Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Circulation. 1996;93:1043-1065. [PMID: 8598068 DOI: 10.1161/01.cir.93.5.1043]

Variability of R-R, P wave-to-R wave, and R wave-to-T wave intervals

We analyzed the effect of changing posture from supine to standing on the variability of R-R, P-R, and R-T intervals in 10 healthy volunteers using power spectral analysis. An electrocardiogram and respiratory trace were recorded before and after posture change. Variability in the P-R and R-T intervals was much less than in the R-R interval and demonstrated a lower-frequency (LF)-to-high-frequency (HF) ratio. Changing from a supine to a standing position showed no change in indexes of vagal influence on the P-R and R-T variability, in contrast to the well-documented decrease in the indexes of vagal influence on the R-R variability (HF power decreased from 2.33 to 0.41 ms2, P = 0.003; amplitude of the respiration-to-heart rate impulse response decreased from 31.6 to 14.4 ms.ml-1.s-1, P = 0.03; and LF/HF increased from 1.96 to 5.22, P = 0.005). We concluded from this study that the effects of standing were an observed reduction in vagal influence on the heart rate variability of the R-R interval and maintenance of lung volume-related vagal modulation of the P-R and R-T intervals.

Low variability of cycle lengths in nonsustained ventricular tachycardia as an independent predictor of mortality after myocardial infarction

In a group of 191 postinfarction patients, the low variability of cycle lengths in nonsustained ventricular tachycardia was associated with poor prognosis during follow-up. By use of Cox model analysis it was found that reduced ventricular rate variability was a powerful independent predictor of sudden death and all-cause mortality in this group of patients.

Alpha 2-adrenergic modulation of colonic tone during hyperventilation

Our aims were to assess the role of adrenergic modulation in the hyperventilation-induced increase in colonic tone. Of 40 healthy volunteers, 12 received placebo (saline) and the remaining 28 received either clonidine, yohimbine, phenylephrine, or ritodrine. Time-frequency mapping of heart rate based on Wigner distribution assessed variations in parasympathetic and sympathetic activity during hyperventilation. Tone in the descending colon was recorded by a barostat balloon before, during, and after 5 min of hyperventilation. Heart rate spectral analysis suggested diminished sympathetic and vagal activity during hyperventilation and increased sympathetic and vagal activity after hyperventilation. Adrenergic agents influenced (P = 0.01) the tonic response after, but not during, hyperventilation. Yohimbine reduced the increment in colonic tone after hyperventilation compared with saline (P < 0.05) and clonidine (P = 0.002); phenylephrine and ritodrine had no effects. Different mechanisms modulate the increase in colonic tone during and after hyperventilation. Yohimbine attenuates the increase in colonic tone after hyperventilation probably by enhancing inhibitory sympathetic input to the colon.

Heart rate variability: origins, methods, and interpretive caveats

Components of heart rate variability have attracted considerable attention in psychology and medicine and have become important dependent measures in psychophysiology and behavioral medicine. Quantification and interpretation of heart rate variability, however, remain complex issues and are fraught with pitfalls. The present report (a) examines the physiological origins and mechanisms of heart rate variability, (b) considers quantitative approaches to measurement, and (c) highlights important caveats in the interpretation of heart rate variability. Summary guidelines for research in this area are outlined, and suggestions and prospects for future developments are considered.

Depressed arterial baroreflex sensitivity and not reduced heart rate variability identifies patients with chronic heart failure and nonsustained ventricular tachycardia: the effect of high ventricular filling pressure

In chronic heart failure (CHF) the contributing role of increased sympathetic activity and hemodynamic dysfunction in the genesis of ventricular arrhythmias has not been well established. To assess the relation between severe ventricular arrhythmias, hemodynamic impairment, and autonomic nervous system derangement, 142 patients with CHF in sinus rhythm underwent 24-hour electrocardiographic recording, right-sided heart catheterization, and evaluation of sympathovagal balance by heart rate variability (HRV) and baroreflex sensitivity (BRS). Patients were grouped according to the absence (without nonsustained ventricular tachycardia [NSVT]; n = 87) or presence (with NSVT; n = 55) of NSVT. Patients with NSVT had higher pulmonary artery and capillary pressures and more pronounced signs of sympathetic activation and parasympathetic withdrawal compared with those without NSVT. However, logistic regression analysis revealed that depressed BRS but not reduced HRV was significantly associated with the presence of NSVT, at both univariate analysis and after adjustment for clinical and hemodynamic variables. Moreover, it was found that when depressed BRS was associated with high pulmonary capillary pressure, the odds ratio for having NSVT rose markedly from 3.8 to 6.5. In conclusion, this study indicates that in stable CHF the assessment of arterial baroreflex function, but not HRV analysis, allows identification of patients at high risk of NSVT. It is suggested that the effect of depressed BRS is strengthened by the simultaneous presence of increased myocardial wall stress. These data support the hypothesis of a contributory role of autonomic nervous system dysfunction as expressed by the inability to activate effective vagal reflexes and an indirect index of ventricular stretch in the genesis of life-threatening arrhythmias.

Short- and long-term reproducibility of heart rate variability in patients with long-standing type I diabetes mellitus

Heart rate variability (HRV) has been used to assess cardiac autonomic function noninvasively, understand the pathophysiologic mechanisms of heart disease, evaluate therapy, and assess long-term prognosis. We examined both the short- and long-term reproducibility of the time and frequency domain HRV parameters in 23 type I diabetics over a 12-month interval. Entry criteria included juvenile onset diabetes before age 35 years, >24-year duration of diabetes, diabetes difficult to control, and albuminuria. Standardized noninvasive autonomic testing and 24-hour ambulatory electrocardiographic recordings were obtained. Fifteen men and 8 women (mean age 36.7 years) were enrolled. Fifty-three percent of the men and 75% of the women were smokers, and women had higher cholesterol than men. All HRV parameters were markedly decreased when compared with normal persons. Using Pearson correlation, the time domain indicators of parasympathetic activity demonstrated very strong correlations at 3 and 6 months compared with baseline, with good correlations at 1 year. The average SD of all 5-minute RR intervals maintained a very strong correlation for the entire year (r >0.94). In the frequency domain, the measures of parasympathetic and sympathetic activity maintained a solid correlation for the entire study period. Reproducibility of HRV was also examined using repeated-measures analysis of variance. The time and frequency domain parameters demonstrated very little variation over the study period of 12 months. Thus, our investigation demonstrated that HRV in long-term diabetics using 24-hour ambulatory recordings is abnormal and reproducible over a 12-month interval; very little variation in all HRV parameters, especially in parameters of parasympathetic activity, occurred during the study period.

