Reliability of Ultra‐Short ECG Indices for Heart Rate Variability

Background: Heart rate variability (HRV) is an accepted and reliable means for assessing autonomic nervous system dysfunction. A 5‐minute measurement of HRV is considered methodologically adequate. Several studies have attempted to use shorter recordings of 1–2 minutes or 10 seconds. The aim of this study was to determine the reliability of HRV parameters calculated from ultra‐short electrocardiogram recordings. Methods: Seventy healthy volunteers were recruited for the study. HRV was evaluated for 5 minutes according to accepted procedures. Thereafter, HRV parameters were recalculated from randomly selected 1‐minute and 10‐second intervals. The standard and ultra‐short measurements were correlated using intraclass correlation coefficients. Results: Good correlations between the 5‐minute electrocardiograms (ECGs) and both the 1‐minute and 10‐second ECGs were noted for average RR interval, and root mean square of successive differences in RR intervals (RMSSD). No correlation was noted for standard deviation of the RR interval (SDNN) and several other HRV parameters. Conclusions: RMSSD, but not SDNN, seem a reliable parameter for assessing HRV from ultra‐short (1 minute or 10 seconds) resting electrocardiographic recordings. Power spectral analysis and evaluation of other HRV parameters require longer recording periods. Further research is required to evaluate the importance of ultra‐short RMSSD for cardiovascular risk stratification. Ann Noninvasive Electrocardiol 2011;16(2):117–122     

心率和心率变异性用于评定颈部手法刺激对自主神经系统的影响

目的应用心率和心率变异性分析,评定颈部手法刺激对自主神经系统的影响。方法选择正常青年男性志愿者,对受试者进行颈部手法刺激,刺激前和刺激后各记录5min动态心电图,以心率和心率变异性作为观测指标,判断颈部手法刺激对自主神经系统的影响。结果对30名正常青年男性志愿者观察发现,颈部手法刺激后,心率显著降低(RR间期延长);时域分析中SDNN有显著性增加,频域分析中VLF和总功力谱有显著性增加。结论心率和心率变异性是一项评定颈部手法刺激对自主神经系统效应的有用指标。     

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.     

QT离散度昼夜的变化与心率变异性的联系

目的 探讨QT离散度的昼夜改变与心率变异性的关系。方法 测量计算20例正常人24小时动态心电图的QT、QTc、QT与QTc离散度及心率变异参数。结果 发现QT、QTd、QTcd、RR间期、RMSSD、HF、LH/HF存在昼夜的明显差异。QTd、QTcd与RR间期、RMSSD、HF呈现明显的负性相关，与LF/HF呈明显的正性相关。结论 QT离散度的增加与交感神经活动的增加和迷走神经活动的减弱密切相关。     

Incipient cardiovascular autonomic imbalance revealed by wavelet analysis of heart rate variability in Type 2 diabetic patients.

AIM: Incipient cardiovascular autonomic imbalance is not readily diagnosed by conventional methods. Spectral analysis of heart rate variability (HRV) by wavelet transform (WT) was used to measure cardiovascular autonomic function in patients with Type 2 diabetes. METHODS: Thirty-two diabetic patients without (D), 26 with cardiovascular autonomic neuropathy (DAN) and 72 control subjects (C) participated. A 30-min HRV time series was analysed by wavelet transformation and four characteristic frequency intervals were defined: I (0.0095-0.021 Hz), II (0.021-0.052 Hz), III (0.052-0.145 Hz) and IV (0.145-0.6 Hz). RESULTS: When compared with C, in both D and DAN the normalized power and amplitude of interval II were increased and of interval IV decreased, resulting in a significantly higher II/IV ratio. Furthermore, in DAN the normalized power and amplitude of interval I were increased and of interval III decreased when compared with the D and C groups. The diabetic patients were divided in two equal subgroups according to HbA(1c) < 8.0% and >or= 8.0%. In the subgroup with HbA(1c) >or= 8.0%, normalized power in interval II was significantly higher and in interval IV significantly lower than in the subgroup with HbA(1c) < 8.0%. In D, but not in DAN patients prescribed ACE inhibitors, the absolute amplitude and power of oscillations were significantly higher than in patients not taking ACE inhibitor therapy. CONCLUSIONS: Patients with diabetes have increased sympathetic and decreased parasympathetic cardiac activity regardless of the presence of autonomic neuropathy. Glycaemic control and treatment with ACE inhibitors may favourably influence HRV in diabetic patients without autonomic neuropathy.     

