I'm looking for a way to monitor my heart rate using a 3-channel ECG.
The chest strap, like the watch, only offers 1-channel monitoring. The doctor can give you a 24-hour 3 channel ECG logger, so there must be something like that as a wearable for athletes available. A type of chest strap where you stick the three sensors around your heart and then this sensor communicates with the Garmin app or can be evaluated with it.