Validity of telemetric-derived measures of heart rate variability: a systematic review

Heart rate variability (HRV) is a widely accepted indirect measure of autonomic function with widespread application across many settings. Although traditionally measured from the 'gold standard' criterion electrocardiography (ECG), the development of wireless telemetric heart rate monitors (HRMs) extends the scope of the HRV measurement. However, the validity of telemetric-derived data against the criterion ECG data is unclear. Thus, the purpose of this study was twofold: (a) to systematically review the validity of telemetric HRM devices to detect inter-beat intervals and aberrant beats; and (b) to determine the accuracy of HRV parameters computed from HRM-derived inter-beat interval time series data against criterion ECG-derived data in healthy adults aged 19 to 62 yrs. A systematic review of research evidence was conducted. Four electronic databases were accessed to obtain relevant articles (PubMed, EMBASE, MEDLINE and SPORTDiscus. Articles published in English between 1996 and 2016 were eligible for inclusion. Outcome measures included temporal and power spectral indices (Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology (1996). The review confirmed that modern HRMs (Polar® V800™ and Polar® RS800CX™) accurately detected inter-beat interval time-series data. The HRV parameters computed from the HRM-derived time series data were interchangeable with the ECG-derived data. The accuracy of the automatic in-built manufacturer error detection and the HRV algorithms were not established. Notwithstanding acknowledged limitations (a single reviewer, language bias, and the restricted selection of HRV parameters), we conclude that the modern Polar® HRMs offer a valid useful alternative to the ECG for the acquisition of inter-beat interval time series data, and the HRV parameters computed from Polar® HRM-derived inter-beat interval time series data accurately reflect ECG-derived HRV metrics, when inter-beat interval data are processed and analyzed using identical protocols, validated algorithms and software, particularly under controlled and stable conditions

Influence of intervals of radiant heat on performance and pacing dynamics during rowing exercise

Abstract: The purpose of this study was to investigate whether intervals of radiant heat during thermoneutral exercise altered either the performance outcome or the dynamics of pacing within the exercise bout. Eleven male participants ( ; 56 ± 12 ml∙kg-1∙min-1) performed three 5000m exercise trials on a rowing ergometer in three different conditions, in a random order. The participants were either: non-warmed (NW), warmed (W), or periodically warmed in intervals throughout each trial (IW). Warming was achieved using radiant heat lamps to raise the localised environmental temperature from 18 ˚C to 35 ˚C. Intervals of warming were applied over fixed periods of the 5000m bouts between 1000-2000m (W1) and 3000-4000m (W2). The results of the experiment demonstrated that performance time and average power output of the 5000m matched intensity trials were not significantly different between conditions (p=0.10 ; p=0.189). However, the application of warming significantly reduced intra-trial power output during the first (W1) interval in the IW condition (p=0.03) but not during the second (W2) warming interval (p=0.10). Tsk increased by 0.51˚C (p=0.05) in response to the application of warming during W1 in the IW condition and by 0.15 ˚C in W2 (p=0.28). No significant between-condition differences were observed in Tc throughout the trials. These findings suggest that an abrupt change to environmental conditions brought about through intervals of radiant warming can affect the transient pacing dynamics of an exercise bout, but not necessarily impact overall performance time. Performance time appears unaffected by intervals of radiant heat during an exercise bout, although further work is required in more challenging dynamic environmental conditions

Physical activity and cardiovascular mortality risk: possible protective mechanisms?

INTRODUCTION: The biological mechanisms through which increased physical activity or structured exercise training lowers the risk of recurrent cardiac events are incompletely understood. We examined the extent to which modification of primary risk markers explains the association between physical activity and cardiovascular death in participants with diagnosed cardiovascular disease (CVD). METHODS AND RESULTS: In a prospective study of 1429 participants with physician-diagnosed CVD living in England and Scotland (age = 66.5 ± 11.1 yr (mean ± SD), 54.2% men), we measured physical activity and several risk markers (body mass index, total-to-HDL cholesterol ratio, diagnosed diabetes, systolic blood pressure, resting heart rate, C-reactive protein) at baseline. The main outcome was CVD death. There were a total of 446 all-cause deaths during an average of 7.0 ± 3.1 yr of follow-up, of which 213 were attributed to cardiovascular causes. Participation in moderate to vigorous physical activity at least three sessions per week was associated with lower risk of CVD death (hazard ratio = 0.61, 95% confidence interval = 0.38-0.98). Physically active participants demonstrated significantly lower levels of body mass index, diabetes, and inflammatory risk (C-reactive protein). Metabolic (body mass index, total-to-HDL cholesterol ratio, and physician-diagnosed diabetes) and inflammatory risk factors explained an estimated 12.8% and 15.4%, respectively, of the association between physical activity and CVD death. CONCLUSIONS: Physical activity may reduce the risk of secondary CVD events, in part, by improving metabolic and inflammatory risk markers