Heart rate variability spectral indices for haemodynamic classification of haemodialysis patients

The usefulness of spectral indices extracted from the heart rate variability (HRV) in discriminating between hypotension-prone and hypotension-resistant haemodialysis patients was investigated. In 30 patients, classified as hypotension resistant (stable group) or hypotension prone (unstable group), beat-to-beat heart period was measured during haemodialysis sessions terminated without collapses. HRV was analysed in the frequency domain combining classic autoregressive spectral estimation with two eigen decomposition-based techniques: the reduced rank approximation (RRA) of the autocorrelation matrix and the Pisarenko harmonic decomposition (PHD). Five spectral indices were obtained: the ratio between the powers in the LF and HF bands (LF/HF), the same ratio calculated after application of RRA (LF/HFRRA), the frequency of the main oscillatory component of HRV estimated through PHD with a decomposition order equal to 1 (F1) and equal to 2 (F2) and the difference between the frequencies of the two oscillatory components resolved in the latter cas (Fd). The performances of these indices in discriminating between the two groups of patients were evaluated estimating the misclassification probability (Pm) of a Bayesian quadratic classifier. The HRV spectral pattern was markedly different: in the stable patients power was mainly in the low-frequency band, whereas in the unstable group it was mainly in the high-frequency band. The frequency of the main oscillatory component was significantly greater in the unstable group than in the stable one. Spectral indices displayed good discrimination power, increasing with the length of the dialysis interval. Best performances were achieved by LF/HFRRA both over short dialysis periods (Pm approximately 12% over 20 min intervals) and over longer periods (Pm = 3.3% over 160 min); similar results were obtained with Fd over short periods and LF/HF over long periods. Spectral HRV indices demonstrate, therefore, a diagnostic value in discriminating between hypotension-resistant and hypotension-prone patients.

Heart rate variability in idiopathic dilated cardiomyopathy: characteristics and prognostic value

OBJECTIVES

This study was designed to evaluate heart rate variability (HRV) in patients with idiopathic dilated cardiomyopathy (IDC), to determine its correlation with hemodynamic variables and ventricular arrhythmias and to evaluate its prognostic value in IDC.

BACKGROUND

Previous studies have shown that HRV could predict arrhythmic events in patients after infarction, but the characteristics of HRV in IDC have not been fully established.

METHODS

Time domain analysis of HRV on 24-h electrocardiographic (ECG) recording was performed in 93 patients with IDC, and results were compared with those in 63 control subjects.

RESULTS

Patients with IDC, even those without congestive heart failure, had significantly lower values for HRV than those of control subjects. HRV was related to left ventricular shortening fraction (R = 0.5, p = 0.0001) and to peak oxygen uptake (R = 0.53, p = 0.01). HRV was not different in patients with runs of ventricular tachycardia or in patients with late potentials on the signal-averaged ECG. During a mean follow-up period (+/-SD) of 49.5 +/- 35.6 months, patients with reduced HRV had an increased risk of cardiac death or heart transplantation (p = 0.006). On multivariate analysis, cardiac events were predicted by increased left ventricular end-diastolic diameter (p = 0.0001), reduced standard deviation of all normal to normal RR intervals (p = 0.02) and increased pulmonary capillary wedge pressure (p = 0.04).

CONCLUSIONS

Decreased HRV in patients with IDC is related to left ventricular dysfunction and not to ventricular arrhythmias. Analysis of HRV can identify patients with IDC who have an increased risk of cardiac death or heart transplantation.

Risk assessment and risk stratification in sudden cardiac death: a biostatistician's view

Determining individual probabilities of developing lethal arrhythmia over time (risk assessment) and grouping individuals by that probability (risk stratification) are similar to, yet differ in purpose from, screening, diagnosis, risk factor identification, and prognostic staging. Methods of handling bias, use of multiple predictors, and evaluation of results provide challenges. A key purpose of risk assessment and stratification is examined. The role of operational definitions of predictors and events and of methods that account for multiple predictors and known confounding factors is analyzed. Constructed examples illustrate potential pitfalls in assessment and how multivariate techniques can deal with multiple predictors. A trial design to evaluate risk stratification for the identified purpose is elaborated and potential results are interpreted. Bias from predictors regressing to the mean can be minimized either by averaging a number of measurements or by equalizing the bias in comparison groups. An analysis of two predictors and two risk strata illustrates how the discrimination of combined predictors may be greater than the sum of the individual variables' discrimination. Risk stratification can be evaluated in trials that randomize competing interventions within different risk strata. Results of such trials indicate whether the risk strata adequately distinguish individuals by their responsiveness to particular intervention. Potential pitfalls, not easily recognized in risk stratification, can be avoided in the methods and in studies for evaluating those methods. Multivariate techniques maximize the discrimination of multiple predictors, but may increase complexity. Randomized trials of treatment provide evidence for utility of risk stratification.

Heart rate variability used as an arrhythmia risk stratifier after myocardial infarction

Heart rate variability (HRV) is considered to represent a noninvasive tool to assess cardiac autonomic tone at the level of the sinus node. It has been shown to have predictive power for risk assessment in patients surviving acute myocardial infarction. For this purpose, HRV should be assessed from 24-hour Holter recordings obtained 7-10 days following the infarction. Although there is some recovery of HRV during the first 3 months after infarction, HRV remains reduced in postinfarction patients compared to values obtained in healthy individuals. Compared to assessment of left ventricular function as a risk marker, HRV is superior with respect to prediction of arrhythmic events and sudden death whereas both parameters yield comparative power for prediction of total cardiac mortality. Since the predictive power of HRV analysis alone is relatively low, the combined use of HRV measurements together with traditional risk markers (such as ventricular ectopic beats, signal-averaged ECG, or left ventricular function) results in improved risk prediction with positive predictive accuracy in the range of 30%-50%.

