Heart rate, autonomic markers, and cardiac mortality

Sex differences in achieving guideline-recommended heart rate control among a large sample of patients at risk for sudden cardiac arrest

Background

Despite known clinical benefits, guideline-recommended heart rate (HR) control is not achieved for a significant proportion of patients with HF with reduced ejection fraction. The wearable cardioverter-defibrillator (WCD) provides continuous HR monitoring and alerts that could aid medication titration.

Objective

This study sought to evaluate sex differences in achieving guideline-recommended HR control during a period of WCD use.

Methods

Data from patients fitted with a WCD from 2015 to 2018 were obtained from the manufacturer's database (ZOLL). The proportion of patients with adequate nighttime resting HR control at the beginning of use (BOU) and at the end of use (EOU) were compared by sex. Adequate HR control was defined as having a nighttime median HR <70 beats/min.

Results

A total of 21,440 women and a comparative sample of 17,328 men (median 90 [IQR 59-116] days of WCD wear) were included in the final dataset. Among patients who did not receive a shock, over half had insufficient HR control at BOU (59% of women, 53% of men). Although the proportion of patients with resting HR ≥70 beats/min improved by EOU, 43% of women and 36% of men did not achieve guideline-recommended HR control.

Conclusion

A significant proportion of women and men did not achieve adequate HR control during a period of medical therapy optimization. Compared with men, a greater proportion of women receiving WCD shocks had insufficiently controlled HR in the week preceding ventricular tachyarrhythmia/ventricular fibrillation and 43% of nonshocked women, compared with 36% of men, did not reach adequate HR control during the study period. The WCD can be utilized as a remote monitoring tool to record HR and inform adequate uptitration of beta-blockers, with particular focus on reducing the treatment gap in women.

Differences in heart rate responses to upright posture are associated with variations in the high-frequency power of heart rate variability

High resting heart rate is a cardiovascular risk factor, but limited data exist on the underlying hemodynamics and reproducibility of supine-to-upright increase in heart rate. We recorded noninvasive hemodynamics in 574 volunteers [age, 44.9 yr; body mass index (BMI), 26.4 kg/m2; 49% male] during passive head-up tilt (HUT) using whole body impedance cardiography and radial artery tonometry. Heart rate regulation was evaluated using heart rate variability (HRV) analyses. Comparisons were made between quartiles of supine-to-upright heart rate changes, in which heart rate at rest ranged 62.6-64.8 beats/min (P = 0.285). The average upright increases in heart rate in the quartiles 1-4 were 4.7, 9.9, 13.5, and 21.0 beats/min, respectively (P < 0.0001). No differences were observed in the low-frequency power of HRV, whether in the supine or upright position, or in the high-frequency power of HRV in the supine position. Upright high-frequency power of HRV was highest in quartile 1 with lowest upright heart rate and lowest in quartile 4 with highest upright heart rate. Mean systolic blood pressure before and during HUT (126 vs. 108 mmHg) and the increase in systemic vascular resistance during HUT (650 vs. 173 dyn·s/cm5/m2) were highest in quartile 1 and lowest in quartile 4. The increases in heart rate during HUT on three separate occasions several weeks apart were highly reproducible (r = 0.682) among 215 participants. To conclude, supine-to-upright increase in heart rate is a reproducible phenotype with underlying differences in the modulation of cardiac parasympathetic tone and systemic vascular resistance. As heart rate at rest influences prognosis, future research should elucidate the prognostic significance of these phenotypic differences.NEW & NOTEWORTHY Subjects with similar supine heart rates are characterized by variable increases in heart rate during upright posture. Individual heart rate increases in response to upright posture are highly reproducible as hemodynamic phenotypes and present underlying differences in the modulation of cardiac parasympathetic tone and systemic vascular resistance. These results indicate that resting heart rate obtained in the supine position alone is not an optimal means of classifying people into groups with differences in cardiovascular function.

Physiological evidence of stress reduction during a summer Antarctic expedition with a significant influence of previous experience and vigor

Antarctica provides a unique environment for studying human adaptability, characterized by controlled conditions, limited sensory stimulation, and significant challenges in logistics and communication. This longitudinal study investigates the relationship between stress indicators, with a specific focus on mean sleep heart rate, during a COVID-19 quarantine and subsequent 83 days long summer Antarctic expedition at the J. G. Mendel Czech Antarctic Station. Our novel approach includes daily recordings of sleep heart rate and weekly assessments of emotions, stress, and sleep quality. Associations between variables were analyzed using the generalized least squares method, providing unique insights into nuances of adaptation. The results support previous findings by providing empirical evidence on the stress reducing effect of Antarctic summer expedition and highlight the importance of previous experience and positive emotions, with the novel contribution of utilizing physiological data in addition to psychological measures. High-frequency sampling and combination of psychological and physiological data addresses a crucial gap in the research of stress. This study contributes valuable knowledge to the field of psychophysiology and has implications for expedition planners, research organizations, teams in action settings, pandemic prevention protocols, global crises, and long-duration spaceflight missions. Comprehensive insights promote the well-being and success of individuals in extreme conditions.

Interpretable machine learning models for predicting 90-day death in patients in the intensive care unit with epilepsy

PURPOSE

This study aims to develop a machine learning-based model for predicting mortality risk in patients with epilepsy admitted to the intensive care unit (ICU), providing clinicians with an accurate prognostic tool to guide individualized treatment.

METHODS

We collected clinical data from clinical databases (MIMIC IV and eICU-CRD) of epilepsy patients 24 h after ICU admission. The clinical characteristics of ICU patients with epilepsy were carefully feature selected and processed. MIMIC IV as the training set and eICU-CRD database as the test set. Six models were developed and validated, and the best LightGBM model was selected by performance comparison and analysed for interpretability.

RESULTS

The final cohort comprised 429 patients for training and 1217 for testing. The training set exhibited a 90-day mortality rate of 9.32 %, and the test set had an in-hospital 90-day mortality rate of 4.10 %. Utilizing the LightGBM model, we achieved an AUC of 0.956 in the training set. External validation demonstrated promising results with accuracy of 0.898, precision of 0.975, AUC of 0.781, F1 score of 0.945, highlighting the model's potential for guiding clinical decision-making. Significant factors influencing model performance included the severity of illness, as measured by the OASIS score, and clinical parameters like heart rate and body temperature.

CONCLUSION

This study introduces a machine learning-based approach to predict mortality risk in ICU epilepsy patients, offering a valuable tool for clinicians to identify high-risk individuals and devise personalized treatment strategies, thus improving patient prognosis and treatment outcomes.

Unraveling Autonomic Dysfunction in GBA-Related Parkinson's Disease

Background

Patients with Parkinson's disease (PD) and GBA gene mutations (GBA-PD) develop nonmotor complications more frequently than noncarriers. However, an objective characterization of both cardiovascular and sudomotor autonomic dysfunction using extensive clinical and instrumental measures has never been provided so far. Survival is reduced in GBA-PD regardless of age and dementia, suggesting that other hitherto unrecognized factors are involved.

Objectives

To provide instrumental measures of pattern and severity of autonomic dysfunction in GBA-PD and explore their correlation with other non-motor symptoms and implications for clinical practice.

Methods

In this cross-sectional study, 21 GBA-PD and 24 matched PD noncarriers underwent extensive assessment of motor and non-motor features, including neuropsychological testing. Cardiovascular autonomic function was explored through a comprehensive battery of indexes, including power spectral analysis of the R-R intervals and blood pressure short-term variability during resting state and active maneuvers. Dynamic Sweat Test was used to assess post-ganglionic sudomotor dysfunction.

Results

Despite minimal or absent clinical correlates, cardiovagal and sympathetic indexes, heart rate variability parameters and sudomotor postganglionic function were more severely impaired in GBA-PD than noncarriers (overcoming relatively preserved compensatory peripheral sympathetic function), suggesting more prominent cardiac sympatho-vagal demodulation, efferent baroreflex failure and peripheral sympathetic dysfunction in GBA-PD. Cardiovascular dysautonomia showed marginal correlations with cognitive impairment.

Conclusions

Compared to PD noncarriers, GBA-PD display more severe instrumental autonomic abnormalities, which may be underestimated by purely clinical measures, despite their relevance on morbidity and mortality. This supports the necessity of implementing instrumental autonomic assessment in all GBA-PD, regardless of clinically overt symptoms.

Effectiveness of Device-Guided Breathing in Chronic Coronary Syndrome: A Randomized Controlled Study

Background

Chronic coronary syndrome (CCS) is one of the most life-restricting coronary artery diseases, and symptom relief is the main goal in CCS patients who suffer from angina.

Objectives

To assess the potential benefits of device-guided breathing in CCS patients with angina in this randomized, controlled, single-blinded study.

Methods

Fifty-one patients with CCS received device-guided breathing for 7 days/8 weeks. Exercise capacity [exercise stress test], cardiac function [transthoracic echocardiography], and angina severity [Canadian Cardiovascular Society Classification] were evaluated initially and after the training. Device-guided breathing was performed at the lowest resistance of the device (POWERbreathe® Classic LR) for the control group (n = 17). The low load training group (LLTG; n = 18) and high load training group (HLTG; n = 16) were trained at 30% and 50% of maximal inspiratory pressure. Baseline characteristics were compared using one-way ANOVA and Kruskal-Wallis test. Categorical data were compared using the chi-square test. ANCOVA was performed to compare changes between three groups. A p value < 0.05 was considered statistically significant.

Results

Metabolic equivalent values were significantly improved in both HLTG and LLTG groups (p < 0.001, p = 0.003). The Duke treadmill score significantly improved and shifted to low-risk both in the HLTG (p < 0.001) and LLTG (p < 0.001) groups. Angina severity significantly alleviated after the training in both HLTG and LLTG groups (p < 0.001, p = 0.002).

