Heart rate: control mechanisms, pathophysiology and assessment of the neurocardiac system in health and disease

Association between instantaneous heart rate sequence during the awake period and cardiovascular events: a study based on Sleep Heart Health Study

BACKGROUND

Heart rate variability (HRV) has been reported to be associated with cardiovascular diseases (CVD), while few studies focused on the instantaneous heart rate (IHR). This study aimed to establish models to predict the occurrence of cardiovascular events based on the IHR sequence.

METHODS

A total of 2977 participants with useful electrocardiogram (ECG) data and free of CVD events at baseline from the Sleep Heart Health Study (SHHS) database were included in this retrospective cohort study. All IHR indicators were measured during the awake period before sleep. The logistic regression, random forest, and XGBoost methods were used to develop the predictive models. The model performance was quantified by calculating the area under the curve (AUC).

RESULTS

Of theses 2977 participants, 1460 (49.04%) participants had CVD events during the 15-year follow-up. Higher standard deviation of IHR (SDHR) (OR=0.906; 95% CI, 0.832-0.986), coefficient of variation of IHR (CVHR) (OR=0.910; 95% CI, 0.835-0.990), power in low frequency (LF) (OR=0.896; 95% CI, 0.822-0.975), power in high frequency (HF) (OR=0.872; 95% CI, 0.796-0.955), and total power (TP) (OR=0.887; 95% CI, 0.813-0.967) were associated with the lower risk of CVD events, while ratio of semi-minor axis and semi-major axis in Poincare plot (SDratio) (OR=1.105; 95% CI, 1.012-1.206) was related to the higher risk of CVD events. The AUCs of the logistic regression, random forest, and the XGBoost models were 0.734 (95% CI, 0.701-0.767), 0.794 (95% CI, 0.764-0.823) and 0.828 (95% CI, 0.801-0.855) in the testing set, respectively.

CONCLUSIONS

IHR sequences were important predictors of cardiovascular events. The IHR indicators should be paid more attention to in future clinical researches on CVD.

Effect of mean heart rate on 30-day mortality in older patients with sepsis: Data from the MIMIC-IV database

BACKGROUND

Sepsis is a critical condition with a significant risk of mortality. Advanced age is one factor in increasing mortality in intensive care.

OBJECTIVES

The aim of this study is to investigate the association between mean heart rate (MHR) and 30-day mortality among older patients with sepsis in the intensive care unit (ICU).

METHODS

All older patients (age 65 or older) with sepsis for first time in ICU admission in Medical Information Mart for Intensive Care-IV (MIMIC-IV) were included in this retrospective study. The effect of MHR within 24 h of ICU admission on 30-day mortality was assessed according to multivariable Cox regression models, restricted cubic splines and two-piecewise Cox regression models.

RESULTS

The total number of participants was 6598 (mean heart rate, 83.8 ± 14.3 bpm). A total of 1295 (19.6%) patients died within 30 days after ICU admission. MHR within 24 h of admission was associated with 30-day mortality (J-shaped association) in older patients with sepsis in the ICU, with an inflection point at about 74 bpm and a minimal risk observed at 73 to 82 bpm of MHR.

CONCLUSIONS

In this retrospective cohort study, there was a J-shaped association between MHR and 30-day mortality in older patients with sepsis admitted to the ICU and a minimal risk observed at 73 to 82 bpm of MHR. If further confirmed, this association may provide a theoretical basis for formulating the target strategy of heart rate therapy for these patients.

