Marked abnormalities in heart rate variability are associated with progressive deterioration of renal function in type I diabetic patients with overt nephropathy

Intra-Individual Relationship between Heart Rate Variability and the Underlying Heart Rate in Children and Adolescents

Background/Objective: The relationship between heart rate and heart rate variability (HRV) indices has been repeatedly studied in adults but limited data are available on the relationship in paediatric populations. Methods: Continuous 12-lead electrocardiograms were recorded in 1016 healthy children and adolescents (534 females) aged 4 to 19 years during postural manoeuvres with rapid changes between 10-min positions of supine → sitting → standing → supine → standing → sitting → supine. In each position, the averaged RR interval was measured together with four HRV indices, namely the SDNN, RMSSD, quasi-normalised high-frequency components (qnHF), and the proportions of low- and high-frequency components (LF/HF). In each subject, the slope of the linear regression between the repeated HRV measurements and the corresponding RR interval averages was calculated. Results: The intra-subject regression slopes, including their confidence intervals, were related to the age and sex of the subjects. The SDNN/RR, RMSSD/RR, and qnHF/RR slopes were significantly steeper (p < 0.001) and the (LF/HF)/RR slopes were significantly shallower (p < 0.001) in younger children compared to older children and adolescents. Conclusions: The study suggests that sympathetic and vagal influences on heart rate are present in both younger and older children. With advancing age, the sympatho-vagal balance gradually develops and allows the vagal control to suppress the sympathetic drive towards higher heart rates seen in younger age children.

The Role of Heart Rate Variability (HRV) in Different Hypertensive Syndromes

Cardiac innervation by the parasympathetic nervous system (PNS) and the sympathetic nervous system (SNS) modulates the heart rate (HR) (chronotropic activity) and the contraction of the cardiac muscle (inotropic activity). The peripheral vasculature is controlled only by the SNS, which is responsible for peripheral vascular resistance. This also mediates the baroreceptor reflex (BR), which in turn mediates blood pressure (BP). Hypertension (HTN) and the autonomic nervous system (ANS) are closely related, such that derangements can lead to vasomotor impairments and several comorbidities, including obesity, hypertension, resistant hypertension, and chronic kidney disease. Autonomic dysfunction is also associated with functional and structural changes in target organs (heart, brain, kidneys, and blood vessels), increasing cardiovascular risk. Heart rate variability (HRV) is a method of assessing cardiac autonomic modulation. This tool has been used for clinical evaluation and to address the effect of therapeutic interventions. The present review aims (a) to approach the heart rate (HR) as a CV risk factor in hypertensive patients; (b) to analyze the heart rate variability (HRV) as a "tool" to estimate the individual risk stratum for Pre-HTN (P-HTN), Controlled-HTN (C-HTN), Resistant and Refractory HTN (R-HTN and Rf-HTN, respectively), and hypertensive patients with chronic renal disease (HTN+CKD).

The Diabetic Cardiorenal Nexus

The end-stage of the clinical combination of heart failure and kidney disease has become known as cardiorenal syndrome. Adverse consequences related to diabetes, hyperlipidemia, obesity, hypertension and renal impairment on cardiovascular function, morbidity and mortality are well known. Guidelines for the treatment of these risk factors have led to the improved prognosis of patients with coronary artery disease and reduced ejection fraction. Heart failure hospital admissions and readmission often occur, however, in the presence of metabolic, renal dysfunction and relatively preserved systolic function. In this domain, few advances have been described. Diabetes, kidney and cardiac dysfunction act synergistically to magnify healthcare costs. Current therapy relies on improving hemodynamic factors destructive to both the heart and kidney. We consider that additional hemodynamic solutions may be limited without the use of animal models focusing on the cardiomyocyte, nephron and extracellular matrices. We review herein potential common pathophysiologic targets for treatment to prevent and ameliorate this syndrome.

Cardiovascular autonomic neuropathy and incident diabetic kidney disease in patients with type 2 diabetes

AIMS

We investigated the association between cardiovascular autonomic neuropathy (CAN) and incident diabetic kidney disease (DKD).

METHODS

This retrospective longitudinal study included 2,033 patients with type 2 diabetes (mean age 57.2 years, 57.4% male, and median diabetes duration 8.0 years), free of renal dysfunction or cardiovascular disease at initiation. Cardiovascular autonomic reflex tests were performed once at baseline, and CAN was defined as ≥ 2 abnormal parasympathetic test results. Urine ACR and eGFR were concurrently measured at baseline and every 3-6 months thereafter. Incident DKD was defined as the development of ACR ≥ 30 mg/g at two or more follow-up examinations or eGFR < 60 ml/min/1.73 m² with ≥ 25% decrease from baseline.