Conclusions

An 8-week long program of short-term respiratory muscle training provided positive gains in exercise capacity and angina severity in CCS patients with angina. The effects of long-term training programs on CCS patients should be investigated clinically because of the possibility of helping to decrease the need for invasive treatments.

RyR2 and Calcium Release in Heart Failure

Heart Failure (HF) is defined as the inability of the heart to efficiently pump out enough blood to maintain the body's needs, first at exercise and then also at rest. Alterations in Ca2+ handling contributes to the diminished contraction and relaxation of the failing heart. While most Ca2+ handling protein expression and/or function has been shown to be altered in many models of experimental HF, in this review, we focus in the sarcoplasmic reticulum (SR) Ca2+ release channel, the type 2 ryanodine receptor (RyR2). Various modifications of this channel inducing alterations in its function have been reported. The first was the fact that RyR2 is less responsive to activation by Ca2+ entry through the L-Type calcium channel, which is the functional result of an ultrastructural remodeling of the ventricular cardiomyocyte, with fewer and disorganized transverse (T) tubules. HF is associated with an elevated sympathetic tone and in an oxidant environment. In this line, enhanced RyR2 phosphorylation and oxidation have been shown in human and experimental HF. After several controversies, it is now generally accepted that phosphorylation of RyR2 at the Calmodulin Kinase II site (S2814) is involved in both the depressed contractile function and the enhanced arrhythmic susceptibility of the failing heart. Diminished expression of the FK506 binding protein, FKBP12.6, may also contribute. While these alterations have been mostly studied in the left ventricle of HF with reduced ejection fraction, recent studies are looking at HF with preserved ejection fraction. Moreover, alterations in the RyR2 in HF may also contribute to supraventricular defects associated with HF such as sinus node dysfunction and atrial fibrillation.

Racial disparities in sleep-related cardiac function in young, healthy adults: Implications for cardiovascular-related health

STUDY OBJECTIVES

Considerable evidence shows that individuals from marginalized racial/ethnic groups in the US experience greater rates of sleep disturbance and cardiovascular complications. Because sleep is a modifiable factor that is critically involved in cardiovascular health, improved understanding of the association between sleep and cardiovascular health during early adulthood can prevent cardiovascular disparities. This study examined racial/ethnic differences in cardiovascular function during sleep using heart-rate and heart-rate-variability analyses.

METHODS

Participants in this laboratory-based sleep study included healthy, "good sleepers" who were in early adulthood and resided in the US at the time of participation [14 non-Hispanic Black (NHB; age=30.9(6.6), 57% female), 12 Asian (Asian, age=26.0(5.2), 42% female), and 24 non-Hispanic white (NHW; age=24.6(5.8), 79% female)].

RESULTS

After adjusting for demographic factors and an apnea-hypopnea index, we found significantly higher heart rate within NREM Stage 2 (N2) (b=-22.6, p=.04) and REM sleep (b=-25.8, p=.048) and lower heart rate variability during N2 sleep (b=-22.6, p=.04) among NHB individuals compared to NHW individuals. Further, NHB and Asian participants demonstrated significantly lower percent of time in slow wave sleep (SWS) compared to NHW participants (NHB: b=-22.6, p=.04; Asian: b=-22.6, p=.04). Individuals' percent of time in SWS significantly mediated differences in heart rate during N2 [indirect=0.94, 95% CI (0.03, 2.68)] and REM sleep [indirect=1.02, 95% CI (0.04, 3.04)].

CONCLUSIONS

Our results showed disparities in sleep-related cardiovascular function in early adulthood that are mediated by SWS. These data suggest targeting sleep health in early adulthood might help reduce cardiovascular disease burden on individuals from marginalized groups.

Effect of heart rate on hospital mortality in critically ill patients may be modified by age: a retrospective observational study from large database

BACKGROUND

Heart rate has been found associated with mortality in critically ill patients. However, whether the association differs between the elderly and non-elderly patients was unknown.

METHODS

We conducted a retrospective observational study of adult patients admitted to the intensive care unit (ICU) in the United States. Demographic, vital signs, laboratory tests, and interventions were extracted and compared between the elderly and non-elderly patients. The main exposure was heart rate, the proportion of time spent in heart rate (PTS-HR) was calculated. The primary outcome was hospital mortality. The multivariable logistic regression model was performed to assess the relationship between PTS-HR and hospital mortality, and interaction between PTS-HR and age categories was explored.

RESULTS

104,276 patients were included, of which 52,378 (50.2%) were elderly patients and 51,898 (49.8%) were non-elderly patients. The median age was 66 (IQR 54-76) years. After adjusting for confounders, PTS-HR < 60 beats per minute (bpm) (OR 0.972, 95% CI [0.945, 0.998], p = 0.031, P_interaction = 0.001) and 60-80 bpm (OR 0.925, 95% CI [0.912, 0.938], p < 0.001, P_interaction = 0.553) were associated with decreased risk of mortality; PTS-HR 80-100 bpm was associated with decreased mortality in the non-elderly patients (OR 0.955, 95% CI [0.941,0.975], p < 0.001) but was associated with increased mortality in the very elderly patients (OR 1.018, 95% CI [1.003,1.029], p = 0.017, P_interaction < 0.001). PTS-HR > 100 bpm (OR 1.093, 95% CI [1.081,1.105], p < 0.001, P_interaction = 0.004) was associated with increased mortality.

CONCLUSIONS

The effect of heart rate on hospital mortality differs between the elderly and non-elderly critically ill patients.

Baroreflex Sensitivity in Patients With Atrial Fibrillation

Background

It has been reported that atrial fibrillation (AF) may contribute to impairment of baroreflex sensitivity (BRS). However, the difference of BRS between patients with persistent AF (PeAF) and those with paroxysmal AF (PAF) is unknown. We tested the hypothesis that patients with PeAF have a more impaired BRS compared with those with PAF.

Methods and Results

From October 2015 onwards, a total of 67 patients (14 women [20.9%]; mean age 65.2±10.1 years) with PAF (n=46, 68.7%) and PeAF (n=21, 31.3%), who underwent catheter ablation, were prospectively enrolled. The baseline BRS was evaluated during sinus rhythm. The baseline BRS in patients with PeAF was significantly lower than those with PAF (2.97 [0.52–6.62] ms/mm Hg versus 4.70 [2.36–8.37] ms/mm Hg, P=0.047). The BRS was significantly depressed after catheter ablation in all the patients (4.66 [1.80–7.37] ms/mm Hg versus 0.55 [−0.15 to 1.22] ms/mm Hg, P<0.001). However, the depression of BRS because of catheter ablation appeared attenuated in patients with PeAF when compared with those with PAF. The number of patients who did not show depression of BRS was significantly greater, that is, patients with PeAF (3/12, 25%) than those with PAF (0/46, 0%, P<0.01).

Conclusions

Our findings demonstrated that the baseline BRS was more depressed in patients with PeAF compared with PAF. Catheter ablation depressed BRS irrespective of the type of AF, with a greater effect in patients with PAF than PeAF.

Impaired baroreflex sensitivity and cardiac autonomic functions are associated with cardiovascular disease risk factors among patients with metabolic syndrome in a tertiary care teaching hospital of South-India

BACKGROUND & AIM

Baroreflex sensitivity (BRS) and heart rate variability (HRV) have been proposed to assess early autonomic dysfunction in metabolic syndrome (MetS) patients. Autonomic dysfunction in MetS patients may increase the risk of developing cardiovascular disease (CVD). However, the association of BRS and HRV with CVD risk factors remains elusive in MetS. The primary aim of this study was to assess the BRS and HRV in MetS patients among South-Indian adults and check whether BRS and HRV are associated with CVD risk factors.

METHODS

We performed anthropometric indices, body composition, physiological parameters such as BRS, HRV, and other autonomic function tests in 176 subjects divided into MetS patients (n = 88) and healthy controls (n = 88). Fasting blood samples were collected for biochemical profiles and calculated insulin resistance indices, atherogenic index (AI), and rate pressure product (RPP).

RESULTS

When compared to controls, we found significantly reduced BRS and an increased ratio of low-frequency (LF) to high-frequency (HF) power of HRV (LF/HF) in the MetS group. We observed significant differences in body composition and biochemical profiles among the MetS group. BRS and LF/HF ratio of HRV have shown a significant association with CVD risk factors in the MetS group.

CONCLUSIONS

We observed autonomic dysfunction as low BRS and high LF/HF ratio of HRV in MetS patients. Additionally, the present results emphasize that the association of BRS and LF/HF ratio with anthropometric, glucose, lipid parameters, and other CVD risk factors may increase the susceptibility of MetS patients to higher CVD risk.

Differences in heart rate among recent marijuana use groups

BACKGROUND

Marijuana use increases cardiac sympathetic activity within minutes of its use and this effect may begin to decrease as soon as one hour after marijuana use. However, the cardiovascular effects of marijuana use more than an hour after use is poorly characterized. The purpose of the current study is to compare heart rate, a marker of cardiac sympathetic activity, across recent marijuana use groups (never used: N.=63; recent use [in the past 24 hours; subacute] N.=13; in the past 7 days, but not in the past 24 hours: N.=17). Overall, the current sample included 93 African American/Black college students, with a mean age of 20.03±2.21 years.

METHODS

Participants completed a demographic form, a brief battery of psychological questionnaires, and had their heart rate assessed at baseline.

RESULTS

Analysis of covariance showed that heart rate was statistically significantly lower in the recent use group (62.38 bpm) compared with the non-users group (73.92 bpm). This difference persisted before and after statistically adjusting for demographic covariates.

CONCLUSIONS

These results suggest that there may be a cardiovascular process that occurs when using marijuana that results in a compensatory, reduced heart rate.

