Changes in Heart Rate Variability with Age

Depressed heart rate variability (HRV) after a myocardial infarction is associated with increased mortality. This is thought to be due to reduced parasympathetic activity and heightened sympathetic activity. Aging is associated with depressed HRV, but little is known of the affect of aging on parasympathetic activity. This study examined 56 healthy subjects (age range 40–102 years; 39 women). None had a history of heart disease or were on medication that would affect cardiac function. All had normal resting ECGs, normal heart size on chest X ray, and normal electrolytes. In all subjects, 24-hour Holter recordings were performed and used to measure HRV. In particular, the study examined the affect of age on HRV triangular index, which gives an estimate of overall HRV, and on RMSSD (square root of the mean squared differences of successive normal-to-normal RR intervals), which gives an estimate of short-term components of HRV and is thought to reflect the overall extent of vagal modulations of heart rates. Both these parameters were compared in patients younger and older than 70 years. Each recording lasted at least 17 hours; the majority of recordings were longer than 20 hours. There was a significant decrease in HRV triangular index with age (r =?0.4, P < 0.05) and no significant change in RMSSD with age(r =?0.08, P = NS). There was a significant difference in HRV index in those > 70 years compared with those < 70 years (38.0 ± 9.3 vs 31.0 ± 11, respectively, P <0.02). There was no significant difference in RMSSD between the two age groups (26.7 ± 8.2 ms vs 28.4 ± 11.3 ms, respectively, P = NS). Thus, the study concludes that aging reduces the global measure of HRV and may reflect reduced responsiveness of autonomic activity to external environmental stimuli with age. However, the time-domain short-term components of HRV are not affected by age and, therefore, the fast and presumably vagal modulations of heart rate appear to be maintained.     

Heart Rate Variability in Emergency Department Patients with Sepsis

OBJECTIVE: To test the hypothesis that heart rate variability (HRV) can provide an early indication of illness severity among patients presenting to the emergency department (ED) with sepsis. METHODS: The authors enrolled a convenience sample of 15 ED patients meeting the American College of Chest Physicians/Society of Critical Care Medicine criteria for sepsis. Each patient had continuous Holter monitoring performed in the ED. Acute Physiology and Chronic Health II (APACHE II) and Sequential Organ Failure (SOFA) scores were calculated for the day of presentation. Holter tapes obtained in the ED were analyzed off-line to calculate HRV variables for the 5-minute segment with the least artifact and non-sinus beats. These variables were correlated with APACHE II and SOFA scores. RESULTS: LFnu (normalized low-frequency power), an assessment of the relative sympathetic contribution to overall HRV, was correlated with increased illness severity as calculated using APACHE II (r = -0.67, r(2) = 0.43) and SOFA (r = -0.80, r(2) = 0.64) scores. LF/HF ratio (low-frequency/high-frequency ratio), a measure of sympathovagal balance, was correlated with the SOFA score [r = -0.54 (95% CI = -0.83 to -0.01), r(2) = 0.29]. All five patients who required critical care monitoring or ventilatory support or who died during the first 5 days of their hospitalization had LFnu values below 0.5 and LF/HF ratios less than 1.0. None of the patients with measurements greater than these threshold values died or required these interventions during the five days following admission. CONCLUSIONS: A single variable, LFnu, which reflects sympathetic modulation of heart rate, accounted for 40-60% of the variance in illness severity scores among patients presenting to the ED with sepsis. HRV, as reflected in LFnu and the LF/HF ratio and measured with a single brief (5-minute) period of monitoring while in the ED, may provide the emergency physician with a readily available, noninvasive, early marker of illness severity. The threshold effect of LFnu and LF/HF in the prediction of early clinical deterioration was an unexpected finding and should be regarded as hypothesis-generating, pending further study.     

24-Hour Heart Rate Variability in Patients with Vasovagal Syncope

Since alterations in the autonomic nervous system are thought to play a major role in the pathogenesis of vasovagal syncope, we characterized the chronic autonomic profile of 44 patients with syncope and 20 healthy subjects by means of heart rate variability using 24-hour Holter recordings (time- and frequency-domain indexes), and evaluated whether the different types of responses to tilting (vasodepressive versus cardioinhibitory) could be associated with different cardiac autonomic patterns. Twenty-three patients exhibited a positive response to tilting, which was vasodepressive in 11 patients and cardioinhibitory in 12 patients. All vasodepressive patients had a standard deviation of the averages of NN (SDANN) intervals in all 5-minute segments lower than 100 ms. Patients with vasodepressive syncope also had significantly lower values of RMSSD (the 24-hour square root of the mean of the sum of the squares of differences between adjacent normal RR intervals) than those with cardioinhibitory response, and lacked the day-night rhythm of the low frequency/high frequency ratio. However, only SDANN values correctly identified patients with vasodepressive response to tilting. We conclude that (1) the population of patients with vasovagal syncope is heterogeneous, (2) patients with vasodepressive syncope have a peculiar chronic autonomic profile as assessed by 24-hour heart rate variability analysis, and (3) the evaluation of the autonomic profile in 24-hour Holter recordings could be of value in the diagnosis of patients with syncope.     