RESULTS

During a median follow-up of 2.9 years (1.1 - 4.8), 290 (14.3%) patients developed DKD, comprising 79.7% (N = 231) cases of new-onset albuminuria alone, 14.5% (N = 42) cases of eGFR decline alone, and 5.8% (N = 17) cases of both. Compared to those without CAN, patients with CAN had a significantly higher risk of incident DKD in a multivariable Cox regression model (HR 1.56, 95% CI 1.15 - 2.12; P = 0.005).

CONCLUSION

CAN is may be a useful marker for long-term complications including DKD in patients with type 2 diabetes. Monitoring of CAN helps to identify high risk patients of future renal impairment.

Prevalence and Diagnosis of Diabetic Cardiovascular Autonomic Neuropathy in Beijing, China: A Retrospective Multicenter Clinical Study

Cardiovascular autonomic neuropathy (CAN) is a debilitating condition occurring among diabetic patients especially those with long duration of disease. Whereas incidences and treatment of CAN has been well described for Western populations, fewer studies have been conducted among the Chinese. This study, therefore, aimed to assess the prevalence of CAN among sampled Chinese diabetic patients. Accordingly, 2,048 participants with a history of type 1 diabetes mellitus (T1DM, 73) and type 2 diabetes mellitus (T2DM, 1975) were randomly sampled from 13 hospitals. Patients’ biodata were recorded, and autonomic nervous system function tests performed to aid in the preliminary diagnosis of CAN. The final CAN diagnosis was based on the Ewing’s test in which heart rate variation (HRV) values were evaluated through deep-breathing (DB), lying-to-standing (LS), and Valsalva (V) tests. Systolic blood pressure (SBP) variation values were also evaluated through LS. In the T1DM group, 61.6% patients were diagnosed with CAN and no differences were observed in the baseline and clinical data between this group and those without CAN (P > 0.05). In the T2DM group, 62.6% patients were diagnosed with CAN and statistically significant differences were found between the CAN and non- CAN group with regards to age, duration of diabetes, metformin treatment, retinopathy, and hypertension history (P < 0.05). The most common manifestations of CAN included weakness (28.6%), dizziness (23.4%), frequent urination (19.6%), upper body sweating (18.3%), and nocturia (15.9%). Additionally, duration of disease and age were independent risk factors for CAN in T1DM and T2DM, respectively. On diagnosis, a combination of the V test + LS test provided the highest sensitivity of detecting CAN among T1DM group (sensitivity = 97.6%, AUC = 0.887) while for T2DM category, DB test had the highest sensitivity (83.6%), and maximal AUC (0.856) was found with V test + DB test. The overall prevalence of diabetes with CAN in the study was up to 63%.

Update on the Impact, Diagnosis and Management of Cardiovascular Autonomic Neuropathy in Diabetes: What Is Defined, What Is New, and What Is Unmet

The burden of diabetic cardiovascular autonomic neuropathy (CAN) is expected to increase due to the diabetes epidemic and its early and widespread appearance. CAN has a definite prognostic role for mortality and cardiovascular morbidity. Putative mechanisms for this are tachycardia, QT interval prolongation, orthostatic hypotension, reverse dipping, and impaired heart rate variability, while emerging mechanisms like inflammation support the pervasiveness of autonomic dysfunction. Efforts to overcome CAN under-diagnosis are on the table: by promoting screening for symptoms and signs; by simplifying cardiovascular reflex tests; and by selecting the candidates for screening. CAN assessment allows for treatment of its manifestations, cardiovascular risk stratification, and tailoring therapeutic targets. Risk factors for CAN are mainly glycaemic control in type 1 diabetes mellitus (T1DM) and, in addition, hypertension, dyslipidaemia, and obesity in type 2 diabetes mellitus (T2DM), while preliminary data regard glycaemic variability, vitamin B12 and D changes, oxidative stress, inflammation, and genetic biomarkers. Glycaemic control prevents CAN in T1DM, whereas multifactorial intervention might be effective in T2DM. Lifestyle intervention improves autonomic function mostly in pre-diabetes. While there is no conclusive evidence for a disease-modifying therapy, treatment of CAN manifestations is available. The modulation of autonomic function by SGLT2i represents a promising research field with possible clinical relevance.

Heart Rate Variability and Its Relation to Chronic Kidney Disease: Results From the PREVEND Study

OBJECTIVE

In the general population, reduced heart rate variability (HRV) has been associated with cardiovascular disease. However, its relation to chronic kidney disease (CKD) is debated. We therefore investigated the relation between low HRV and renal outcomes.

METHODS

In the population-based Prevention of REnal and Vascular ENdstage Disease study, renal outcomes (CKD, estimated glomerular filtration rate [eGFR], urinary albumin) were measured at baseline and three consecutive examinations. HRV measures (among which SDNN [standard deviation of normal-to-normal RR intervals]) were calculated from time series of beat-to-beat pulse wave recordings at baseline. The lowest (risk) quartile was compared with the upper three quartiles combined, in multivariable survival and linear mixed-effects analyses.

