreover, diabetic cardiomyopathy is characterized by an adverse structural and functional cardiac phenotype which may predispose to the development of AF [3]. In this review, we discuss the pathophysiological and mechanistic relationships between obesity, diabetes and AF, and the challenges posed in the management of this high-risk group of individuals.

Diabetic cardiovascular autonomic neuropathy: clinical implications

Diabetic cardiovascular autonomic neuropathy (DCAN), the impairment of the autonomic balance of the cardiovascular system in the setting of diabetes mellitus (DM), is frequently observed in both Type 1 and 2 DM, has detrimental effects on the quality of life and portends increased mortality. Clinical manifestations include: resting heart rate disorders, exercise intolerance, intraoperative cardiovascular lability, orthostatic alterations in heart rate and blood pressure, QT-interval prolongation, abnormal diurnal and nocturnal blood pressure variation, silent myocardial ischemia and diabetic cardiomyopathy. Clinical tests for autonomic nervous system evaluation, heart rate variability analysis, autonomic innervation imaging techniques, microneurography and baroreflex analysis are the main diagnostic tools for DCAN detection. Aldose reductase inhibitors and antioxidants may be helpful in DCAN therapy, but a regular, more generalized and multifactorial approach should be adopted with inclusion of lifestyle modifications, strict glycemic control and treatment of concomitant traditional cardiovascular risk factors, in order to achieve the best therapeutic results. In the present review, the authors provide aspects of DCAN pathophysiology, clinical presentation, diagnosis and an algorithm regarding the evaluation and management of DCAN in DM patients.

Diabetic autonomic neuropathy

Autonomic neuropathy, once considered to be the Cinderella of diabetes complications, has come of age. The autonomic nervous system innervates the entire human body, and is involved in the regulation of every single organ in the body. Thus, perturbations in autonomic function account for everything from abnormalities in pupillary function to gastroparesis, intestinal dysmotility, diabetic diarrhea, genitourinary dysfunction, amongst others. "Know autonomic function and one knows the whole of medicine!" It is now becoming apparent that before the advent of severe pathological damage to the autonomic nervous system there may be an imbalance between the two major arms, namely the sympathetic and parasympathetic nerve fibers that innervate the heart and blood vessels, resulting in abnormalities in heart rate control and vascular dynamics. Cardiac autonomic neuropathy (CAN) has been linked to resting tachycardia, postural hypotension, orthostatic bradycardia and orthostatic tachycardia (POTTS), exercise intolerance, decreased hypoxia-induced respiratory drive, loss of baroreceptor sensitivity, enhanced intraoperative or perioperative cardiovascular lability, increased incidence of asymptomatic ischemia, myocardial infarction, and decreased rate of survival after myocardial infarction and congestive heart failure. Autonomic dysfunction can affect daily activities of individuals with diabetes and may invoke potentially life-threatening outcomes. Intensification of glycemic control in the presence of autonomic dysfunction (more so if combined with peripheral neuropathy) increases the likelihood of sudden death and is a caveat for aggressive glycemic control. Advances in technology, built on decades of research and clinical testing, now make it possible to objectively identify early stages of CAN with the use of careful measurement of time and frequency domain analyses of autonomic function. Fifteen studies using different end points report prevalence rates of 1% to 90%. CAN may be present at diagnosis, and prevalence increases with age, duration of diabetes, obesity, smoking, and poor glycemic control. CAN also cosegregates with distal symmetric polyneuropathy, microangiopathy, and macroangiopathy. It now appears that autonomic imbalance may precede the development of the inflammatory cascade in type 2 diabetes and there is a role for central loss of dopaminergic restraint on sympathetic overactivity. Restoration of dopaminergic tone suppresses the sympathetic dominance and reduces cardiovascular events and mortality by close to 50%. Cinderella's slipper can now be worn!

Neurocardiology: therapeutic implications for cardiovascular disease

The term "neurocardiology" refers to physiologic and pathophysiological interplays of the nervous and cardiovascular systems. This selective review provides an update about cardiovascular therapeutic implications of neurocardiology, with emphasis on disorders involving primary or secondary abnormalities of catecholamine systems. Concepts of scientific integrative medicine help understand these disorders. Scientific integrative medicine is not a treatment method or discipline but a way of thinking that applies systems concepts to acute and chronic disorders of regulation. Some of these concepts include stability by negative feedback regulation, multiple effectors, effector sharing, instability by positive feedback loops, allostasis, and allostatic load. Scientific integrative medicine builds on systems biology but is also distinct in several ways. A large variety of drugs and non-drug treatments are now available or under study for neurocardiologic disorders in which catecholamine systems are hyperfunctional or hypofunctional. The future of therapeutics in neurocardiology is not so much in new curative drugs as in applying scientific integrative medical ideas that take into account concurrent chronic degenerative disorders and interactions of multiple drug and non-drug treatments with each other and with those disorders.

