QT interval prolongation in type 2 (non-insulin-dependent) diabetic patients with cardiac autonomic neuropathy

Advanced glycation end products modulate electrophysiological remodeling of right ventricular outflow tract cardiomyocytes: A novel target for diabetes-related ventricular arrhythmogenesis

Diabetes mellitus is associated with cardiovascular disease and cardiac arrhythmia. Accumulation of advanced glycation end products closely correlates with cardiovascular complications through mitochondrial dysfunction or oxidative stress and evoke proliferative, inflammatory, and fibrotic reactions, which might impair cardiac electrophysiological characteristics and increase the incidence of cardiac arrhythmia. This study examined the mechanisms how advanced glycation end products may contribute to arrhythmogenesis of right ventricular outflow tract-a unique arrhythmogenic substrate. A whole-cell patch clamp, conventional electrophysiological study, fluorescence imaging, Western blot, and confocal microscope were used to study the electrical activity, and Ca2+ homeostasis or signaling in isolated right ventricular outflow tract myocytes with and without advanced glycation end products (100 μg/ml). The advanced glycation end products treated right ventricular outflow tract myocytes had a similar action potential duration as the controls, but exhibited a lower L-type Ca2+ current, higher late sodium current and transient outward current. Moreover, the advanced glycation end products treated right ventricular outflow tract myocytes had more intracellular Na+ , reverse mode Na+ -Ca2+ exchanger currents, intracellular and mitochondrial reactive oxygen species, and less intracellular Ca2+ transient and sarcoplasmic reticulum Ca2+ content with upregulated calcium homeostasis proteins and advanced glycation end products related signaling pathway proteins. In conclusions, advanced glycation end products modulate right ventricular outflow tract electrophysiological characteristics with larger late sodium current, intracellular Na+ , reverse mode Na+ -Ca2+ exchanger currents, and disturbed Ca2+ homeostasis through increased oxidative stress mediated by the activation of the advanced glycation end products signaling pathway.

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

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

Diabetes and Arrhythmias: Pathophysiology, Mechanisms and Therapeutic Outcomes

The prevalence of diabetes is rapidly increasing and closely associated with cardiovascular morbidity and mortality. While the major cardiovascular complication associated with diabetes is coronary artery disease, it is becoming increasingly apparent that diabetes impacts the electrical conduction system in the heart, resulting in atrial fibrillation, and ventricular arrhythmias. The relationship between diabetes and arrhythmias is complex and multifactorial including autonomic dysfunction, atrial and ventricular remodeling and molecular alterations. This review will provide a comprehensive overview of the link between diabetes and arrhythmias with insight into the common molecular mechanisms, structural alterations and therapeutic outcomes.

Leptin decreases heart rate associated with increased ventricular repolarization via its receptor

Leptin has been proposed to modulate cardiac electrical properties via β-adrenergic receptor activation. The presence of leptin receptors and adipocytes in myocardium raised a question as to whether leptin can directly modulate cardiac electrical properties such as heart rate and QT interval via its receptor. In this work, the role of local direct actions of leptin on heart rate and ventricular repolarization was investigated. We identified the protein expression of leptin receptors at cell surface of sinus node, atrial, and ventricular myocytes isolated from rat heart. Leptin at low doses (0.1-30 μg/kg) decreased resting heart rate; at high doses (150-300 μg/kg), leptin induced a biphasic effect (decrease and then increase) on heart rate. In the presence of high-dose propranolol (30 mg/kg), high-dose leptin only reduced heart rate and sometimes caused sinus pauses and ventricular tachycardia. The leptin-induced inhibition of resting heart rate was fully reversed by leptin antagonist. Leptin also increased heart rate-corrected QT interval (QTc), and leptin antagonist did not. In isolated ventricular myocytes, leptin (0.03-0.3 μg/ml) reversibly increased the action potential duration. These results supported our hypothesis that in addition to indirect pathway via sympathetic tone, leptin can directly decrease heart rate and increase QT interval via its receptor independent of β-adrenergic receptor stimulation. During inhibition of β-adrenergic receptor activity, high concentration of leptin in myocardium can cause deep bradycardia, prolonged QT interval, and ventricular arrhythmias.

