Relationships between heart rate variability, functional capacity, and left ventricular function following myocardial infarction: an evaluation after one week and six months

Fitbit Data to Assess Functional Capacity in Patients Before Elective Surgery: Pilot Prospective Observational Study

BACKGROUND

Preoperative assessment is crucial to prevent the risk of complications of surgical operations and is usually focused on functional capacity. The increasing availability of wearable devices (smartwatches, trackers, rings, etc) can provide less intrusive assessment methods, reduce costs, and improve accuracy.

OBJECTIVE

The aim of this study was to present and evaluate the possibility of using commercial smartwatch data, such as those retrieved from the Fitbit Inspire 2 device, to assess functional capacity before elective surgery and correlate such data with the current gold standard measure, the 6-Minute Walk Test (6MWT) distance.

METHODS

During the hospital visit, patients were evaluated in terms of functional capacity using the 6MWT. Patients were asked to wear the Fitbit Inspire 2 for 7 days (with flexibility of -2 to +2 days) after the hospital visit, before their surgical operation. Resting heart rate and daily steps data were retrieved directly from the smartwatch. Feature engineering techniques allowed the extraction of heart rate over steps (HROS) and a modified version of Non-Exercise Testing Cardiorespiratory Fitness. All measures were correlated with 6MWT.

RESULTS

In total, 31 patients were enrolled in the study (n=22, 71% men; n=9, 29% women; mean age 76.06, SD 4.75 years). Data were collected between June 2021 and May 2022. The parameter that correlated best with the 6MWT was the Non-Exercise Testing Cardiorespiratory Fitness index (r=0.68; P<.001). The average resting heart rate over the whole acquisition period for each participant had r=-0.39 (P=.03), even if some patients did not wear the device at night. The correlation of the 6MWT distance with the HROS evaluated at 1% quantile was significant, with Pearson coefficient of -0.39 (P=.04). Fitbit step count had a fair correlation of 0.59 with 6MWT (P<.001).

CONCLUSIONS

Our study is a promising starting point for the adoption of wearable technology in the evaluation of functional capacity of patients, which was strongly correlated with the gold standard. The study also identified limitations in the availability of metrics, variability of devices, accuracy and quality of data, and accessibility as crucial areas of focus for future studies.

Mental Distress Factors and Exercise Capacity in Patients with Coronary Artery Disease Attending Cardiac Rehabilitation Program

PURPOSE

There is still insufficient data on mental distress factors contributing to exercise capacity (EC) improvement before and after cardiac rehabilitation (CR) in patients with coronary artery disease (CAD). The aim of our study was to evaluate the associations between various mental distress factors and EC before and after exercise-based CR (EBCR).

METHODS

Over 12 months, 223 CAD patients (70% men, mean age 58 ± 9 years) were evaluated for socio-demographic, clinical, and mental distress symptoms as measured by the Hospital Anxiety and Depression scale (HADS), Beck Depression Inventory-II (BDI-II), and Spielberger State-Trait Anxiety Inventory (STAI). Patients were tested for EC at baseline and after EBCR.

RESULTS

In a multivariate linear regression model, EC before EBCR was associated with HADS anxiety subscale (β = -.186, p = .002) and BDI-II somatic/affective subscale (β = -.249, p < .001). EC after EBCR was associated with HADS anxiety and depression subscales (β = -.198, p < .001; β = -.170, p = .002, respectively) and BDI-II (β = -.258, p < .001). The BDI-II somatic/affective subscale was the best predictor of reduced EC before and after EBCR.

CONCLUSIONS

Mental distress and somatic/affective symptoms of depression are strongly associated with EC both at the beginning and after EBCR. Analysis of possible mediating or moderating factors was beyond the scope of our study. Future studies should focus on comprehensive evaluation of EC risk factors including other mental distress characteristics, subjectively experienced fatigue, and post-operative CAD symptoms.

Reduction in heart rate variability with traffic and air pollution in patients with coronary artery disease

INTRODUCTION

Ambient particulate pollution and traffic have been linked to myocardial infarction and cardiac death risk. Possible mechanisms include autonomic cardiac dysfunction.

METHODS

In a repeated-measures study of 46 patients 43-75 years of age, we investigated associations of central-site ambient particulate pollution, including black carbon (BC) (a marker for regional and local traffic), and report of traffic exposure with changes in half-hourly averaged heart rate variability (HRV), a marker of autonomic function measured by 24-hr Holter electrocardiogram monitoring. Each patient was observed up to four times within 1 year after a percutaneous intervention for myocardial infarction, acute coronary syndrome without infarction, or stable coronary artery disease (4,955 half-hour observations). For each half-hour period, diary data defined whether the patient was home or not home, or in traffic.

RESULTS

A decrease in high frequency (HF; an HRV marker of vagal tone) of 16.4% [95% confidence interval (CI), 20.7 to 11.8%] was associated with an interquartile range of 0.3-microg/m3 increase in prior 5-day averaged ambient BC. Decreases in HF were independently associated both with the previous 2-hr averaged BC (10.4%; 95% CI, 15.4 to 5.2%) and with being in traffic in the previous 2 hr (38.5%; 95% CI, 57.4 to 11.1%). We also observed independent responses for particulate air matter with aerodynamic diameter < or = 2.5 microm and for gases (ozone or nitrogen dioxide).

CONCLUSION

After hospitalization for coronary artery disease, both particulate pollution and being in traffic, a marker of stress and pollution, were associated with decreased HRV.