Methods of investigation for cardiac autonomic dysfunction in human research studies

This consensus document provides evidence-based guidelines regarding the evaluation of diabetic cardiovascular autonomic neuropathy (CAN) for human research studies; the guidelines are the result of the work of the CAN Subcommittee of the Toronto Diabetic Neuropathy Expert Group. The subcommittee critically reviewed the limitations and strengths of the available diagnostic approaches for CAN and the need for developing new tests for autonomic function. It was concluded that the most sensitive and specific approaches currently available to evaluate CAN in clinical research are: (1) heart rate variability, (2) baroreflex sensitivity, (3) muscle sympathetic nerve activity, (4) plasma catecholamines, and (5) heart sympathetic imaging. It was also recommended that efforts should be undertaken to develop new non-invasive and safe CAN tests to be used in clinical research, with higher sensitivity and specificity, for studying the pathophysiology of CAN and evaluating new therapeutic approaches.

Autonomic imbalance: prophet of doom or scope for hope?

It has long been recognized that cardiac autonomic neuropathy increases morbidity and mortality in diabetes and may have greater predictive power than traditional risk factors for cardiovascular events. Significant morbidity and mortality can now be attributable to autonomic imbalance between the sympathetic and parasympathetic nervous system regulation of cardiovascular function. New and emerging syndromes include orthostatic tachycardia, orthostatic bradycardia and an inability to use heart rate as a guide to exercise intensity because of the resting tachycardia. Recent studies have shown that autonomic imbalance may be a predictor of risk of sudden death with intensification of glycaemic control. This review examines an association of autonomic dysregulation and the role of inflammatory cytokines and adipocytokines that promote cardiovascular risk. In addition, conditions of autonomic imbalance associated with cardiovascular risk are discussed. Potential treatment for restoration of autonomic balance is outlined.

Multimodality imaging in diabetic heart disease

Diabetic heart disease is currently defined as left ventricular dysfunction that occurs independently of coronary artery disease and hypertension. Its underlying etiology is likely to be multifactorial, acting synergistically together to cause myocardial dysfunction. Multimodality cardiac imaging, such as echocardiography, nuclear, computed tomography, and magnetic resonance imaging, can provide invaluable insight into different aspects of the disease process, from imaging at the cellular level for altered myocardial metabolism to microvascular and endothelial dysfunction, autonomic neuropathy, coronary atherosclerosis, and finally, interstitial fibrosis with scar formation. Furthermore, cardiac imaging is pivotal in diagnosing diabetic heart disease. Thus, the aim of the present review is to illustrate the role of multimodality cardiac imaging in elucidating the underlying pathophysiologic mechanisms of diabetic heart disease.

Emerging drugs for diabetic neuropathy

IMPORTANCE OF THE FIELD

Diabetic neuropathy (DN) is a very common and disabling diabetes-related complication. DN is associated with significant morbidity and mortality. Diabetic peripheral neuropathy (DPN) can be painful in the earlier stages of the disease before becoming painless. Most of the currently available therapies are symptomatic (focusing on pain relief) rather than disease-modifying. With the exception of good glycemic control, there is currently no effective treatment to slow the progression of or reverse DPN.

AREAS COVERED IN THIS REVIEW

In this article, we review the epidemiology, pathogenesis, currently available and future treatments for DPN, and the potential development issues/challenges related to such new therapies. Literature search was performed using PubMed, Medline and Pharmaprojects from 1950 onwards. Search terms include a combination of terms such as diabetic neuropathy, pathogenesis, pathophysiology, mechanisms, treatment, therapy, oxidative/nitrosative stress, anti-oxidants, serotonin, nitrotyrosine, protein kinase C, aldose reductase, sodium channels, taurine, lipoic acid and poly (ADP-ribose) polymerase.

