Heart rate variability before the occurrence of silent myocardial ischemia during ambulatory monitoring

Ischemia and no obstructive coronary arteries (INOCA): A narrative review

Myocardial ischemia with no obstructive coronary arteries (INOCA) is a chronic coronary syndrome condition that is increasingly being recognized as a substantial contributor to adverse cardiovascular mortality and outcomes, including myocardial infarction and heart failure with preserved ejection fraction (HFpEF). While INOCA occurs in both women and men, women are more likely to have the finding of INOCA and are more adversely impacted by angina, with recurrent hospitalizations and a lower quality of life with this condition. Abnormal epicardial coronary vascular function and coronary microvascular dysfunction (CMD) have been identified in a majority of INOCA patients on invasive coronary function testing. CMD can co-exist with obstructive epicardial coronary artery disease (CAD), diffuse non-obstructive epicardial CAD, and with coronary vasospasm. Epicardial vasospasm can also occur with normal coronary arteries that have no atherosclerotic plaque on intravascular imaging. While all predisposing factors are not clearly understood, cardiometabolic risk factors, and endothelium dependent and independent mechanisms that increase oxidative stress and inflammation are associated with microvascular injury, CMD and INOCA. Cardiac autonomic dysfunction has also been implicated in abnormal vasoreactivity and persistent symptoms. INOCA is under-recognized and under-diagnosed, partly due to the heterogenous patient populations and mechanisms. However, diagnostic testing methods are available to guide INOCA management. Treatment of INOCA is evolving, and focuses on cardiac risk factor control, improving ischemia, reducing atherosclerosis progression, and improving angina and quality of life. This review focuses on INOCA, relations to HFpEF, available diagnostics, current and investigational therapeutic strategies, and knowledge gaps in this condition.

Gender-Related Differences in Chest Pain Syndromes in the Frontiers in CV Medicine Special Issue: Sex & Gender in CV Medicine

Coronary artery disease (CAD) is the leading cause of morbidity and mortality among both women and men, yet women continue to have delays in diagnosis and treatment. The lack of recognition of sex-specific biological and socio-cultural gender-related differences in chest pain presentation of CAD may, in part, explain these disparities. Sex and gender differences in pain mechanisms including psychological susceptibility, the autonomic nervous system (ANS) reactivity, and visceral innervation likely contribute to chest pain differences. CAD risk scores and typical/atypical angina characterization no longer appear relevant and should not be used in women and men. Women more often have ischemia with no obstructive CAD (INOCA) and myocardial infarction, contributing to diagnostic and therapeutic equipoise. Existing knowledge demonstrates that chest pain often does not relate to obstructive CAD, suggesting a more thoughtful approach to percutaneous coronary intervention (PCI) and medical therapy for chest pain in stable obstructive CAD. Emerging knowledge regarding the central and ANS and visceral pain processing in patients with and without angina offers explanatory mechanisms for chest pain and should be investigated with interdisciplinary teams of cardiologists, neuroscientists, bio-behavioral experts, and pain specialists. Improved understanding of sex and gender differences in chest pain, including biological pathways as well as sociocultural contributions, is needed to improve clinical care in both women and men.

Heart Rate Variability During a Standard Dive: A Role for Inspired Oxygen Pressure?