慢性肺心病患者的心率变异性

目的：观察慢性肺心病患者心率变异性，了解其自主神经功能的变化。方法：对25例慢性肺心病，25例健康对照者（对照组）作前瞻性对照研究，记录24h动态心电图，作时域和频域分析，结果：与对照组比较，肺心病组相邻心搏的R－R间期之差＞50ms的心搏数占R－R间期数的百分(pNN50)，每5min正常R－R间期标准差的平均值（SDANN），频域指标的高频（HF）明显降低，低频与高频的比值（LF／HF），明显升高，差异均有非常显著意义（P均＜0．01），而频域指标的低频（LF）无明显变化（P＞0．05），经过治疗后，肺心病组处于缓解期，与治疗前比较，HF，PNN50，SDANN等指标明显增加，而LF／HF明显降低，差异均有非常显著意义（P均＜0．01），肺心病组病人治疗后HF，pNN50,SDANN等指标均低于对照组，而LF／HF明显高于对照组，差异均有非常显著意义（P均＜0．01），肺心病组治疗后LF与治疗前及对照组比较，差异不具显著意义（P＞0．05）。结论：肺心中层得不仅交感神经活动占优势，同时并存迷走神经功能受损，自主神经功能可能存在连续性障碍。     

慢性充血性心力衰竭患者的心率变异性分析

目的：评价心率变异性在慢性充血性心力衰竭患者中的变化。方法：用24h动态心电图研究慢性充血性心力衰竭患者与对照组的心率变异性及比较其他心脏结构及功能参数。结果：慢性充血性心力衰竭组的SDNN，SDANN，LF，HF，LF／HF均较对照组显著降低（P＜0．05），且随心衰严重程度增加，心率变异性呈递减，并与LVEF，LVEDD及LVSF改变相关（P＜0．05或P＜0．01）。结论：心率变异性可作为了解心衰程度、指导治疗和判定预后的参考指标之一。     

Heart Rate Variability in Passive Tilt Test: Comparative Evaluation of Autoregressive and FFT Spectral Analyses

The dynamic response of the autonomic nervous system during tilting is assessed by changes in the low (LF) and high frequency (HF) components of the RR series power spectral density (PSD). Although results of many studies are consistent, some doubts related to different methodologies remain. Specifically, the respective relevance of autoregressive (AR) and fast Fourier transform (FFT) methods is often questioned. Reat-to-beat RR series were recorded during 90° passive tilt in 18 healthy subfects (29 ± 5 years, eight females). FFT-based (50% overlap, Manning window) and AR-based (Levinson-Durbin algorithm) PSDs were calculated on the same RR intervals. Powers in very low frequency (VLF: < 0.04 Hz), LF (0.04–0.15 Hz), and HF (0.15–0.40 Hz) bands were calculated either by spectrum integration (FFT and AR_IN), by considering the highest AR component in each band (AR_HP), or by summation of all AR components (AR_AP). LF and HF raw powers (ms²) were normalized by total power (%P) and by total power after removal of the VLF component (nu). AR and FFT total powers were not different, regardless of body position. In supine condition, when compared to AR_HP and AR_AP. FFT underestimated VLF and overestimated LF, whereas in tilt position FFT overestimated HF and underestimated LF. However, supine/tilt trends were consistent in all methods showing a clear reduction of HF and a less marked increase of LF. Both normalization procedures provided a significant LF increase and further magnified the HF decrease. Results obtained with AR_IN were remarkably close to those obtained with FFT. In conclusion, significant differences between AR and FFT spectral analyses do exist, particularly in supine position. Nevertheless, dynamic trends provided by the two approaches are consistent. Normalization is necessary to evidence the LF increase during tilt.     