Nasal turbinate lymphatic obstruction: a proposed new paradigm in the etiology of essential hypertension

Hypertension affects an estimated 1.3 billion people worldwide and is considered the number one contributor to mortality via stroke, heart failure, renal failure, and dementia. Although the physiologic mechanisms leading to the development of essential hypertension are poorly understood, the regulation of cerebral perfusion has been proposed as a primary cause. This article proposes a novel etiology for essential hypertension. Our hypothesis developed from a review of nuclear medicine scans, where the authors observed a significantly abnormal increase in nasal turbinate vasodilation in hypertensive patients using quantitative region of interest analysis. The authors propose that nasal turbinate vasodilation and resultant blood pooling obstruct the flow of cerebrospinal fluid passing through nasal turbinate lymphatics, thereby increasing intracranial pressure. The authors discuss the glymphatic/lymphatic clearance system which is impaired with age, and at which time hypertension also develops. The increased intracranial pressure leads to compensatory hypertension via Cushing's mechanism, i.e., the selfish brain hypothesis. The nasal turbinate vasodilation, due to increased parasympathetic activity, occurs simultaneously along with the well-established increased sympathetic activity of the cardiovascular system. The increased parasympathetic activity is likely due to an autonomic imbalance secondary to the increase in worldwide consumption of processed food. This hypothesis explains the rapid worldwide rise in essential hypertension in the last 50 years and offers a novel mechanism and a new paradigm for the etiology of essential hypertension. This new paradigm offers compelling evidence for the modulation of parasympathetic nervous system activity as a novel treatment strategy, specifically targeting nasal turbinate regulation, to treat diseases such as hypertension, idiopathic intracranial hypertension, and degenerative brain diseases. The proposed mechanism of essential hypertension presented in this paper is a working hypothesis and confirmatory studies will be needed.

Respiratory modulation of the heart rate: A potential biomarker of cardiorespiratory function in human

In recent decade, wearable digital devices have shown potentials for the discovery of novel biomarkers of humans' physiology and behavior. Heart rate (HR) and respiration rate (RR) are most crucial bio-signals in humans' digital phenotyping research. HR is a continuous and non-invasive proxy to autonomic nervous system and ample evidence pinpoints the critical role of respiratory modulation of cardiac function. In the present study, we recorded longitudinal (7 days, 4.63 ± 1.52) HR and RR of 89 freely behaving human subjects (Female: 39, age 57.28 ± 5.67, Male: 50, age 58.48 ± 6.32) and analyzed their dynamics using linear models and information theoretic measures. While HR's linear and nonlinear characteristics were expressed within the plane of the HR-RR directed flow of information (HR→RR - RR→HR), their dynamics were determined by its RR→HR axis. More importantly, RR→HR quantified the effect of alcohol consumption on individuals' cardiorespiratory function independent of their consumed amount of alcohol, thereby signifying the presence of this habit in their daily life activities. The present findings provided evidence for the critical role of the respiratory modulation of HR, which was previously only studied in non-human animals. These results can contribute to humans' phenotyping research by presenting RR→HR as a digital diagnosis/prognosis marker of humans' cardiorespiratory pathology.

Neuroimmune modulation mediated by IL-6: A potential target for the treatment of ischemia-induced ventricular arrhythmias

BACKGROUND

Neural remodeling in the left stellate ganglion (LSG), as mediated by neuroimmune reactions, promotes cardiac sympathetic nerve activity (SNA) and thus increases the incidence of ventricular arrhythmias (VAs). Interleukin-6 (IL-6) is an important factor of the neuroimmune interaction.

OBJECTIVE

The present study explored the effects of IL-6 on LSG hyperactivity and the incidence of VAs.

METHODS

Eighteen beagles were randomly allocated to a control group (saline with myocardial infarction [MI], n  =  6), adeno-associated virus (AAV) group (AAV with MI, n  =  6), and IL-6 group (overexpression of IL-6 via AAV vector with MI, n  =  6). Ambulatory electrocardiography was performed before and 30 days after AAV microinjection into the LSG. LSG function and ventricular electrophysiology were assessed at 31 days after surgery, and a canine MI model was established. Samples of the LSG were collected for immunofluorescence staining and molecular biological evaluation. Blood samples and 24-hour Holter data were obtained from 24 patients with acute MI on the day after they underwent percutaneous coronary intervention to assess the correlation between IL-6 levels and SNA.