室上性心动过速发作前后心率变异的观察

分析21例SVT发作前后5min心率变异性旨在阐明植物神经系统异常在SVT发作中的作用。结果显示SVT发作前SDNN明显降低,LF、LFP、LF/HF明显升高,HF、HFP明显降低,LF/HF与SVT持续时间呈正相关(r=0.54,P<0.05 。)提示SVT发作前交感-迷走神经平衡向着交感神经张力增高,迷走神经张力消退的方向偏移,使SVT易于发作和持续。     

Metabolic syndrome and short‐term heart rate variability in young adults

Aims Heart rate variability (HRV) can be used to estimate autonomic nervous control of the cardiovascular system. In middle‐aged subjects, the metabolic syndrome (MetS) is associated with lower HRV. We hypothesized that alterations in autonomic balance are already present in young adults with the MetS, and analysed the association of short‐term HRV with the MetS (using the National Cholesterol Education Program definition), in 1889 subjects aged 24–39 years. Methods Short‐term (3 min) HRV analysis included high‐frequency (HF), low‐frequency (LF) and total (TP) spectral components of HRV and LF/HF ratio. Results The presence of the MetS was associated with lower HF, LF and TP in men and women, and with higher LF/HF ratio in women. In men, waist circumference was the strongest individual MetS component that associated with HRV. After adjustments for age and heart rate, MetS was associated with lower HF and higher LF/HF ratio in women, but only with a lower TP in men (all P < 0.05). Conclusions MetS is associated with lower HRV in young adults. The individual components of MetS are differentially associated with HRV in men and in women. Our results are consistent with lower vagal activity and a possible increase in sympathetic predominance in women with the MetS. This sex difference in vagal activity and sympathovagal balance may partly explain the greater increase in cardiovascular risk associated with MetS in women than in men.     

Heart rate variability in patients with orthotopic heart transplantation: Long-term follow-up

To evaluate heart rate variability (expressed as the standard deviation of RR intervals) within 5 years of follow-up, we studied 20 patients (14 males, 6 females, mean age 44 ± 12 years) who underwent orthotopic heart transplantation. Six measurements were taken: one in the first 3 weeks after transplantation, and the others once annually, for 5 years. Twenty healthy subjects (mean age 44 ± 7 years) constituted the control group. Heart rate variability increased significantly in the first 3 years of follow-up (7.2 ± 1 vs. 11.1 ± 4, p < 0.001; 11.1 ±4vs. 15.2±4, p<0.01; 15.2±4vs. 18.9±5, p< 0.05); in the following years this trend slackened and values did not reach a statistically significant difference (18.9 ± 5 vs. 21.4 ± 5; 21.4 ± 5 vs. 22.5 ± 5). The mean standard deviation was invariably greater in the control group (63.6 ± 12). These findings show that sinus rhythm variability in the denervated heart progressively increased over 5 years of follow-up. The absence of presynaptic uptake, which is responsible for adrenergic hypersensitivity to circulating catecholamines and intrinsic cardiac reflexes, does not appear to cause this phenomenon, since these mechanisms are not able to evolve in time after cardiac transplantation. Therefore, an enhanced beta-adrenergic receptors density or affinity to circulating catecholamines or a limited sympathetic reinnervation may be the more probable underlying mechanism.     

阻塞性睡眠呼吸暂停综合征心率变异性的变化及其意义

目的 :研究阻塞性睡眠呼吸暂停综合征 （OSAS）患者心率变异性 （HRV ）的变化。方法 :经夜间多导睡眠图（PSG） 7h监测及动态心电图检查 ,选取重度 OSAS患者及正常受试者各 2 0例 ,采用时域法和频域法分析 HRV。结果 :OSAS组与对照组比较时域指标 SDANN ,SDNN ,r MSSD显著增高 ,SDNN- index则显著降低 ,频域指标VL F,L F,HF,L Fnrom,HFnorm及 L F/HF均较对照组显著增高。结论 :OSAS患者交感神经及副交感神经活动均增强 ,交感神经活动增强占优势     

Heart rate recovery fast‐to‐slow phase transition: Influence of physical fitness and exercise intensity

Background

Postexercise heart rate (HR) recovery presents an exponential decay, with two distinct phases: a fast phase, characterized by abrupt decay of HR, and determined by parasympathetic reactivation; and a slow phase, characterized by gradual decay of HR, and predominantly determined by sympathetic withdrawal. Although several methods have been proposed to assess postexercise HR recovery, none of those methods selectively assesses the time of transition from the fast to the slow phase of the HR recovery curve (HRR_PT), and the magnitude of decay prior to (HRR_FP) and after this point (HRR_SP). Therefore, the aim of the present study was to propose a method to identify HRR_PT, HRR_FP, and HRR_SP and to verify the effects of exercise intensity and physical fitness on such parameters.

