Effects of consecutive administration of central and peripheral anticholinergic agents on respiratory sinus arrhythmia in normal subjects

Respiratory sinus arrhythmia is reduced after pulmonary vein isolation in patients with paroxysmal atrial fibrillation

INTRODUCTION

Respiratory sinus arrhythmia (RSA) describes heart rate (HR) changes in synchrony with respiration. It is relevant for exercise capacity and mechanistically linked with the cardiac autonomic nervous system. After pulmonary vein isolation (PVI), the current therapy of choice for patients with paroxysmal atrial fibrillation (AF), the cardiac vagal tone is often diminished. We hypothesized that RSA is modulated by PVI in patients with paroxysmal AF.

MATERIAL AND METHODS

Respiratory sinus arrhythmia, measured by using a deep breathing test and heart rate variability parameters, was studied in 10 patients (64 ±3 years) with paroxysmal AF presenting in stable sinus rhythm for their first catheter-based PVI. Additionally, heart rate dynamics before and after PVI were studied during sympathetic/parasympathetic coactivation by using a cold-face test. All tests were performed within 24 h before and 48 h after PVI.

RESULTS

After PVI RSA (E/I difference: 7.9 ±1.0 vs. 3.5 ±0.6 bpm, p = 0.006; E/I ratio: 1.14 ±0.02 vs. 1.05 ±0.01, p = 0.003), heart rate variability (SDNN: 31 ±3 vs. 14 ±3 ms, p = 0.006; RMSSD: 17 ±2 vs. 8 ±2 ms, p = 0.002) and the HR response to sympathetic/parasympathetic coactivation (10.2 ±0.7% vs. 5.7 ±1.1%, p = 0.014) were diminished. The PVI-related changes in RSA correlated with the heart rate change during sympathetic/parasympathetic coactivation before vs. after PVI (E/I difference: r = 0.849, p = 0.002; E/I ratio: r = 0.786, p = 0.007). One patient with vagal driven arrhythmia experienced AF recurrence during follow-up (mean: 6.5 ±0.6 months).

CONCLUSIONS

Respiratory sinus arrhythmia is reduced after PVI in patients with paroxysmal AF. Our findings suggest that this is related to a decrease in cardiac vagal tone. Whether and how this affects the clinical outcome including exercise capacity need to be determined.

Comparison of pulse rate variability and heart rate variability for high frequency content estimation

Heart Rate Variability (HRV) analysis can be of precious help in most of clinical situations because it is able to quantify the Autonomic Nervous System (ANS) activity. The HRV high frequency (HF) content, related to the parasympathetic tone, reflects the ANS response to an external stimulus responsible of pain, stress or various emotions. We have previously developed the Analgesia Nociception Index (ANI), based on HRV high frequency content estimation, which quantifies continuously the vagal tone in order to guide analgesic drug administration during general anesthesia. This technology has been largely validated during the peri-operative period. Currently, ANI is obtained from a specific algorithm analyzing a time series representing successive heart periods measured on the electrocardiographic (ECG) signal. In the perspective of widening the application fields of this technology, in particular for homecare monitoring, it has become necessary to simplify signal acquisition by using e.g. a pulse plethysmographic (PPG) sensor. Even if Pulse Rate Variability (PRV) analysis issued from PPG sensors has been shown to be unreliable and a bad predictor of HRV analysis results, we have compared PRV and HRV both estimated by ANI as well as HF and HF/(HF+LF) spectral analysis on both signals.

An efficient algorithm for R-R intervals series filtering

Spectral analysis of heart rate variability (HRV) constitute a simple and non invasive way to study the autonomic nervous system (ANS) activity. On-line implementation of this technique would allow to follow the evolution of the ANS activity and to track transient events during medical procedures. However, continuous spectral analysis of HRV is not reliable enough due to the difficulty to obtain a noiseless ECG signal during a long period. Indeed, the consequential effects of each ECG signal perturbation on the R-R intervals gives an erroneous evaluation of HRV spectral analysis. In this article, we describe a real time filtering algorithm for R-R intervals series. This filter is able to detect each disturbed area and to replace the erroneous samples with the most probable ones. Therefore, this method allows detecting and replacing up to 90 % of R-R series erroneous samples while keeping the real recording time and without having any effect, beyond measure, on the frequency analysis result.