Introduction: Heart rate variability (HRV) during underwater diving has been infrequently investigated because of environment limitations and technical challenges. This study aims to analyze HRV changes while diving at variable hyperoxia when using open circuit (OC) air diving apparatus or at constant hyperoxia using a closed-circuit rebreather (CCR). We used HRV analysis in time and frequency domain adding nonlinear analysis which is more adapted to short-time analysis and less dependent on respiratory rate (Sinus respiratory arrhythmia). Materials and Methods: 18 males, 12 using OC (30 mfw for 20 min) and 6 using CCR (30 mfw for 40 min.). HRV was recorded using a polar recorder. Four samples of R-R intervals representing the dive were saved for HRV analysis. Standard deviation of normal-to-normal intervals (SDNN), square root of the mean squared differences between successive RR intervals (rMSSD), and average RR intervals (RR) in time-domain; low frequency (LF) and high frequency (HF) in frequency domain were investigated. Nonlinear analysis included fractal dimension (FrD). Results: SDNN and rMSSD were significantly increased during descent and at depth with OC, not with CCR. Mean RR interval was longer at depth with OC, but only during ascent and after the dive with CCR. HF power was higher than baseline during the descent both with OC and CCR and remained elevated at depth for OC. The LF/HF ratio was significantly lower than baseline for descent and at depth with both OC and CCR. After 30 min of recovery, the LF/HF ratio was higher than baseline with both OC and CCR. Nonlinear analysis detected differences at depth for OC and CCR. Discussion: Increased parasympathetic tone was present during diving. RR duration, SDNN; rMSSD, HF spectral power all increased during the dive above pre-dive levels. Conversely, HF power decreased (and the LF/HF increased) 30 min after the dive. Using FrD, a difference was detected between OC and CCR, which may be related to differences in partial pressure of oxygen breathed during the dive.

Home Monitoring of Heart Rate as a Predictor of Imminent Cardiovascular Events

Introduction: Previous studies have documented that day-to-day variability of heart rate (HR) has prognostic significance for cardiovascular (CV) events in general population. It is unknown how HR dynamics variate before imminent CV event in patients with coronary artery disease (CAD). Our aim was to study day-to-day variation in HR dynamics before the occurrence of CV event in patients with initially stable CAD.

Methods: Forty-four patients with angiographically documented CAD from ARTEMIS study measured R-R intervals on a weekly basis at home for 2 years. Home measurements were performed in controlled conditions (3 min at supine and sitting) 1–2 times per week. Eleven patients had a CV event (7 acute coronary syndromes, 1 cardiac death, 2 new onset of arrhythmia needing hospitalization and 1 stroke), which occurred 11 ± 7 months after enrolment. Mean R-R interval was analyzed prospectively from the home measurements. For the patients with new CV event, average, and standard deviation (SD) of the mean R-R interval over 8 weeks preceding the CV event were calculated. For the patients without new CV event, corresponding period was determined by the median follow-up at the occurrence of new CV event.

Results: There were no differences in the mean R-R interval analyzed over 8 weeks between the patients with and without new CV event. The variability of mean R-R interval over 8 weeks was greater in the patients with new CV event compared to the patients without new CV event at the supine (95 ± 34 vs. 59 ± 26 ms, p < 0.001) and sitting positions (92 ± 28 vs. 62 ± 24 ms, p < 0.001).

Conclusion: Day-to-day variability of mean R-R interval is greater before the new CV event in CAD patients suggesting to a more unstable cardiac autonomic regulation preceding these events.

Quantification of autonomic nervous activity by heart rate variability and approximate entropy in high ultrafiltration rate during hemodialysis

BACKGROUND

Few studies have focused on the imbalance of the autonomic nervous system in ultrafiltration rate (UFR) subjects without blood pressure variation during maintenance hemodialysis (HD), although the role of autonomic nervous system activation during HD has been proposed to be an important factor for the maintenance of blood pressure.

METHODS

Variations over time in autonomic nervous activity due to differences in UFR were evaluated by measuring heart rate variability (HRV) and approximate entropy (ApEn) in 35 HD patients without blood pressure variations during HD session. The subjects were divided into 3 groups, those with UFR <10 ml/h/kg; ≥10 ml/h/kg but ≤15 ml/h/kg; and >15 ml/h/kg, and Holter ECG was recorded continuously during HD session using frequency analysis of RR intervals. High frequency (HF) and low frequency (LF) spectral components are found to be representative of the parasympathetic nervous system and sympathovagal balance, respectively, with the ratio of LF to HF of HRV providing a measure of sympathetic nervous system.

RESULTS

In subjects with UFR >15 ml/h/kg, HF components were significantly lower, and LF/HF and ApEn values were significantly higher, in the latter half of an HD session than before starting HD.

CONCLUSION

Removing water from these subjects would promote sustained sympathetic nervous overactivity. These findings indicate that the UFR during HD needs to be set at ≤15 ml/h/kg.