The long-term prognostic significance of 6-minute walk test distance in patients with chronic heart failure

Background. The 6-minute walk test (6-MWT) is used to assess patients with chronic heart failure (CHF). The prognostic significance of the 6-MWT distance during long-term followup ( > 5 years) is unclear. Methods. 1,667 patients (median [inter-quartile range, IQR]) (age 72 [65-77] ; 75% males) with heart failure due to left ventricular systolic impairment undertook a 6-MWT as part of their baseline assessment and were followed up for 5 years. Results. At 5 years' followup, those patients who died (n = 959) were older at baseline and had a higher log NT pro-BNP than those who survived to 5 years (n = 708). 6-MWT distance was lower in those who died [163 (153) m versus 269 (160) m; P 360 m. 6-MWT distance was a predictor of all-cause mortality (HR 0.97; 95% CI 0.96-0.97; Chi-square = 184.1; P < 0.0001). Independent predictors of all-cause mortality were decreasing 6-MWT distance, increasing age, increasing NYHA classification, increasing log NT pro-BNP, decreasing diastolic blood pressure, decreasing sodium, and increasing urea. Conclusion. The 6-MWT is an important independent predictor of all-cause mortality following long-term followup in patients with CHF. © 2014 Lee Ingle et al

Pre-participation Cardiac Screening in Young Athletes: Models and Criteria

This is the second of two review articles focusing on the value of preparticipation cardiac screening in young athletes. The article focuses on the efficacy of the resting 12-lead electrocardiogram (ECG), physical examination, and medical history questionnaire, which commonly make up the first stage of a cardiac screening protocol. The review then focuses on specific structural and electrical abnormalities which are responsible for sudden cardiac death (SCD) in young athletes – the most common of which is hypertrophic cardiomyopathy. The identification of appropriate ‘red flag’ signs and symptoms is essential for teasing out potential pathological conditions and allowing differentiation from often benign physiological adaptations. The final section provides guidance on how the resting 12-lead ECG can be used to separate pathological from physiological adaptations in young athletes

Prognostic Significance of the Double Pressure Reserve in Patients with Chronic Heart Failure

Abstract: Introduction: The double pressure reserve (DPR) has recently been shown to have greater prognostic powerthan metabolic equivalents, heart rate indices, and systolic blood pressure in healthy subjects. It is unclear whether DPRoffers any prognostic value in a heart failure population where variables derived from metabolic gas exchange data provideimportant prognostic information.Methods: Patients underwent a symptom-limited, treadmill-based exercise test with metabolic gas exchange measurementsusing the modified Bruce protocol. DPR was calculated as the product of peak systolic blood pressure and peakheart rate subtracted from the product of resting systolic blood pressure and resting heart rate values.Results: 363 patients (mean ± SD; age 74±11 years; 81% males; left ventricular ejection fraction 34±6%; peak VO2 19.0 ±5.1 mL·kg-1·min-1; VE/VCO2 slope 37 ± 9; double pressure reserve 10,510 ± 6,046 mmHg·beat-1) were included in thestudy. Peak VO2 (hazard ratio (HR) = 0.87;

Effectiveness of a six-week high-intensity interval training programme on cardiometabolic markers in sedentary males

High-intensity interval training (HIT) has been proposed as an effective, time efficient strategy to elicit similar cardiometabolic health benefits as traditional moderate-intensity endurance training. This is an important consideration as "lack of time" is a common cited barrier to regular physical activity

Influence of appendicular skeletal muscle mass on resting metabolic equivalents in patients with cardiovascular disease: Implications for exercise training and prescription

The metabolic equivalent (MET) is a widely used physiological concept for quantifying levels of habitual physical activity and cardiorespiratory fitness (CRF). The MET conveys the oxygen consumption requirements of physical activities as multiples of the resting or basal metabolic rate (RMR). It may also be used to prescribe workloads for exercise training in patient groups, including those attending cardiac rehabilitation. One MET is considered to be equivalent to the oxygen consumed per kilogram of body mass at rest (while sitting) and, due to practical issues with direct metabolic cart measurements, it is conventionally approximated as 3.5 ml/kg–1/min–1. This expression of resting energy expenditure has been incorporated within physical activity position statements and guidelines. However, a number of factors – including age, sex, body mass (fat-free mass), cardiometabolic health and CRF – influence the RMR, which might limit the broad applicability of the conventional 1 MET at a population level. Widely prescribed cardiac drugs (i.e. beta blockers) have also been cited to influence the RMR, with some inconsistent findings in men. We aimed to evaluate the potential limitations of using the estimated MET in a cohort of patients with coronary heart disease (CHD), in whom we recently reported a positive association between skeletal muscle mass and peak oxygen uptake (O2peak). We hypothesized that patients with a lower skeletal muscle mass would also have a lower RMR, determined by resting respiratory gas analysis, and this would affect the accuracy of the aerobic exercise prescription based on METs