Dexmedetomidine Exerted Anti-arrhythmic Effects in Rat With Ischemic Cardiomyopathy via Upregulation of Connexin 43 and Reduction of Fibrosis and Inflammation

Background

Persistent myocardial ischemia post-myocardial infarction can lead to fatal ventricular arrhythmias such as ventricular tachycardia and fibrillation, both of which carry high mortality rates. Dexmedetomidine (Dex) is a highly selective α2-agonist used in surgery for congenital cardiac disease because of its antiarrhythmic properties. Dex has previously been reported to prevent or terminate various arrhythmias. The purpose of the present study was to determine the anti-arrhythmic properties of Dex in the context of ischemic cardiomyopathy (ICM) after myocardial infarction.

Methods and Results

We randomly allocated 48 rats with ICM, created by persistent ligation of the left anterior descending artery for 4 weeks, into six groups: Sham (n = 8), Sham + BML (n = 8), ICM (n = 8), ICM + BML (n = 8), ICM + Dex (n = 8), and ICM + Dex + BML (n = 8). Treatments started after ICM was confirmed (the day after echocardiographic measurement) and continued for 4 weeks (inject intraperitoneally, daily). Dex inhibited the generation of collagens, cytokines, and other inflammatory mediators in rats with ICM via the suppression of NF-κB activation and increased the distribution of connexin 43 (Cx43) via phosphorylation of adenosine 5′-monophosphate-activated protein kinase (AMPK). Dex reduced the occurrence of spontaneous ventricular arrhythmias (ventricular premature beat or ventricular tachycardia), decreased the inducibility quotient of ventricular arrhythmias induced by PES, and partly improved cardiac contraction. The AMPK antagonist BML-275 dihydrochloride (BML) partly weakened the cardioprotective effect of Dex.

Conclusion

Dex conferred anti-arrhythmic effects in the context of ICM via upregulation of Cx43 and suppression of inflammation and fibrosis. The anti-arrhythmic and anti-inflammatory properties of Dex may be mediated by phosphorylation of AMPK and subsequent suppression of NF-κB activation.

Cardiac electrical instability in newly diagnosed/chronic epilepsy tracked by Holter and ECG patch

OBJECTIVE

We hypothesized that cardiac electrical instability and abnormal autonomic tone result from cumulative cardiac injury sustained in recurrent seizures. We tested this hypothesis by comparing T-wave alternans (TWA) and heart rate variability (HRV), both established markers of sudden cardiac death (SCD) risk, in patients with chronic as compared to newly diagnosed epilepsy.

METHODS

In this prospective, observational cohort study, patients (newly diagnosed epilepsy, n = 6, age 41.8 ± 6.8 years; chronic epilepsy, n = 6, age 40.2 ± 5.6 years [p = 0.85]) were monitored either with Holter recorder alone or simultaneously with 14-day Zio XT extended continuous ECG patch monitor. TWA was assessed by Food and Drug Administration-cleared Modified Moving Average analysis; HRV was calculated by rMSSD.

RESULTS

TWA levels in chronic epilepsy were significantly higher than in newly diagnosed epilepsy (62 ± 5.4 vs 35 ± 1.3 μV, p < 0.002); the latter did not differ from healthy control adults. In all patients with chronic epilepsy, TWA exceeded the established ≥47-μV TWA cutpoint and rMSSD HRV was inversely related to TWA levels. Patients with chronic epilepsy exhibited elevated TWA levels equivalently on Holter and ECG patch recordings (p = 0.38) with a high correlation (r ² = 0.99, p < 0.01) across 24 hours.

CONCLUSION

Based on the limited number of patients studied, it appears that chronic epilepsy, the common use of sodium channel antagonists, or other factors are associated with higher TWA levels and simultaneously with lower rMSSD HRV, which is suggestive of autonomic dysfunction or higher sympathetic tone. The ECG patch monitor used has equivalent accuracy to Holter monitoring for TWA and HRV and permits longer-term ECG sampling.

Adaptation of ventricular repolarization duration and dispersion during changes in heart rate induced by atrial stimulation

BACKGROUND

The duration of ventricular repolarization (VR) and its spatial and temporal heterogeneity are central elements in arrhythmogenesis. We studied the adaptation of VR duration and dispersion and their relationship in healthy human subjects during atrial pacing.

METHODS

Patients 20-50 years of age who were scheduled for ablation of supraventricular tachycardia without preexcitation but otherwise healthy were eligible. Vectorcardiography recordings with Frank leads were used for data collection. Incremental atrial pacing from a coronary sinus electrode was performed by decrements of 10ms/cycle from just above sinus rate, and then kept at a fixed heart rate (HR) just below the Wenckebach rate for ≥5min and then stopped. VR duration was measured as QT and VR dispersion as T area, T amplitude and ventricular gradient. The primary measure (T90 End) was the time to reach 90% change from baseline to the steady state value during and after pacing.

RESULTS

A complete study protocol was accomplished in 9 individuals (6 women). VR duration displayed a monophasic adaptation during HR acceleration lasting on average 20s. The median (Q1-Q3) T90 End for QT was 85s (51-104), a delay by a factor >4. All dispersion measures displayed a tri-phasic response pattern during HR acceleration and T90 End was 3-5 times shorter than for VR duration.

CONCLUSIONS

Even during close to "physiological" conditions, complex and differing response patterns in VR duration and dispersion measures followed changes in HR. Extended knowledge about these responses in disease conditions might assist in risk evaluation and finding therapeutic alternatives.

Sinus Bradycardia During Targeted Temperature Management: A Systematic Review and Meta-Analysis

The beneficial effect of sinus bradycardia during targeted temperature management (TTM) in cardiac arrest patients remains doubtful. We aimed to investigate the impact of sinus bradycardia on survival and neurological outcome. MEDLINE (PubMed), Cochrane, Google Scholar, and ClinicalTrials.gov databases were searched for studies reporting on comatose postcardiac arrest patients presenting sinus bradycardia during TTM. Outcomes were the 180-day survival and final neurologic function assessed by the Cerebral Performance Category scale. The effect size on study outcomes is presented as odds ratio (OR) with 95% confidence interval (CI). Two studies with 681 patients were included. Compared to no-sinus bradycardia group, in patients with sinus bradycardia below 50 bpm, a significant effect of sinus bradycardia on reduction of 180-day mortality was reported (OR = 0.42; 95% CI: 0.29-0.59). No heterogeneity was detected. Sinus bradycardia below 50 bpm during TTM may be protective and should be considered in comatose postcardiac arrest patients.

Genomics of Cardiovascular Measures of Autonomic Tone

The autonomic nervous system exerts broad control over the involuntary functions of the human body through complex equilibrium between sympathetic and parasympathetic tone. Imbalance in this equilibrium is associated with a multitude of cardiovascular outcomes, including mortality. The cardiovascular static state of this equilibrium can be quantified using physiological parameters such as heart rate (HR), blood pressure, and by spectral analysis of HR variability. Here, we review the current state of knowledge of the genetic background of cardiovascular measurements of autonomic tone. For most parameters of autonomic tone, a large portion of variability is explained by genetic heritability. Many of the static parameters of autonomic tone have also been studied through candidate-gene approach, yielding some insight into how genotypes of adrenergic receptors affect variables such as HR. Genome-wide approaches in large cohorts similarly exist for static variables such as HR and blood pressure but less is known about the genetic background of the dynamic and more specific measurements, such as HR variability. Furthermore, because most autonomic measures are likely polygenic, pathway analyses and modeling of polygenic effects are critical. Future work will hopefully explain the control of autonomic tone and guide individualized therapeutic interventions.

Effect of physical activity on the cardiometabolic profiles of non-obese and obese subjects: Results from the Korea National Health and Nutritional Examination Survey

Background

Physical inactivity is an important but often neglected risk factor for various cardiovascular diseases. We hypothesized that physical inactivity might have deleterious effects on metabolic health in obese and non-obese subjects.

Methods

We evaluated the effect of physical activity on the cardiometabolic profiles of a nationwide cohort of non-obese and obese individuals who did not have overt cardiovascular diseases. A total of 3,830 study subjects were divided into two groups based on their body mass index (BMI). Within each BMI group, participants were divided according to their physical activity level. To ascertain their cardiometabolic profiles, we collected data regarding the homeostasis model assessment-estimated insulin resistance (HOMA-IR) index, high-density lipoprotein (HDL)-cholesterol level, systolic blood pressure, heart rate, and high-sensitivity C-reactive protein (hsCRP) level.

Results

Physically inactive subjects demonstrated markedly elevated HOMA-IR index and heart rates in each BMI category, even after adjustments for baseline covariates. They also tended to have worse profiles for HDL-cholesterol, systolic blood pressure, and hsCRP levels. A significant elevation in cardiometabolic risk was noted across the four physical activity/obesity groups (p<0.05). HOMA-IR index was largely affected by obesity, but within each BMI category, physical inactivity independently elevated the risk for worsening insulin resistance. In addition, physical inactivity significantly increased the risk of elevated heart rate in both non-obese and obese individuals. Notably, the detrimental effect of physical activity on heart rate was not modified by obesity.

Conclusions

Physical activity was associated with favorable cardiometabolic risk profiles with regard to insulin resistance status and heart rate level in both BMI groups. Our results suggest that increasing physical activity could be a helpful strategy for improving the cardiometabolic health in the Korean population, regardless of obesity status.