RESULTS

In 4605 participants (49% males, age range = 33-80, 0.6% blacks), we observed 341 new participants of CKD during a median follow-up duration of 7.4 years. Low SDNN was associated with higher incidence of CKD (crude HR = 1.66, 95% CI = 1.30 to 2.12, p < .001), but this association was no longer significant after adjustment for age, sex, and cardiovascular risk factors (adjusted HR = 1.13, 95% CI = 0.86 to 1.48, p = .40, similar for other HRV measures). No associations between SDNN and eGFR trajectories were found in the total sample. However, in a subgroup of participants with baseline CKD (n = 939), we found a significant association of low SDNN (but not other HRV measures) with lower baseline eGFR, even after multivariable adjustment (adjusted βlevel difference = -3.73 ml/min/1.73 m, 95% CI = -6.70 to -0.75, p = .014), but not with steeper eGFR decline.

CONCLUSIONS

These results suggest that reduced HRV may be a complication of CKD rather than a causal factor.

Predictors of Cardiovascular Autonomic Neuropathy Onset and Progression in a Cohort of Type 1 Diabetic Patients

AIM

The prevalence of cardiovascular autonomic neuropathy (CAN) in diabetes mellitus is well documented. However, the rate and predictors of both the development and progression of CAN have been less studied. Hereby, we assessed the rate and the major risk factors for CAN initiation and progression in a cohort of type 1 diabetic patients followed over a three-year period.

METHODS

175 type 1 diabetic patients (mean age: 50 ± 11 years; female/male: 76/99) with positive bedside screening for CAN were included and underwent 2 standardized autonomic testings using 4 standardized tests (deep breathing, Valsalva maneuver, 30/15 ratio, and changes in blood pressure during standing), separated by 3 ± 1 years. CAN staging was achieved according to the Toronto Consensus Panel on Diabetic Autonomic Neuropathy into 4 categories: absent, possible, confirmed, or severe CAN.

RESULTS

Out of the 175 patients included, 31.4% were free of CAN, 34.2% had possible CAN, 24.6% had confirmed CAN, and 9.7% exhibited severe CAN at the first assessment. Among the 103 patients with nonsevere CAN at inclusion, forty-one (39.8%) had an increase of at least one category when reassessed and 62 (60.2%) remained stable. A bivariate analysis indicated that only BMI and exposure to selective serotonin reuptake inhibitors (SSRIs) were significantly different in both groups. A multivariate analysis indicated that lower BMI (OR: 0.15, CI 95%: 0.05-0.48, p = 0.003) and SSRI exposure (OR: 4.18, CI 95%: 1.03-16.97, p = 0.04) were the sole predictors of CAN deterioration. In the 55 patients negative for CAN at the first laboratory assessment, 12 became positive at the second assessment.

CONCLUSION

No clear predictive factor for CAN onset was identified. However, once present, CAN progression was related to low BMI and SSRI exposure.

Heart Rate Variability in Patients with Acute Ischemic Stroke at Different Stages of Renal Dysfunction: A Cross-sectional Observational Study

Background:

Renal function is associated with mortality and functional disabilities in stroke patients, and impaired autonomic function is common in stroke, but little is known regarding its effects on stroke patients with renal dysfunction. This study sought to evaluate the association between autonomic function and stroke in patients with renal dysfunction.

Methods:

This study comprised 232 patients with acute ischemic stroke consecutively enrolled from February 2013 to November 2014 at Guangdong Provincial Hospital of Chinese Medicine in China. All patients recruited underwent laboratory evaluation and 24 h Holter electrocardiography (ECG). Autonomic function was measured based on the heart rate variability (HRV) using 24 h Holter ECG. Renal damage was assessed through the estimated glomerular filtration rate (eGFR), and stroke severity was rated according to the National Institutes of Health Stroke Scale (NIHSS). The Barthel index and modified Rankin score were also determined following admission. All the clinical covariates that could potentially affect autonomic outcome variables were adjusted with linear regression.

Results:

In the patients with a mild or moderate decreased eGFR, the values for the standard deviation of the averaged normal-to-normal RR interval (SDANN) index (P = 0.022), very low frequency (VLF) (P = 0.043), low frequency (LF) (P = 0.023), and ratio of low-to-high frequency power (LF/HF) (P = 0.001) were significantly lower than those in the patients with a normal eGFR. A multinomial linear regression indicated that eGFR (t = 2.47, P = 0.014), gender (t = −3.60, P < 0.001), and a history of hypertension (t = −2.65, P = 0.008) were the risk factors of LF/HF; the NIHSS score (SDANN index: t = −3.83, P < 0.001; VLF: t = −3.07, P = 0.002; LF: t = −2.79, P = 0.006) and a history of diabetes (SDANN index: t = −3.58, P < 0.001; VLF: t = −2.54, P = 0.012; LF: t = −2.87, P = 0.004) were independent factors for the SDANN index, VLF, and LF; the Oxfordshire Community Stroke Project (t = −2.38, P = 0.018) was related to the SDANN index.