Methods

Ten healthy young participants (24 ± 3 years; 23.6 ± 1.7 kg/m²) randomly underwent two exercise sessions (30 min of cycling), at moderate (MI) and high intensity (HI); followed by 5 min of inactive recovery. HR was continuously recorded during the sessions. The algorithm for HRR_PT analysis was written in Python and is freely available online.

Results

HRR_PT and HRR_SP were increased in HI session compared with MI (81 ± 24 vs. 60 ± 20 s; 8 ± 10 vs. 1 ± 5 bpm; p = .04), and there was no difference in HRR_FP between sessions (49 ± 15 vs. 46 ± 10 bpm; p = .17). In addition, HRR_PT for MI exercise session was significantly and negatively associated with VO_2max (r = ‐0.85, p < .05).

Conclusion

The method herein presented was sensitive to exercise intensity, and partially responsive to aerobic fitness. Next studies should perform the pharmacological and clinical validations of the method.

     

自主神经在阵发性心房颤动发生中的作用

目的 探讨自主神经在阵发性心房颤动发生中的作用。方法 分析31例阵发性房颤患者47次房颤（〉30s）发作前动态心电图心率变异性时域和频域指标。患者分为器质性心脏病组（19例）和非器质性心脏病组（12例）。根据房颤发作前频域指标变化，将阵发性房颤分为3组：房颤发作前心率变异性频域指标低频（LF）成分增加，LFIHF比例增加为交感神经介导房颤，房颤发作前心率变异性频域指标高频（HF）成分增加，LF／HF比例减小为迷走神经介导房颤，其余的为未分类房颤。结果 器质性心脏病组房颤发作28次，其中交感神经介导房颤17次（60．7％），非器质性心脏病组房颤发作19次，迷走神经介导房颤12次（63．2％）。结论 自主神经在房颤的发作中起着重要的作用，器质性心脏病中的阵发性房颤多为交感神经介导房颤。非器质性心脏病中的阵发性房颤多为迷走神经介导房颤。     

年龄及平均心率对心率变异指标的影响

为探讨年龄及平均心率对心率变异(HRV)的影响,观察心绞痛(n=66)、心肌梗塞(n=51)和正常人(n=75)3组对象短程体表心电图正常R-R间距之标准差(SD)及变异系数(CV)参数.结果表明多数情况下SD与平均心率显著负相关,而CV与平均心率的相关性较小.同时发现心绞痛及心肌梗塞组SD与年龄显著负相关(P<0.05),但CV与年龄无显著关系(P>0.05).故认为以CV作为HRV指标更能客观反映心脏自主神经功能状况.     

冠心病心率变异性及其诊断价值

本文应用２４ｈ动态心电图对健康人（对照组）和冠心病心绞痛、心肌梗死患者进行心率变异性研究。结果发现:心绞痛组和前壁心梗组的正常ＲＲ间期总体标准差（ＳＤＮＮ）、每连续５ｍｉｎ时段正常ＲＲ间期均值的标准差（ＳＤＡＮＮ）及其平均值（ＳＤＮＮｉｎｄｅｘ）、心率总功率（ＴＰ）、极低频功率（ＶＬＦ）、低频功率（ＬＦ）和高频功率（ＨＦ）等均低于对照组（均Ｐ＜０．０１）；下壁心梗组的ＳＤＮＮ，ＳＤＮＮｉｎｄｅｘ和ＬＦ低于对照组（均Ｐ＜０．０５）；前壁心梗组的ＳＤＮＮ，ＳＤＡＮＮ和ＬＦ低于心绞痛组（均Ｐ＜０．０５）。心率变异诊断冠心病的阳性标准取低于对照组上述任一项指标９５％区间下限值，则其特异性为９３．９％，心绞痛组敏感性为５１．２％，心梗组为７１．４％。提示心率变异下降对冠心病的诊断有一定的参考价值。     

The effects of fasting on heart rate variability in hypertensive patients

ABSTRACT

Heart rate variability (HRV) is an independent indicator of increased mortality in patients with myocardial infarction and congestive heart failure. The effects of fasting on the HRV are not known in hypertensive patients. Therefore, studying the effects of Ramadan fasting on hypertensive patients’ HRV seems reasonable to address.