Prognostic Value of Heart Rate Variability in Patients Awaiting Cardiac Transplantation

Time and frequency domain parameters of heart rate variability (HRV) were determined in patients with severe end stage heart failure awaiting cardiac transplantation (HTX). These parameters were then correlated with mortality to investigate the performance of HRV in discriminating between groups with high and low risk of death. The standard deviation of five consecutive RR intervals (SDANN) was found to be the parameter with the greatest sensitivity (90%) and specificity (91%). Patients with SDANN values of < 55 msec had a twenty-fold increased risk of death (90% confidence limits: 4–118, P < 0.001). The results furthermore suggest that measurements of HRV are superior to other prognostic markers such as left ventricular ejection fraction, pulmonary artery wedge pressure, cardiac index, and serum sodium levels. We conclude that HRV is a powerful, noninvasive tool to assess the risk of death in candidates for HTX. HRV measurements can therefore be used as a supplement to other markers of risk to determine the optimal therapeutic strategy in patients with severe congestive heart failure.     

Decreased Heart Rate Variability in Patients with Congestive Heart Failure and Chronotropic Incompetence

Heart rate variability was studied in 41 patients (aged 48 ± 12 years) with congestive heart failure secondary to idiopathic dilated cardiomyopathy. All patients underwent a treadmill exercise test and 24-hour Holter ECC monitoring. Chronotropic incompetence was defined as the failure to achieve > 80% of the predicted maximal heart rate response given by 220 – age (years) at peak exercise. Spectral heart rate variability was analyzed from 24-hour Holter ECCs and was expressed as total (0.01–1.00 Hz), low (0.04–0.15 Hz), and high (0.15–0.40 Hz) frequency components. The standard deviation of all normal RR intervals (SDNN) was also computed. Chronotropic incompetence was observed in ten patients. Peak oxygen consumption was significantly lower in patients witb chronotropic incompetence compared with those without chronotropic incompetence. The total (5.11 ± 1.26 In [ms²] vs 6.41 ± 0.92 In [ms²]; P = 0.009) and low (3.38 ± 1.65 In [ms²] vs 5.45 ± 1.34 In [ms²];P = 0.003), but not the high (3.42 ± 1.04 In [ms²] vs 4.00 ± 1.12 in [ms²]; P = 0.249) frequency components of heart rate variability were significantly lower in patients with chronotropic incompetence, although there was no significant difference in mean heart rate (88 ± 20 beats/min vs 86 ± 15 beats/min; P = 0.831) or left ventricular ejection fraction (22%± 10% vs 24%± 10%; P = 0.619). SDNN was also significantly lower in patients with chronotropic incompetence compared witb those without chronotropic incompetence (64 ± 34 ms vs 102 ± 37 ms; P = 0.030). Conclusions: The observation that heart rate variability is significantly decreased in patients with congestive heart failure who have chronotropic incompetence suggests that chronotropic incompetence may relate to an abnormal autonomic influence on the heart in these patients.     

针灸并用对卒中后抑郁患者心率变异性的影响

目的观察针灸并用对卒中后抑郁患者心率变异性(HRV)的影响。方法将120例患者分为对照组(n=60)和治疗组(n=60)。两组均给予口服百忧解及针刺治疗,治疗组配合艾灸疗法,比较两组治疗前后汉密尔顿抑郁量表(HAMD)17项评分及HRV改变。结果治疗后,治疗组HAMD评分低于对照组,减分率高于对照组(P0.05);两组24 h正常R-R间期标准差(SDNN)、24 h每5分钟平均正常R-R间期标准差(SDANN)均较治疗前增加(P0.05),治疗组大于对照组(P0.05);24 h相邻R-R间期差值的均方根(RMSSD)、24 h相邻R-R间期差值50 ms的百分数(PNN50)较治疗前降低(P0.05),治疗组小于对照组(P0.05);两组低频功率(LF)、高频功率(HF)及LF/HF均大于治疗前(P0.05),治疗组大于对照组(P0.05)。结论针灸结合较单纯针刺能更好地调整卒中后抑郁患者自主神经功能,改善其抑郁状态。     

