Potential and feasibility of wearable based long term daily ECG analysis: comparison between heart transplant recipients and healthy controls

Background

Wearables are becoming increasingly important in modern cardiology and provide a simple way to monitor high-risk patients such as heart transplant recipients via reliable ECG recordings. However, there is yet little information about the impact of heart transplantation (HTX) on wearable ECG recordings or about possible variations in different ECG parameters compared with healthy individuals.

Purpose

Investigation of long-term wearable ECG recordings in HTX patients and healthy subjects, including comparison of mean values and longitudinal fluctuations of ECG parameters.

Methods

Single-lead Apple Watch ECGs were recorded over a period of 30 days in six post-HTX patients (some directly after HTX, i.e., <3 months, and some >3 months after HTX) and six healthy subjects. A template-matching quality control algorithm was used, and peaks and onsets/offsets of waves were detected with the NeuroKit2 algorithm. The amplitude and duration of the R wave, P wave, and T wave, as well as the duration of the PR and RT intervals, were examined. Here, we focused on the analysis of relative changes for mean amplitude/duration for each parameter from the previous day to assess subtle intraindividual changes over time. We used a mixed model to handle repeated measures while in the figures, the entire dataset was used for a clearer presentation

Results

An exemplary direct comparison between an HTX patient (Figure A) and a healthy subject (Figure B) shows that the absolute values of the two individuals differ markedly. Clear differences were also observed in the percentage deviation from the previous day: the HTX patient showed relative T-wave deviations of approximately 100%, whereas the healthy subject showed deviations of only about 20%.

Figures C–J show the percentage day-to-day changes of various ECG parameters in comparison between post-HTX patients and healthy subjects. Significant differences were found in the T-wave amplitude (p=0.002, mean ± SD (HTX resp. Healthy)=49.7±30.4% resp. 20.9%±9.4%), as well as in the duration of the P-wave (p=0.010, 15.3%±10.4% resp. 8.1%±4.2%), T-wave duration (p=0.001, 29.0%±25.3% resp. 7.3%±3.7%) and RT-interval duration (p=0.003, 36.7%±50.3% resp. 5.8%±2.9%). There were no differences in the changes of the P-wave amplitude (p=0.989), R-wave amplitude (p=0.304) and the duration of the R-wave (p=0.103) and PR interval (p=0.591).

Conclusion

Our analysis shows that it is feasible and reliable to measure and automatically analyze wearable-based daily ECG-recordings. Post-HTX patients show greater day-to-day variability of ECG parameters, this could also allow for close monitoring of intraindividual changes in cardiac conduction properties and offer a sensitive and broadly available tool for the surveillance of cardiac high-risk patients. The next planned step will be a correlation of the daily changes with clinically significant events, such as transplant rejection episodes in our patient cohort.Figures_A+BFigures_C-J