Validation of polar H10 chest strap and Fitbit Inspire 2 smartwatch for measuring 24-hour continuous heart rate in different cardiac patient populations

Abstract

Objectives: In the last decade, heart rate (HR) monitors have become popular consumer tools for training guidance and physical activity monitoring. HR tracking could assist in following-up of cardiac patients. However, a profound validation of such monitors in cardiac populations, with HR monitors worn for a long period of time and compared to the gold standard Holter monitoring, is lacking. Therefore, this pilot study assessed the accuracy of 2 HR monitors (Polar H10 chest strap and Fitbit Inspire 2 smartwatch) compared to Holter in patients with atrial fibrillation (AF), heart failure (HF) and following cardiac rehabilitation (CR). Methods: A total of 15 patients (5 AF, 5 HF and 5 CR) with a scheduled 24-hour Holter monitor were asked to wear both Polar H10 chest strap and Fitbit Inspire 2 smartwatch simultaneously with their Holter. All three devices were perfectly aligned in time. To be comparable with raw Polar and Fitbit data, Holter data was represented as moving average of 3 and 5 data points, respectively. Accuracy was assessed using Pearson correlation coefficients (r), mean absolute error (MAE), mean absolute percent error (MAPE, criterion: ≤10%) and Bland-Altman analysis (95% Limits of Agreement, LOA). Results: Polar H10 HR data showed a strong correlation (r = 0.91), a MAE of 4.02 beats per minute (bpm) and a MAPE of 5.64%. Fitbit Inspire 2 HR data showed a weak correlation (r = 0.67), a MAE of 8.93 bpm and a MAPE of 14.47%. These findings varied per patient group (Table 1), with highest accuracies in the CR group and lowest in the AF group (based on MAE/MAPE) and HF group (based on correlation). Bland-Altman analysis indicated that Polar H10 equally over-and underestimated HR (mean bias =-0.79 bpm, LOA =-16.16 to 14.58 bpm), except for the HF group (more undershooting). In contrast, Fitbit Inspire 2 smartwatch overestimated HR more frequently than underestimating it (mean bias = 3.22 bpm, LOA =-5.06 to 31.50 bpm), both overall and for the groups separately. Conclusions: Compared to gold standard Holter monitoring, Polar H10 chest strap is very accurate at assessing heart rate over a 24h time window, while the accuracy of Fitbit Inspire 2 smartwatch is weaker. The results differ between several cardiac patient groups. We are exploring technical possibilities to detect and correct artefacts that influence accuracy, striving for an improved and automatic way to continuously track HR in cardiac patients.