Assessment of Physical Activity by Wearable Technology During Rehabilitation After Cardiac Surgery: Explorative Prospective Monocentric Observational Cohort Study

Abstract

Background: Wearable technology is finding its way into clinical practice. Physical activity describes patients' functional status after cardiac surgery and can be monitored remotely by using dedicated trackers.

Objective: The aim of this study was to compare the progress of physical activity in cardiac rehabilitation by using wearable fitness trackers in patients undergoing coronary artery bypass surgery by either the conventional off-pump coronary artery bypass (OPCAB) or the robotically assisted minimally invasive coronary artery bypass (RA-MIDCAB). We hypothesized faster recovery of physical activity after RA-MIDCAB in the first weeks after discharge as compared to OPCAB.

Methods: Patients undergoing RA-MIDCAB or OPCAB were included in the study. Each patient received a Fitbit Charge HR (Fitbit Inc, San Francisco, CA) physical activity tracker following discharge. Rehabilitation progress was assessed by measuring the number of steps and physical activity level daily. The physical activity level was calculated as energy expenditure divided by the basic metabolic rate.

Results: A total of 10 RA-MIDCAB patients with a median age of 68 (min, 55; max, 83) years and 12 OPCAB patients with a median age of 69 (min, 50; max, 82) years were included. Baseline characteristics were comparable except for body mass index (RA-MIDCAB: 26 kg/m²; min, 22; max, 28 versus OPCAB: 29 kg/m²; min, 27; max, 33; P<.001). Intubation time (P<.05) was significantly lower in the RA-MIDCAB group. A clear trend, although not statistically significant, was observed towards a higher number of steps in RA-MIDCAB patients in the first week following discharge.

Conclusions: RA-MIDCAB patients have an advantage in recovery in the first weeks of revalidation, which is reflected by the number of steps and physical activity level measured by the Fitbit Charge HR, as compared to OPCAB patients. However, unsupervised assessment of daily physical activity varied widely and could have consequences with regard to the use of these trackers as research tools.

Keywords: cardiac rehabilitation; cardiac surgery; coronary artery bypass; exercise; fitness trackers; physical activity; postoperative care; wearable.

Figure 1

Timeline of the study design constructed in three evaluation time points: a preoperative inclusion, a 14-day Fitbit-wearing period after discharge, and a 7-day Fitbit-wearing period after a follow-up consult, 4 weeks after discharge. ICF: Informed Consent Form; DAT: Daily Activity Tracking.

Figure 2

Study flowchart. CABG: coronary artery bypass graft; RA-MIDCAB: robotically assisted minimally invasive direct coronary artery bypass; OPCAB: off-pump coronary artery bypass; AKI: acute kidney injury.

Figure 3

Weekly average number of steps in robotically assisted minimally invasive direct coronary artery bypass (RA-MIDCAB) and off-pump coronary artery bypass (OPCAB) patients plotted over time. Weekly average step count is plotted as median over time. n indicates the number of patients included in the cohort result. P value is for the Mann Whitney U test for the difference between the two groups at that time point. Χ² results of repeated measures Friedman t test.

Figure 4

Boxplots of weekly average number of steps in robotically assisted minimally invasive direct coronary artery bypass (RA-MIDCAB) and off-pump coronary artery bypass (OPCAB) patients. Weekly average step counts is shown as box and whisker plots, presenting medians, 25% and 75% quartiles, minimums, and maximums. n indicates the number of patients included in the cohort result. M_W1: MIDCAB result in week 1; O_W1: OPCAB results in week 1; M_W2: MIDCAB results in week 2; O_W2: OPCAB results in week 2; M_W5: MIDCAB results in week 5; O_W5: OPCAB results in week 5.