WHAT THE READER WILL GAIN

The reader will gain an overview of the epidemiology, clinical features and risk factors of DN. In addition, the reader will have a better understanding of the mechanisms that underpin the development of DPN and their relationships to the current and future therapies. The reader will also develop an insight into the limitations of the current approach to DPN treatment and the potential avenues for future research.

TAKE HOME MESSAGE

DN is a very common and disabling complication that currently has no effective treatments other than diabetes control. The pathogenesis of DPN is complex and multi-factorial. Several disease-modifying and symptomatic treatments are currently under development. Oxidative and nitrosative stress have been identified as key pathogenic factors in the development of DPN and new treatments target these pathways and/or their downstream consequences. Gene therapy and growth factors have also emerged as potential new therapies that target particular cellular compartments as opposed to being delivered systemically. The recognition of the difficulty in reversing established DN has focused efforts on slowing its progression.

Cardiac autonomic neuropathy in patients with diabetes and no symptoms of coronary artery disease: comparison of 123I-metaiodobenzylguanidine myocardial scintigraphy and heart rate variability

Purpose

The purpose of this study was to evaluate the prevalence of cardiac autonomic neuropathy (CAN) in a cohort of patients with type 2 diabetes, truly asymptomatic for coronary artery disease (CAD), using heart rate variability (HRV) and ¹²³I-metaiodobenzylguanidine (¹²³I-mIBG) myocardial scintigraphy.

Methods

The study group comprised 88 patients with type 2 diabetes prospectively recruited from an outpatient diabetes clinic. In all patients myocardial perfusion scintigraphy, CAN by HRV and ¹²³I-mIBG myocardial scintigraphy were performed. Two or more abnormal tests were defined as CAN-positive (ECG-based CAN) and one or fewer as CAN-negative. CAN assessed by ¹²³I-mIBG scintigraphy was defined as abnormal if the heart-to-mediastinum ratio was <1.8, the washout rate was >25%, or the total defect score was >13.

Results

The prevalence of CAN in patients asymptomatic for CAD with type 2 diabetes and normal myocardial perfusion assessed by HRV and ¹²³I-mIBG scintigraphy was respectively, 27% and 58%. Furthermore, in almost half of patients with normal HRV, ¹²³I-mIBG scintigraphy showed CAN.

Conclusion

The current study revealed a high prevalence of CAN in patients with type 2 diabetes. Secondly, disagreement between HRV and ¹²³I-mIBG scintigraphy for the assessment of CAN was observed.

Early autonomic dysfunction in type 1 diabetes: a reversible disorder?

AIMS/HYPOTHESIS

Cardiac autonomic neuropathy is associated with increased morbidity and mortality rates in patients with type 1 diabetes. The prevalence of early autonomic abnormalities is relatively high compared with the frequency of manifest clinical abnormalities. Thus, early autonomic dysfunction could to some extent be functional and might lead to an organic disease in a subgroup of patients only. If this is true, manoeuvres such as slow deep-breathing, which can improve baroreflex sensitivity (BRS) in normal but not in denervated hearts, could also modify autonomic modulation in patients with type 1 diabetes, despite autonomic dysfunction.

METHODS

We compared 116 type 1 diabetic patients with 36 matched healthy control participants and 12 heart-transplanted participants with surgically denervated hearts. Autonomic function tests and spectral analysis of heart rate and blood pressure variability were performed. BRS was estimated by four methods during controlled (15 breaths per minute) and slow deep-breathing (six breaths per minute), and in supine and standing positions.

RESULTS

Conventional autonomic function tests were normal, but resting spectral variables and BRS were reduced during normal controlled breathing in patients with type 1 diabetes. However, slow deep-breathing improved BRS in patients with type 1 diabetes, but not in patients with surgically denervated hearts. Standing induced similar reductions in BRS in diabetic and control participants.

CONCLUSIONS/INTERPRETATION

Although we found signs of increased sympathetic activity in patients with type 1 diabetes, we also observed a near normalisation of BRS with a simple functional test, indicating that early autonomic derangements are to a large extent functional and potentially correctable by appropriate interventions.

Role of interleukin-6 levels in cardiovascular autonomic dysfunction in type 2 diabetic patients

PURPOSE

Increased serum interleukin-6 (IL-6) levels are associated with an increased risk of cardiovascular disease, and cardiovascular autonomic dysfunction is associated with high mortality in type 2 diabetic patients. However, the relationship between IL-6 levels and cardiovascular autonomic dysfunction has not been fully elucidated. The aim of this study was to determine whether serum IL-6 levels are associated with cardiovascular autonomic dysfunction in type 2 diabetic patients.