A time to fight: Circadian control of aggression and associated autonomic support

The central circadian clock, located in the suprachiasmatic nucleus of the mammalian hypothalamus (SCN), regulates daily behavioral rhythms including the temporal propensity for aggressive behavior. Such aggression propensity rhythms are regulated by a functional circuit from the SCN to neurons that drive attack behavior in the ventromedial hypothalamus (VMH), via a relay in the subparaventricular zone (SPZ). In addition to this pathway, the SCN also regulates sleep-wake and locomotor activity rhythms, via the SPZ, in a circuit to the dorsomedial hypothalamus (DMH), a structure that is also known to play a key role in autonomic function and the sympathetic "fight-or-flight" response (which prepares the body for action in stressful situations such as an agonistic encounter). While the autonomic nervous system is known to be under pronounced circadian control, it is less apparent how such autonomic rhythms and their underlying circuitry may support the temporal propensity for aggressive behavior. Additionally, it is unclear how circadian and autonomic dysfunction may contribute to aberrant social and emotional behavior, such as agitation and aggression. Here we review the literature concerning interactions between the circadian and autonomic systems and aggression, and we discuss the implications of these relationships for human neural and behavioral pathologies.

Association between resting heart rate and hypertension in Chinese with different waist-to-height ratio: a population-based cross-sectional study

Elevated resting heart rate (RHR) and obesity are important risk factors for hypertension. However, studies are rare on the combined impact of RHR and obesity on prehypertension and hypertension. This study aimed to investigate the association between RHR and hypertension with different waist-to-height ratio (WHtR) in Chinese. The population-based cross-sectional study was conducted during 2013-2015 in Henan province, China, and 15,536 participants aged ≥15 years were included. RHR was classified according to sex-specific quartiles. The cutoff value of WHtR was 0.5 in both sexes. Multilinear and multilogistic regression models were used to evaluate the association of RHR and WHtR with prehypertension and hypertension. In both sexes, higher RHR was associated with higher blood pressure and lower pulse pressure. Compared with the lowest RHR quartile, participants in the highest RHR quartile had an increased risk of prehypertension (odds ratio [OR]: 1.40, 95% confidence interval [CI]: 1.18-1.65; OR: 1.27, 95% CI: 1.09-1.48) and hypertension (OR: 1.75, 95% CI: 1.43-2.15; OR: 1.36, 95% CI: 1.13-1.63) for male and female, respectively, after fully adjusting the data. In addition, adjusted ORs for prehypertension and hypertension of participants with high WHtR and high RHR were 2.91 (95% CI: 2.38-3.55) and 6.28 (4.96-7.97) for male and 2.45 (2.05-2.93) and 4.63 (3.66-5.85) for female, respectively, compared with the normal WHtR and normal RHR. In conclusion, elevated RHR was significantly associated with the risk of prehypertension and hypertension in Chinese and WHtR as a measure of abdominal obesity further increased this association.

Resting Heart Rate and Chronotropic Response to Exercise: Prognostic Implications in Heart Failure Across the Left Ventricular Ejection Fraction Spectrum

BACKGROUND

We studied the relationship between resting heart rate (HR), chronotropic response to exercise, and clinical outcomes in patients with heart failure (HF) across the spectrum of left ventricle ejection fraction (LVEF).

METHODS AND RESULTS

Resting HR and chronotropic index (CIx) were assessed in 718 patients with HF (53 ± 14 years of age, 66% male) referred for exercise testing. Associations with the composite outcome of left ventricular assist device implantation, transplantation, or death (151 events, 4.4 [range 3.0-5.8] years of follow-up) were assessed with the use of Cox models adjusted for age, sex, HF etiology, diabetes, LVEF, beta-blocker use, device therapy, estimated glomerular filtration rate, and peak oxygen uptake. Resting HR was 73 ± 15 beats/min, CIx was 0.60 ± 0.26, LVEF was 34% ± 15%, and 39% had an LVEF ≥40%. Resting HR correlated poorly with CIx (r = 0.08; P = .04) and did not predict (P = .84) chronotropic incompetence (CIx <0.60). Both higher resting HR (per 5 beats/min increase: adjusted hazard ratio [HR] -1.05, 95% confidence interval [CI] 1.00-1.11) and CIx (per SD change: adjusted HR -0.77, 95% CI 0.62-0.94) were independent prognostic markers. No heterogeneity of effect was noted based on LVEF (P >.05).

CONCLUSION

Higher resting HR and lower CIx are both associated with more severe HF, but correlated poorly with each other. They provide independent and additive prognostic information in HF across the LVEF spectrum.

How Heart Rate Should Be Controlled in Patients with Atherosclerosis and Heart Failure

PURPOSE OF REVIEW

Resting heart rate is an independent risk factor for all-cause and cardiovascular mortality in patients with heart failure. The main objectives are to discuss the prognosis of heart rate, its association with coronary atherosclerosis, and the modalities of control of the heart rate in sinus rhythm and in the rhythm of atrial fibrillation in patients with chronic heart failure.

RECENT FINDINGS

As a therapeutic option for control heart rate, medications such as beta-blockers, digoxin, and finally ivabradine have been studied. Non-dihydropyridine calcium channel blockers are contraindicated in patients with heart failure and reduced ejection fraction. The influence of the magnitude of heart rate reduction and beta-blocker dose on morbidity and mortality will be discussed. Regarding the patients with heart failure and atrial fibrillation, there are different findings in heart rate control with the use of a beta-blocker. Patients eligible for ivabradine have clinical benefits and increased ejection fraction. Vagal nerve stimulation has low efficacy for the control of heart rate. Complementary therapies such as tai chi and yoga showed no effect on heart rate. In this review, we discuss the main therapeutic options for the control of heart rate in patients with atherosclerosis and heart failure. More research is needed to examine the effects of therapeutic options for heart rate control in different population types, as well as their effects on clinical outcomes and impact on morbidity and mortality.

Resting heart rate is an independent predictor of advanced colorectal adenoma recurrence

Background and aim

High heart rate is an independent predictor of total cancer incidence and all-cause mortality in patients with cancer. We aimed to evaluate the impact of resting heart rate on the recurrence of colorectal polyp, using long-term surveillance follow-up data of colorectal cancer survivors.

Methods

Three hundred patients were selected from the colorectal cancer survivor cohort of Severance Hospital, Seoul, Korea. Resting heart rate, physical activity, and body composition analysis at the time of 5-year survival, and clinical data including colonoscopy surveillance results were collected for mean follow-up duration of 8 years.

Results

Patients with a high resting heart rate showed a significantly higher recurrence rate of advanced adenoma than those with a low resting heart rate (quartile 1, 45–66 beats per minute (b.p.m.); quartile 2, 67–73 b.p.m.; quartile 3, 74–80 b.p.m.; quartile 4, 81–120 b.p.m.; 3.8% vs. 7.9% vs. 10.0% vs. 14.7%, p for trend = 0.018). After adjustment for various risk factors, patients in the highest quartile of resting heart rate (≥ 81 b.p.m.) had a significantly higher risk of advanced adenoma recurrence (hazard ratio [HR]: 6.183, 95% confidence interval [CI]: 1.181–32.373, p = 0.031), compared to those in the lowest quartile (≤ 66 b.p.m.). In subgroup analysis, the association of resting heart rate with advanced adenoma recurrence appeared to be stronger among patients who had more than normal body fat mass or sedentary life style.

Conclusions

Elevated resting heart rate was independently associated with a higher rate of advanced adenoma recurrence in colorectal cancer survivors.

Comparison of central hemodynamic parameters for young basketball athletes and control group

BACKGROUND

Long-term exercise training may have negative effects on cardiovascular functions. Measurement and calculation of central hemodynamic parameters can comprehensively evaluate the cardiovascular functions. This study aims to compare the central hemodynamics between young basketball athletes and matched controls.

METHODS

Total 19 young long-term trained male basketball athletes and 17 matched male recreationally active controls participated. The central hemodynamic parameters such as central blood pressure, pulse pressure, heart rate (HR), augmentation index normalised to 75 bpm (AIx@HR75), augmentation index (AIx), ejection duration (ED), sub-endocardial viability ratio (SEVR) were measured, and total peripheral resistance (TPR), stroke volume (SV) and cardiac output (CO) were calculated. Non-parameter tests and t-test were used to analyse the central hemodynamic parameters between athletes and controls.

RESULTS

HR (56 ± 5 bpm versus 79 ± 9 bpm, p < .001), AIx@HR75 (-8 ± 10% versus -1 ± 10%, p < .05), ED (28 ± 2% versus 36 ± 3%, p < .001) and TPR (0.004 ± 0.006 mmHg s/mL versus 0.012 ± 0.006 mmHg s/mL, p < .001) were significantly lower in basketball athletes compared to the controls. SEVR (231 ± 32% versus 159 ± 21%, p < .001) and SV (154 ± 50 mL versus 101 ± 43 mL, p < .01) were significantly higher in basketball athletes than those in the controls. However, there were no significant differences in central blood pressure, pulse pressure, AIx and CO between them.

CONCLUSIONS

There is no negative effect on central hemodynamics in young basketball athletes after long-term exercise training. The young basketball athletes have a higher myocardial perfusion, higher efficiency of blood supply, stronger vascular functions and better balance of myocardial oxygen of supply and demand than the controls in this central hemodynamic parameters analysis.

Novel method to assess intrinsic heart rate recovery in ambulatory ECG recordings tracks cardioprotective effects of chronic autonomic regulation therapy in patients enrolled in the ANTHEM-HF study

BACKGROUND

Postexercise heart rate recovery (HRR) is a powerful and independent predictor of mortality. Autonomic regulation therapy (ART) with chronic vagus nerve stimulation (VNS) has been shown to improve ventricular function in patients with chronic heart failure. However, the effect of ART on HRR in patients with heart failure remains unknown.

METHODS

A new measure involving quantification of intrinsic HRR was developed for 24-hr ambulatory ECG (AECG) recordings based on spontaneous heart rate changes observed during daily activity in patients with symptomatic heart failure and reduced ejection fraction. Intrinsic HRR values were compared in 21 patients enrolled in the ANTHEM-HF study (NCT01823887) before and after 12 months of chronic ART (10 Hz, 250 μs pulse width, 18% duty cycle, maximum tolerable current amplitude after 10 weeks of titration) and to values from normal subjects (PhysioNet database, n = 54).