We conducted a prospective study including 20 hypertensive patients with sinus rhythm. HRV was determined twice by ambulatory 24-hour Holter recordings at fasting during and after Ramadan.

Subjects mean age was 55 ± 11.8 years. Sex-ratio was 1.5. When two groups compared, statistically significant differences were found in terms of SDNN (113 ± 71 vs 140 ± 38, p = 0.001), SDANN (109.7 ± 45 vs 134.8 ± 48.3, p = 0.008), T power (2368.7 ± 121.3 vs 3660.5 ± 170.9, p = 0.03) and LF (552.2 ± 31.3 vs 903.7 ± 48.9, p < 0.0001) values.

HRV parameters were found to be decreased in Ramadan. Thus, Ramadan fasting enhances the activity of the sympathetic system in hypertensive patients.     

Activity-responsive pacing produces long-term heart rate variability

INTRODUCTION: Long-term heart rate variability (HRV) measures, including the standard deviation of means of successive 5-minute epochs of R-R interval intervals (SDANN) and the power law slope (beta), are important prognostic measures, yet their physiologic basis is unknown. We tested the hypothesis that long-term HRV arises from physical activity in a randomized cross-over study in patients with rate-responsive pacemakers. METHODS AND RESULTS: Ten patients with complete heart block and dual-chamber pacemakers underwent 24-hour periods of ambulatory ECG in each of three pacing modes: atrially tracked, fixed-rate, and rate-responsive pacing. SDANN, ultra low frequency (ULF; frequencies <0.0033 Hz), and beta slope were calculated; and high-frequency power and root mean square of consecutive normal R-R intervals (rMSSD) were calculated as measures of short-term HRV, which have autonomic origins. Long-term HRV measures were similar with atrially tracked and rate-responsive pacing and were much greater than in fixed-rate pacing (SDANN P = 0.0001; ULF P = 0.0001; beta slope P = 0.0002). Short-term HRV measures were similarly low in fixed-rate and rate-responsive pacing (P = NS) and were significantly lower than with atrially tracked pacing (P = 0.0034). CONCLUSION: Rate-responsive pacing reproduces long-term, but not short-term, measures of HRV, suggesting that they may be markers of heart rate responses to patient activity.     

Current clinical applications of heart rate variability

Heart rate variability (HRV) has become a popular method for the studies of physiologic mechanisms responsible for the control of heart rate fluctuations, in which the autonomic nervous system appears to play a primary role. Depression of HRV has been observed in many clinical scenarios, including autonomic neuropathy, heart transplantation, congestive heart failure, myocardial infarction (MI), and other cardiac and noncardiac diseases. However, it is important to realize that clinical implication of HRV analysis has been clearly recognized in only two clinical conditions: (1) as a predictor of risk of arrhythmic events or sudden cardiac death after acute MI, and (2) as a clinical marker of evolving diabetic neuropathy. Recently, its role in evaluation and management of heart failure has also been recognized. It is pertinent to recognize the limitations of HRV as far as its clinical utility at present is concerned. The methodology of HRV had remained poorly standardized until the recent publication of the Special Report of the Task Force of ESC/NASPE, and thus has been presenting difficulty in comparing earlier existing data. Also, determination of the exact sensitivity, specificity, and predictive value of HRV, as well as the normal values of standard measures in the general population, still require further investigation before better standards can be set for existing and future clinical applications. This article reviews the major concepts of HRV measurements, their clinical relevance, and the recent advances in this field.     

Interleukin-6 levels are inversely correlated with heart rate variability in patients with decompensated heart failure