Use of QT intervals for a more accurate diagnose of syncope and evaluation of syncope severity

BACKGROUND

This study aimed to evaluate the use of QT intervals, their diagnostic predictive value in patients with syncope and their relationship with syncope severity.

METHODS

One hundred and forty nine patients with a diagnosis of syncope were admitted to Internal Medicine departments at the University of Palermo, Italy, between 2006 and 2012, and 140 control subjects hospitalised for other causes were enrolled. QT maximum, QT minimum, QTpeak, QT corrected, QT dispersion and Tpeak-to-Tend interval were compared between two groups. The paper medical records were used for scoring with San Francisco Syncope Rule (SFSR), Evaluation of Guidelines in SYncope Study (EGSYS) score and Osservatorio Epidemiologico sulla Sincope nel Lazio (OESIL) risk score.

RESULTS

Mean QTc (p < 0.0005), mean QTmax (p < 0.0005), mean QTdisp (p < 0.0005), mean QTpeak (p = 0.005) and mean TpTe (p = 0.018) were significantly longer in patients with syncope compared with control subjects. A QTc > 424.8 ms (sensibility: 81.88 - specificity: 57.86) showed the greatest predictive value for diagnosis of syncope. On the EGSYS score and on the OESIL score, QTc was significantly prolonged in high-risk patients compared with low-risk patients. On the San Francisco Syncope Rule, QTc and QTdisp were significantly prolonged in high-risk patients compared with low-risk patients.

CONCLUSION

Mean QTc, mean QTdisp, mean TpTe, mean QTmax and mean QTpeak were significantly longer in patients with syncope compared with control subjects. Furthermore, prolonged QTc and QTdisp were associated with major severe syncope according to San Francisco Syncope Rule, EGSYS and OESIL risk scores.

Cardiac autonomic neuropathy in diabetes mellitus: prevalence, risk factors and utility of corrected QT interval in the ECG for its diagnosis

OBJECTIVES

To study the prevalence and risk factors for cardiac autonomic neuropathy (CAN) and the utility of prolongation of corrected QT interval (QTc) in the ECG to diagnose CAN in patients with diabetes mellitus.

DESIGN AND SETTING

Cross-sectional study conducted among patients attending the diabetic clinic of a teaching hospital.

METHODS

The prevalence of CAN among 100 patients with type 1 and type 2 diabetes mellitus was assessed by the five autonomic function tests by Eving's methodology. The CAN score in each patient and its relationship to the QTc interval were analysed. Possible influences of age, duration of diabetes and coexistent peripheral neuropathy on the occurrence of CAN also were studied.

RESULTS

The prevalence of CAN was 60%. Univariate analysis showed a significant association between CAN and higher age (odds ratio (OR) 15.75), prolongation of QTc (OR 5.55), duration of disease over 10 years (OR 2) and peripheral neuropathy (p<0.001) in patients with type 1 diabetes. Significant risks for CAN among patients with type 2 diabetes were coexistent peripheral neuropathy (OR 14), prolonged QTc (OR 9.75), higher age (OR 7.2) and disease duration over 10 years (OR 1.92) in univariate analysis, but none of them showed independent risk in multivariate analysis. Disease duration over 10 years resulted in QTc prolongation in a significant numbers of cases with type 1 (p<0.001) and type 2 (p = 0.006) diabetes. The sensitivity, specificity and positive predictive value of QTc prolongation for the diagnosis of CAN were 77%, 62.5% and 77% in type 1 and 76.5%, 75% and 81.3% in type 2, respectively. Higher CAN scores correlated with longer QTc intervals (coefficient of correlation 0.73; p<0.001).

CONCLUSIONS

The prevalence of CAN in diabetes mellitus is high. Higher age, longer duration of diabetes and peripheral neuropathy are significant risk factors. QTc interval in the ECG can be used to diagnose CAN with reasonable sensitivity, specificity and positive predictive value.