RESULTS

With chronic ART, average intrinsic HRR was improved as indicated by a shortening of the rate-recovery time constant by 8.9% (from 12.3 ± 0.1 at baseline to 11.2 ± 0.1 s, p < .0001) among patients receiving high-intensity stimuli (≥2 mA). In addition, mean heart rate decreased by 8.5 bpm (from 75.9 ± 2.6 to 67.4 ± 2.9 bpm, p = .005) and left ventricular ejection fraction (LVEF) increased by 4.7% (from 32.6 ± 2.0% to 37.3 ± 1.9%, p < .005).

CONCLUSION

Using a new technique adapted for 24-hr AECG recordings, intrinsic HRR was found to be impaired in patients with symptomatic HF compared to normal subjects. Chronic ART significantly improved intrinsic HRR, indicating an improvement in autonomic function.

Comparison of yoga and walking-exercise on cardiac time intervals as a measure of cardiac function in elderly with increased pulse pressure

OBJECTIVE

Arterial aging along with increased blood pressure(BP) has become the major cardiovascular(CV) risk in elderly. The aim of the study was to compare the effects of yoga program and walking-exercise on cardiac function in elderly with increased pulse pressure (PP).

METHODS

An open label, parallel-group randomized controlled study design was adopted. Elderly individuals aged ≥60 years with PP≥60mmHg were recruited for the study. Yoga (study) group (n=30) was assigned for yoga training and walking (exercise) group (n=30) for walking with loosening practices for one hour in the morning for 6days in a week for 3 months. The outcome measures were cardiac time intervals derived from pulse wave analysis and ECG: resting heart rate (RHR), diastolic time(DT), ventricular ejection time(LVET), upstroke time(UT), ejection duration index (ED%), pre-ejection period (PEP), rate pressure product (RPP) and percentage of mean arterial pressure (%MAP).

RESULTS

The mean within-yoga group change in RHR(bpm) was 4.41 (p=0.031), PD(ms): -50.29 (p=0.042), DT(ms): -49.04 (p=0.017), ED%: 2.107 (p=0.001), ES(mmHg/ms): 14.62 (p=0.118), ET(ms): -0.66 (p=0.903), UT(ms): -2.54 (p=0.676), PEP(ms): -1.25 (p=0.11) and %MAP: 2.08 (p=0.04). The mean within-control group change in HR (bpm) was 0.35 (p=0.887), PD (ms): 11.15(p=0.717), DT (ms): 11.3 (p=0.706), ED%: -0.101 (p=0.936), ES (mmHg/ms): 0.75 (p=0.926), ET(ms): 2.2 (p=0.721), UT(ms):4.7(p=455), PEP (ms): 2.1(p=0.11), %MAP: 0.65 (p=0.451). A significant difference between-group was found in RHR (p=0.036), PD (p=0.02), ED% (p=0.049), LVET (p=0.048), DT (p=0.02) and RPP (p=0.001).

CONCLUSIONS

Yoga practice for 3 months showed a significant improvement in diastolic function with a minimal change in systolic function. Yoga is more effective than walking in improving cardiac function in elderly with high PP.

Multicenter Ozone Study in oldEr Subjects (MOSES): Part 1. Effects of Exposure to Low Concentrations of Ozone on Respiratory and Cardiovascular Outcomes

INTRODUCTION

Exposure to air pollution is a well-established risk factor for cardiovascular morbidity and mortality. Most of the evidence supporting an association between air pollution and adverse cardiovascular effects involves exposure to particulate matter (PM). To date, little attention has been paid to acute cardiovascular responses to ozone, in part due to the notion that ozone causes primarily local effects on lung function, which are the basis for the current ozone National Ambient Air Quality Standards (NAAQS). There is evidence from a few epidemiological studies of adverse health effects of chronic exposure to ambient ozone, including increased risk of mortality from cardiovascular disease. However, in contrast to the well-established association between ambient ozone and various nonfatal adverse respiratory effects, the observational evidence for impacts of acute (previous few days) increases in ambient ozone levels on total cardiovascular mortality and morbidity is mixed.

Ozone is a prototypic oxidant gas that reacts with constituents of the respiratory tract lining fluid to generate reactive oxygen species (ROS) that can overwhelm antioxidant defenses and cause local oxidative stress. Pathways by which ozone could cause cardiovascular dysfunction include alterations in autonomic balance, systemic inflammation, and oxidative stress. These initial responses could lead ultimately to arrhythmias, endothelial dysfunction, acute arterial vasoconstriction, and procoagulant activity. Individuals with impaired antioxidant defenses, such as those with the null variant of glutathione S-transferase mu 1 (GSTM1), may be at increased risk for acute health effects.

The Multicenter Ozone Study in oldEr Subjects (MOSES) was a controlled human exposure study designed to evaluate whether short-term exposure of older, healthy individuals to ambient levels of ozone induces acute cardiovascular responses. The study was designed to test the a priori hypothesis that short-term exposure to ambient levels of ozone would induce acute cardiovascular responses through the following mechanisms: autonomic imbalance, systemic inflammation, and development of a prothrombotic vascular state. We also postulated a priori the confirmatory hypothesis that exposure to ozone would induce airway inflammation, lung injury, and lung function decrements. Finally, we postulated the secondary hypotheses that ozone-induced acute cardiovascular responses would be associated with: (a) increased systemic oxidative stress and lung effects, and (b) the GSTM1-null genotype.

METHODS

The study was conducted at three clinical centers with a separate Data Coordinating and Analysis Center (DCAC) using a common protocol. All procedures were approved by the institutional review boards (IRBs) of the participating centers. Healthy volunteers 55 to 70 years of age were recruited. Consented participants who successfully completed the screening and training sessions were enrolled in the study. All three clinical centers adhered to common standard operating procedures (SOPs) and used common tracking and data forms. Each subject was scheduled to participate in a total of 11 visits: screening visit, training visit, and three sets of exposure visits, each consisting of the pre-exposure day, the exposure day, and the post-exposure day. The subjects spent the night in a nearby hotel the night of the pre-exposure day.

On exposure days, the subjects were exposed for three hours in random order to 0 ppb ozone (clean air), 70 ppb ozone, and 120 ppm ozone, alternating 15 minutes of moderate exercise with 15 minutes of rest. A suite of cardiovascular and pulmonary endpoints was measured on the day before, the day of, and up to 22 hours after, each exposure. The endpoints included: (1) electrocardiographic changes (continuous Holter monitoring: heart rate variability [HRV], repolarization, and arrhythmia); (2) markers of inflammation and oxidative stress (C-reactive protein [CRP], interleukin-6 [IL-6], 8-isoprostane, nitrotyrosine, and P-selectin); (3) vascular function measures (blood pressure [BP], flow-mediated dilatation [FMD] of the brachial artery, and endothelin-1 [ET-1]; (4) venous blood markers of platelet activation, thrombosis, and microparticle-associated tissue factor activity (MP-TFA); (5) pulmonary function (spirometry); (6) markers of airway epithelial cell injury (increases in plasma club cell protein 16 [CC16] and sputum total protein); and (7) markers of lung inflammation in sputum (polymorphonuclear leukocytes [PMN], IL-6, interleukin-8 [IL-8], and tumor necrosis factor-alpha [TNF-α]). Sputum was collected only at 22 hours after exposure.

The analyses of the continuous electrocardiographic monitoring, the brachial artery ultrasound (BAU) images, and the blood and sputum samples were carried out by core laboratories. The results of all analyses were submitted directly to the DCAC.

The variables analyzed in the statistical models were represented as changes from pre-exposure to post-exposure (post-exposure minus pre-exposure). Mixed-effect linear models were used to evaluate the impact of exposure to ozone on the prespecified primary and secondary continuous outcomes. Site and time (when multiple measurements were taken) were controlled for in the models. Three separate interaction models were constructed for each outcome: ozone concentration by subject sex; ozone concentration by subject age; and ozone concentration by subject GSTM1 status (null or sufficient). Because of the issue of multiple comparisons, the statistical significance threshold was set a priori at P < 0.01.

RESULTS

Subject recruitment started in June 2012, and the first subject was randomized on July 25, 2012. Subject recruitment ended on December 31, 2014, and testing of all subjects was completed by April 30, 2015. A total of 87 subjects completed all three exposures. The mean age was 59.9 ± 4.5 years, 60% of the subjects were female, 88% were white, and 57% were GSTM1 null. Mean baseline body mass index (BMI), BP, cholesterol (total and low-density lipoprotein), and lung function were all within the normal range.

We found no significant effects of ozone exposure on any of the primary or secondary endpoints for autonomic function, repolarization, ST segment change, or arrhythmia. Ozone exposure also did not cause significant changes in the primary endpoints for systemic inflammation (CRP) and vascular function (systolic blood pressure [SBP] and FMD) or secondary endpoints for systemic inflammation and oxidative stress (IL-6, P-selectin, and 8-isoprostane). Ozone did cause changes in two secondary endpoints: a significant increase in plasma ET-1 (P = 0.008) and a marginally significant decrease in nitrotyrosine (P = 0.017). Lastly, ozone exposure did not affect the primary prothrombotic endpoints (MP-TFA and monocyte-platelet conjugate count) or any secondary markers of prothrombotic vascular status (platelet activation, circulating microparticles [MPs], von Willebrand factor [vWF], or fibrinogen.).