冠心病患者心率变异性与室性心律失常的关系

目的　探讨冠心病患者心律变异性 (HRV )与室性心率失常之间的关系。方法　对 88例冠心病患者 ,根据动态心电图上室性早搏 (室早 )频次分为冠心病频发室早组 ( 4 2例 )和冠心病无室早组 ( 4 6例 )进行比较 ,并分别与正常对照组( 3 0例 )进行比较 ,观察HRV的时域指标和室性心律失常。结果　冠心病患者HRV时域指标SDNN、SDANN、SDNNin dex、rMSSD和PNN50 均明显低于正常对照组 (P <0 .0 5～ 0 .0 1) ,而冠心病频发室早组除rMSSD外 ,余各项指标也明显低于冠心病无室早组 (P <0 .0 5～ 0 .0 1) ;SDNN与冠心病室性早搏频次存在明显的相关性。结论　冠心病患者HRV减低 ,反映了冠心病患者心脏自主神经调节功能失衡 ,尤其在伴有频发室早的患者中更为明显 ;冠心病室早的发生与交感神经活性增强有关 ,通过长时HRV分析 ,能对此作出客观评价     

204例无症状性心肌缺血患者心率变异生的分析

目的：探讨老年冠心病患无症状肌缺血心率变异生的变化情况,方法：204例冠心病患在日常生活状态下进行24h三通道动态心电图监测,并详细记录日常活动和相关症状,同时对无症状心肌缺血进行心率变异性分析。结果：无症状心肌缺血与心绞痛均可引起心率变异性多个参数的减低,204例患出现823次心肌缺血,其中624次为无症状心肌缺血,无症状心肌缺血组心率变异性及多个参数均低于有症状心肌缺血和正常对照组比后降低幅度更大,P均＜0．05,结论：三通道动态心电图是检测无症状心肌缺血心率变异性的有效方法,老年冠心病患无症状心肌缺血心率变异性多个参数均低于心绞痛和正常对照组,提示无症状心肌缺血更易引起心血管事件的发生,应引起临床的重视。     

胎儿心率变异功率谱与胎儿窘迫状态的关系

目的：评价胎心率变异功率谱与胎儿窘迫状态的关系。方法：对301例单胎妊娠孕妇行产前胎儿电子监护,将所得胎心率模拟信号转化为数字信号后再行功率谱分析,分析极低频（verylowfrequency1,VLF）、低频1（lowfrequency,LFl）、LF2、高频1（highfrequency1,HFl）、HF2、HF3、HF4功率谱密度与脐动脉血血气分析指标、脐血促红细胞生成素和肾上腺素浓度的关系。结果：LF2与碳酸氢根（HCO3）、二氧化碳总量（TCO2）呈正相关（P〈0．01）;HFl与碳酸氢根（HCq）、二氧化碳总量（TCO2）呈负相关（P〈0．01）;VLF与促红细胞生成素浓度呈负相关（P〈0．01）;LFI与肾上腺素浓度呈正相关（P〈0．05）。结论：胎心率变异性的功率谱密度反映了胎儿窘迫不同发展阶段的状态。     

Heart Rate Variability and Major Arrhythmic Events in Patients with Idiopathic Dilated Cardiomyopathy

This prospective study of 71 patients with idiopathic dilated cardiomyopathy (IDC) and preserved sinus rhythm was designed to evaluate the relation between heart rate variability (HRV) and subsequent major arrhythmic events. Standard time- and frequency-domain HRV parameters were obtained from analysis of 24-hour Holter ECG recordings. During a mean follow-up of 15 ± 5 months, major arrhythmic events including sustained ventricular tachycardia, ventricular fibrillation, and sudden cardiac death occurred in 10 of the 71 study patients (14%). Neither time- nor frequency-domain indices of HRV differed significantly between patients with and patients without subsequent major arrhythmic events. However, there was a trend toward a lower standard deviation of the average normal RR interval for all 5-minute segments of the 24-hour recording (68 ± 17 ms vs 80 ± 31 ms; P = 0.06) in patients with major arrhythmic events. In addition, the percentage of adjacent normal RR intervals differing > 50 ms over the recording period tended to be lower in patients with major arrhythmic events (6%± 3% vs 9%± 6%; P = 0.08). Our results indicate a tendency toward attenuated parasympathetic activity in IDC patients with subsequent major arrhythmic events compared to arrhythmia-free patients. Larger studies with longer follow-up periods are necessary to clarify the role of HRV measurements for arrhythmia risk prediction in patients with IDC.     