METHODS

Eighty type 2 diabetic patients who did not have organic heart disease were categorized into a high IL-6 group (>2.5 pg/ml, n = 40, age 59 +/- 12 years) or a non-high IL-6 group (<2.5 pg/ml, n = 40, 61 +/- 12 years). Cardiac autonomic function was assessed by baroreflex sensitivity, heart rate variability, plasma norepinephrine concentrations and (123)I-metaiodobenzylguanidine (MIBG) scintigraphy.

RESULTS

The body mass index values (BMI), fasting insulin levels and homeostasis model assessment index values were higher in the high IL-6 group than in the non-high IL-6 group (p < 0.01). Early and delayed (123)I-MIBG myocardial uptake values were lower (p < 0.01), and the percent washout rate of (123)I-MIBG was higher (p < 0.05) in the high IL-6 group than in the non-high IL-6 group. Furthermore, multiple regression analysis revealed that the IL-6 level was independently predicted by the BMI and the myocardial uptake of (123)I-MIBG during the delayed phase.

CONCLUSIONS

The results indicate that elevated IL-6 levels are associated with depressed cardiovascular autonomic function and obesity in type 2 diabetic patients.

Relationship between abnormal microvolt T-wave alternans and poor glycemic control in type 2 diabetic patients

BACKGROUND

Abnormal microvolt T-wave alternans (TWA) predicts the risk of ventricular arrhythmias and sudden cardiac death. Although type 2 diabetes is associated with an increased risk of these events, there is a dearth of available data on microvolt TWA measurements in type 2 diabetic populations.

METHODS

We studied 59 consecutive type 2 diabetic outpatients without manifest cardiovascular disease (CVD) and 35 non-diabetic controls who were matched for age, sex, and blood pressure values. Microvolt TWA analysis was performed non-invasively using the CH-2000 system during a sub-maximal exercise with the patient sitting on a bicycle ergometer.

RESULTS

The frequency of abnormal TWA was significantly higher in diabetic patients than in controls (25.4 vs 5.7%; P < 0.01). Among diabetic patients, those with abnormal TWA (n = 15) had remarkably higher hemoglobin A1c (HbA1c) (8.1 +/- 0.9 vs 7.1 +/- 0.8%, P < 0.001) and slightly smaller time-domain heart rate variability parameters (i.e., RMSSD, root mean square of difference of successive R-R intervals) than those with normal TWA (n = 44). Gender, age, body mass index, lipids, blood pressure values, cigarette smoking, diabetes duration, microvascular complication status, QTc interval, and current use of medications did not significantly differ between the groups. In multivariate regression logistic analysis, HbA1c (OR 13.6, 95% CI 2.0-89.1; P = 0.0076) predicted abnormal TWA independent of RMSSD values and other potential confounders.

CONCLUSIONS

Our findings suggest that abnormal TWA is a very common condition (approximately 25%) among people with type 2 diabetes without manifest CVD and is closely correlated to glycemic control.

Impact of liver transplantation on cardiac autonomic denervation in familial amyloid polyneuropathy