Conclusions:

Autonomic dysfunction is aggravated with the progression of eGFR stage in patients with acute ischemic stroke; the eGFR is an independent factor of LF/HF in the adjusted models. Stroke severity and a history of diabetes are more significantly associated with HRV in patients with acute ischemic stroke at different stages of renal dysfunction.

Oxidative stress is associated with decreased heart rate variability in patients with chronic kidney disease

OBJECTIVES

Elevated oxidative stress and reduced heart rate variability (HRV) is prevalent in patients with chronic kidney disease (CKD) and is associated with increased morbidity and mortality. Previous studies have identified a positive association between elevated oxidative stress and autonomic dysfunction, however this relationship has not yet been investigated in the CKD population.

METHODS

Plasma was collected from 78 patients with stage 3-4 CKD (estimated glomerular filtration rate 25-60 ml/min/1.73 m²) for the assessment of oxidative stress, including plasma total F2-isoprostanes, glutathione peroxidase activity and total antioxidant capacity. Time and frequency HRV parameters were measured from a three lead electrocardiogram.

RESULTS

Participants with elevated F2-isoprostanes had reduced HRV compared to patients with normal levels of F2-isoprostanes. A number of HRV parameters were found to be inversely correlated with F2-isoprostanes in all CKD patients, including SDNN (r = -0.337; P < 0.01), VLF (r = -0.281, P = 0.01), LF (r = -0.315, P < 0.01) and total power (r = -0.288, P = 0.01). Multiple linear regression found F2-isoprostanes to be an independent predictor of SDNN (r² = 0.287, β = -0.272, P = 0.01).

DISCUSSION

Oxidative stress is significantly and independently associated with HRV in patients with CKD. Identifying oxidative stress in the pathogenesis of autonomic dysfunction may help target therapeutic strategies.

Complexity and time asymmetry of heart rate variability are altered in acute mental stress

We aimed to study the complexity and time asymmetry of short-term heart rate variability (HRV) as an index of complex neurocardiac control in response to stress using symbolic dynamics and time irreversibility methods. ECG was recorded at rest and during and after two stressors (Stroop, arithmetic test) in 70 healthy students. Symbolic dynamics parameters (NUPI, NCI, 0V%, 1V%, 2LV%, 2UV%), and time irreversibility indices (P%, G%, E) were evaluated. Additionally, HRV magnitude was quantified by linear parameters: spectral powers in low (LF) and high frequency (HF) bands. Our results showed a reduction of HRV complexity in stress (lower NUPI with both stressors, lower NCI with Stroop). Pattern classification analysis revealed significantly higher 0V% and lower 2LV% with both stressors, indicating a shift in sympathovagal balance, and significantly higher 1V% and lower 2UV% with Stroop. An unexpected result was found in time irreversibility: significantly lower G% and E with both stressors, P% index significantly declined only with arithmetic test. Linear HRV analysis confirmed vagal withdrawal (lower HF) with both stressors; LF significantly increased with Stroop and decreased with arithmetic test. Correlation analysis revealed no significant associations between symbolic dynamics and time irreversibility. Concluding, symbolic dynamics and time irreversibility could provide independent information related to alterations of neurocardiac control integrity in stress-related disease.

Heart rate variability is a predictor of mortality in chronic kidney disease: a report from the CRIC Study

BACKGROUND/AIMS

Low heart rate variability (HRV) is a risk factor for adverse outcomes in the general population. We aimed to determine the factors associated with HRV and evaluate the association between low HRV and clinical outcomes in patients with chronic kidney disease (CKD).

METHODS

A 10-second electrocardiogram was obtained at baseline in the Chronic Renal Insufficiency Cohort (CRIC) Study. HRV was measured by the standard deviation of all R-R intervals (SDNN) and the root mean square of successive differences between R-R intervals (RMSSD).

RESULTS

In 3,245 CRIC participants with available baseline SDNN and RMSSD, lower HRV was associated with older age, lack of exercise, heart failure, elevated phosphorus and hemoglobin A1c, and low estimated glomerular filtration rate. After a median follow-up of 4.2 years, in fully adjusted models, lower HRV was not associated with renal [SDNN: hazard rate, HR = 0.96 (95% confidence interval, CI 0.88-1.05); RMSSD: HR = 0.97 (95% CI 0.88-1.07)] or cardiovascular outcomes [SDNN: HR = 1.02 (95% CI 0.92-1.13); RMSSD: HR = 1.00 (95% CI 0.90-1.10)]. There was a nonlinear relationship between RMSSD and all-cause mortality with increased risk with both low and high RMSSD (p = 0.04).

CONCLUSIONS

In a large cohort of patients with CKD, multiple risk factors for renal and cardiovascular diseases were associated with lower HRV. Lower HRV was not associated with increased risk for renal or cardiovascular outcomes, but both low and high RMSSD were associated with increased risk for all-cause mortality. In conclusion, HRV measured by RMSSD may be a novel and independent risk factor for mortality in CKD patients.