Estimating a cardiac age by means of heart rate variability

A data set of R-R intervals recorded for at least 15 min in 141 healthy individuals of different ages and under two different conditions ("resting" and "tilted" states) has been considered. The data have been subjected to spectral analysis by fast Fourier transform methods and considered in view of the possibility to work out a model in which the chronological and cardiac age could be compared. Understanding the results was greatly facilitated by 1) working out a number of derived variables from the original ones to highlight the presence of small but conceptually important variability factors; 2) extraction of the principal components from the original as well as from the derived variables to exclude redundancies and correlation effects; and 3) automatic clustering of the subjects in age classes, which allowed removal of individual variability within each class. The main conclusion is that, within the examined individuals, cardiac and chronological ages do not match for ages higher than approximately 50 years; this could reflect the presence of subtle (and difficult-to-envisage) biases in the data analysis or a real discrepancy. The latter hypothesis should be confirmed by similar observations in different systemic contexts. The use of a simple equation relating chronological and cardiac age, derived from a careful regression analysis on our data set and of general use for screening purposes, is demonstrated.

Paroxetine increases heart rate variability in panic disorder

Panic patients have decreased heart rate variability, a risk factor for sudden cardiac death, and increased rates of cardiac death and stroke. Imipramine has been found to further reduce heart rate variability in panic. This study uses power spectral analysis to compare autonomic components of heart rate variability in 16 unmedicated control subjects and 17 panic patients before and after treatment with paroxetine at 20 mg/day for 4 weeks. Patients had higher predrug reclining and standing sympathetic activity than control subjects. After drug, patients' total sympathetic activity decreased. Predrug patients failed to increase sympathetic activity on orthostasis, lacking the normal baroreflex response found in control subjects. After drug, patients normalized this sympathetic component of the baroreflex response. Before drug, patients' parasympathetic reclining and standing activity did not differ from control subjects, and patients showed the normal orthostatic parasympathetic decrease. After drug, patients' total parasympathetic activity increased, whereas the baroreflex response was preserved. Nine medicated patients had more than a 50% reduction of panic attacks. In view of paroxetine's increase of heart rate variability, potential benefits of selective serotonin reuptake inhibitors in decreasing cardiac mortality in panic disorder are discussed.

Incidence of arrhythmias and heart rate variability in wild-type rats exposed to social stress

Psychological stressors of different natures can induce different shifts of autonomic control on cardiac electrical activity, with either a sympathetic or a parasympathetic prevalence. Arrhythmia occurrence, R-R interval variability, and plasma catecholamine elevations were measured in male wild-type rats exposed to either a social stressor (defeat) or a nonsocial challenge (restraint). Electrocardiograms were telemetrically recorded, and blood samples were withdrawn through jugular vein catheters from normal, freely moving animals. Defeat produced a much higher incidence of arrhythmias (mostly ventricular premature beats), which were mainly observed in the 60-s time periods after attacks. The social challenge also induced a much stronger reduction of average R-R interval, a lower R-R interval variability (as estimated by the time-domain parameters standard deviation of mean R-R interval duration, coefficient of variance, and root mean square of successive differences in R-R interval duration), and higher elevations of venous plasma catecholamines compared with restraint. These autonomic and/or neuroendocrine data indicate that a social stressor such as defeat is characterized by both a higher sympathetic activation and a lower parasympathetic antagonism compared with a nonsocial restraint challenge, which results in a higher risk for ventricular arrhythmias.

Electrocardiographic and signal monitoring in ischaemic heart disease: state of the art and perspective

The current role of ECG and signal monitoring in the diagnosis of Ischaemic Heart Disease is outlined in relation to imaging techniques giving accurate information on myocardial anatomy and function. ECG monitoring during stress testing remains the first step non-invasive method providing pathophysiological information. Long term continuous monitoring of the ECG and of other signals (e.g. arterial blood pressure and respiration) is commonly used to control patients with suspected or ascertained IHD. Progress of technology and of signal processing methods are driving the exploitation of signal information for diagnosis, prognosis and therapy control of ischaemic patients.

Comparison between iodine 123 metaiodobenzylguanidine scintigraphy and heart rate variability for the assessment of cardiac sympathetic activity in mild to moderate heart failure

This study demonstrates that in patients with mild to moderate heart failure, cardiac metaiodobenzylguanidine (MIBG) washout positively correlates with normalized low-frequency power in the heart rate variability spectrum. Alterations of the cardiac sympathetic nervous system could be detected with MIBG scintigraphy in patients with normal plasma norepinephrine levels. Therefore cardiac MIBG washout may be a valuable noninvasive technique to assess early alterations in cardiac sympathetic activity that may have potential clinical implications in patients with mild to moderate heart failure.

Assessment of autonomic function at rest and during tilt testing in patients with vasovagal syncope

This study evaluated autonomic nervous system function in 30 patients with syncope and a positive tilt test result, 20 with a negative test result, and 20 healthy controls. Indexes of heart rate variability were measured during the intervals immediately before and after tilt, while all subjects were asymptomatic, and over a 24-hour period. There were no significant differences among the groups in any of the indexes of heart rate variability over the 24-hour period. In patients with a positive tilt result, tilting caused a decrease in low-frequency (LF) and high-frequency (HF) bands, although the LF/HF ratio did not significantly change. In patients with a negative tilt result there was a decrease in the HF band but no other significant changes. In the controls there was an increase in the LF band and LF/HF ratio and a decrease in the HF band. Our findings showed that patients with vasovagal syncope have no chronic differences from normal subjects in autonomic nervous system activity, but that these patients respond differently to the orthostatic stimulus.