Familial amyloid polyneuropathy (FAP) is a rare and severe hereditary form of amyloidosis, due to the deposition of a genetic variant transthyretin essentially produced by the liver, and characterized by both sensorimotor and autonomic neuropathy. Liver transplantation (LT) is the most effective treatment to stop the progression of the disease. Cardiac amyloid infiltration is usually associated with cardiac denervation, restrictive cardiomyopathy, conduction disturbances, and sometimes sudden death. Whether the cardiac involvement related to amyloid deposition may be altered after LT remains unclear. We conducted the present study to define the outcome of cardiac involvement after LT in 31 patients with FAP (age, 39 +/- 12 yr). Patients were evaluated before and after LT (24 +/- 15 mo). Cardiac sympathetic denervation was assessed by both iodine-123 metaiodobenzylguanidine (MIBG) scintigraphy and heart rate variability (HRV) analysis. The scintigraphic importance of sympathetic denervation was evaluated globally on planar imaging using heart-to-mediastinum activity ratio (H/M) measured 4 hours after injection, and regionally using single-photon emission tomography (SPET) imaging. Amyloid myocardial infiltration was assessed by echocardiography. Diffuse sympathetic denervation was found when using cardiac MIBG planar imaging in patients evaluated before LT and compared with 12 control subjects (H/M: 1.45 +/- 0.29 vs. 1.98 +/- 0.35, p < 0.001). On SPET images, defects were diffuse in 12 patients and focal in 19 patients, with predominance at the inferior and apical segments. No change in sympathetic innervation was found in patients after LT as assessed either with planar imaging (H/M after LT: 1.46 +/- 0.28, p = not significant vs. H/M before LT) or with SPET imaging. HRV nonspectral indexes showed that the standard deviation of all cycles was significantly lower in patients compared with control subjects, and remained unchanged after LT. Conduction disturbances and ventricular arrhythmias were associated with low cardiac MIBG uptake, and progressed after LT. The left ventricular wall was slightly thickened in patients, and a further increase was observed after LT (posterior wall from 9.2 +/- 1.8 to 10.1 +/- 2.3 mm, p = 0.02; septal wall from 10.6 +/- 2.7 to 12.1 +/- 4, p = 0.046). Neurologic status stabilized in 26 patients, but worsened in the 5 patients who had the most severe cardiac sympathetic denervation before LT as measured by MIBG imaging. The magnitude of the cardiac sympathetic denervation remained stable 2 years after LT in patients with FAP, whereas the cardiac amyloid infiltration progressed. The importance of cardiac sympathetic denervation found in FAP patients before LT was associated with a neurologic worsening after LT.

Sudden cardiac death in diabetes mellitus: risk factors in the Rochester diabetic neuropathy study

OBJECTIVES

To determine risk factors for sudden cardiac death and the role of diabetic autonomic neuropathy (DAN) in the Rochester diabetic neuropathy study (RDNS).

METHODS

Associations between diabetic and cardiovascular complications, including DAN, and the risk of sudden cardiac death were studied among 462 diabetic patients (151 type 1) enrolled in the RDNS. Medical records, death certificates, and necropsy reports were assessed for causes of sudden cardiac death.

RESULTS

21 cases of sudden cardiac death were identified over 15 years of follow up. In bivariate analysis of risk covariates, the following were significant: ECG 1 (evolving and previous myocardial infarctions): hazard ratio (HR) = 4.4 (95% confidence interval (CI), 1.6 to 12.1), p = 0.004; ECG 2 (bundle branch block or pacing): HR = 8.6 (2.9 to 25.4), p<0.001; ECG 1 or ECG 2: HR = 4.2 (1.3 to 13.4), p = 0.014; and nephropathy stage: HR = 2.1 (1.3 to 3.4), p = 0.002. Adjusting for ECG 1 or ECG 2, autonomic scores, QTc interval, high density lipoprotein (HDL) cholesterol, 24 hour microalbuminuria, and 24 hour total proteinuria were significant. However, adjusting for nephropathy, none of the autonomic indices, QTc interval, HDL cholesterol, microalbuminuria, or total proteinuria was significant. At necropsy, all patients with sudden cardiac death had coronary artery or myocardial disease.

CONCLUSIONS

Sudden cardiac death was correlated with atherosclerotic heart disease and nephropathy, and to a lesser degree with DAN and HDL cholesterol. Although DAN is associated with sudden cardiac death, it is unlikely to be its primary cause.

Diabetic cardiomyopathy: evidence, mechanisms, and therapeutic implications

The presence of a diabetic cardiomyopathy, independent of hypertension and coronary artery disease, is still controversial. This systematic review seeks to evaluate the evidence for the existence of this condition, to clarify the possible mechanisms responsible, and to consider possible therapeutic implications. The existence of a diabetic cardiomyopathy is supported by epidemiological findings showing the association of diabetes with heart failure; clinical studies confirming the association of diabetes with left ventricular dysfunction independent of hypertension, coronary artery disease, and other heart disease; and experimental evidence of myocardial structural and functional changes. The most important mechanisms of diabetic cardiomyopathy are metabolic disturbances (depletion of glucose transporter 4, increased free fatty acids, carnitine deficiency, changes in calcium homeostasis), myocardial fibrosis (association with increases in angiotensin II, IGF-I, and inflammatory cytokines), small vessel disease (microangiopathy, impaired coronary flow reserve, and endothelial dysfunction), cardiac autonomic neuropathy (denervation and alterations in myocardial catecholamine levels), and insulin resistance (hyperinsulinemia and reduced insulin sensitivity). This review presents evidence that diabetes is associated with a cardiomyopathy, independent of comorbid conditions, and that metabolic disturbances, myocardial fibrosis, small vessel disease, cardiac autonomic neuropathy, and insulin resistance may all contribute to the development of diabetic heart disease.