Heart rate and blood pressure: any possible implications for management of hypertension?

Hypertension is a common clinical problem and a major risk factor for cardiovascular disease and stroke. Elevated heart rate is associated with elevated blood pressure, increased risk for hypertension, and, among hypertensives, increased risk for cardiovascular disease. Despite these important relationships, heart rate is generally not a major consideration in choosing antihypertensive medications. In part, this is due to a lack of evidence supporting heart rate lowering as a therapeutic strategy in hypertension. Additionally, while there is a positive correlation between heart rate and peripheral blood pressure, there is an inverse relationship between heart rate and central blood pressure. The use of antihypertensive medications, specifically medications that affect heart rate, may not reliably reduce central blood pressure to a similar extent as observed peripherally. We review the relationship between heart rate and peripheral and central blood pressure, with a focus on the implications for chronotropic therapy in hypertension.

Reduced heart rate variability among youth with type 1 diabetes: the SEARCH CVD study

OBJECTIVE

This study compared heart rate variability (HRV) parameters in youth with and without type 1 diabetes and explored potential contributors of altered HRV.

RESEARCH DESIGN AND METHODS

HRV parameters were measured among 354 youth with type 1 diabetes (mean age 18.8 years, diabetes duration 9.8 years, and mean A1C 8.9%) and 176 youth without diabetes (mean age 19.2 years) participating in the SEARCH CVD study. Multiple linear regression was used to assess the relationship between diabetes status and HRV parameters, adjusting for covariates.

RESULTS

Compared with control subjects, youth with type 1 diabetes had reduced overall HRV (10.09 ms lower SD of NN intervals [SDNN]) and markers of parasympathetic loss (13.5 ms reduced root mean square successive difference of NN intervals [RMSSD] and 5.2 normalized units (n.u.) reduced high frequency [HF] power) with sympathetic override (5.2 n.u. increased low frequency [LF] power), independent of demographic, anthropometric, and traditional cardiovascular risk factors. Older age, female sex, higher LDL cholesterol and triglyceride levels, and presence of microalbuminuria were independently associated with lower HRV but did not account for the observed differences between youth with and without diabetes. Youth with type 1 diabetes and A1C levels ≥7.5% had significantly worse HRV parameters than control subjects; however, in youth with optimal glycemic control (A1C <7.5%), HRV parameters did not differ significantly from control subjects.

CONCLUSIONS

Youth with type 1 diabetes have signs of early cardiac autonomic neuropathy: reduced overall HRV and parasympathetic loss with sympathetic override. The main driver of these subclinical abnormalities appears to be hyperglycemia.

Prognostic indicators of cardiovascular risk in renal disease

Although the annual mortality rate for end-stage renal disease (ESRD) is decreasing, likely due to an increase in kidney transplantation rate, the survival probability for ESRD patients from day one of dialysis has not changed, and is still poor with a 5-year survival rate of approximately 34%. This is contributed to by a high prevalence of cardiovascular disease, which is the leading cause of death in ESRD patients. In order to improve survival outcomes, patients at high risk of cardiovascular related mortality need to be identified. Heart rate variability (HRV), baroreceptor sensitivity, and baroreceptor reflex effectiveness index can be used to assess heart rate control and may predict cardiovascular mortality. This paper will discuss how HRV, baroreceptor sensitivity, and baroreceptor reflex effectiveness index are altered in renal disease and the utility of these indices as markers of cardiac risk in this patient population.

Predictors of heart rate variability and its prognostic significance in chronic kidney disease

BACKGROUND

Heart rate variability (HRV), a noninvasive measure of autonomic dysfunction and a risk factor for cardiovascular disease (CVD), has not been systematically studied in nondialysis chronic kidney disease (CKD).

METHODS

HRV was assessed using 24-h Holter monitoring in 305 subjects from the Renal Research Institute-CKD Study, a four-center prospective cohort of CKD (Stages 3-5). Multiple linear regression was used to assess predictors of HRV (both time and frequency domain) and Cox regression used to predict outcomes of CVD, composite of CVD/death and end-stage renal disease (ESRD).

RESULTS

A total of 47 CVD, 67 ESRD and 24 death events occurred over a median follow-up of 2.7 years. Lower HRV was significantly associated with older age, female gender, diabetes, higher heart rate, C-reactive protein and phosphorus, lower serum albumin and Stage 5 CKD. Lower HRV (mostly frequency domain) was significantly associated with higher risk of CVD and the composite end point of CVD or death. Significantly, lower HRV (frequency domain) was associated with higher risk of progression to ESRD, although this effect was relatively weaker.

CONCLUSIONS

This study draws attention to the importance of HRV as a relatively under recognized predictor of adverse cardiovascular and renal outcomes in patients with nondialysis CKD. Whether interventions that improve HRV will improve these outcomes in this high-risk population deserves further study.