A new view of a stationarity of the RR series for sinusal variability analysis

The influence of ANS in sinusal variability is studied through analysis of RR series, and particularly RR interval variations during time. Different kinds of RR series signal analysis are applied to clinical situations found in cardiology. However, some of the RR series may be stationary as well as non-stationary. Statistical tests applied to the RR series will establish determinism and stationarity of these signals. The aim of this article is to characterize the statistical behaviour pattern of RR series in order to identify precautions that should be observed when time-frequency transform techniques are used in sinusal clinical investigations. Eight kinds of RR series concerning sinusal variability were submitted to the statistical tests. The results showed the uncertain character of the RR series and their non-stationarity. This result is consequently a warning against using several techniques of time-frequency transform for sinusal variability analysis. Some of the techniques studied are adapted to non-stationary signals under some conditions.

Genetic factors contribute to the variance in frequency domain measures of heart rate variability

Power spectral analysis of heart rate variability (HRV) provides quantitative phenotypic markers of autonomic nervous system activity. Reported determinants of HRV only partially explain its variability in the population. The purpose of this study was to estimate the contribution of genetic factors to the variance in HRV measures and assess the heritability of HRV. Subjects who underwent Holter recordings at a routine examination were eligible, excluding subjects with congestive heart failure, coronary artery disease, diabetes mellitus and those taking cardioactive medications. We analyzed the low-frequency power (LF), high-frequency power (HF), LF/HF ratio, very low-frequency power (VLF) and total power (TP). Heritability analysis was done by studying correlations between siblings (n = 682, in 291 sibships, 517 pairs) and between spouse pairs (n = 206 pairs). Adjustments were made for sex, age, systolic and diastolic blood pressure, heart rate, coffee and alcohol intake. SAS procedure MIXED was used to estimate and test significance of correlation within sibling pairs and within spouse pairs. Results from separate models were combined to estimate the components of variance of each phenotype, i.e. variance attributable to measured covariates, additive genetic effects (heritability) and household effects. After adjusting for covariates, the correlations were consistently higher among siblings (0.21-0.26) compared to spouses (0.01-0.19). The measured covariates in general accounted for 13-40% of the total phenotypic variance, whereas genes accounted for 13-23% of the variation among HRV measures. Genetic factors contribute towards a substantial proportion of the variance in heart rate and HRV. Recognition of the genetic determinants of HRV may provide additional insight into the pathophysiology of the autonomic nervous system and offer clues toward its modulation.

Inadequate sympathovagal balance in response to orthostatism in patients with unexplained syncope and a positive head up tilt test

AIM

To analyse the immediate response of heart rate variability (HRV) in response to orthostatic stress in unexplained syncope.

SUBJECTS

69 subjects, mean (SD) age 42 (18) years, undergoing 60 degrees head up tilt to evaluate unexplained syncope.

METHODS

Based on 256 second ECG samples obtained during supine and upright phases, spectral analyses of low (LF) and high frequency (HF) bands were calculated, as well as the LF/HF power ratio, reflecting the sympathovagal balance. All variables were measured just before tilt during the last five minutes of the supine position, during the first five minutes of head up tilt, and just before the end of passive tilt.