Heart rate variability and critical flicker fusion frequency changes during and after parachute jumping in experienced skydivers

PURPOSE

The purpose of this study was (1) to further explore the heart rate dynamics and assess a potential cardiovascular risk in response to 4000 m jumps in experienced skydivers; (2) to assess whether there is an impact of such jumps on skydivers' cortical arousal or not, which may impact their decision making processes.

METHOD

18 experienced skydivers performed successive jumps from a plane at 4000 m of height. Heart rate dynamics and cortical arousal were assessed by the use of heart rate variability and Critical Flicker Fusion Frequency (CFFF), respectively.

RESULTS

CFFF did not differ between the three measurement time points (p > 0.05). Mean heart rate increased during the jump (p < 0.001) and came back to pre-jump values after the jump (p < 0.001). Percentage of the differences of successive NN intervals greater than 50 ms (pNN50) decreased during the jump (p < 0.001) and kept lower values after the jump compared to pre-jump (p < 0.05). High-frequency power (HF) did not differ during the jump (p > 0.05) but decreased after the jump compared to both pre-jump (p < 0.01) and jump (p < 0.05). Sample entropy decreased during the jump (p < 0.001) and came back to pre-jump values after the jump (p > 0.05).

CONCLUSION

These results confirm a vagal input reduction associated with a rise of the sympathetic tone during the jump and suggests that the experienced skydiver is not exposed to a high cardiovascular risk. This study also shows that environmental stresses induced by free fall could not hamper the perceptual vigilance of experienced skydivers.

Differences in heart rate variability in non-hypertensive diabetic patients correlate with the presence of underlying cerebrovascular disease

We previously showed that diabetes contributes to the development of sclerotic lesions in cerebral arteries. In this study, we attempted to clarify whether differences in heart rate variability in non-hypertensive diabetic patients were dependent on the presence or absence of underlying cerebrovascular disease. Thirty diabetic subjects between 40 and 59 years of age and who had no prior history of hypertension were used in this study. Lacunar lesions (LA) were detected with magnetic resonance imaging and atherosclerotic lesions (AS) were detected using intra- and extracranial magnetic resonance angiography, and by ultrasonographic scanning of the carotid artery. Patients underwent a full clinical laboratory screening and a power spectrum analysis of their heart rate variability. Subjects were divided into two groups: those with and without LA. The low frequency/high frequency ratio (LF/HF ratio) was found to be significantly increased (P<0.01) in subjects with LA (2.2 +/- 0.3) compared to those without LA (1.3 +/- 0.1). When subjects were divided into groups based on their presence or absence of AS, high-frequency power was found to be significantly reduced (P<0.05) in the subjects with AS (12.8 +/- 3.4 ms) compared to those without AS (19.4 +/- 1.7 ms). The LF/HF ratio was found to be significantly increased (P<0.05) in the subjects with AS (2.2 +/- 0.3) compared to those without AS (1.4 +/- 0.1). Our data suggested that atherosclerotic lesions in cerebrovascular diseased linked to decrease of vagal nerve activity in non-hypertensive diabetic patients.

On the genesis of myocardial ischemia

About three quarters of myocardial ischemic events are triggered by the autonomic nervous system. The pathognomonic constellation is a combination of an almost complete withdrawal of tonic vagal activity with increased sympathetic activity. The reduction of tonic vagal activity, which is characteristic for ischemic heart disease, and the acute withdrawal of vagal drive preceding the onset of ischemia are not dependent on coronary artery disease. In this paper, the pathophysiological steps that lead from sympathetic-parasympathetic imbalance to myocardial ischemia shall be discussed. A considerable increase of aerobic glycolysis within the myocardium as a result of the autonomic imbalance is of special importance in this process.

Changes in heart rate and heart rate variability before ambulatory ischemic events(1)

OBJECTIVES

The aim of this study was to determine the time course of autonomic nervous system activity preceding ambulatory ischemic events.

BACKGROUND

Vagal withdrawal can produce myocardial ischemia and may be involved in the genesis of ambulatory ischemic events. We analyzed trajectories of heart rate variability (HRV) 1 h before and after ischemic events, and we examined the role of exercise and mental stress in preischemic autonomic changes.