Sex differences in baroreflex sensitivity, heart rate variability, and end organ damage in the TGR(mRen2)27 rat

The aim of this investigation was to evaluate sex differences in baroreflex and heart rate variability (HRV) dysfunction and indexes of end-organ damage in the TG(mRen2)27 (Ren2) rat, a model of renin overexpression and tissue renin-angiotensin-aldosterone system overactivation. Blood pressure (via telemetric monitoring), blood pressure variability [BPV; SD of systolic blood pressure (SBP)], spontaneous baroreflex sensitivity, HRV [HRV Triangular Index (HRV-TI), standard deviation of the average NN interval (SDNN), low and high frequency power (LF and HF, respectively), and Poincaré plot analysis (SD1, SD2)], and cardiovascular function (pressure-volume loop analysis and proteinuria) were evaluated in male and female 10-wk-old Ren2 and Sprague Dawley rats. The severity of hypertension was greater in Ren2 males (R2-M) than in Ren2 females (R2-F). Increased BPV, suppression of baroreflex gain, decreased HRV, and associated end-organ damage manifested as cardiac dysfunction, myocardial remodeling, elevated proteinuria, and tissue oxidative stress were more pronounced in R2-M compared with R2-F. During the dark cycle, HRV-TI and SDNN were negatively correlated with SBP within R2-M and positively correlated within R2-F; within R2-M, these indexes were also negatively correlated with end-organ damage [left ventricular hypertrophy (LVH)]. Furthermore, within R2-M only, LVH was strongly correlated with indexes of HRV representing predominantly vagal (HF, SD1), but not sympathetic (LF, SD2), variability. These data demonstrated relative protection in females from autonomic dysfunction and end-organ damage associated with elevated blood pressure in the Ren2 model of hypertension.

Pulsatile intermittent intravenous insulin therapy for attenuation of retinopathy and nephropathy in type 1 diabetes mellitus

Many hormones are secreted in a pulsatile fashion that is more efficient than continuous secretion when tested in vivo. A trial of multiple daily insulin doses with or without the addition of weekly pulsatile insulin infusion therapy was designed to determine if deterioration of renal and retinal function could be blunted. Sixty-five study subjects were evaluated prospectively in 7 centers. Thirty-six patients were randomly allocated to the infusion group and 29 to the standard therapy group. Mean serum creatinine was 1.6 mg/dL in both groups. Subjects were excluded if clearance was less than 30 mL/min. There were no significant differences between the groups with respect to age, duration of diabetes, sex distribution, glycohemoglobin, blood pressure, angiotensin-converting enzyme inhibitor use, proteinuria, or baseline diabetic retinopathy (DR) severity level (all eyes exhibited DR; 8 were deemed technically not amenable to evaluation). Progression of DR was noted in 31.6% of 57 patients (32.3% treated, 30.8% control; P = 1.0) with both eyes evaluable. For patients with 12 or more months of follow-up, 27.9% of 43 patients demonstrated progression of DR (32.0% treated, 22.2% control; P = .57). There were no significant differences between study groups with respect to progression or marked progression, nor was there any influence of duration of follow-up. Progression of DR was noted in 18.8% of 122 eyes that could be adequately evaluated (17.9% of 67 treated, 20% of 55 controls; P = .39). Serum creatinine increased to 1.7 mg/dL in the treatment group and to 1.9 mg/dL in the control group (P = .03). Statistically significant preservation of renal function by pulsatile insulin infusion was not matched by a statistically significant prevention of DR progression compared with standard diabetes care. Inadequate statistical power or duration of the study, or lack of further benefit of pulsatile insulin infusion on the retina in the presence of angiotensin-converting enzyme inhibition may be responsible.

Improvements in heart rate variability with exercise therapy

Heart rate variability (HRV) is a noninvasive, practical and reproducible measure of autonomic nervous system function. A heart rate that is variable and responsive to demands is believed to bestow a survival advantage, whereas reduced HRV may be associated with poorer cardiovascular health and outcomes. In recent years, many researchers have investigated the prognostic implications of HRV in a variety of clinical populations. Evidence suggests that reduced HRV has prognostic significance for individuals with myocardial infarction, chronic heart failure, unstable angina and diabetes mellitus. Interventions to increase HRV, such as exercise therapy, have also been examined. The findings of the present review suggest that exercise therapy may improve HRV in myocardial infarction, chronic heart failure and revascularization patients by increasing vagal tone and decreasing sympathetic activity. One hypothesis is that a shift toward greater vagal modulation may positively affect the prognosis of these individuals. While the underlying mechanisms by which exercise training improves vagal modulation are speculative at present, angiotensin II and nitric oxide may be potential mediators.