Heart rate variability in patients with hypertrophic cardiomyopathy: association with clinical and echocardiographic features

Autonomic dysfunction has been reported in patients with hypertrophic cardiomyopathy. To evaluate the influence of different clinical and echocardiographic features of the disease on sympathovagal balance, as assessed by heart rate variability, 33 patients with hypertrophic cardiomyopathy and 33 healthy volunteers underwent echocardiographic examination and 24-hour electrocardiogram Holter recording. Measures of vagal modulation of heart rate were lower in patients with hypertrophic cardiomyopathy than in controls, particularly in those exhibiting syncope, exertional chest pain, dyspnea, or moderate or severe mitral regurgitation. Furthermore, the age-corrected multiple regression analysis showed that the parasympathetic cardiac control was inversely related to left atrial dimension and directly related to left ventricular end-systolic dimension. Therefore in hypertrophic cardiomyopathy the parasympathetic withdrawal is more evident in patients with symptoms than in those without; the reduction in left ventricular end-systolic dimension and the increase in left atrial size are the echocardiographic features that most influence the sympathovagal balance.

Is there an expanded role for digoxin in patients with heart failure and sinus rhythm? A protagonist viewpoint

The evidence supporting the efficacy of digoxin in patients with heart failure who are in sinus rhythm is substantial. Digoxin improves hemodynamics, exercise capacity, symptoms, and quality of life and reduces hospitalizations. All of this is accomplished with a drug that is very inexpensive and can be given once daily. Its safety has been established through the DIG trial. Although digoxin does not decrease mortality beyond that of diuretics and ACE inhibitors, it does not increase mortality, unlike many positive inotropes. Furthermore, digoxin, in addition to ACE inhibitors and a diuretic, decreases the hospitalization rate due to worsening of heart failure. From a managed care perspective, as well as that of the patient, this is of enormous benefit. A pharmacoeconomic analysis estimated that continuation of digoxin in patients with stable congestive heart failure could save the healthcare system an estimated $ 400 million, based on costs from one hospital. The issue is not whether to use digoxin in these patients, but rather, how early to initiate therapy. From some of the recent data in patients with systolic dysfunction and mild heart failure, as well as knowledge of the neurohormonal activation that occurs early in these patients, it could be suggested that early use of neurohormonal modulators, including digoxin, would decrease the progression of heart failure. Thus, rather than waiting for symptoms despite optimal doses of an ACE inhibitor and diuretic, as suggested by the AHCPR practice guideline for heart failure, initiation of digoxin therapy in patients as early as NYHA class II at a dosage that will achieve a serum concentration of 1.0 ng/mL or less should occur. With the understanding of digoxin's effect on the neurohormonal systems, its role in patients with preserved systolic function needs to be reexplored. The debate can now focus on asymptomatic patients or those with preserved systolic function. Could these patients benefit from therapy with digoxin as well?

Blunted parasympathetic modulation in salt-sensitive patients with essential hypertension: evaluation by power-spectral analysis of heart-rate variability

OBJECTIVE

To evaluate autonomic nervous function by power-spectral analysis of heart-rate variability in salt-sensitive and non-salt-sensitive patients with essential hypertension under the conditions of low and high salt intakes.

DESIGN AND METHODS

The blood pressures, heart rates, and electrocardiogram R-R intervals of 20 hypertensive patients were measured at intervals of 30 min during a 24 h period using a portable recorder (TM-2425) on the last day of the high- (250 mmol NaCl/day) and low-salt (25 mmol NaCl/day) diet periods. The patients whose 24 h average mean blood pressures were increased by more than 10% by the high salt intake were defined as salt-sensitive (n = 10); the other patients were considered non-salt-sensitive (n = 10). Power-spectral analysis of R-R intervals was performed to obtain the low-frequency component (0.05-0.15 Hz) and the high-frequency component (0.15-0.40 Hz).

RESULTS

The average 24 h blood pressure in the salt-sensitive patients was increased by the high salt intake [by 19.1 +/- 2.0/9.1 +/- 0.8 mmHg (mean +/- SEM)], whereas the heart rate did not change. In contrast, the increase in 24 h blood pressure in the non-salt-sensitive patients caused by the high salt intake was not significant and the heart rate was decreased significantly by the high salt intake (by 5.9 +/- 1.4 beats/min). The high-salt diet increased significantly the high-frequency component and decreased the low-frequency:high-frequency component ratio both during the daytime and during the night-time for the non-salt-sensitive patients. In contrast, the high-frequency component and the night-time low-frequency: high-frequency component ratio of the salt-sensitive patients did not respond to dietary salt manoeuvres.

CONCLUSIONS

Responses of the parasympathetic and sympathetic nervous systems to dietary salt manoeuvres were blunted in salt-sensitive patients. These altered modulations of the autonomic nervous system may contribute to the salt sensitivity of the blood pressure in patients with essential hypertension.

Atrioventricular block after administration of atropine in patients following cardiac transplantation

BACKGROUND

Atropine is widely used as a parasympatholytic agent during diagnostic and therapeutic procedures. We observed an unexpected paradoxical response to atropine after cardiac transplantation.

METHODS

In a study investigating the occurrence of autonomic reinnervation after cardiac transplantation, atropine, at 0.015 mg/kg body weight, was given intravenously to 23 patients (mean age, 56+/-8 years) 98 days to 6.4 years after transplantation.

RESULTS

Two patients experienced a witnessed syncope 40 and 150 min after administration of atropine. Second-degree atrioventricular (AV) block was documented in the first patient immediately afterward, and third-degree AV block was seen on 24-hr electrocardiogram monitoring in the second patient. A third patient developed documented AV block 15 min after atropine but experienced no sequelae because of a previously implanted pacemaker.

CONCLUSIONS

Although the underlying mechanism is not clear, these findings suggest that atropine may paradoxically cause high-degree AV block in patients after transplantation. Accordingly, it should be used with caution and appropriate monitoring in these patients.