Although our hypothesis focused on possible acute cardiovascular effects of exposure to low levels of ozone, we recognized that the initial effects of inhaled ozone involve the lower airways. Therefore, we looked for: (a) changes in lung function, which are known to occur during exposure to ozone and are maximal at the end of exposure; and (b) markers of airway injury and inflammation. We found an increase in forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV₁) after exposure to 0 ppb ozone, likely due to the effects of exercise. The FEV₁ increased significantly 15 minutes after 0 ppb exposure (85 mL; 95% confidence interval [CI], 64 to 106; P < 0.001), and remained significantly increased from pre-exposure at 22 hours (45 mL; 95% CI, 26 to 64; P < 0.001). The increase in FVC followed a similar pattern. The increase in FEV₁ and FVC were attenuated in a dose-response manner by exposure to 70 and 120 ppb ozone. We also observed a significant ozone-induced increase in the percentage of sputum PMN 22 hours after exposure at 120 ppb compared to 0 ppb exposure (P = 0.003). Plasma CC16 also increased significantly after exposure to 120 ppb (P < 0.001). Sputum IL-6, IL-8, and TNF-α concentrations were not significantly different after ozone exposure. We found no significant interactions with sex, age, or GSTM1 status regarding the effect of ozone on lung function, percentage of sputum PMN, or plasma CC16.

CONCLUSIONS

In this multicenter clinical study of older healthy subjects, ozone exposure caused concentration-related reductions in lung function and presented evidence for airway inflammation and injury. However, there was no convincing evidence for effects on cardiovascular function. Blood levels of the potent vasoconstrictor, ET-1, increased with ozone exposure (with marginal statistical significance), but there were no effects on BP, FMD, or other markers of vascular function. Blood levels of nitrotyrosine decreased with ozone exposure, the opposite of our hypothesis. Our study does not support acute cardiovascular effects of low-level ozone exposure in healthy older subjects. Inclusion of only healthy older individuals is a major limitation, which may affect the generalizability of our findings. We cannot exclude the possibility of effects with higher ozone exposure concentrations or more prolonged exposure, or the possibility that subjects with underlying vascular disease, such as hypertension or diabetes, would show effects under these conditions.

Chronic Treatment with Ivabradine Does Not Affect Cardiovascular Autonomic Control in Rats

A low resting heart rate (HR) would be of great benefit in cardiovascular diseases. Ivabradine—a novel selective inhibitor of hyperpolarization-activated cyclic nucleotide gated (HCN) channels- has emerged as a promising HR lowering drug. Its effects on the autonomic HR control are little known. This study assessed the effects of chronic treatment with ivabradine on the modulatory, reflex and tonic cardiovascular autonomic control and on the renal sympathetic nerve activity (RSNA). Male Wistar rats were divided in 2 groups, receiving intraperitoneal injections of vehicle (VEH) or ivabradine (IVA) during 7 or 8 consecutive days. Rats were submitted to vessels cannulation to perform arterial blood pressure (AP) and HR recordings in freely moving rats. Time series of resting pulse interval and systolic AP were used to measure cardiovascular variability parameters. We also assessed the baroreflex, chemoreflex and the Bezold-Jarish reflex sensitivities. To better evaluate the effects of ivabradine on the autonomic control of the heart, we performed sympathetic and vagal autonomic blockade. As expected, ivabradine-treated rats showed a lower resting (VEH: 362 ± 16 bpm vs. IVA: 260 ± 14 bpm, p = 0.0005) and intrinsic HR (VEH: 369 ± 9 bpm vs. IVA: 326 ± 11 bpm, p = 0.0146). However, the chronic treatment with ivabradine did not change normalized HR spectral parameters LF (nu) (VEH: 24.2 ± 4.6 vs. IVA: 29.8 ± 6.4; p > 0.05); HF (nu) (VEH: 75.1 ± 3.7 vs. IVA: 69.2 ± 5.8; p > 0.05), any cardiovascular reflexes, neither the tonic autonomic control of the HR (tonic sympathovagal index; VEH: 0.91± 0.02 vs. IVA: 0.88 ± 0.03, p = 0.3494). We performed the AP, HR and RSNA recordings in urethane-anesthetized rats. The chronic treatment with ivabradine reduced the resting HR (VEH: 364 ± 12 bpm vs. IVA: 207 ± 11 bpm, p < 0.0001), without affecting RSNA (VEH: 117 ± 16 vs. IVA: 120 ± 9 spikes/s, p = 0.9100) and mean arterial pressure (VEH: 70 ± 4 vs. IVA: 77 ± 6 mmHg, p = 0.3293). Our results suggest that, in health rats, the long-term treatment with ivabradine directly reduces the HR without changing the RSNA modulation and the reflex and tonic autonomic control of the heart.

Effects of aerobic exercise on the resting heart rate, physical fitness, and arterial stiffness of female patients with metabolic syndrome

[Purpose] The purpose of this study was to investigate the effects of aerobic exercise on the resting heart rate, physical fitness, and arterial stiffness or female patients with metabolic syndrome. [Subjects and Methods] Subjects were randomly assigned to an exercise group (n=12) or a control group (n=11). Subjects in the exercise group performed aerobic exercise at 60-80% of maximum heart rate for 40 min 5 times a week for 12 weeks. The changes in metabolic syndrome risk factors, resting heart rate, physical fitness, and arterial stiffness were measured and analyzed before and after initiation of the exercise program to determine the effect of exercise. Arterial stiffness was assessed based on brachial-ankle pulse wave velocity (ba-PWV). [Results] Compared to the control group; The metabolic syndrome risk factors (weight, % body fat, waist circumference, systolic blood pressure, diastolic blood pressure, and HDL-Cholesterol) were significantly improved in the exercise: resting heart rate was significantly decreased; VO2max, muscle strength and muscle endurance were significantly increased; and ba-PWV was significantly decreased. [Conclusion] Aerobic exercise had beneficial effects on the resting heart rate, physical fitness, and arterial stiffness of patients with metabolic syndrome.

Testing an association between baseline resting pulse rate averages and short-term changes in resting pulse rates: A pilot study

INTRODUCTION

Resting heart (pulse) rate (RPR) monitoring may be a useful neurological assessment tool in chiropractic practice. Lower RPR generally reflects a better level of fitness and health status than higher RPR. However, the clinical significance of short-term changes in RPR remains unknown. The purpose of this study was to take an initial step towards understanding the clinical significance of short-term RPR changes, first, by describing short-term RPR changes between duplicated measurements, and second, by comparing RPR changes between groups with lower and higher baseline RPR.

METHODS

Seventy-three healthy adult volunteers received an RPR measurement on two days within a 1-week period. The mean difference between the two measurements (RPR change) in patients with lower versus higher baseline RPR was compared.

RESULTS

Mean RPR change in the low baseline group was -0.3 BPM (95% confidence interval [CI] = -2.7 to 2.1 BPM) whereas in the high baseline group, it was +4.4 BPM (95% CI = 1.2 to 7.6). This difference between groups was statistically significant (P = 0.02) Testing an association between baseline resting pulse rate averages and short-term changes in resting pulse rates: A pilot study with a large effect size (Cohen's d = 0.57).

CONCLUSION

In this pilot study, a higher RPR at baseline was associated with increased RPR change, whereas a lower baseline RPR was associated with a stable or reduced RPR change. A future main study with a larger sample size and longer follow-up period is needed to better characterize both the natural variation of RPR over multiple repeated measurements, and the clinical significance of short-term RPR changes in terms of predicting longer-term health outcomes.

Sinus bradycardia during hypothermia in comatose survivors of out-of-hospital cardiac arrest - a new early marker of favorable outcome?

BACKGROUND

Bradycardia is a common finding in patients undergoing therapeutic hypothermia (TH) following out-of-hospital cardiac arrest (OHCA), presumably as a normal physiological response to low body temperature. We hypothesized that a normal physiological response with sinus bradycardia (SB) indicates less neurological damage and therefore would be associated with lower mortality.

METHODS

We studied 234 consecutive comatose survivors of OHCA with presumed cardiac etiology and shockable primary rhythm, who underwent a full 24-h TH-protocol (33°C) at a tertiary heart center (years: 2004-2010). Primary endpoint was 180-day mortality; secondary endpoint was favorable neurological outcome (180-day cerebral performance category: 1-2).

RESULTS

SB, defined as sinus rhythm <50 beats per minute during TH, was present in 115 (49%) patients. Baseline characteristics including sex, witnessed arrest, bystander cardiopulmonary resuscitation and time to return of spontaneous circulation were not different between SB- and no-SB patients. However, SB-patients were younger, 57±14 vs. 63±14 years, p<0.001 and less frequently had known heart failure (7% vs. 20%, p<0.01). Patients experiencing SB during the hypothermia phase of TH had a 17% 180-day mortality rate compared to 38% in no-SB patients (p<0.001), corresponding to a 180-day hazard ratio (HRadjusted=0.45 (0.23-0.88, p=0.02)) in the multivariable analysis. Similarly, SB during hypothermia was directly associated with lower odds of unfavorable neurological outcome (ORunadjusted=0.42 (0.23-0.75, p<0.01).

CONCLUSION

Sinus bradycardia during therapeutic hypothermia is independently associated with a lower 180-day mortality rate and may thus be a novel, early marker of favorable outcome in comatose survivors of OHCA.