INTRODUCTION: Increased local and systemic elaboration of cytokines have an important role in the pathogenesis of congestive heart failure (CHF) through diverse mechanisms. Because cytokines are known to act at the neuronal level in both the peripheral and central nervous system, we sought to determine whether increased cytokine levels are associated with the autonomic dysfunction that characterizes CHF. METHODS AND RESULTS: We studied 64 patients admitted for decompensated CHF (mean age 59+/-12 years). Autonomic function was assessed using time- and frequency-domain heart rate variability (HRV) measures, obtained from 24-hour Holter recordings. In addition, norepinephrine, tumor necrosis factor-alpha (TNF-alpha), and interleukin-6 (IL-6) were measured in all patients. TNF-alpha levels did not correlate with any of the HRV measures. IL-6 inversely correlated with the time-domain parameters of standard deviation of RR intervals (SDNN) (r = -0.36, P = 0.004) and standard deviation of all 5-minute mean RR intervals (SDANN) (r = -0.39, P = 0.001), and with the frequency-domain parameters of total power (TP) (r = -0.37, P = 0.003) and ultralow-frequency (ULF) power (r = -0.43, P = 0.001). No correlation was found between IL-6 and indices of parasympathetic modulation. Using multiple linear regression models, adjusting for clinical variables and drug therapies, the strong inverse relationship between IL-6 and SDNN (P = 0.006), SDANN (P = 0.001), TP (P = 0.04), and ULF power (P = 0.0007) persisted. CONCLUSION: Reduction of long-term HRV indices is associated with increased levels of IL-6 in patients with decompensated heart failure. The ability of long-term HRV parameters to better reflect activation of diverse hormonal systems may explain their greater prognostic power for risk stratification in patients with CHF.     

糖尿病患者心率减速力与心率变异性分析

目的探讨心率减速力（decelerationcapacityofhearrate,DC）与心率变异性（heartratevariability,HRV）在评价糖尿病患者自主神经功能方面的应用。方法对73例2型糖尿病患者和65名正常人群对照组进行24h动态心电图检查,离线计算DC、HRV时域指标并进行比较和相关分析。结果2型糖尿病患者的DC及HRV各时域指标均比对照组降低,差异均有统计学意义（P〈0．05）。相关分析结果显示,2型糖尿病组DC与HRV中的总标准差（SDNN）呈正相关（r=O．597,P〈O．01）,与差值均方根（RMSSD）呈正相关（r=O．569,P〈0．01）,与pNN50呈正相关（r=0．501．P〈0．05）。结论DC和HRV各时域指标有较好的相关性,可作为2型糖尿病患者自主神经功能检测的指标。     

Factors influencing heart rate variability in patients with severe aortic valve disease

Background and hypothesis: Heart rate variability (HRV) is an accepted tool for the assessment of cardiovascular autonomic tone. There are no sufficient data concerning its application to patients with severe aortic valve disease (AVD) requiring cardiac surgery. Methods: It was the aim of this study to examine HRV and its physiologic correlates in patients with severe aortic valve disease requiring cardiac surgery. The correlates of time domain indices of HRV obtained from 24-h Holter electrocardiographic recordings were analyzed in 36 consecutive patients (23 men and 13 women, mean age 62 ± 11 years) with AVD prior to cardiac surgery (aortic stenosis: 17 patients, aortic valve regurgitation: 3 patients, combined aortic valve disease: 16 patients). Results: Low values of HRV were found in the entire study group: SDNN 96.8 ± 30.9 ms, SDNNI 39.3 ± 14.4 ms, SDANN 86 ± 28.9 ms, and RMSSD 30 ± 18.1 ms. In a univariate analysis, there was no significant correlation between the time domain measures of HRV and age, gender, medication, left ventricular ejection fraction, peak aortic pressure gradient, fraction of aortic valve regurgitation, and left ventricular mass assessed by echocardiography. Patients in advanced functional classes of heart failure [New York Heart Association (NYHA) III or IV] had significantly lower values for SDNN (83.8 ± 33.6 vs. 107.3 ± 24.7 ms; p<0.05) and SDANN (72.7 ± 29.4 vs. 96.6 ± 24.3 ms; p<0.05) than patients in NYHA class I or II. Reassessment of HRV 1 week after aortic valve replacement was performed in 17 patients and showed a significant further decrease of SDNN (102.4 ± 29.7 vs. 61.5 ± 23.5 ms; p<0.001), SDNNI (40.7 ± 13.6 vs. 23.4 ± 12.4 ms; p<0.001) and SDANN (91.8 ±29.2 vs. 54.2 ± 22.8 ms;p<0.001). Conclusion: Patients with AVD requiring cardiac surgery reveal reduced time domain indices of HRV. This observation is pronounced in patients with a progressed clinical class of heart failure, whereas hemodynamic and echocardiographic parameters seem to have no significant influence on HRV parameters in this population. In addition, there is evidence of a further reduction of HRV time domain indices 1 week after uncomplicated aortic valve replacement.