Changes in Heart Rate, Heart Rate Variability, and Heart Rate Turbulence during Evolving Reperfused Myocardial Infarction

Depressed cardiac parasympathetic activity is associated with electrical instability and adverse outcomes after myocardial infarction (MI). Heart rate turbulence (HRT), reflecting reflex vagal activity, and heart rate variability (HRV), reflecting tonic autonomic variations are both reduced in the subacute phase of MI. However, the evolution of these components of cardiac autonomic control between subacute and chronic phase of MI has not been defined. We prospectively studied 100 consecutive patients with a recent first MI with ST-segment elevation, who underwent successful direct percutaneous coronary interventions. Beta-adrenergic blockers and angiotensin-converting enzyme (ACE) inhibitors were administered according to the state-of-the-art medical practice guidelines. HRT and HRV were measured from 24-hour ambulatory electrocardiographic recordings 10 days and 12 months after the index MI. There was no significant difference in mean RR interval between the subacute and chronic phase of MI (875 ± 145 versus 859 ± 122 ms). Indices of HRV increased significantly during the observation period (SDNN: from 88.8 ± 26.8 to 116.0 ± 35.7 ms, P < 0.001; SDNNi: from 37.9 ± 15.9 to 46.0 ± 16.3 ms, P < 0.001; SDANN: from 79.6 ± 34.7 to 105.6 ± 35.4 ms, P < 0.001). In contrast, there were no significant changes in indices of HRT (turbulence onset: from −0.008 ± 0.022 to −0.012 ± 0.025%; turbulence slope: from 7.78 ± 5.9 to 8.06 ± 6.8 ms/beat). In contrast to reflex autonomic activity, there was a significant recovery of tonic autonomic activity within 12 months after MI. These different patterns of recovery of reflex versus tonic cardiac autonomic control after MI need to be considered when risk stratifying post-MI patients.     

Heart Rate Variability in Myocardial Infarction With and Without Malignant Arrhythmias: Comparison with Heart Transplant Recipients and Normal Subjects

Myocardial autonomic denervation occurs after acute MI. This process is followed by a reduction of heart rate variability (HRV) and an increase of malignant ventricular arrhythmias and sudden death. This study investigated whether there are any significant differences in HRV among the population of MI who did and did not have malignant ventricular arrhythmias (MVAs), normal subjects and heart transplant recipients, the paradigm of the denervated heart. We studied 25 subjects aged 42 ± 17 years, with normal clinical and cardiac noninvasive evaluation (group A); 70 patients aged 57 ± 14 years, who had MI hut no arrhythmic event in 36 months of follow-up (group B); 13 patients with MI aged 65 ± 9 years, who had had sustained VT, VF, or sudden death (group C); and 16 cardiac transplant recipients aged 35 ± 14 years (group D). The ECG was sampled for 256 seconds. We calculated, in time and frequency domain, the standard deviation of the RR cycle length and the spectral component's very low frequency (< 0.05 Hz), low frequency (0.05–0.15 Hz), and high frequency (0.15–0.35 Hz). The values of HRV in group A were significantly greater than in groups B, C, and D (P < 0.001) and greater in group B than in groups C and D (P < 0.001). Groups C and D did not differ (P = 0.610). These data indicate that HRV of patients who have had an MI and MVAs is very similar to that of heart transplant recipients. This is an indirect evidence that myocardial autonomic denervation may play an important role in the genesis of malignant arrhythmic events.     

Heart Rate Variability in Isolated Rabbit Hearts

The presence of heart rate variability (HRV) in patients with cardiac denervation after heart transplantation raised our interest in HRV of isolated, denervated hearts. Hearts from seven adult white ELCO rabbits were transferred to a perfusion apparatus. All hearts were perfused in the working mode and in the Langendorff mode for 20 minutes each. HRV was analyzed in the frequency domain. A computer simulated test ECG at a constant rate of 2 Hz was used for error estimation of the system. In the isolated, denervated heart, HRV was of random, broadband fluctuations, different from the well-characterized oscillations at specific frequencies in intact animals. Mean NN was 423 ± 51 ms in the Langendorff mode, 406 ± 33 ms in the working heart mode, and 500 ms in the test ECG. Total power was 663 ± 207 ms², 817 ± 318 ms², and 3.7 ms², respectively. There was no significant difference in any measure of HRV between Langendorff and working heart modes. The data provide evidence for the presence of HRV in isolated, denervated rabbit hearts. Left atrial and ventricular filling, i.e., the working heart mode, did not alter HRV, indicating that left atrial or ventricular stretch did not influence the sinus nodal discharge rate.     