Arg16Gly and Gln27Glu β2 adrenergic polymorphisms influence cardiac autonomic modulation and baroreflex sensitivity in healthy young Brazilians

The association between functional β2 adrenergic receptor (β2-AR) polymorphisms and cardiac autonomic modulation is still unclear. Thus, two common polymorphisms in the β2-AR gene (Gln27Glu β2 and Arg16Gly β2) were studied to determine whether they might affect tonic and reflex cardiac sympathetic activity in healthy young subjects. A total of 213 healthy young white subjects of both genders (53% female), aged 18-30 years (23.5±3.4 y), had their continuous blood pressure curves noninvasively recorded by Finometer at baseline, and other hemodynamic parameters, as cardiac autonomic modulation, baroreflex sensitivity, and allele, genotype, and diplotype frequencies calculated. Associations were made between Arg16Gly β2 and Gln27Glu β2 polymorphisms and between β2-AR diplotypes and all variables. The heart rate was significantly lower (P<0.001) in the presence of homozygous Arg/Arg alleles (60.9±1.5 bpm) than in that of Arg/Gly heterozygotes (65.9±1.0 bpm) or Gly/Gly homozygotes (66.3±1.2 bpm). Homozygous carriers of Arg16 allele had an alpha index (19.2±1.3) significantly higher (P<0.001) than that of the subjects with the Gly allele Gly/Gly (14.5±0.7) or Arg/Gly (14.6±0.7). Furthermore, the recessive Glu27Glu and the heterozygous Gln27Glu genotypes had a higher percentage of low-frequency components (LF%) than the homozygous Gln27Gln (15.1% vs. 16.0% vs. 8.2%, P=0.03, respectively). In healthy young subjects, the presence of β2-AR Arg16 allele in a recessive model was associated with higher baroreflex sensitivity, and increased parasympathetic modulation in studied individuals.

Associations of daytime, nighttime, and 24-hour heart rate with four distinct markers of inflammation in hypertensive patients: the Styrian Hypertension Study

The current study assessed which measure of heart rate (HR) is most associated with inflammatory activity. Among 368 hypertensive patients (mean age±standard deviation, 60.6±10.8; 52.9% women), mean daytime (from 6 am to 10 pm), nighttime (from 10 pm to 6 am), and 24-hour HR were recorded using a continuous 24-hour ambulatory blood pressure monitoring portable device. Associations of daytime, nighttime, and 24-hour HR with leukocytes, platelets, C-reactive protein (CRP), and 25-hydroxyvitamin D were calculated using multivariate linear regression, reporting unstandardized coefficients (B) with standard errors (SEs). Mean daytime, nighttime, and 24-hour HR were 73, 64, and 71 beats per minute, respectively. All HR measures were positively associated with leukocytes after adjustment. Nighttime HR was additionally related with higher CRP. When all HR measures were simultaneously added to a single multivariate model, only the positive associations of nighttime HR with leukocytes (B [SE]=0.06 [0.03], P=.04), as well as with CRP (B [SE]=0.20 [0.07], P=.005), persisted. Nighttime HR was more closely associated with inflammatory activity. These observations lend some insight toward the pathophysiological mechanisms that implicate HR in cardiovascular risk and provide valuable direction for forthcoming investigations.

The interplay between sympathetic overactivity, hypertension and heart rate variability (review, invited)

The control of arterial pressure is a complex interaction of the long- and short-term influences of hormones, local vascular factors, and neural mechanisms. The autonomic nervous system and its sympathetic arm play important roles in the regulation of blood pressure, and overactivity of sympathetic nerves may have an important role in the development of hypertension and related cardiovascular disorders. The baroreceptor system opposes either increases or decreases in arterial pressure, and the primary purpose of the arterial baroreflex is to keep blood pressure close to a particular set point over a relatively short period of time. The ability of the baroreflex to powerfully buffer acute changes in arterial pressure is well established, but the role of the arterial baroreceptor reflex in long-term control of arterial pressure has been a topic of many debate and controversy for decades. The sympathetic nervous system and arterial baroreceptor reflex control of renal sympathetic nerve activity has been proposed to play a role in long-term control of arterial pressure. The aim of this paper has been to review the postulated role of sympathetic activation.

Cardiovascular function alterations induced by acute paradoxical sleep deprivation in rats

Sleep loss has been implicated in triggering the hypertension. The goal of the present study was investigated the possible mechanisms underlying cardiovascular alterations after acute paradoxical sleep deprivation (PSD). Male Wistar rats were assigned in two experimental groups: (1) control and (2) PSD for 24 h using the modified single platform method. Paradoxical sleep deprived rats exhibited higher blood pressure, heart rate (HR) and impaired baroreceptor sensitivity. After pharmacological autonomic double blockade (propranolol and methylatropine administration), intrinsic heart rate was decreased after PSD. The PSD rats showed a reduction in the vagal tone without affecting sympathetic tone. Isoproterenol administration (0.001, 0.01 and 1 µg/kg) induced an increase in ΔHR responses in PSD group. Electrocardiographic analysis in response to β-adrenergic stimulation indicated that PSD contributed to ventricular cardiac arrhythmias. Our findings suggest that acute paradoxical sleep loss induce cardiovascular alterations, autonomic imbalance accompanied by impaired baroreflex sensitivity and increased arrhythmia susceptibility.

Association of resting heart rate with cardiovascular function: a cross-sectional study in 522 Finnish subjects

Background

High resting heart rate (HR) is associated with increased cardiovascular risk in general populations, possibly due to elevated blood pressure (BP) or sympathetic over-activity. We studied the association of resting HR with cardiovascular function, and examined whether the hemodynamics remained similar during passive head-up tilt.

Methods

Hemodynamics were recorded using whole-body impedance cardiography and continuous radial pulse wave analysis in 522 subjects (age 20–72 years, 261 males) without medication influencing HR or BP, or diagnosed diabetes, coronary artery, renal, peripheral arterial, or cerebrovascular disease. Correlations were calculated, and results analysed according to resting HR tertiles.

Results

Higher resting HR was associated with elevated systolic and diastolic BP, lower stroke volume but higher cardiac output and work, and lower systemic vascular resistance, both supine and upright (p < 0.05 for all). Subjects with higher HR also showed lower supine and upright aortic pulse pressure and augmentation index, and increased resting pulse wave velocity (p < 0.001). Upright stroke volume decreased less in subjects with highest resting HR (p < 0.05), and cardiac output decreased less in subjects with lowest resting HR (p < 0.009), but clear hemodynamic differences between the tertiles persisted both supine and upright.

Conclusions

Supine and upright hemodynamic profile associated with higher resting HR is characterized by higher cardiac output and lower systemic vascular resistance. Higher resting HR was associated with reduced central wave reflection, in spite of elevated BP and arterial stiffness. The increased cardiac workload, higher BP and arterial stiffness, may explain why higher HR is associated with less favourable prognosis in populations.

Trial registration

ClinicalTrials.gov, NCT01742702

Screening entire health system ECG databases to identify patients at increased risk of death

BACKGROUND

Current methods to identify patients at higher risk for sudden cardiac death, primarily left ventricular ejection fraction ≤35%, miss ≈80% of patients who die suddenly. We tested the hypothesis that patients with elevated QRS-scores (index of myocardial scar) and wide QRS-T angles (index abnormal depolarization-repolarization relationship) have high 1-year all-cause mortality and could be further risk stratified with clinical characteristics.

METHODS AND RESULTS

We screened all 12-lead ECGs over 6 months at 2 large hospital systems and analyzed clinical characteristics and 1-year mortality. Patients with ECGs obtained in hospital areas with known high mortality rates were excluded. At the first hospital, QRS-score ≥5 and QRS-T angle ≥105° identified 8.0% of patients and was associated with an odds ratio of 2.79 (95% confidence interval, 2.10-3.69) for 1-year mortality compared with patients below both ECG thresholds (13.9% versus 5.5% death rate). Left ventricular ejection fraction was >35% in 82% of the former group of patients, and addition of ECG measures to left ventricular ejection fraction increased the discrimination of death risk (P<0.0001). At the second hospital, the odds ratio was 2.42 (1.95-3.01) for 1-year mortality (8.8% versus 3.8%). Adjustment for patient characteristics eliminated interhospital differences. Multivariable adjusted odds ratio combining data from both hospitals was 1.53 (1.28-1.83). Increasing heart rate and chronic renal impairment further predicted mortality.

CONCLUSIONS

Screening hospital ECG databases with QRS-scoring and QRS-T angle analysis identifies patients with high 1-year all-cause mortality and predominantly preserved left ventricular ejection fraction. This approach may represent a widely available method to identify patients at increased risk of death.

Association between heart rate variability and manual pulse rate

INTRODUCTION

One model for neurological assessment in chiropractic pertains to autonomic variability, tested commonly with heart rate variability (HRV). Since HRV may not be convenient to use on all patient visits, more user-friendly methods may help fill-in the gaps. Accordingly, this study tests the association between manual pulse rate and heart rate variability. The manual rates were also compared to the heart rate derived from HRV.

METHODS

Forty-eight chiropractic students were examined with heart rate variability (SDNN and mean heart rate) and two manual radial pulse rate measurements. Inclusion criteria consisted of participants being chiropractic students. Exclusion criteria for 46 of the participants consisted of a body mass index being greater than 30, age greater than 35, and history of: a) dizziness upon standing, b) treatment of psychiatric disorders, and c) diabetes. No exclusion criteria were applied to the remaining two participants who were also convenience sample volunteers. Linear associations between the manual pulse rate methods and the two heart rate variability measures (SDNN and mean heart) were tested with Pearson's correlation and simple linear regression.

RESULTS

Moderate strength inverse (expected) correlations were observed between both manual pulse rate methods and SDNN (r = -0.640, 95% CI -0.781, -0.435; r = -0.632, 95% CI -0.776, -0.425). Strong direct (expected) relationships were observed between the manual pulse rate methods and heart rate derived from HRV technology (r = 0.934, 95% CI 0.885, 0.962; r = 0.941, 95% CI 0.897, 0.966).

CONCLUSION

Manual pulse rates may be a useful option for assessing autonomic variability. Furthermore, this study showed a strong relationship between manual pulse rates and heart rate derived from HRV technology.

Thoracolumbar spinal manipulation and the immediate impact on exercise performance

OBJECTIVE

The purpose of this study was to determine if thoracolumbar chiropractic manipulative therapy (CMT) had an immediate impact on exercise performance by measuring blood lactate concentration, exercise heart rate, and rating of perceived exertion during a treadmill-based graded exercise test (GXT).