Functional Neuroimaging of Sympathetic Innervation of the Heart

Many concepts about acute and chronic effects of stress depend on alterations in sympathetic nerves supplying the heart. Physiologic, pharmacologic, and neurochemical approaches have been used to evaluate cardiac sympathetic function. This article describes a fourth approach that is based on nuclear scanning to visualize cardiac sympathetic innervation and function and relationships between the neuroimaging findings and those from other approaches. Multiple-system atrophy with orthostatic hypotension (formerly the Shy-Drager syndrome) features normal cardiac sympathetic innervation and normal entry of norepinephrine into the coronary sinus (cardiac norepinephrine spillover), in contrast to Parkinson disease with orthostatic hypotension, which features neuroimaging and neurochemical evidence for loss of cardiac sympathetic nerves. This difference may have important implications not only for diagnosis but also for understanding the etiology of Parkinson disease. By analysis of curves relating myocardial radioactivity with time (time-activity curves) after injection of a sympathoneural imaging agent, it is possible to obtain information about cardiac sympathetic function. Abnormal time-activity curves are seen in common disorders such as heart failure and diabetic neuropathy and provide an independent, adverse prognostic index. Analogous abnormalities might help explain increased cardiovascular risk in psychiatric disorders such as melancholic depression.

Sympathetic mediated vasomotion and skin capillary permeability in diabetic patients with peripheral neuropathy

AIMS/HYPOTHESIS

A loss of sympathetic function could lead to changes in capillary fluid filtration in diabetic patients. We investigated whether a decreased sympathetically mediated vasomotion in the skin in diabetic patients with peripheral neuropathy is associated with an abnormal capillary leakage.

METHODS

Three matched groups were studied: 18 diabetic patients with documented peripheral neuropathy (DN), 18 diabetic patients without peripheral neuropathy (D), and 18 healthy control subjects (C). Sensory and motor nerve function of the distal extremities were assessed by standard neurography, and expressed in a sensory-motor nerve function score. Sympathetic vasomotion of the skin microcirculation was assessed by determining the power of blood flow variability in the low-frequency (0.02-0.14 Hz) band by spectral analysis of laser Doppler flowmetry at the median ankle. Skin capillary leakage was evaluated by sodium fluorescein videodensitometry at the same site of the foot.

RESULTS

Sympathetically mediated vasomotion of the foot skin microcirculation was lower in diabetic patients with documented peripheral neuropathy compared with diabetic patients without peripheral neuropathy and control subjects (p<0.001). Capillary sodium fluorescein leakage was larger in 18 diabetic patients with documented peripheral neuropathy than in diabetic patients without peripheral neuropathy (p<0.02) and C (p<0.005). Multiple regression analysis disclosed that a reduced sympathetically mediated vasomotion, together with a lower sensory-motor nerve function score, independently contributed to the variance in sodium fluorescein leakage, for 30% (p<0.001) and 17% (p<0.01), respectively.

CONCLUSIONS

A loss of sympathetic tone, apart from sensory-motor nerve dysfunction, seems to be a major determinant of an increased capillary permeability in diabetic patients with neuropathy.

Distribution of cardiac nerves in patients with diabetes mellitus: an immunohistochemical postmortem study of human hearts

BACKGROUND

Autonomic neuropathy and functional cardiac denervation are complications of diabetes mellitus (DM). It is unknown if DM patients show histopathologic evidence of cardiac denervation.