METHODS

Male patients with stable coronary artery disease (n = 19; 62.1 +/- 9.3 years) underwent 48-h ambulatory electrocardiographic monitoring. Frequency domain HRV measures were assessed for 60 min before and after each of 68 ischemic events and during nonischemic heart rate-matched control periods.

RESULTS

High-frequency HRV decreased from -60, -20 to -10 min before ischemic events (4.8 +/- 1.3; 4.6 +/- 1.3; 4.4 +/- 1.2 ln [ms(2)], respectively; p = 0.04) and further from -4, -2 min, until ischemia (4.4 +/- 1.3; 4.1 +/- 1.3; 3.7 +/- 1.2 ln [ms(2)]; p's < 0.01). Low frequency HRV decreases started at -4 min (p < 0.05). Ischemic events occurring at high mental activities were preceded by depressed high frequency HRV levels compared with events at low mental activity (p = 0.038 at -4 min, p = 0.045 at -2 min), whereas the effects of mental activities were not observed during nonischemic control periods. Heart rate variability measures remained significantly decreased for 20 min after recovery of ST-segment depression when events were triggered by high activity levels.

CONCLUSIONS

Autonomic changes consistent with vagal withdrawal can act as a precipitating factor for daily life ischemia, particularly in episodes triggered by mental activities.

Circadian variation of heart rate variability and the rate of autonomic change in the morning hours in healthy subjects and angina patients

BACKGROUND

Incidence of sudden cardiac death peaks during the early morning hours when there is a rapid withdrawal of vagal and an increase of sympathetic tone. The rate of autonomic change could be of prognostic importance.

PATIENTS AND METHODS

A total of 65 patients with angina pectoris, free from other diseases and drug free, were Holter monitored for 24 h. A total of 30 patients were also monitored on isosorbide-5-mononitrate (IS-5-MN) and on metoprolol respectively. A total of 33 age-matched healthy subjects served as controls. Spectral components of heart rate variability (HRV) were analysed hourly, with special reference to the rapid changes of autonomic tone during the night and early morning hours. Circadian variation was assessed in two ways: (1) Mean HRV day (8 a.m.-8 p.m.) and night (0-5 a.m.) were compared. (2) For the morning/night hours (0-10 a.m.), individual hourly values for max. and min. HRV, the difference max.-min. (gradient), the rate of change per hour between max. and min. (velocity) and the largest difference between two consecutive hours (max. velocity) were recorded and the mean value for the group calculated.

RESULTS

During the night/morning hours, healthy controls demonstrated faster HF max. velocity (P=0.002) and higher HF gradient (P=0.011) than angina patients. Metoprolol and IS-5-MN increased the HF gradient (P=0.008 and P=0.003, respectively), and metoprolol tended to increase the max. velocity (P=0.02). Metoprolol substantially decreased the LF/HF gradient (P=0.001), velocity (P=0.008) and max. velocity (P=0.0001).

CONCLUSION

Rapid vagal withdrawal seemed to be a sign of a healthy autonomic nervous system in the control group but was significantly slower in angina patients. IS-5-MN and metoprolol tended to normalise vagal withdrawal and metoprolol slowed down the rapid increase in sympathetic predominance in the morning in patients.

Autonomic nervous system activity before and during episodes of myocardial ischemia in patients with stable coronary artery disease during daily life

Spectral analysis of heart rate variability (HRV) was used to assess changes in the autonomic nervous system (ANS) 10 minutes before, during, and 10 minutes after 110 ischemic episodes (IEs) in 38 patients (25 men, age 61 +/- 10 years) with stable coronary artery disease. In 26 of 77 diurnal IEs (07:00-22:59) there were no changes in the spectral indexes (LF and HF) during the study period. In the remainder there was an increase in the LF:HF ratio due to HF withdrawal that started before the onset of the IE. All 33 nocturnal episodes also showed an increase in the LF:HF ratio, which was due not only to HF withdrawal, but also to a simultaneous increase in LF. Although it is not the only cause, the ANS plays a significant role in triggering IEs during daily life in patients with stable coronary artery disease. The common factor in all such episodes is a gradual withdrawal of parasympathetic tone.