RESULTS

IL-6 overexpression increased cardiac SNA and worsened postinfarction VAs. Furthermore, sustained IL-6 overexpression enhanced LSG function, promoted expression of nerve growth factor, c-fos, and fos B in the LSG, and activated the signal transducer and activator of transcription 3/regulator of G protein signalling 4 signaling pathway. Clinical sample analysis revealed a correlation between serum IL-6 levels and heart rate variability frequency domain index as well as T-wave alternans.

CONCLUSION

IL-6 levels are correlated with cardiac SNA. Chronic overexpression of IL-6 mediates LSG neural remodeling through the signal transducer and activator of transcription 3/regulator of G protein signalling 4 signaling pathway, elevating the risk of VA after MI.

Possible Role of Fibrinaloid Microclots in Postural Orthostatic Tachycardia Syndrome (POTS): Focus on Long COVID

Postural orthostatic tachycardia syndrome (POTS) is a common accompaniment of a variety of chronic, inflammatory diseases, including long COVID, as are small, insoluble, 'fibrinaloid' microclots. We here develop the argument, with accompanying evidence, that fibrinaloid microclots, through their ability to block the flow of blood through microcapillaries and thus cause tissue hypoxia, are not simply correlated with but in fact, by preceding it, may be a chief intermediary cause of POTS, in which tachycardia is simply the body's exaggerated 'physiological' response to hypoxia. Similar reasoning accounts for the symptoms bundled under the term 'fatigue'. Amyloids are known to be membrane disruptors, and when their targets are nerve membranes, this can explain neurotoxicity and hence the autonomic nervous system dysfunction that contributes to POTS. Taken together as a system view, we indicate that fibrinaloid microclots can serve to link POTS and fatigue in long COVID in a manner that is at once both mechanistic and explanatory. This has clear implications for the treatment of such diseases.

Short-term exposure to ultrafine and fine particulate matter with multipollutant modelling on heart rate variability among seniors and children from the CorPuScula (coronary, pulmonary, sanguis) longitudinal study in Germany

Background

Short-term exposure particulate matter with a diameter of 10 µm or less (PM10) and fine particulate matter (PM2.5) has been associated with heart rate variability (HRV), but exposure to ultrafine particles (UFP) has been less well examined. We investigated the associations between the HRV outcomes and short-term exposure to UFP, PM10 and PM2.5 among school-aged children and seniors.

Methods

CorPuScula (Coronary, Pulmonary and Sanguis) is a longitudinal, repeated-measure panel study conducted in 2000-2002 in Munich, Germany including 52 seniors (58-94 years old) with 899 observations and 50 children (6-10 years old) with 925 observations. A 10-min resting electrocardiogram was performed to assess resting HRV outcomes [Standard Deviation of Normal to Normal Intervals (SDNN), Root Mean Square of Successive Differences between Normal Heartbeats (RMSSD), Low Frequency power (LF), High Frequency power (HF), ration between low and high frequency (LF/HF)]. UFP and PM exposures were measured near the care home and school yard for seniors and children, respectively. Mean exposures during the day of examination (9-21 h) as well as 3-h, 12-h, 24-h, one-day, and two-day lags were assessed. Linear mixed-effect models were used to investigate the associations between short-term air pollution and HRV outcomes separately in children and seniors. The models were adjusted for sex, age, weather conditions (temperature, precipitation, and water vapor pressure), BMI, lifestyle and medical information. Two and multipollutant models adjusted for NO2 and O3 were performed.

Results

Among seniors, we observed increases in SDNN, LF, HF and LF/HF ratio after short-term exposure to UFP (hourly and daily lags) in contrast to decreases in SDNN and RMSSD after exposure to PM10. Associations were generally robust to two- and multipollutant adjustment. Among children, we observed increases of the LF/HF ratio after short-term exposures to UFP at lags 12 and 24 h. In contrast, we observed decreases of the ratio after exposure to PM2.5 and PM10. Results were largely unchanged for multipollutant modelling, however we found a more pronounced increase in SDNN and LF/HF (UFP lag 12 and 24 h) after adjusting for NO2.