Tone-entropy analysis on cardiac recovery after dynamic exercise

Autonomic controls on heart rate variability have been investigated; however, sympathovagal interactive modulations remain unexplored. The purpose of this study is to present a new method, tone-entropy analysis (T-E analysis) of heart period fluctuations, and to make clear an intensive cooperation of autonomic networks in heart recovery. On the basis of evidence obtained in animal experiments, we hypothesized that heart periods are lengthened or shortened beat to beat by assumed physiological mediators: accelerator and inhibitor. Their operations were evaluated through a normalized successive variation of the period, that is, the percentage index (PI). The process was described through PI distributions by using two indexes, tone and entropy, standard values of which were obtained through pharmacological autonomic blockade experiment. T-E analysis was applied to heart recovery (70 min) after dynamic exercise by 12 female athletes. Interactive autonomic modulations were expressed by a curved path in tone-entropy space. Results suggested that heart rate decay proceeds not by withdrawal of one pathway but by increasing activity of both pathways as vagosympathetic balance inclines slightly but significantly to the vagus division in the course of recovery. The process was examined through Fourier spectral analysis as well.

Heart rate variability before and after treatment with electroconvulsive therapy

It has been suggested that depression may be associated with decreased parasympathetic activity. Based on this work, we tested the hypothesis that treatment of depression with electroconvulsive therapy (ECT) would result in a relative increase in cardiac vagal (parasympathetic) activity. Changes in respiratory sinus arrhythmia, a marker of cardiac parasympathetic activity, were examined in nine patients with depressive episodes before and after ECT using spectral analysis. Hamilton Depression Rating Scale scores decreased significantly. In terms of the heart rate measures, RR interval tended to decrease and the amplitude of respiratory sinus arrhythmia decreased significantly following the course of ECT. This reduction in respiratory sinus arrhythmia contributed to the overall decrease in RR interval variability. Additionally, the magnitude of symptom improvement as measured by the Hamilton Scale correlated with the decrease in amplitude of the respiratory sinus arrhythmia. We report that treatment of depression with ECT was associated with a relative decrease in parasympathetic activity, in contrast to our initial hypothesis of a relative increase. This finding may not be related to the ECT per se but rather to the resolution of depression, as there was a significant correlation between the decrease in Hamilton Depression Rating Scale scores and decrease in parasympathetic activity. Further work is necessary to better understand the autonomic changes associated with depressive illness and the clinical risks and benefits associated with various treatment modalities.

Vagal control of heart rate variability in vasovagal syncope: studies based on 24-h electrocardiogram recordings

The autonomic nervous system has an important role in the pathophysiology of vasovagal syncope. The purpose of this investigation was to evaluate to what extent the autonomic system is involved in the mechanism of fainting and to characterize the profile of heart rate variability of individuals who are prone to undergo a critical event. Thirty patients (mean age 41 years) with vasovagal syncope and 15 comparable controls were monitored by 24-h electrocardiography. Heart rate variability was analysed over the whole 24 h and during the daytime and night-time using time domain parameters (average of heart periods, RR; standard deviation of heart periods, SDNN; standard deviation of the average of RR intervals over all the 5-min segments of the entire recording, SDANN; percentage of the total number of all RR intervals of pairs of adjacent RR intervals differing more than 50 ms over the entire recording, pNN50; the square root of the sum of the square of differences between adjacent RR intervals, rMSSD), as indicated by the Task Force for Clinical Use of Standard Measurements of Heart Rate Variability. These parameters explore the influence of the autonomic nervous system on sinus node function and provide information about the vagal control to the heart. Among these parameters, pNN50 and rMSSD were significantly reduced in individuals with vasovagal syncope when compared with controls, over each time period considered. The two parameters are related to high-frequency oscillations in the frequency domain and to the vagal influence of the heart. These results indicate that the vagal tone to the heart is altered in subjects who suffer from vasovagal syncope. The results of this study provide an insight into the pathophysiological mechanism of fainting and may offer another means of evaluating patients with syncope.

Autonomic response to change of posture among normal and mild-hypertensive adults: investigation by time-dependent spectral analysis

In this study, we applied the time-dependent spectral analysis approach (SDA) to investigate the autonomic changes occurring during a transition from supine to standing position (CP), in normal and unmedicated mild hypertensive subjects. The SDA method enables an accurate follow-up of the instantaneous changes in autonomic activity, even during the unsteady phase of the transition, where sudden changes in heart rate (HR) and arterial blood pressure (ABP) are observed. We were able to quantify the vagal withdrawal (reflected in the high frequency component of the time-dependent spectrum of HR fluctuations) in the immediate response to CP and the more slowly following sympathetic increase (reflected in the low frequency component of ABP). This general pattern was observed in both groups. In addition, our results identified an altered sympathetic response to CP in mild-hypertensives, as compared to normal adults. Their basal sympathetic activity is enhanced (higher mean HR and increased low frequency fluctuations in ABP) and their response to CP is reduced, as reflected only in the LF content of ABP fluctuations, relative to normals. No difference was observed in HR fluctuations, showing that there is no parasympathetically mediated alteration of the baroreflex control of HR in mild-hypertension.

Anxiety, antisocial behavior, and heart rate regulation in adolescent males

We explored relationships between anxiety and antisocial behavior and autonomic heart rate regulation in a homogenous sample (N = 175) of 15-year-old males. Measures of anxiety and antisocial behavior were obtained at yearly intervals over a period of 4-6 years. Components of heart rate variability associated with postural (sympathetic) and respiratory (vagal) change and transfer of respiratory to heart rate variability were estimated at age 15 using spectral analytic techniques. Anxiety and antisocial behavior were predictably related to enhanced and diminished levels of mean heart rate, respectively. Anxiety was also predictably related to enhanced sympathetic mediation of phasic postural effects on heart rate. Antisocial behavior was unexpectedly related to disruption of vagally mediated, phasic respiratory effects on heart rate. Anxiety and antisocial behavior showed distinct relationships to heart rate, and to the autonomically mediated components of heart rate variability from postural and respiratory sources. Spectral analytic techniques helped elucidate these unique regulatory patterns, suggesting utility for future research in this area.