METHODS AND RESULTS

Nine sites were sampled at fixed distances from the atrioventricular valves from 27 postmortem hearts. Sections were stained with antibodies to S100 protein and to neurofilament (NF). Samples were visualized by light microscopy using the avidin-biotin peroxidase technique. The amount of cardiac nerves was graded blindly using semiquantitative methods according to the following criteria: Grade 0=presence of nerves in the epicardium only; Grade 1=strictly perivascular nerves; Grade 2=Grade 1 and nerve sprouts between myocardial cells sporadically; Grade 3=Grade 2 and nerve sprouts throughout the myocardium and endocardium. Specimens were divided into four groups. Control group consisted of patients with neither myocardial infarction (MI) nor DM. Experimental groups consisted of MI (n=7), MI with DM (n=6), and DM without MI (n=8). Average age of all patients was 57.3+/-15.7 years. No age differences existed among groups. Heterogeneous nerve distribution existed in all groups. S100-positive nerve density for control, MI, DM and MI, and DM without MI are 1.95+/-0.40, 1.66+/-0.54, 1.54+/-0.37, and 1.81+/-0.14, respectively (P=ns). NF-positive nerve density in the same groups were 1.10+/-0.18, 1.31+/-0.24, 1.13+/-0.12, and 1.19+/-0.42, respectively (P=ns). No differences in nerve densities between anterior and inferoposterior sections of the left ventricle existed.

CONCLUSION

In postmortem human hearts, cardiac nerve distribution was heterogeneous among normal, MI, and DM patients. No evidence of cardiac denervation in patients with DM was demonstrated.

Serial change in 123I-MIBG myocardial scintigraphy in non-insulin-dependent diabetes mellitus

PURPOSE

We performed 123I-MIBG (MIBG) myocardial scintigraphy twice in patients with non-insulin-dependent diabetes mellitus (NIDDM) to investigate whether MIBG distribution was improved by pertinent clinical control. To determine the influential factors for MIBG distribution, we investigated the association between various clinical parameters and the serial change in MIBG uptake parameters.

PATIENTS AND METHODS

Twenty NIDDM patients with no cardiac disorders were evaluated. Planar images were taken at 30 minutes (early) and 3 hours (delayed) after MIBG injection. The heart-to-upper-mediastinum uptake ratio (H/M) and washout ratio (WR) were calculated as parameters for estimating cardiac sympathetic function. Patients were divided into two groups, eight in the improved group and twelve in the unimproved group, according to the serial change in H/M. The mean interval between the baseline and the follow up study was 2.1 +/- 0.6 year. Differences between the means of the laboratory data in patients in both groups were compared for the baseline and the follow up study by using the paired t-test. As a means of determining the influential factors for a serial change of MIBG uptake, Fisher's exact test was performed to evaluate the association between the serial change in cardiac MIBG parameters and changes in other clinical parameters, such as blood sugar (BS) control, BS control method (insulin therapy), serum cholesterol control, and severity of diabetic complications. We also analyzed the association between the changes in CV(R-R) (coefficient variance of R-R intervals at rest ECG) or NCV (velocity of posterior tibial nerve) and those of other clinical parameters. Associations among these neurological parameters (MIBG parameters, CV(R-R) and NCV) were also analyzed.

RESULTS

Paired t-tests showed a significant decrease in fasting blood sugar and fructosamine in the improved group in the follow up study compared to those in the baseline study. Nevertheless, Fisher's exact test showed no significant association between FBS, HbA1C, fructosamine and the improvement in cardiac MIBG uptake. The only significant association was observed between the serial change in H/M and the BS-control method (insulin therapy). Within the neurological parameters, a significant association was noted between the serial changes in H/M and CV(R-R).

CONCLUSION

Although BS control was likely to be an important factor, it did not always ameliorate cardiac MIBG uptake. Based on the significant association between the BS-control method (insulin therapy) and MIBG uptake change, the severity of diabetes mellitus was likely to be a more influential factor. It was suggested that cardiac MIBG uptake could improve within the mild stage if controlled by diet therapy or an oral hypoglycemic agent in NIDDM.

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.

Blood pressure response to standing in the diagnosis of autonomic neuropathy: the EURODIAB IDDM Complications Study

Autonomic neuropathy is associated with poor prognosis. Cardiovascular reflexes are essential for the diagnosis of autonomic nerve dysfunction. Blood pressure response to standing is the most simple test for the evaluation of sympathetic integrity, however it is still discussed which diagnostic criteria of abnormal response should be considered as optimal. The EURODIAB IDDM Complications Study involved the examination of randomly selected Type 1 diabetic patients from 31 centres in 16 European counties. Data from 3007 patients were available for the present evaluation. Two tests of autonomic function (response of heart rate /R-R ratio/ and blood pressure from lying to standing) just as the frequency of feeling faint on standing up were assessed. R-R ratio was abnormal in 24% of patients. According to different diagnostic criteria of abnormal BP response to standing (>30 mmHg, >20 mmHg, and >10 mmHg fall in systolic BP), the frequency of abnormal results was 5.9%, 18% and 32%, respectively (p < 0.001). The frequency of feeling faint on standing was 18%, thus, it was identical with the prevalence of abnormal blood pressure response to standing when >20 mmHg fall in systolic blood pressure was considered as abnormal. Feeling faint on standing correlated significantly with both autonomic test results (p < 0.001). A fall >20 mmHg in systolic blood pressure after standing up seems to be the most reliable criterion for the assessment of orthostatic hypotension in the diagnosis of autonomic neuropathy in patients with Type 1 diabetes mellitus.