Cardiorespiratory requirements of the 6-min walk test in patients with left ventricular systolic disfunction and no major structural heart disease

The six-minute walk test (6-MWT) is widely used to assess functional status in patients with chronic heart failure (CHF). The aims of the present study were: (1) to compare metabolic gas exchange during the 6-MWT in older patients with left ventricular systolic dysfunction (LVSD) and in breathless patients with no major structural heart disease (MSHD); (2) to determine the exercise intensity of the 6-MWT relative to peak oxygen uptake; (3) to establish the accuracy and reproducibility of the Metamax 3B ergospirometer during an incremental workload. Twenty four older patients with LVSD (19 male; age 76 ± 5 years; BMI 27 ± 4), and 18 patients with no MSHD (12 male; age 75 ± 8 years; BMI 27 ± 4) attended on consecutive days at the same time. Patients completed a 6-MWT with metabolic gas exchange measurements using the Metamax 3B portable ergospirometer, and an incremental cycle ergometry test using both the Metamax 3B and Oxycon Pro metabolic cart. Patients returned and performed a second 6-MWT and an incremental treadmill test, metabolic gas exchange was measured with the Metamax 3B. In patients with LVSD, the 6-MWT was performed at a higher fraction of maximal exercise capacity (p = 0.02). The 6-MWT was performed below the anaerobic threshold in patients with LVSD (83 %) and in patients with no MSHD (61 %). The Metamax 3B showed satisfactory to high accuracy at 10 W and 20 W in patients with LVSD (r = 0.77 - 0.97, p < 0.05), and no MSHD (r = 0.76 - 0.94, p < 0.05). Metabolic gas exchange variables measured during the 6-MWT showed satisfactory to high day-to-day reproducibility in patients with LVSD (ICC = 0.75 - 0.98), but a higher variability was evident in participants with no MSHD (ICC = 0.62 - 0.97). The Metamax 3B portable ergospirometer is an accurate and reproducible device during submaximal, fixed rate exercise in older patients with LVSD and no MSHD. In elderly patients with LVSD and no MSHD, the 6-MWT should not be considered a maximal test of exercise capacity but rather a test of submaximal exercise performance. Our study demonstrates that the 6-MWT takes place at a higher proportion of peak oxygen uptake in patients with LVSD compared to those with no MSHD, and may be one reason why fatigue is a more prominent symptom in these patients

Development of a composite model derived from cardiopulmonary exercise tests to predict mortality risk in patients with mild-to-moderate heart failure

Objective: Cardiopulmonary exercise testing (CPET) is used to predict outcome in patients with mild-to-moderate heart failure (HF). Single CPET-derived variables are often used, but we wanted to see if a composite score achieved better predictive power. Methods: Retrospective analysis of patient records at the Department of Cardiology, Castle Hill Hospital, Kingston-upon-Hull. 387 patients [median (25th-75th percentile)] [age 65 (56-72) years; 79% males; LVEF 34 (31-37) %] were included. Patients underwent a symptomlimited, maximal CPET on a treadmill. During a median follow up of 8.6 ± 2.1 years in survivors, 107 patients died. Survival models were built and validated using a hybrid approach between the bootstrap and Cox regression. Nine CPET-derived variables were included. Z-score defined each variable's predictive strength. Model coefficients were converted to a risk score. Results: Four CPET-related variables were independent predictors of all-cause mortality in the survival model: the presence of exertional oscillatory ventilation (EOV), increasing slope of the relation between ventilation and carbon dioxide production (VE/VCO2 slope), decreasing oxygen uptake efficiency slope (OUES), and an increase in the lowest ventilatory equivalent for carbon dioxide (VEqCO2 nadir). Individual predictors of mortality ranged from 0.60 to 0.71 using Harrell’s C-statistic, but the optimal combination of EOV + VE/VCO2 slope + OUES + VEqCO2 nadir reached 0.75. The Hull CPET risk score had a significantly higher area under the curve (0.78) when compared to the Heart Failure Survival Score (AUC=0.70;