RESULTS

Symptoms occurred in 42 subjects (vasovagal syncope in 37; psychogenic syncope in five). Resting haemodynamics and HRV indices were similar in subjects with and without syncope. Immediately after assuming the upright posture, adaptation to orthostatism differed between the two groups in that the LF/HF power ratio decreased by 11% from supine (from 2.7 (1.5) to 2.4 (1.2)) in the positive test group, while it increased by 11.5% (from 2.8 (1.5) to 3.1 (1.7)) in the negative test group (p = 0.02). This was because subjects with a positive test did not have the same increment in LF power with tilting as those with a negative test (11% v 28%, p = 0.04), while HF power did not alter. A decreased LF/HF power ratio persisted throughout head up tilt and was the only variable found to discriminate between subjects with positive and negative test results (p = 0.005, multivariate analysis). During the first five minutes of tilt, a decreased LF/HF power ratio occurred in 33 of 37 subjects in the positive group and three of 27 in the negative group. Thus a decreased LF/HF ratio had 89% sensitivity, 89% specificity, a 92% positive predictive value, and an 86% negative predictive value.

CONCLUSIONS

Through the LF/HF power ratio, spectral analysis of HRV was highly correlated with head up tilt results. Subjects developing syncope late during continued head up tilt have a decrease in LF/HF ratio immediately after assuming the upright posture, implying that although symptoms have not developed the vasovagal reaction may already have begun. This emphasises the major role of the autonomic nervous system in the genesis of vasovagal (neurally mediated) syncope.

Heritability of heart rate variability: the Framingham Heart Study

BACKGROUND

There is evolving evidence that heart rate (HR) is genetically determined. Heart rate variability (HRV) measured by power spectral analysis provides quantitative phenotypic markers of autonomic nervous system activity. Reported determinants of HR and HRV only partially explain their variability in the population. The purpose of this study was to assess the heritability of HR and HRV and estimate the contribution of genetic factors to their variance.

METHODS AND RESULTS

Subjects who underwent ambulatory recordings at a routine examination were eligible; subjects with congestive heart failure, coronary artery disease, diabetes mellitus, and those taking cardioactive medications were excluded. We analyzed high-frequency power, low-frequency power, very low-frequency power, total power, low-frequency/high-frequency ratio, and the standard deviation of normal R-R intervals from 2-hour continuous ECG recordings. Heritability analysis was done by studying correlations between siblings (n=682, in 291 sibships, 517 pairs) and between spouse pairs (n=206 pairs) after adjusting for important covariates. Results from separate models were combined to estimate the components of variance attributable to measured covariates, additive genetic effects (heritability), and household effects. After adjusting for covariates, the correlations were consistently higher among siblings (0.21 to 0.26) compared with spouses (0.01 to 0.19). The measured covariates in general accounted for 13% to 40% of the total phenotypic variance, whereas genetic factors accounted for 13% to 23% of the variation among HR and HRV measures.

CONCLUSIONS

Heritable factors may explain a substantial proportion of the variance in HR and HRV. These results highlight the contribution of genetic versus environmental factors to autonomic nervous system activity.

Nicotine enhances presynaptic and postsynaptic glutamatergic neurotransmission to activate cardiac parasympathetic neurons

Although peripheral cholinergic neurotransmission has long been known to play a pivotal role in the control of heart rate and blood pressure, recent evidence has suggested that central cholinergic mechanisms may be involved in the genesis of hypertension, anxiety, cardiorespiratory control, and, in particular, the respiratory modulation of heart rate. Yet, the sites, mechanisms, and receptor subtypes involved in the action of nicotine within the central nervous system are controversial. The present study demonstrates that nicotine has at least 3 sites of action to increase the activity of vagal cardiac neurons. Nicotine, but not muscarinic agonists, activates postsynaptic receptors and a depolarizing inward current in vagal cardiac neurons studied with the perforated patch-clamp technique in a visualized brain stem slice. In addition, nicotine acts at different presynaptic and postsynaptic sites to facilitate glutamatergic neurotransmission. Presynaptic nicotinic receptors increase the frequency of transmitter release and are sensitive to block by alpha-bungarotoxin. Nicotine also elicits a previously undescribed augmentation of postsynaptic non-NMDA currents. The presynaptic and postsynaptic receptors may prove to be future targets in the search for agonists to increase vagal cardiac activity and reduce the fatality associated with cardiac hyperexcitability and for antagonists to reduce cardiac vagal activity in pathological conditions associated with abnormally low heart rates and cardiac function such as sudden infant death syndrome.