Heart rate variability, trait anxiety, and perceived stress among physically fit men and women

BACKGROUND

It is unclear from prior reports whether the relationships between self-ratings of anxiety or emotional stress and parasympathetic nervous system components of heart rate variability are independent of personality and cardiorespiratory fitness. We examined those relationships in a clinical setting prior to a standardized exercise test.

METHODS AND RESULTS

Heart rate variability (HRV) was measured during 5 min of supine rest among 92 healthy men (N=52) and women (N=40) who had above-average cardiorespiratory fitness as indicated by peak oxygen uptake measured during grade-incremented treadmill exercise. HRV datasets were decomposed into low-frequency (LF; 0.05-0.15 Hz) and high-frequency (HF; 0.15-0.5 Hz) components using spectral analysis. Self-ratings of trait anxiety and perceived emotional stress during the past week were also assessed.

CONCLUSIONS

There was an inverse relationship between perceived emotional stress during the past week and the normalized HF component of HRV (P=0.038). This indicates a lower cardiac vagal component of HRV among men and women who perceived more stress. That relationship was independent of age, gender, trait anxiety, and cardiorespiratory fitness. It was also independent of heart rate; mean arterial blood pressure; and respiration rate, factors which can influence HRV and might be elevated among people reporting anxiety and perceived stress. We conclude that vagal modulation of heart period appears to be sensitive to the recent experience of persistent emotional stress, regardless of a person's level of physical fitness and disposition toward experiencing anxiety.

Heart rate variability in healthy volunteers during normobaric and hyperbaric hyperoxia

Inhaled supranormal partial pressure of oxygen induces bradycardia and peripheral vasoconstriction. The exact mechanism of the decreasing heart rate is not clear, but the autonomic nervous system is partly involved. In the present study the role of the autonomic nervous system in hyperoxic bradycardia was evaluated by using the power spectral analysis of heart rate variability. Ten healthy volunteers participated in four experiments: (i) hyperbaric oxygen treatment (100% oxygen at 2.5 ATA), (ii) hyperbaric air treatment (O2 21% at 2.5 ATA), (iii) oxygen treatment at normal pressure (100% O2, 1 ATA) and (iv) air breathing at normal pressure (21% O2, 1 ATA). During the experiments, ECG was registered and subjected to power spectral analysis. The volunteers rated their perception of temperature, ear discomfort, sweating and excitement on a visual analogue scale. Statistical comparison of the results of the four trials was conducted with a two-way ANOVA for repeated measurements. Heart rate decreased during all interventions, but there were no statistically significant differences between the sessions. High frequency variability of heart rate variability and Hayano's index of HF power increased and LF/HF ratio decreased with increasing partial pressure of oxygen. Our results suggest, that normobaric and hyperbaric hyperoxia increase parasympathetic influence in the regulation of the heart.

Wavelet transform analysis of heart rate variability during dipyridamole-induced myocardial ischemia: relation to angiographic severity and echocardiographic dyssynergy

BACKGROUND

Analysis of heart rate variability (HRV) is a valuable noninvasive method for quantifying autonomic cardiac control in humans and has been utilized during dipyridamole echocardiographic test to differentiate positive from negative test results.

HYPOTHESIS

We aimed to evaluate, by means of HRV analysis, the influence of the angiographic severity of coronary artery disease on cardiac autonomic control during dipyridamole-induced myocardial ischemia.

METHODS

We analyzed RR interval variability changes during dipyridamole-induced myocardial ischemia in 31 selected patients (mean age 54 +/- 9 years) with available coronary angiography and positive dipyridamole echocardiographic test. Spectral components of HRV were assessed by means of wavelet transform analysis for the last 5 min before the beginning of the test (baseline) and for 5 min after the onset of ischemia-related events (peak dipyridamole effect).