Physical consequences of schizophrenia and its treatment: the metabolic syndrome

Schizophrenia is a life shortening illness. Unnatural causes and natural causes are put forward as reasons for this excess mortality. In terms of the latter, a host of different physical disorders occur with increased frequency in schizophrenia. When taken together, some of these illnesses such as type 2 diabetes mellitus and cardiovascular disorders constitute the Metabolic Syndrome; a characteristic phenotype of those with this syndrome is excessive visceral fat distribution. The exact reasons why this particular syndrome occurs in schizophrenia is as yet unclear though factors such as life style, poor diet and lack of exercise may contribute to it's development. Alternatively, overactivity of the hypothalamic-pituitary-adrenal axis leading to hypercortisolaemia can also result in excessive visceral fat accumulation. This minireview aims to explore the potential role of these issues and medication in terms of the increased morbidity and mortality observed in schizophrenia.

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

OBJECTIVE

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

DESIGN

Cross-sectional population-based cohort.

SETTING

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

SUBJECTS

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

MAIN OUTCOMES MEASURES

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

RESULTS

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

CONCLUSIONS

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

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

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

QT dispersion in uncomplicated human obesity

OBJECTIVE

Because obese patients generally may be prone to ventricular arrhythmias, this study was designed to measure the interval between Q- and T-waves of the electrocardiogram (QT) interval dispersion (QTD) in uncomplicated overweight and obese patients. QTD is an electrocardiographic parameter whose prolongation is thought to be predictive of the possibility of sudden death caused by ventricular arrhythmias. To better evaluate the association between obesity per se and QTD, the study population was intentionally selected because they were free of complications.

RESEARCH METHODS AND PROCEDURES

QTD (defined as the difference between the maximum and the minimum QT corrected interval [QTc] across the 12-lead electrocardiogram) was measured manually in 54 obese patients (Group A: mean body mass index [BMI] of 38.1 +/- 0.9 kg/m2 [SEM], 15 males and 39 females), 35 overweight patients (Group B: mean BMI of 27.3 +/- 0.2 kg/m2, 10 males and 25 females), and 57 normal weight healthy control subjects (Group C: mean BMI of 21.9 +/- 0.2 kg/m2, 17 males and 40 females). The obese and overweight patients had no heart disease, hypertension, diabetes, or impaired glucose tolerance and did not have any hormonal, hepatic, renal or electrolyte disorders. The study subjects were matched in terms of age (mean age 38.4 +/- 1.2 years) and sex.

RESULTS

The QTDs were comparable among the three groups: Group A, 56.4 +/- 2.6 ms; Group B, 56.7 +/- 2.1 ms; and Group C, 59.4 +/- 2.1 ms; not significant. The QTc intervals of Group A and Group B were similar to that of Group C (411.8 +/- 3.3, 407.2 +/- 3.9, and 410.3 +/- 3.9 ms, respectively [not significant]) and did not correlate with BMI. An association was found between QTD and QTc (r = 0.24, p < 0.005). Using multivariate stepwise regression analysis of the study population, QTD did not correlate with age, BMI, waist circumference, or abdominal sagittal diameter.

DISCUSSION

These data suggest that QTD in uncomplicated obese or overweight subjects is comparable with that in age- and sex-matched normal weight healthy controls. In this study population, no association was found between QTD and anthropometric parameters reflecting body fat distribution.

The relationship of plasma glucose and electrocardiographic parameters in elderly women with different degrees of glucose tolerance

Plasma glucose has been regarded as a risk factor for macrovascular complications in diabetes, but less is known about its role in the development of cardiac impairment other than coronary heart disease (CHD). The aim of our study was to determine the relationship between basal and post-OGTT (Oral Glucose Tolerance Test) plasma glucose levels and some ECG parameters in a group of elderly women with normal or impaired glucose tolerance (IGT). One-hundred and one women with normal fasting glucose (<6.0 mmol/L) and no familial history or clinical signs of CHD and diabetes underwent an OGTT and a resting ECG. Based on the degree of glucose tolerance, we identified 24 women with a diagnostic OGTT for either IGT or diabetes; the 77 women (age range 52-88 years) with normal glucose tolerance were further divided into two groups according to their post-OGTT area under the curve (AUCG): below and above the median value (32 and 45 women, respectively). Basal plasma glucose and insulin levels, as well as lipid profile and percent of hypertensive patients were similar in the three groups. Mean corrected QT (QTc) was prolonged as a function of progressive worsening of glucose tolerance even after adjustment for possible confounding factors (p=0.03). A similar relationship was apparent when post-OGTT plasma glucose peak (GP) was considered. In a multiple regression analysis, AUCG and GP were the only factors independently related to both QTc and Sokolow index. Our observations suggest that, even in the presence of a normal glucose tolerance, plasma glucose concentrations during an OGTT are associated with peculiar ECG signs potentially combined with an increased risk of sudden death, arrhythmias, or cardiovascular mortality.