Nicotine excites cardiac vagal neurons via three sites of action

1. Nicotine is involved in many cardio-respiratory diseases, including hypertension and sudden infant death syndrome (SIDS), which is the most common cause of death in infants between 1 month and 1 year of age. While the aetiology of SIDS remains largely unknown, recent clinical studies suggest maternal cigarette smoking is a major risk factor in SIDS and an abnormality of cardio-respiratory control, particularly a centrally mediated slowing of the heart that precedes or accompanies apnoea, is involved. 2. Because the sites, mechanisms of action and diverse receptor types of nicotine within the central nervous system are controversial and poorly understood, in the present study we examined the effects of nicotine on specific brainstem neurons that control heart rate. Cardiac vagal neurons were identified in an in vitro slice preparation using a retrograde fluorescent tracer and were studied using both whole-cell and perforated patch-clamp electrophysiological techniques. 3. We have found there are different pre- and post-synaptic nicotinic receptors that have dramatic effects on glutamatergic neurotransmission as well as directly activating vagal cardio-inhibitory neurons.

Autonomic neurotoxicity of alcohol assessed by heart rate variability

Measurement of heart rate variability (CVR-R) provides a promising approach for evaluation of the autonomic nervous function. Specifically, high- and low-frequency component coefficients of variation of the CVR-R (C-CVHF and C-CVLF), computed from component spectral powers by autoregressive spectral and component analyses, are inferred to reflect parasympathetic and sympathetic activities, respectively. To assess the acute and chronic effects of alcohol on parasympathetic and sympathetic activities, ECGs in the supine posture were obtained in 11 male healthy volunteers, and in 23 male patients with severe alcoholic dependency together with the same number of age-matched healthy men. Significant changes in the CVR-R and heart rate were found 1 h after ethanol intake in the volunteers; also, the 1-h alteration in heart rate after intake was inversely correlated with that in the C-CVHF. The CVR-R, C-CVHF and C-CVLF were significantly depressed in the alcoholics compared to the matched controls. In the alcoholics, the age-adjusted correlation coefficients between not only the CVR-R but also C-CVHF and heart rate were negatively significant. These data suggest that acute and habitual intake of alcohol affects cardiac autonomic functions including sympathetic and parasympathetic activities; and, increase of heart rate in relation to alcohol, at least in alcoholics, seems to occur through reducing the parasympathetic activity.

Time-frequency analysis of slow cortical activity and cardiovascular fluctuations in a case of Alzheimer's disease

The dynamics and relationship of slow cortical activity (amplitude modulation of electroencephalograph at 0.02-0.05 Hz) and cardiovascular fluctuations (0.01-0.05 Hz range) was studied by time-frequency mapping (modified Wigner distribution) in a patient with Alzheimer's disease. The amplitude modulating at rest basal alpha and theta activity (lead Oz) was exaggerated compared with control subjects. Fluctuations at respiratory and nonrespiratory (0.01-0.05 Hz) frequencies in R-R intervals and blood pressure were present and within normal range. Spontaneous hypotension (by 20 to 80 mmHg lasting 15-20 s) accompanied by cardioacceleration occurred repeatedly in the supine position and during hyperventilation. Slow cortical activity and nonrespiratory fluctuations (0.01-0.05 Hz) in blood pressure increased concurrently with hypotensions. No signs of peripheral autonomic dysfunction or malfunction of baroreceptors were observed and the vasomotor instability appeared to be of central origin. The results suggested that slow cortical activity was functionally related to the central autonomic nervous system and reflected cortico-thalamo-brainstem interaction.