RESULTS

Patients were divided into three groups according to the number of coronary diseased vessels (Group A, single-vessel disease; Group B, double-vessel disease; Group C, triple-vessel disease). No difference was detectable at baseline among the three groups. After dipyridamole, low-frequency power, a measure of sympathetic modulation of heart rate, increased and echocardiographic wall motion score index worsened in all groups (p < 0.001). The increase in low-frequency power was more evident in Group C patients than in the other two groups (p < 0.005). Furthermore, after dipyridamole, a direct correlation was found between low-frequency power and wall motion score index (r = 0.59; p < 0.001).

CONCLUSIONS

These data suggest that HRV analysis performed during dipyridamole echocardiographic test provides useful information to assess the severity of coronary artery disease.

Time-dependent changes of heart rate variability after percutaneous transluminal angioplasty

OBJECTIVES

It is not known whether the improvement of myocardial perfusion by percutaneous transluminal coronary angioplasty (PTCA) is followed by a response of the autonomic nervous system depending on the recovery of the myocardium. In this study we investigated changes of heart rate variability parameters in patients before and after PTCA at different time intervals.

METHODS

In 42 patients with coronary artery disease documented on angiography, before and after PTCA 24-hour measurements of heart rate variability (HRV) were performed from Holter tapes. The time elapsed between the two measurements was 3 to 4 days in 26 patients and 6 to 8 months in 16 patients. Time domain parameters of HRV were calculated.

RESULTS

Comparison of the two recordings showed that the parameters rMSSD, pNN50, and SDNN index decreased, whereas SDNN and SDANN increased. These changes were not statistically significant. A subgroup analysis revealed different results for patients with and without previous myocardial infarction: the parasympathetically and more sympathetically influenced parameters revealed different changes in these groups. Other variables such as ejection fraction or severity of coronary artery disease did not influence the HRV results. Although no statistically significant difference was seen on comparison of the patients with different recording intervals, patients with a longer interval between the two measurement periods showed higher values of all HRV parameters closer to normalized values. This observation may be explained by a delayed recovery of myocardial function after successful revascularization by PTCA.

Circadian rhythm of autonomic activity in patients with obstructive sleep apnea syndrome

BACKGROUND AND HYPOTHESIS

Although the immediate effects of sleep apnea on hemodynamics and the neurological system have been studied, little is known about the circadian rhythm of heart rate variability in patients with obstructive sleep apnea syndrome (OSAS). The purpose of the present study was to investigate the effects of sleep apnea on the autonomic activity during daytime, which may play some role in the pathogenesis of cardiovascular complications in OSAS.

METHODS

We studied 18 middle-aged male patients with OSAS and 10 age-matched control subjects. Patients with OSAS were classified according to the severity of OSAS: patients with an apnea index (AI) < 20 were considered to have mild OSAS (Group 1, n = 8) and patients with an AI > or = 20 were considered to have severe OSAS (Group 2, n = 10). Heart rate variability was calculated from the 24-h ambulatory electrocardiograms by the Fourier transformation. Power spectra were quantified at 0.04-0.15 Hz [low frequency power (LF)ln(ms2)] and 0.15-0.40 Hz [high frequency power (HF)ln(ms2)]. The HF component and the ratio of LF to HF were used as indices of the parasympathetic and sympathetic activity, respectively.

RESULTS

The circadian rhythms of the LF, HF, and LF/HF ratio differed significantly in Group 2 compared with Group 1 and control subjects (p < 0.05). Hypertension (> 160/95 mm Hg) was found in 7 (70.0%) of 10 patients in Group 2, and in 1 (12.5%) of 8 patients in Group 1. Echocardiographic evidence of left ventricular hypertrophy (LVH) (an interventricular septal thickness or a left ventricular posterior wall thickness > or = 12 mm) was found in 3 (30.0%) of 10 patients in Group 2, and in 1 (12.5%) of 8 patients in Group 1. The mean HF from 4 A.M. to 12 noon was significantly lower in Group 2 than in Group 1 and the control group, and it correlated significantly with the lowest nocturnal SaO2 (r = 0.58, p < 0.05). The mean LF/HF ratio during the same period was significantly higher in Group 2 than in Group 1 and the control group, and it correlated significantly with total time of the nocturnal oxygen saturation < 90% (r = 0.64, p < 0.005) and the lowest nocturnal SaO2 (r = 0.56, p < 0.05). Ventricular tachycardia was found in the early morning in one patient, ST-T depression in two patients, and sinus arrest in two patients in Group 2.