QT interval and mortality from coronary artery disease

Abnormalities in the QT interval can be divided into 3 types, prolongation of the QT interval, increases in the dispersion of the QT interval, and abnormalities in the heart rate dependent behavior of the QT interval. Abnormalities may be found in short or long-term recordings. Prolongation of the QT interval may reflect factors associated with an adverse prognosis in coronary disease and may in itself be arrhythmogenic. The data to date suggest that there is an association between adverse prognosis and QT interval prolongation in coronary disease, both before and after acute myocardial infarctions. This relationship is weak, however, and is not clinically useful. The data as to whether increased QT dispersion postmyocardial infarction relates to adverse prognosis is weak because there is no convincing evidence yet. If there is a relationship it is weak. Abnormalities in the rate dependent behavior of the QT interval are widely found, but as no large scale prospective study with mortality as an endpoint has yet been undertaken the significance of rate dependent abnormalities is uncertain. The widespread introduction of beat-to-beat QT analysis of 24 hour Holter tapes may take QT intervalology into the realm of clinical practice.

QTc interval, and autonomic and somatic nerve function in diabetic neuropathy

QTc intervals were measured using an electrocardiogram and other autonomic function tests, in 66 neuropathy patients with non-insulin-dependent diabetes mellitus (59.0 +/- 12.5 years; mean +/- SD). The change in R-R interval did not influence the QTc interval, as calculated by the equation: QTc = QT + (1000 - R-R)/7 (ms), compared with the conventional Bazett's equation which appeared to overcompensate in the case of a small R-R interval. The QTc interval in the diabetic patients was significantly longer than that in age-matched controls. The QTc interval showed an inverse correlation with the coefficient of variation of the R-R interval and skin blood flow at rest. However, no correlation was found between QTc interval and blood pressure change, change in heart rate on standing, or results of the sympathetic skin response. The QTc interval did not correlate significantly with motor or sensory nerve conduction parameters. We conclude that the QTc interval can be a simple and useful autonomic indicator for diabetic neuropathy relatively independent of other abnormalities of autonomic and somatic nervous system function.

Use of corrected QT interval in autonomic function testing: assessment of reproducibility

QT interval duration is influenced by the autonomic nervous system and has been proposed as an additional tool in the diagnosis of diabetic autonomic neuropathy. The study aimed to assess in normal subjects the reproducibility of QT interval duration compared with that of cardiovascular tests commonly used to explore the function of the autonomic nervous system. Fifty-nine healthy subjects (31 males, 28 females; mean age 35.1 +/- 17.7 years) performed five cardiovascular tests: deep breathing test (DBT), lying to standing test (LST), Valsalva manoeuvre (VM), postural blood pressure test (PBPT) and cough test (CT). QT interval duration was measured on an electrocardiogram (ECG) registered after a 15-min rest in the supine position. Corrected QT interval (QTc) was calculated according to Bazett's formula. The QTc interval duration for each subject was expressed as the mean of the QTc calculated by two observers. Each subject was submitted to the cardiovascular test battery and the ECG twice in 1 week. The coefficient of variation (CV) was calculated to assess the reproducibility. The observed CV values were as follows: DBT 15.8%, LST 8.0%, VM 9.5%, CT 7.2%, PBPT 176%, QTc 3.4%. Our data confirm the reproducibility of heart rate cardiovascular tests: the QTc interval is a reproducible, easily measurable parameter, which has the advantage of not requiring patient cooperation.