Conclusions

Overall, among seniors, we observed associations of UFP and PM10 exposure with sympathetic responses of the ANS, which play an important role in sudden heart attacks or arrhythmia. Among children we found more inconsistent associations between UFP and a delayed increase in HRV. Adjusting for co-pollutants including NO2 and O3 yielded robust results.

Risk stratification and predictive value of serum sodium fluctuation for adverse prognosis in acute coronary syndrome patients

BACKGROUND

Serum sodium fluctuation (SF) as an indicator of the extent of changes in serum sodium is associated with increased mortality in hospitalized patients. However, there is no consensus on diagnostic criteria for SF, and its impact on the outcome of patients with acute coronary syndrome (ACS) remains uncertain. We defined SF and assessed its association with adverse prognosis in hospitalized ACS patients.

METHODS

Patients diagnosed with ACS were consecutively recruited. The serum SF rate (SFR) was defined as the ratio of the difference between the highest and lowest serum sodium levels during hospitalization to the initial serum sodium level on admission. The Cox proportional hazards model was performed to evaluate the association between SFR and mortality. The dose-response relationships of SFR with mortality was characterized by restricted cubic splines (RCS) model. The predictive performance of SF for mortality was assessed by the area under the receiver operating characteristic curves (AUCs).

RESULTS

The study retrospectively enrolled 1856 ACS patients, of which 36 (1.94%) patients dead within 1 year. Multivariate Cox analysis showed that SFR was independently associated with higher risk of 1-year mortality (HR = 1.17, 95% CI: 1.111-1.244, P < 0.001). RCS analysis showed the optimal threshold for SFR was 5%, and the 1-year cumulative mortality was higher in the abnormal SF group (SFR ≥ 5%) compared with the normal SF group (SFR < 5%, P < 0.01). The AUCs of SF for predicting mortality within 1 month, 6 months, and 1 year were 0.842 (95% CI: 0.781-0.904), 0.830 (95% CI:0.736-0.926), 0.703 (95% CI:0.595--0.811), respectively. Even in patients with normal baseline serum sodium, abnormal SF group demonstrated a significantly higher 1-year mortality compared to normal SF group (HR = 4.955, 95% CI: 1.919-12.795).

CONCLUSION

The SFR during hospitalization is an adequate predictor of adverse outcomes in ACS patients, independent of serum sodium level at admission. Additional research is warranted to ascertain whether interventions targeting SF confer measurable clinical benefits.

Study design exploring Qigong and Tai Chi Easy (QTC) on cardiometabolic risk factors

BACKGROUND

Cardiovascular disease is the leading cause of death in the United States paralleled with several cardiometabolic risk factors that are on the rise such as obesity, hypertension, and diabetes. Many of these cardiometabolic risk factors are preventable by lifestyle changes in physical activity and dietary patterns. Qigong and Tai Chi Easy (QTC) exercises are considered meditative movement practices that have been shown to reduce cardiometabolic risk factors such as psychosocial stress, poor sleep quality and weight gain and is particularly suitable for older adults. Heart rate variability (HRV) is a common factor known to be related to reduction of these risks and may be enhanced using HRV biofeedback to specifically optimize effects of QTC.

METHODS

The protocol presented describes a two-group parallel randomized controlled trial testing effects of QTC vs QTC plus HRV biofeedback "priming" on HRV parameters (primary), and cardiometabolic risk factors and sequelae (secondary) (e.g., waist circumference/percent body fat, sleep quality, stress, anxiety/depression, emotional regulation, eating behaviors, and cognitive performance). We will enroll 50 adults aged 55-85 years old to participate in an 8-week intervention. Self-reported body measurements, psychosocial and behavioral questionnaires, and cognitive performance assessments will be conducted before and after the intervention.

CONCLUSIONS

Findings from this study are expected to assess effects of QTC and elucidate the potential role of HRV in QTC relative to cardiometabolic risk factors and sequelae. Implications for how HRV may play a central role and be optimized in a meditative movement practice are discussed.