心脑血管疾病患者心率变异性与阿司匹林抵抗的研究

目的阿司匹林抵抗患者心率变异性指标的变化。方法服用阿司匹林（100 mg/d）至少7天以上的心脑血管患者作为入选标准。二磷酸腺苷（adenosine disphosphate,ADP）和花生四烯酸（arachidonic acid,AA）作诱导剂在Chrono-log 560 Ca上测定血小板聚集功能。记录受检者24小时动态心电图。结果阿司匹林抵抗发生率为12.5%（n=21）。阿司匹林抵抗组HRV时域参数和频域参数与阿司匹林敏感组比较均有统计学意义（P〈0.01）。阿司匹林抵抗组高血压患者的比率（42.9%）与阿司匹林敏感组（29.3%）比较有显著差别（P=0.01）。结论阿司匹林抵抗组HRV时域参数和频域参数与阿司匹林敏感组比较均有统计学意义,这提示我们HRV下降的患者服用阿司匹林时,要定期检测血小板聚集功能,一旦发生阿司匹林抵抗,应提示这类患者要及时调整抗血小板药物,加大阿司匹林的剂量或换用其他抗血小板药物。     

Effect of Transdermal Scopolamine on Heart Rate Variability in Patients with Severe Coronary Heart Disease

A decrease in cardiac parasympathetic tone is a recognized finding in patients with ischemia heart disease, correlating closely with disease severity and overall survival. The aim of this study was to assess whether transdermal Scopolamine (Tds), which increases parasympathetic tone in healthy volunteers, increases vagal tone in patients with severe CAD and whether it might have an antiischemic effect. Fifteen patients (10 men, aged 55 ± 8 years) with three-vessel CAD, but with no prior MI and preserved ventricular function, underwent 24-hour Holter monitoring and exercise testing before and after wearing a Scopolamine patch for 24 hours. Time-domain measures of heart rate variability (HRV) and the total number and duration of ischemic episodes were obtained from the Holter recordings for each patient. Tds significantly (P < 0.05) increased the values of all HRV measures. Tds also reduced the total number of ischemic episodes (from 273 to 159, P < 0.05) and their total duration (from 136 to 46 min per patient, P < 0.05). Tds also increased treadmill exercise duration from 293 ± 101 to 345 ± 95 seconds (P <0.05) and the time to 1-mm ST depression from 177 ± 105 to 244 ± 128 seconds (P < 0.02), while maximum ST depression was reduced from 2.86 ± 0.6 to 2.3 ± 0.3 (P < 0.05). No significant side effects were observed. Tds modifies the autonomic balance in patients with severe CAD toward a condition associated with a better prognosis. It may also be useful as an adjunctive treatment for ischemic heart disease.     

Intraindividual Reproducibility of Heart Rate Variability

Heart rate variability was determined from three consecutive Holter recordings performed on days 1, 7, and 28 in 17 normal subjects, in 13 patients with angiographically normal coronary arteries, and in 9 patients with remote myocardial infarctions. Group data of several time and frequency domain measures of heart rate variability were highly reproducible (correlation coefficients 0.629–0.894). However, some individuals exhibited considerably larger day-to-day variations in heart rate variability. Single heart rate indices differed by up to 50% between two Holter recordings. Such potential differences must be considered when repeated heart rate variability determinations are used to assess changes in neurocardiac reflex regulation or effects of therapeutic interventions.     

Relationship Between Spectral Measures of Heart Rate Variability and Ventricular Ectopic Activity in Patients with Idiopathic Ventricular Tachycardia

This study examines the relationship of hourly spectral measures of heart rate variability (HRV) to the occurrence of ventricular ectopic (VE) activity in 20 patients with idiopathic ventricular tachycardia and frequent VE's. Spectral measures of HRV were obtained from 24-hour Holler recordings from the patients in a drug free state and included the total energies in the spectrum, the low frequency components (1) (0.04–0.15 Hz) representing predominantly sympathetic lone with some contribution from the parasympathetic and high frequency components (H) (0. 15–0.4 Hz) representing mainly parasympathetic tone. A high H component (parasympathetic) was defined as area > 12 msec and high L components (sympathetic) as area > 30 msec. On an hourly analysis of spectral components in relation to VE activity, VE's occurred significantly more frequently during periods of low H and low L (F = 20.5, DF = 3, P < 0.0001). The number of VE's did not differ statistically in the other combinations of H and L components flow H, low L = 612.8 (50.1); high H, low L = 180.1 (36.8); low H, high L = 338.4 (58.9); high H, high L - 204.9 (17.7) VE's/hr (SEM). The results suggest that VE's are more frequent during periods of low H and low L and are diminished when either H or L are increased in patients with idiopathic ventricular tachycardia. The results would be consistent with the hypothesis that the parasympathetic nervous system has an electro physiologically stabilizing effect on the myocardium.