CONCLUSION

These findings suggest that sleep-disordered breathing associated with severe oxygen desaturation might influence heart rate variability not only during sleep but also during daytime. OSAS per se might contribute to altered circadian rhythm in autonomic activity leading to the development of cardiovascular diseases.

Perioperative myocardial ischemia is associated with a prolonged cardiac vagal dysfunction after non-cardiac surgery

BACKGROUND

Heart rate variability (HRV), a measure of cardiac autonomic balance seems to be linked to coronary artery disease (CAD). Impaired vagal input facilitates the generation of fatal arrhythmias and has a great impact on morbidity and mortality. The purpose of this study was to determine the relationship between perioperative HRV and the incidence of silent myocardial ischemia (SMI) and ventricular dysrhythmias in CAD-patients undergoing non-cardiac surgery.

METHODS

31 patients were studied by continuous Holter electrocardiography preoperatively and again on the evening before surgery until postoperative day 3. Three frequency and one time domain measures of HRV (TP, 0.01-1.00 Hz: total power of the amplitude spectral plot; LF, 0.04-0.15 Hz: low-frequency power; HF, 0.15-0.40 Hz: high-frequency power; MeanRR: mean of all coupling RR-intervals between normal beats) as well as ischemic events and ventricular couplets and runs were computed.

RESULTS

Depending on the presence of ischemic episodes, each patient was assigned to either the no SMI-group (13 pts) or the SMI-group (18 pts). MeanRR, TP and LF significantly declined in both groups over time. The parasympathetically dominated index HF, however, only decreased in the SMI-group. Normalized HF power (HF/TP) even increased in the no SMI-group resulting in a postoperative decrease in LF/HF ratio. TP, LF, and HF inversely correlated with ischemia parameters whereas HF/TP and HF/LF ratio correlated with the number of ventricular couplets. Incidence and severity of SMI significantly increased after surgery.

CONCLUSION

Postoperatively, a prolonged vagal withdrawal occurred in CAD-patients exhibiting perioperative SMI. Whether the increased incidence of SMI after surgery in conjunction with the observed parasympathetic derangement contributes to adverse cardiac outcome still has to be determined.

Heart rate variability in myocardial ischemia during daily life

The aim of this investigation was to evaluate the role of autonomic nervous activity before and during transient ischemic events. Forty-one ischemic episodes detected on Holter recordings were analyzed for heart rate and heart rate variability (HRV). A time-dependent index of HRV the windowed median successive difference, which is a continuous measure of respiratory sinus arrhythmia and therefore a marker of vagal efferent activity was used. A small window consisting of five beats, which represented one respiratory cycle, was chosen. This method permitted continuous assessment of short-term alterations of vagal modulation. With two exceptions, all ischemic episodes were preceded by an acute almost complete suppression of respiratory sinus arrhythmia. During the entire ischemic episode, HRV stayed at this reduced level, and preceding the end of the ischemia, it increased again. This suppression of intrinsic heart period variations reflects an almost complete withdrawal of modulated vagal outflow immediately before and during ischemic episodes. In 26 cases (63%), Fast Fourier Transformations were carried out when the heart rate was almost constant in two segments around the onset of ischemia. In the other 15 cases we did not perform Fast Fourier Transformations because there was no stationary stage in the data. High-frequency power always decreased drastically at the onset of ischemia, confirming a significant loss of modulated vagal activity (P < .01). The low frequency/high frequency ratio did not increase, indicating that sympathetic activity did not increase significantly at the onset of ischemia in about two-thirds of our cases. The extent to which this suppression of modulated vagal activity reflects a similar suppression of vagal efferent activity is discussed, as well as whether this withdrawal of vagal outflow is cause or consequence of the ischemic event. The results suggest that a vagal depression may influence the onset of myocardial ischemia during daily life.

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 ischemic 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.