Heart rate variability predicts ESRD and CKD-related hospitalization

Autonomic imbalance, a feature of both diabetes and hypertension, may contribute to adverse cardiovascular outcomes. In animal models, sympathetic nerve activity contributes to renal damage but the extent to which autonomic dysfunction precedes the development of CKD and ESRD in humans is unknown. We measured resting heart rate and heart rate variability in 13,241 adults (45- to 64-years old) followed for a median of 16 years in the Atherosclerosis Risk in Communities (ARIC) Study. We examined heart rate parameters by quartiles, defining those in the lowest quartile (by time and frequency domain measures separately) as the risk group of interest. We identified 199 cases of incident ESRD and 541 patients with CKD-related hospitalizations; higher resting heart rate and lower heart rate variability associated with both outcomes. The fully adjusted hazard ratios for ESRD were 1.98 (95% confidence interval [CI] 1.45 to 2.70) among those in the highest heart rate quartile and 1.56 (95% CI 1.14 to 2.14) for high-frequency power. Other time and frequency domain measures were similarly and significantly associated with ESRD and CKD-related hospitalizations. These results suggest that autonomic dysfunction may be an important risk factor for ESRD and CKD-related hospitalizations and call for further studies to define the mechanisms that underlie these associations.

Cardiac autonomic regulation is impaired in girls with major depression

We aimed to study short-term heart rate variability (HRV) as an index of cardiac autonomic control in never-treated major depressive disorder (MDD) adolescent patients using linear and nonlinear analysis.

METHODS

We have examined 20 MDD girls and 20 healthy age-matched girls at the age of 15 to 18yr. The ECG was recorded in three positions: the 1st supine rest, orthostasis, the 2nd supine position. HRV magnitude was quantified by time and frequency-domain analysis (mean RR interval, SDRR, RMSSD, spectral powers in low [LF] and high frequency [HF] bands). In addition to linear measures, HRV complexity was assessed by nonlinear (symbolic dynamics) indices: normalized complexity index (NCI), normalized unpredictability index (NUPI), and pattern classification measures (0V%, 1V%, 2LV%, 2UV%).

RESULTS

HRV magnitude (RMSSD, SDRR, LF and HF powers) was significantly decreased in MDD group in a supine rest and after posture change. HRV complexity was significantly reduced (lower NCI) in the standing position. Pattern classification analysis revealed significantly higher 0V% and lower 2LV% in MDD group in supine position and orthostasis.

CONCLUSION

The HRV linear and nonlinear analysis revealed decreased magnitude and complexity of heart rate time series indicating altered neurocardiac regulation in girls with major depression without pharmacotherapy.

Cardiac autonomic neuropathy as a predictor of deterioration of the renal function in normoalbuminuric, normotensive patients with type 2 diabetes mellitus

Our study was performed to determine whether cardiac autonomic neuropathy can predict deterioration of the renal function in normoalbuminuric, normotensive people with type 2 diabetes mellitus (DM). One hundred and fifty-six normoalbuminuric, normotensive people with type 2 DM were included in our retrospective longitudinal study. We categorized normal patterns, early patterns, and definite or severe patterns according to the results of the cardiac autonomic function test. Of 156 patients included, 54 had normal patterns, 75 had early patterns, 25 had definite or severe patterns, and 2 had atypical patterns. During a median follow-up of nine years, glomerular filtration rates (GFR) remained stable in the normal and early pattern groups (mean changes, 4.50% and 0.77%, respectively) but declined in those with definite or severe patterns (mean change, -10.28%; p=0.047). An abnormal heart response to the deep breathing test of the cardiac autonomic function tests was an independent predictor of GFR decline. Our data suggest that cardiac autonomic neuropathy, especially with a definite or severe pattern, might be associated with a subsequent deterioration in renal function in normoalbuminuric, normotensive people with type 2 DM.

Recurrences in heart rate dynamics are changed in patients with diabetes mellitus

Detection of subclinical autonomic dysfunction in patients with diabetes mellitus (DM) is of vital importance for risk stratification and subsequent management. Heart rate variability (HRV) analysis is a sensitive tool for assessment of cardiovascular autonomic dysfunction. As the heart is controlled by non-linear deterministic system, the non-linear dynamics measures should be preferred. Recurrence plot (RP) is able to analyse recurrences within system dynamics. The aim of the study was to detect heart rate dysregulation in DM by RP and to ascertain which of the recurrence quantification analysis (RQA) measures are changed in patients with DM compared to control group. We analysed HRV recordings from 17 young patients with type 1 DM and 17 healthy matched control subjects. RQA was performed on RPs with a fixed value of recurrence points percentage. From RQA measures based on diagonal lines, we have found higher percentage of determinism in DM group (P=0.038). Trapping time measure was also higher in DM (P=0.022). RQA revealed changes in dynamics recurrences with reduced complexity of heart rate control in young diabetic patients. As RQA parameters are independent of overall HRV, parameters of RP should be used together with linear HRV parameters for better description of heart rate dysregulation in patients with diabetics.

Short-term heart rate complexity is reduced in patients with type 1 diabetes mellitus

OBJECTIVE

The aim of this study was to test whether new heart rate variability (HRV) complexity measures provide diagnostic information regarding early subclinical autonomic dysfunction in diabetes mellitus (DM).