Cardiac autonomic function and sensitivity to pain in postmenopausal women with angina and normal coronary arteries

An increased sensitivity to painful stimuli and an abnormal cardiac autonomic function have previously been reported in patients with angina and angiographically normal coronary arteries, a syndrome that mainly affects postmenopausal women. In this study we compared both general sensitivity to pain, by evaluating time to forearm ischemic pain (FIP) provoked by sphygmomanometer cuff inflation, and cardiac autonomic function, by measuring heart rate variability (HRV), and QT and QT(c) intervals on 24-hour Holter recordings, in 25 postmenopausal women with angina and normal coronary arteries and in 22 healthy postmenopausal women. Compared with controls, patients had a reproducible strikingly lower time to FIP (149 +/- 121 vs 295 +/- 158 seconds, p <0.001), whereas there were no differences between the 2 groups in HRV variables and mean 24-hour QT and QT(c) intervals. HRV indexes, and QT and QT(c) intervals also showed similar circadian patterns. Thus, our data show that postmenopausal women with angina and normal coronary arteries have an enhanced sensitivity to systemic painful stimuli, but no detectable impairment in cardiac autonomic function compared with a well-matched control group of postmenopausal healthy women.

Does digoxin provide additional hemodynamic and autonomic benefit at higher doses in patients with mild to moderate heart failure and normal sinus rhythm?

OBJECTIVES

This study sought to examine the hemodynamic and autonomic dose response to digoxin.

BACKGROUND

Previous studies have demonstrated an increase in contractility and heart rate variability with digitalis preparations. However, little is known about the dose-response to digoxin, which has a narrow therapeutic window.

METHODS

Nineteen patients with moderate heart failure and a left ventricular ejection fraction < 0.45 were studied hemodynamically using echocardiography and blood pressure at baseline and after 2 weeks of low dose (0.125 mg daily) and 2 weeks of moderate dose digoxin (0.25 mg daily). Loading conditions were altered with nitroprusside at each study. Autonomic function was studied by assessing heart rate variability on 24-h Holter monitoring and plasma norepinephrine levels during supine rest.

RESULTS

Low dose digoxin provided a significant increase in ventricular performance, but no further increase was seen with the moderate dose. Low dose digoxin reduced heart rate and increased heart rate variability. Moderate dose digoxin produced no additional increase in heart rate variability or reduction in sympathetic activity, as manifested by heart rate, plasma norepinephrine or low frequency/high frequency power ratio. In addition, we did not find that either low or moderate dose digoxin increased parasympathetic activity.

CONCLUSIONS

We conclude that moderate dose digoxin provides no additional hemodynamic or autonomic benefit for patients with mild to moderate heart failure over low dose digoxin. Because higher doses of digoxin may predispose to arrhythmogenesis, lower dose digoxin should be considered in patients with mild to moderate heart failure.

Characterization and natural course of cardiac autonomic nervous dysfunction in HIV-infected patients

OBJECTIVE

To examine the degree, pattern, and natural history of cardiac autonomic nervous dysfunction in patients infected with HIV.

DESIGN

Cross-sectional and prospective longitudinal cohort study.

SETTING

Primary care and tertiary referral university centre.

PARTICIPANTS

Thirty-five consecutive HIV-infected patients who had either not yet developed AIDS (15 pre-AIDS patients) or who were at the Centers for Disease Control and Prevention (CDC) AIDS stage (n = 20), and 29 healthy age- and sex-matched HIV-negative controls.

METHODS

Computer-aided power spectral analysis of 15 standardized parameters of heart-rate variability (HRV).

RESULTS

Pre-AIDS patients as a group did not exhibit any HRV parameters to be significantly different from healthy controls (P > 0.017), whereas AIDS patients demonstrated reduced HRV in 14 parameters (93.3%) compared with healthy subjects (p > 0.017). Median proportion of abnormal HRV parameters (< 10th percentile of controls) per individual was 9.1% in pre-AIDS patients and 61.3% in AIDS patients (P = 0.0347). Progressive CDC stages inversely correlated to 10 HRV parameters (66.7%; -0.50 < or = r < or = -0.36; P < 0.05). Follow-up testing in 10 pre-AIDS and six AIDS patients after 6-16 months (median, 12.5 months) did not reveal deterioration of HRV (P < 0.05). A dysautonomia symptom score correlated to 10 HRV parameters (66.7%; -0.14 < r < -0.55; P < 0.05).

CONCLUSIONS

Cardiac autonomic nervous dysfunction is severe in AIDS patients, although not significant in pre-AIDS patients. Cardiac autonomic nervous dysfunction proceeds with HIV disease progression, although its individual course is slow.

Evidence of increased sympathetic vasomotor drive with shorter acting dihydropyridine calcium channel antagonists in human hypertension: a study using spectral analysis of RR interval and systolic arterial pressure variability

We studied the effects of common antihypertensive regimens on autonomic cardiovascular control. We considered calcium channel antagonists (nicardipine twice a day and isradipine once a day, respectively) and also examined, as reference treatments, once-a-day atenolol and cilazapril. A noninvasive evaluation of autonomic cardiovascular profile was obtained with spectral analysis of RR interval and systolic arterial pressure variability. We studied moderate essential hypertensives before and after 2 weeks of treatment, both at rest and during active standing and mental arithmetic. All treatments reduced arterial pressure equally well; however, marked differences in spectral profiles were observed. The low-frequency spectral component of RR interval variability [in normalized units, marker of sympathetic modulation of the sinoatrial (SA) node] tended to be greater at rest and during stimuli (p < 0.001) in subjects treated with dihydropyridines. No differences at rest, but striking increases of the low-frequency component of systolic arterial pressure variability were observed in nicardipine-treated patients during both standardized excitatory stimuli, suggesting a marked increase in sympathetic vasomotor drive. As to reference treatments, patients treated with atenolol displayed the lowest values, and patients treated with cilazapril (for 4 weeks) provided intermediate values. In conclusion, shorter acting dihydropyridine calcium channel antagonists may induce an exaggerated increase in sympathetic vasomotor drive during standardized laboratory stressors.

Does low-frequency variability of heart period reflect a specific parasympathetic mechanism?