Assessment of cardiac sympathetic nerve integrity with positron emission tomography

The autonomic nervous system plays a critical role in the regulation of cardiac function. Abnormalities of cardiac innervation have been implicated in the pathophysiology of many heart diseases, including sudden cardiac death and congestive heart failure. In an effort to provide clinicians with the ability to regionally map cardiac innervation, several radiotracers for imaging cardiac sympathetic neurons have been developed. This paper reviews the development of neuronal imaging agents and discusses their emerging role in the noninvasive assessment of cardiac sympathetic innervation.

New imaging techniques for cardiovascular autonomic neuropathy: a window on the heart

Cardiovascular autonomic neuropathy (CAN) is a common complication of diabetes, which results in disabling clinical manifestations and may predispose to sudden cardiac death. Recently, direct scintigraphic assessment of cardiac sympathetic integrity has become possible with the introduction of radiolabeled analogues of norepinephrine, which are actively taken up by the sympathetic nerve terminals of the heart. This article reviews how these techniques have been utilized to improve understanding of CAN complicating diabetes. Quantitative scintigraphic assessment of cardiac sympathetic innervation heart is possible with either [123I]-metaiodobenzylguanidine (MIBG) and single photon emission computed tomography (SPECT) or [11C]-hydroxyephedrine (HED) and positron emission tomography (PET). Studies in diabetic patients have explored the sensitivity of these techniques to detect CAN, characterize the effects of glycemic control on the progression of CAN and evaluate the effects of CAN on myocardial electrophysiology, blood flow regulation and function. Deficits of left ventricular (LV) [123I]-MIBG and [11C]-HED retention have been identified in diabetic subjects without abnormalities on cardiovascular reflex testing consistent with increased sensitivity to detect CAN. Poor glycemic control results in the progression of LV tracer deficits, which can be prevented or reversed by the institution of near-euglycemia. Deficits begin distally in the LV and may extend proximally. Paradoxically, however, absolute HED retention is increased in the proximal segments of the severe CAN subjects consistent with regional "hyperinnervation." These regions also exhibit abnormal blood flow regulation. Impaired myocardial MIBG uptake correlates with altered LV diastolic filling and myocardial electrophysiological deficits and is predictive of sudden death. Scintigraphic studies have provided unique insights into the effects of diabetes on cardiac sympathetic integrity and the pathophysiological consequences of LV sympathetic dysinnervation. Future studies using complementary neurotransmitter analogues will allow different aspects of regional dysfunction to be characterized with the aim of developing therapeutic strategies to prevent or reverse CAN.

Long-term effect of acetyl-L-carnitine on myocardial 123I-MIBG uptake in patients with diabetes

Carnitine derivatives may have beneficial effects on cardiac and nerve function in patients with diabetes. The aim of this study was to investigate the effect of acetyl-L-carnitine (ALC) on myocardial sympathetic nervous function as measured with 123I-meta-iodobenzyl guanidine (MIBG) and single-photon emission tomography (SPET) in 19 patients with diabetes (placebo group, n = 6; ALC group, n = 13) at the beginning and at the end of a 1-year randomized, placebo-controlled, double-blind trial. The coefficient of variation for the MIBG analysis was 4%. In patients who were given a placebo, global myocardial MIBG uptake deteriorated during the study (MIBG uptake 1-year follow-up/baseline, 0.86 +/- 0.05, mean +/- standard error of mean), whereas in patients treated with ALC, MIBG uptake did not change significantly (1-year follow-up/baseline, 1.07 +/- 0.08; p = 0.03 between the groups). On the basis of these preliminary data, we conclude that long-term treatment with ALC may be of potential value in preventing the progressive loss of myocardial sympathetic nervous function in patients with diabetes. MIBG-SPET is a sensitive and thus valuable method in assessing the development of myocardial sympathetic nervous dysfunction.