The Frontier X can measure continuous ECG and provide real-time alerts on Heart Rate, Breathing Rate and Cardiac Strain based on the parameters chosen for alert settings in the app. It can also analyze the ECG (once data is synced) for cardiac rhythm changes.
https://support.fourthfrontier.com/article/4-setting-your-alert-levels
https://support.fourthfrontier.com/article/cardiac-rhythm-feature-overview