Heart rate variability reproducibility and stability using commercially available equipment in coronary artery disease with daily life myocardial ischemia

Heart rate variability (HRV) appears to be a strong predictor of death. The reproducibility of HRV measurements in patients with stable coronary artery disease (CAD) who have daily life myocardial ischemia, however, is unknown. Thirty patients with stable CAD (25 men and 5 women; aged 62 +/- 8 years) with daily life ischemia were studied with 2 consecutive 24-hour Holter monitoring recordings. Intra- and interobserver reproducibility of the HRV measures was high, with correlations ranging from 0.990 to 0.999 (p < 0.0001). Strong correlations between time and frequency domain HRV measures were observed (range 0.912 to 0.963; p < 0.0001). Both the frequency and duration of ischemia, measured by ST change, varied significantly by day for each patient (s = 155.5; p < 0.0001; s = 232.5, p < 0.0001, respectively). Correlations for HRV measurements between days remained high (range 0.871 to 0.983; p < 0.0001), despite stratification by magnitude of daily ischemia. Thus, 24-hour HRV measurements are stable in CAD patients with daily life myocardial ischemia over a short period, despite varying magnitudes of daily ischemia. These results support the use of HRV as a clinical tool and an outcome measure in future CAD intervention studies using commercially available equipment.

Frequency, significance, and mechanism of myocardial ischemia during daily activities detected by Holter dynamic electrocardiogram

Exercise testing (EX) and Holter ECG (DCG) were performed consecutively in 52 patients with ischemic heart disease. A total of 100 episodes of myocardial ischemia (IE) were recorded during DCG in 30 patients, who constituted 94% of the patients with myocardial ischemia under 6 metabolic equivalents (METs) during EX. A significant increase in heart rate (HR) was observed before the development of IE. The duration of this increase in HR was longer in IE than in periods in which the HR increased above the ischemic threshold, but without ischemia. The incidence of IE showed two peaks at 8-10 am and 4-6 pm. The frequency of IE among all of the periods with increased HR was highest at 8-10 am (51%). IE in the morning was associated with a lower HR than that in the afternoon, and LF/HF, which reflects sympathetic activity, evaluated using power spectral analysis, increased before IE in the morning. The early appearance of myocardial ischemia in EX can predict its appearance in daily life. The increase in HR and its duration appear to be associated with the development of IE. The increases in sympathetic activity in the morning and the increase in myocardial oxygen demand accompanied by physical activity in the afternoon most likely contributed to the circadian variation in the incidence of ischemic episodes.

Assessment of time domain and spectral components of heart rate variability immediately before ischemic ST segment depression episodes

In an attempt to study autonomic function during the 5-minute period preceding ischemic ST segment depression (decreases ST) episodes, we selected 138 decreases ST episodes, without preceding decreases ST during the last 15 minutes before each episode, from the Holter tapes of 35 patients with multivessel coronary artery disease. For the 5-minute period preceding each decreases ST episode, we calculated the following heart rate variability (HRV) indices; the mean RR interval (RR5), the standard deviation of all RR intervals (SD Index5), the corresponding coefficient of variation (CV5), and the natural log (Ln) of the spectral components, total power at 0.000 to 0.400 Hz (TP5), low frequency power at 0.040 to 0.150 Hz (LF5), high frequency power at 0.150 to 0.400 Hz (HF5), and the ratio of the low to high frequency power (LF5/HF5). As HRV indices of the 24-hour period, we calculated the respective RR, SD Index, CV, LnTP, LnLF, LnHF, and Ln LF/HF. RR5, SD Index5, CV5, and Ln TP5 were all significantly lower than RR (t = -5.343, p = 3.7 x 10(-7)), SD Index (t = -19.091, p = 1.99 x 10(-40)), CV (t = -15.780, p = 1.28 x 10(-32)), and LnTP (t = -3.210, p = 0.0016), respectively. LnHF5 was inversely correlated with the magnitude of the decreases ST; r = -0.174, P < 0.05, and CV5 was inversely correlated with the natural log (Ln) of the ischemic event duration; r = -0.183, P < 0.05. Analogous results were obtained for both the painful and silent decreases ST episodes. It is concluded that HRV is decreased during the 5-minute period preceding decreases ST episodes, and is inversely related with the magnitude and the duration of the *ST.