Low frequency (LF, approximately 0.1 Hz) spontaneous oscillations of heart period in humans have been attributed to and correlated with the sympathetic efferent control of the heart. However, this interpretation is controversial, because sympathetic blockade does not suppress these oscillations, while parasympathetic blockade strongly affects them. The sympathetic origin of LF of arterial pressure, on the contrary, has been convincingly demonstrated. Four 10 min cycle-by-cycle time series of R-R interval (RR), and systolic (SAP) and diastolic (DAP) arterial pressure were produced by automatic analysis of data obtained with non-invasive methods in 10 healthy humans during supine rest and while standing, both before and after beta 1-selective blockade (atenolol). Time series were analysed by autoregressive transfer function analysis. beta-blockade failed to induce systematic changes on the power of the LF peak of RR, in any condition. The coherence between RR and SAP in the same region remained high (0.77 +/- 0.03) and a constantly negative phase (approximately 50-60 degrees, corresponding to a delay of 1-2 heart beats of RR on SAP) was always seen. beta-blockade decreased the power of the LF peak of SAP, increased the transfer function gain between SAP and RR at LF, and the HF power of RR. We conclude that LF oscillations of RR are not directly generated by the sympathetic drive to the heart but reflect mainly the parasympathetic activity. The results suggest that the LF oscillations of the vagal outflow, and of RR, are generated by the baroreceptor reflex, driven by sympathetically-induced blood pressure LF waves.

Randomised trial of effect of amiodarone on mortality in patients with left-ventricular dysfunction after recent myocardial infarction: EMIAT. European Myocardial Infarct Amiodarone Trial Investigators

BACKGROUND

Ventricular arrhythmias are a major cause of death after myocardial infarction, especially in patients with poor left-ventricular function. Previous attempts to identify and suppress arrhythmias with various antiarrhythmic drugs failed to reduce or actually increase mortality. Amiodarone is a powerful antiarrhythmic drug with several potentially beneficial actions, and has shown benefit in several small-scale studies. We postulated that this drug might reduce mortality in patients at high risk of death after myocardial infarction because of impaired ventricular function, irrespective of whether they had ventricular arrhythmias.

METHODS

The European Myocardial Infarct Amiodarone Trial (EMIAT) was a randomised double-blind placebo-controlled trial to assess whether amiodarone reduced all-cause mortality (primary endpoint) and cardiac mortality and arrhythmic death (secondary endpoints) in survivors of myocardial infarction with a left-ventricular ejection fraction (LVEF) of 40% or less. Intention-to-treat and on-treatment analyses were done.

FINDINGS

EMIAT enrolled 1486 patients (743 in the amiodarone group, 743 in the placebo group). Median follow-up was 21 months. All-cause mortality (103 deaths in the amiodarone group, 102 in the placebo group) and cardiac mortality did not differ between the two groups. However, in the amiodarone group, there was a 35% risk reduction (95% CI 0-58, p = 0.05) in arrhythmic deaths.

INTERPRETATION

Our findings do not support the systematic prophylactic use of amiodarone in all patients with depressed left-ventricular function after myocardial infarction. However, the lack of proarrhythmia and the reduction in arrhythmic death support the use of amiodarone in patients for whom antiarrhythmic therapy is indicated.

A multivariate time-variant AR method for the analysis of heart rate and arterial blood pressure

This paper approaches the problem of short-term mechanisms that regulate heart rate and blood pressure variability signals, by focusing the evident changes of their frequency content during transients (dynamic situations in which the behaviour of these control mechanisms may vary on a beat-to-beat basis). In this study, we suggest an autoregressive time-variant spectral estimation method, which is able to follow such dynamic changes in the signals. This method has also been extended to a multivariate approach in order to take into account more than one process at a time, and to assess the mutual influences between the different controlling systems. The algorithms successfully tested on simulated series have also been used to analyse series recorded during a vaso-vagal syncope episode in a tilt manoeuvre and a physical exercise stress test protocol. The results show how this method is able to follow the changing dynamics of the signals on the basis of a closed-loop model of their interaction on a beat-to-beat basis. After a proper identification procedure of the blocks forming the model, it is possible, therefore, to obtain the classical spectral parameters and the gain of the transfer function between the signals. Such parameters constitute new time series that describe the physiopathology of the cardiovascular control systems, even during non-stationary epochs.

Comparison of verapamil versus felodipine on heart rate variability after acute myocardial infarction

A depressed heart rate variability (HRV) is a powerful predictor of poor outcome in myocardial infarction patients. The beneficial effect of specific interventions on its recovery has been reported, but data concerning calcium antagonists are scarce. We evaluated the effect of a phenylalkylamine derivative, verapamil, and a dihydropyridine derivative, felodipine, on time- and frequency-domain measurements of HRV by 24-hour Holter monitoring in 60 patients with acute myocardial infarction (AMI). After a first Holter recording (65 +/- 8 hours from the onset of symptoms), patients were randomly assigned to continue standard treatment or to also receive verapamil retard (120 mg 3 times daily) or felodipine extended-release (10 mg/day). Holter recording was repeated after 7 days. After verapamil, mean RR interval increased from 823 +/- 92 to 907 +/- 95 ms and the SD of all normal RR (NN) intervals (SDNN) from 99 +/- 24 to 120 +/- 30 ms (p < 0.01); the root mean square successive difference (r-MSSD) and the percent of differences between adjacent NN intervals > 50 ms (pNN50) also increased (p < 0.01). After felodipine, only SDNN increased (p < 0.01). Regarding frequency-domain measurements, after receiving verapamil, very low frequency, low- and high-frequency powers increased (p < 0.01), whereas the low- to high-frequency ratio decreased (p < 0.01). After receiving felodipine, very low-frequency power increased (p < 0.01), whereas low- and high-frequency powers and the low- to high-frequency ratio remained unchanged. This study demonstrates that verapamil, but not felodipine, improves HRV in the early phase after AMI.

Alteration of cardiac function in patients with temporal lobe epilepsy: different roles of EEG-ECG monitoring and spectral analysis of RR variability

PURPOSE

Because several reports have described the relation between epilepsy and cardiac arrhythmias and suggest that changes in autonomic neural control of the heart could be involved in the pathogenesis of sudden unexplained death in patients with epilepsy, the aim of this study was to evaluate cardiac function in patients with temporal lobe epilepsy.