Diabetic foot: a frequently misdiagnosed pathology. A survey on 185 cases

Authors refer to the increasing significance of complications of diabetes mellitus. The most important of them is the diabetic osteoarthropathy of the foot which is often misdiagnosed in general practice. Authors report on 185 cases of diabetic foot treated at their department. iii of them were males and 74 females. Total number of admissions was 258 which means that some patients were repeatedly admitted. In 77 cases amputation was performed. Authors preferred the Burgess technique for below-knee amputation. Minor operations (amputations of digits, resections of metatarsal bones, etc.) were done in 125 cases. Total number of operations was 202. Authors refer to the limited results of conservative treatment. The 2.1 percentage mortality rate was due to the selection of patients suitable for rehabilitation.

Does abnormal QT interval prolongation reflect autonomic dysfunction in diabetic patients? QTc interval measure versus standardized tests in diabetic autonomic neuropathy

The question as to whether the QTc interval correlates with five cardiovascular tests (deep breathing test, 30/15 ratio test, lying to standing test, cough test, and postural blood pressure test) for the diagnosis of diabetic autonomic neuropathy (DAN) was investigated in 168 (38 Type 1, 130 Type 2) consecutive outpatients (mean age 54.9 +/- 11.2 years). QT interval was measured on an ECG recorded at rest and QTc calculated according to Bazett's formula. The percentage of patients with a QTc greater than 0.440 s was: absent DAN = 11% (n = 7), probable DAN = 7% (n = 4), definite DAN = 23% (n = 12) (p < 0.05), and the mean (+/- SD) QTc values were 0.403 +/- 0.028 s, 0.405 +/- 0.023 s, and 0.421 +/- 0.026 s, respectively. A significant correlation between QTc duration and DAN score of autonomic cardiovascular test results (r = 0.34, p < 0.0001) was observed. The calculated specificity, sensitivity, positive and negative predictive values were 89%, 15%, 70% and 37%, respectively. In conclusion, QTc can be considered as an additional specific test in the assessment of diabetic autonomic neuropathy, but cannot replace the standard battery of cardiovascular tests.

Prevalence of QT prolongation in a type 1 diabetic population and its association with autonomic neuropathy. The Neuropathy Study Group of the Italian Society for the Study of Diabetes

The prevalence of QT prolongation in a large random sample of Type 1 diabetic patients in Piemonte, Italy and its association with autonomic neuropathy were assessed. Three hundred and seventy-nine Type 1 diabetic patients (age 15-59) with (94, DAN+) and without (280, DAN-) autonomic neuropathy and 118 non-diabetic control subjects participated in the study. QT interval was measured on an ECG recorded at rest and QTc calculated according to Bazett's formula. QTc was greater than 0.440 s in 7.6% (95% CI 2.9-12.3) of control subjects, 25.6% (21.0-30.0) of diabetic patients, 30.8% (21.5-40.1) of DAN+, 23.9% (18.9-28.9) of DAN-. QTc was greater than 0.460 s (mean + 2SD of QTc in control subjects) in 11.7% (8.5-14.9) of diabetic patients, 18.1% (10.3-25.9) of DAN+, 9.6% (6.2-13.0) of DAN-. QT was above the 95% upper limit for the control subjects in the plot of measured QT against RR interval in 21.4% (17.3-25.5) of diabetic patients, 26.6% (17.7-35.5) of DAN+, 19.3% (14.7-23.9) of DAN-. No correlation was found between QT interval and age or disease duration. The prevalence of QT prolongation was higher in diabetic patients than in control subjects and in DAN+ than in DAN-.

Abnormalities of the corrected QT interval in familial dysautonomia: an indicator of autonomic dysfunction

We report abnormalities in corrected QT intervals with changes in position and after exercise in patients with familial dysautonomia and confirm the previously reported finding of abnormal heart rate and blood pressure responses. Prolonged corrected QT intervals (> 440 msec) with lack of appropriate shortening with exercise is a noninvasive means of demonstrating an aberration in autonomic regulation of cardiac conduction.