Improving physical activity is a core component of secondary prevention and cardiac (tele)rehabilitation. Commercially available activity trackers are frequently used to monitor and promote physical activity in cardiac patients. However studies on the validity of these devices in cardiac patients are scarce. The aim of this study is to determine the accuracy and responsiveness of two wrist-worn activity trackers, Fitbit Charge 2 (FC2) and Mio Slice (MS), for the assessment of energy expenditure (EE) in cardiac patients.

Introduction

Improving physical activity is a core component of secondary prevention and cardiac (tele)rehabilitation. Commercially available activity trackers are frequently used to monitor and promote physical activity in cardiac patients. However studies on the validity of these devices in cardiac patients are scarce. The aim of this study is to determine the accuracy and responsiveness of two wrist-worn activity trackers, Fitbit Charge 2 (FC2) and Mio Slice (MS), for the assessment of energy expenditure (EE) in cardiac patients.

Methods

Eligible patients are recruited by their cardiologist in the outpatient cardiology clinic. If a patient is willing to participate, he/she visits the Máxima Medical Centre once, to perform the study measurements.

EE assessed by both activity trackers is compared with indirect calorimetry (Oxycon Mobile) during a laboratory activity protocol consisting of 14 low-to-moderate intensity activities. The duration of the activities varies between 1 to 5 minutes, while total duration of the protocol is 39 minutes (resting time excluded) Two groups are assessed: patients with stable coronary artery disease (CAD) and patients with heart failure with reduced ejection fraction (HFrEF).

Sample size calculation

To achieve 80% power to detect an intraclass correlation coefficient (ICC) of 0.75 (excellent agreement) under the alternative hypothesis that the ICC is 0.35 (poor agreement), a sample size of 19 subjects per study group (i.e. CAD and HFrEF) is calculated.

Statistical analysis

Accuracy of FC2 and MS will be assessed by calculating mean EE and mean differences in EE compared to the criterion measure (Oxycon Mobile). To identify if agreement is between reasonable limits one-sample T-tests will be performed using mean differences. In addition, Bland-Altman plots will be created to illustrate the level of agreement with mean bias and 95% upper and lower limits of agreement (LoA). Moreover ICC using two-way mixed models with absolute agreement will used. Responsiveness of FC2 and MS will be assessed by using a paired T-test during walking and cycling at different intensities. Significance level will be set at p<0.05 for all analyses.

Inclusion criteria heart failure patients:

• Patients with heart failure with reduced ejection fraction (LVEF < 40%) due to ischemic or dilating cardiomyopathy
• New York Heart Association Class II to III
• Speaking Dutch language

Exclusion criteria heart failure patients:

• Hemodynamically significant valvular disease
• Atrial fibrillation
• Peripheral vascular, neurological and orthopaedic conditions impairing exercise capacity
• Severe psychological or cognitive impairments

Inclusion criteria patients with coronary artery disease

• Stable coronary artery disease regardless of intervention (PCI or CABG)
• Speaking Dutch language

Exclusion criteria patients with coronary artery disease

• Left ventricular ejection fraction < 50%
• Hemodynamically significant valvular disease
• Atrial fibrillation
• Peripheral vascular, neurological and orthopaedic conditions impairing exercise capacity
• Severe psychological and cognitive impairments

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