METHODS

HRV in DM type 1 patients (n=17, 10f, 7m) aged 12.9-31.5 years (duration of DM 12.4+/-1.2 years) was compared to a control group of 17 healthy matched probands. The length of R-R intervals was measured over 1h using a telemetric ECG system. In addition to linear measures, we assessed HRV complexity measures, including multiscale entropy (MSE), compression entropy and various symbolic dynamic measures (Shannon and Renyi entropies, normalized complexity index (NCI), and pattern classification).

RESULTS

HRV magnitude was significantly reduced in patients with DM. Several HRV complexity parameters (MSE at scales 2-4, Renyi entropy, NCI) were also significantly reduced in diabetics. MSE indices and compression entropy did not correlate with linear measures.

CONCLUSIONS

The magnitude and complexity of HRV are reduced in young patients with DM, indicating vagal dysfunction.

SIGNIFICANCE

The quantification of HRV complexity in combination with its magnitude may provide an improved diagnostic tool for cardiovascular autonomic neuropathy in DM.

Left Ventricular Mass Reduction in Type 1 Diabetic Patients With Nephropathy

Left ventricular hypertrophy regression was postulated more likely to occur in diabetic patients when renal function was preserved. Seventeen type 1 diabetic patients followed for 12 months while receiving protocol-driven glycemic and blood pressure control had baseline and 12-month echocardiography. Despite identical treatment resulting in similar blood pressures, patients with better renal function (below the group mean, serum creatinine < or =1.7 mg/dL) demonstrated reduction in left ventricular mass and septal thickness as well as increase in left ventricular fractional fiber shortening not observed in those with worse renal function (above the group mean, serum creatinine >1.7 mg/dL). This latter group also did not experience the improvement in glycemic control observed in those with better renal function. Regression of left ventricular mass and functional improvement can be accomplished with improved glycemic control. In the presence of renal dysfunction, however, efforts to control glycemia and cardiac work are suboptimal. Aggressive glycemic and blood pressure targets to reduce cardiovascular morbidity in this high-risk population should be studied.

Comparison of fast Fourier transform and autoregressive spectral analysis for the study of heart rate variability in diabetic patients

INTRODUCTION

Impaired heart rate variability (HRV) is associated with poor outcome in diabetic patients. The present prospective study compared spectral components of HRV obtained by either fast Fourier transform (FFT) or autoregressive (AR) analyses in diabetic patients.

METHODS

Thirty patients (49+/-12 years; 11 F/19 M; 60% with insulin-dependent type 1 diabetes) underwent 24-h ambulatory electrocardiographic recordings which comprised a 10-min resting period at the onset (n=30) and end (n=12) of the monitoring. Spectral analysis was applied to 5-min sequences at rest, and the total power and power spectra integrated over the very low (VLF), low (LF), and high (HF) frequency bands were obtained.

RESULTS

Fifteen patients had moderately depressed HRV and two patients had highly depressed HRV (standard deviation of the RR intervals over 24-h<100 ms and <50 ms, respectively). Both raw data and ln-transformed data were significantly different between FFT and AR. All spectra component were obtained in each patient using FFT. Using AR, the LF/HF ratio could not be estimated or was zero in 4 and 11 patients, respectively. The AR results were more sensitive than FFT results to minor changes (+/-5%) in the timing of the onset of analysis. The day-to-day reproducibility of FFT was better than that of AR. Finally, using FFT, the LF/HF ratio, LFnu, and HFnu were essentially redundant (nu=normalized units).

CONCLUSIONS

The spectral components of short-term HRV calculated by using the FFT and AR methods were not interchangeable and FFT analysis must be preferred in diabetic patients.

Type 2 diabetes mellitus: a cardiovascular perspective

Diabetes mellitus is a disease, which is at the epitome of cardiovascular risk factors causing considerable morbidity and mortality. In addition to microvascular complications, there is two- to six-fold increased risk of macrovascular diseases, such as coronary artery disease, peripheral artery disease and stroke. While the mortality from coronary artery disease in patients without diabetes has declined over the past 20 years, the mortality in men with type 2 diabetes mellitus has not changed. Furthermore, the prevalence of diabetes in the UK has increased by 30% since 1991 and the same among the world population in 2010 is expected to be twice in 1990. This dramatic increase has serious implications from a cardiovascular perspective and thus the aggressive management of blood pressure, dyslipidaemia and blood glucose in diabetes is of vital importance. The aim of this review is to evaluate the current evidence and to discuss the implications of type 2 diabetes and its relevance to clinical practice in cardiology. We address this broad subject in discussing (i) the pathophysiology of cardiovascular disease in the setting of type 2 diabetes and (ii) the prevalence of cardiovascular risk, complications and prognostic implications in type 2 diabetes, with a discussion of current therapeutic interventions for the prevention or delay of these consequences where relevant.