METHODS

Ten healthy, asymptomatic male and 10 female college students (age = 27.5 ± 3.7 years, height = 1.68 ± 0.09 m, body mass = 71.3 ± 11.6 kg: mean ± SD) were equally randomized into an AB:BA crossover study design. Ten participants were in the AB group, and 10 were in the BA group. The study involved 1 week of rest in between each of the 2 conditions: A (prone Diversified T12-L1 CMT) vs B (no CMT). Participants engaged in a treadmill GXT 5 minutes after each week's condition (A or B). Outcome measures were blood lactate concentration, exercise heart rate, and rating of perceived exertion monitored at the conclusion of each 3-minute stage of the GXT. The exercise test continued until the participant achieved greater than 8 mmol/L blood lactate, which correlates with maximal to near-maximal exercise effort. A dependent-samples t test was used to make comparisons between A and B conditions related to exercise performance.

RESULTS

No statistically significant difference was shown among any exercise response dependent variables in this study.

CONCLUSIONS

The results of this research preliminarily suggest that CMT to T12-L1 does not immediately impact exercise performance during a treadmill-based GXT using healthy college students.

Increased risk of sudden cardiac arrest in obstructive pulmonary disease: a case-control study

Background

We aimed to determine whether (1) patients with obstructive pulmonary disease (OPD) have an increased risk of sudden cardiac arrest (SCA) due to ventricular tachycardia or fibrillation (VT/VF), and (2) the SCA risk is mediated by cardiovascular risk-profile and/or respiratory drug use.

Methods

A community-based case-control study was performed, with 1310 cases of SCA of the ARREST study and 5793 age, sex and SCA-date matched non-SCA controls from the PHARMO database. Only incident SCA cases, age older than 40 years, that resulted from unequivocal cardiac causes with electrocardiographic documentation of VT/VF were included. Conditional logistic regression analysis was used to assess the association between SCA and OPD. Pre-specified subgroup analyses were performed regarding age, sex, cardiovascular risk-profile, disease severity, and current use of respiratory drugs.

Results

A higher risk of SCA was observed in patients with OPD (n = 190 cases [15%], 622 controls [11%]) than in those without OPD (OR adjusted for cardiovascular risk-profile 1.4 [1.2–1.6]). In OPD patients with a high cardiovascular risk-profile (OR 3.5 [2.7–4.4]) a higher risk of SCA was observed than in those with a low cardiovascular risk-profile (OR 1.3 [0.9–1.9]) The observed SCA risk was highest among OPD patients who received short-acting β2-adrenoreceptor agonists (SABA) or anticholinergics (AC) at the time of SCA (SABA OR: 3.9 [1.7–8.8], AC OR: 2.7 [1.5–4.8] compared to those without OPD).

Conclusions

OPD is associated with an increased observed risk of SCA. The most increased risk was observed in patients with a high cardiovascular risk-profile, and in those who received SABA and, possibly, those who received AC at the time of SCA.

mHCN4 genetically modified canine mesenchymal stem cells provide biological pacemaking function in complete dogs with atrioventricular block

BACKGROUND

The study was undertaken to assess the properties of mouse HCN4 (mHCN4)-modified canine mesenchymal stem cells (cMSCs) in dogs with experimentally induced complete atrioventricular (AV) block and electronic pacing.

METHODS

Complete AV block was induced in adult dogs who had undergone implantation of backup electronic pacemakers. cMSCs were transfected with mHCN4 genes. Evidence of successful IHCN4 expression was provided by patch-clamp detection. mHCN4-cMSCs or normal cMSCs were injected subepicardially into the left ventricular anterior wall of the dogs. Cardiac parameters were monitored for 6 weeks. Heart rate variability (HRV) was evaluated using quantitative Poincaré plots of R-RN against R-RN+1 intervals. cMSCs survival and expression of HCN4 in vivo were examined by histological studies and Western blot.

RESULTS

In 2 weeks, the maximum heart rate and the number of impulses generated from the injection sites were much higher in dogs injected with HCN4-modified MSCs than in control dogs.  Basal heart rate increased in the HCN4 group and became fully stabilized by Week 4, evidenced by markedly reduced numbers of electronic pacemaker beats. At Week 2, HRV during exercise was significantly higher in HCN4 dogs than in controls as shown by descriptors of both instantaneous (SD1) and longer term (SD2) beat-to-beat deviations (P < 0.05). Hematoxylin-eosin staining and Western blot proved that cMSCs survive and express HCN4 protein in situ in heart of HCN4 dog.

CONCLUSION

Transplantation of mHCN4-modified cMSCs provided a stable biological pacemaking function that allowed an appropriate chronotropic response to physical exercise for up to 6 weeks.

Dronedarone's inhibition of If current is the primary mechanism responsible for its bradycardic effect

INTRODUCTION

The mechanism(s) whereby dronedarone reduces sinus rate are not well understood, although L-type calcium channel antagonism, beta-adrenergic blockade, and inhibition of If are plausible.

METHODS AND RESULTS

In anesthetized pigs, we compared the effects of dronedarone to the prototypical If inhibitor, ivabradine, and the L-type calcium channel antagonist diltiazem on heart rate, mean arterial blood pressure (MAP), and contractility. Dronedarone's effects on the phenylephrine-induced rise in MAP and on the chronotropic response to isoproterenol were also investigated. Cumulative doses of dronedarone (0.5 mg/kg, i.v., and 5.0 mg/kg, i.v.; plasma level: 80 ± 16.1 nM) progressively reduced heart rate (P < 0.02) without changes in MAP or contractility as assessed by LV dP/dt (N = 6). Ivabradine (0.5 mg/kg, i.v.) similarly reduced heart rate (P < 0.01) without change in MAP (N = 6). Diltiazem (0.8 mg/kg, i.v.) reduced heart rate and MAP and decreased contractility (N = 6). Dronedarone blunted phenylephrine's alpha-receptor-mediated increase in MAP but did not alter the marked beta-adrenergic receptor (BAR)-mediated increase in heart rate induced by isoproterenol. When dronedarone injection was preceded by ivabradine, no further decrease in heart rate or change in MAP was observed (N = 6).

CONCLUSIONS

Dronedarone reduced heart rate without affecting MAP or contractility, effects that differ from L-type calcium channel blockade. Dronedarone did not antagonize BAR stimulation, and its heart-rate lowering effects were eliminated by prior administration of ivabradine. Thus, dronedarone's bradycardic action is likely due to inhibition of If and not to blockade of either L-type calcium channels or BAR.

Short-term effects of fish-oil supplementation on heart rate variability in humans: a meta-analysis of randomized controlled trials

BACKGROUND

The effects of fish oil on heart rate variability in humans remain unclear.

OBJECTIVE

A meta-analysis of randomized controlled trials was performed to investigate the influence of fish oil on heart rate variability.

DESIGN

Human intervention studies were identified by systematic search of PubMed, Embase, The Cochrane Library, and references of related reviews and studies. A random-effects model was applied to estimate the pooled results.

RESULTS

Fifteen studies were included. Results of the meta-analysis showed that the SD of normal-to-normal interval [standardized mean difference (SMD) = 0.10, P = 0.35] and square of successive differences (SMD = 0.05, P = 0.35), 2 of the time-domain parameters of heart rate variability, were not significantly influenced by fish-oil supplementation. For the frequency-domain parameters, the high-frequency power (HF), a surrogate of vagal function, was significantly increased by fish-oil supplementation (SMD = 0.30, P = 0.005), the low-frequency power (LF) was not significantly affected (SMD = 0.03, P = 0.79), and the ratio of LF to HF (LF/HF) showed a trend of reduction (SMD = -0.22, P = 0.08). The trend for a treatment effect on LF/HF became significant at P = 0.01 when the 2 studies with a dose <1000 mg/d were omitted. Subgroup analyses according to predefined study characteristics showed no significant results.

CONCLUSION

Short-term fish-oil supplementation may favorably influence the frequency domain of heart rate variability, as indicated by an enhanced vagal tone, which may be an important mechanism underlying the antiarrhythmic and other clinical effects of fish oil.

Elevated resting heart rate, physical fitness and all-cause mortality: a 16-year follow-up in the Copenhagen Male Study

Objective

To examine whether elevated resting heart rate (RHR) is an independent risk factor for mortality or a mere marker of physical fitness (VO₂Max).

Methods

This was a prospective cohort study: the Copenhagen Male Study, a longitudinal study of healthy middle-aged employed men. Subjects with sinus rhythm and without known cardiovascular disease or diabetes were included. RHR was assessed from a resting ECG at study visit in 1985–1986. VO₂Max was determined by the Åstrand bicycle ergometer test in 1970–1971. Subjects were classified into categories according to level of RHR. Associations with mortality were studied in multivariate Cox models adjusted for physical fitness, leisure-time physical activity and conventional cardiovascular risk factors.

Results

2798 subjects were followed for 16 years. 1082 deaths occurred. RHR was inversely related to physical fitness (p<0.001). Overall, increasing RHR was highly associated with mortality in a graded manner after adjusting for physical fitness, leisure-time physical activity and other cardiovascular risk factors. Compared to men with RHR ≤50, those with RHR >90 had an HR (95% CI) of 3.06 (1.97 to 4.75). With RHR as a continuous variable, risk of mortality increased with 16% (10–22) per 10 beats per minute (bpm). There was a borderline interaction with smoking (p=0.07); risk per 10 bpm increase in RHR was 20% (12–27) in smokers, and 14% (4–24) in non-smokers.

Conclusions

Elevated RHR is a risk factor for mortality independent of physical fitness, leisure-time physical activity and other major cardiovascular risk factors.