METHODS

Sixty-five patients with epilepsy were evaluated by simultaneous ambulatory 24-h EEG-ECG monitoring, and in 30 of these, power spectral analysis of relative-risk (RR) variability also was carried out, both in the supine position and in a passive tilt position at 60 degrees. The power spectrum of RR variability, the two major spectral components detectable at low frequency (LF) and at high frequency (HF), respectively, and the LF/HF ratio were calculated.

RESULTS

By EEG-ECG monitoring, we recorded six partial seizures, and in four cases, discharges were associated with sinus tachycardia. However, interictally the occurrence of ventricular and supraventricular arrhythmias was not different from that in normal subjects. The spectral analysis of RR variability, on the other hand, demonstrated in patients with epilepsy a significant decrease in the total RR variability and in both of its components (LF and HF) in the supine position, and of the LF/HF ratio in orthostatic position.

CONCLUSIONS

These findings suggest that the spectral analysis of RR variability may detect disorders of autonomic cardiac control in patients with epilepsy, even in the absence of abnormal findings during ECG monitoring. This alteration, which is more severe in cases with right EEG focus, could play a role in the pathogenesis of cardiac arrhythmias.

Impaired baroreflex sensitivity is correlated with hemodynamic deterioration of sustained ventricular tachycardia

OBJECTIVES

The goal of this study was to evaluate clinical and autonomic variables (heart rate variability and baroreflex sensitivity) related to hemodynamic tolerability of VT in patients with sustained monomorphic VT and a healed myocardial infarction.

BACKGROUND

Sustained ventricular tachycardia (VT) with hemodynamic deterioration is associated with a worse prognosis than that of well tolerated VT. The causes of hemodynamic deterioration of VT are incompletely understood.

METHODS

Twenty-four consecutive patients with sustained monomorphic VT and a healed myocardial infarction (mean age +/- SD 66 +/- 8 years, left ventricular [LV] ejection fraction 37 +/- 11%) were assigned to group 1 if the VT was well tolerated (n = 11) or to group 2 if faintness or syncope occurred or if systolic blood pressure was < 90 mm Hg with clinical signs of shock (n = 13).

RESULTS

No difference was found between the two groups in age, LV function, rate and duration of the VT or heart rate variability. However, patients in group 2 had a significantly lower baroreflex sensitivity (3.4 +/- 1.1 vs. 7.1 +/- 3.7 ms/mm Hg, p = 0.003). Multiple logistic regression analysis showed that only the value of baroreflex sensitivity (p = 0.0003)-but not age, LV ejection fraction, VT cycle length or SD of the RR interval (all p > 0.25)-correlated with the tolerability of the VT. Finally, LV ejection fraction (p = 0.0001) and baroreflex sensitivity (p = 0.0003)-but not age, cycle length of the tachycardia or SD of the RR interval-predicted cardiac death or unstable VT during follow-up.

CONCLUSIONS

These data suggest that an impaired cardiovascular reflex response may play a key role in the hemodynamic deterioration of sustained VT and that the evaluation of baroreflex sensitivity in patients at high risk for sustained VT may become useful both in risk stratification and in the individualization of treatment.

Clinical relevance of heart rate variability

Heart rate variability (HRV) has recently become a popular noninvasive research tool in cardiology. Clinical assessment of HRV is frequently based on standard long-term ambulatory electrocardiograms, whereas physiologic studies employ spectral analysis of short-term recordings under controlled conditions. From a general point of view, HRV can be used in clinical practice to estimate (1) the integrity of cardiac autonomic innervation, (2) the physiologic status of cardiac autonomic activity, and (3) the vulnerability to various cardiac arrhythmias resulting from autonomic imbalance. Clinical relevance of HRV has been clearly demonstrated in only two clinical conditions: (1) impaired HRV can be used alone or in a combination with other factors to predict risk of arrhythmic events after acute myocardial infarction, and (2) decrease in HRV is a useful clinical marker for evolving diabetic neuropathy. Substantial advances of our knowledge are required to establish and promote clinical applications in other areas of clinical medicine. To accomplish this task, proper hypotheses should be studied and appropriate techniques selected.

A new method of assessing cardiac autonomic function and its comparison with spectral analysis and coefficient of variation of R-R interval

A new non-linear method of assessing cardiac autonomic function was examined in a pharmacological experiment in ten healthy volunteers. The R-R interval data obtained under a control condition and in autonomic blockade by atropine and by propranolol were analyzed by each of the new methods employing Lorenz plot, spectral analysis and the coefficient of variation. With our method we derived two measures, the cardiac vagal index and the cardiac sympathetic index, which indicate vagal and sympathetic function separately. These two indices were found to be more reliable than those obtained by the other two methods. We anticipate that the non-invasive assessment of short-term cardiac autonomic function will come to be performed more reliably and conveniently by this method.

Brain Asymmetry and Autonomic Control of the Heart

Neurocardiology has shown that the dynamic performance of the heart is strongly influenced by the brain, including the cerebral cortex. Neural control is mediated by sympathetic and parasympathetic fibers innervating the pacemaker, conductile, and contractile tissues of the heart. In this review, evidence is presented that autonomic control of the heart is lateralized, each brain side influencing cardiac activity in a different manner. Moreover, it is shown that asymmetries observed at the level of the cerebral hemispheres are characterized by different principles than asymmetries at the levels of the lower brain stem and the peripheral pathways. Findings on lateralized control of the heart are integrated into a general model of brain asymmetry, in which it is postulated that each hemisphere has a unique and comprehensive response system characterizing its cognitive, emotional, and physiological functioning.

[I. Usefulness of the exertion test and other methods based on the electrocardiogram in chronic ischemic disease]

Exercise testing still plays an important role in the management of patients with chronic ischemic heart disease, not only in the diagnosis but also in their prognostic and functional evaluation, and in the assessment of effects of the therapy. Moreover, ambulatory electrocardiography, signal averaged electrocardiography and heart rate variability provide useful information for certain groups of patients. This paper reviews the rationale, methodology and indications of the above mentioned procedures applied to chronic ischemic heart disease, with special reference to exercise testing. Recommendations for their use in clinical practice are also made.