Track beat to beat heart rate apple watch through HRV

After filing an technical support incident (TSI) at Apple about this, they said that it's currently not possible to do this.

Thank you for contacting Apple Developer Technical Support (DTS). Our engineers have reviewed your request and have concluded that there is no supported way to achieve the desired functionality given the currently shipping system configurations.

If you would like for Apple to consider adding support for such features in the future, please submit an enhancement request via the Bug Reporter tool at https://developer.apple.com/bug-reporting/.

If you'd like to see this functionality, please file a bug report!

In iOS 13 Apple released new Heartbeat Series API. You can find more details here:

https://developer.apple.com/documentation/healthkit/samples/reading_and_writing_healthkit_series_data https://developer.apple.com/documentation/healthkit/hkheartbeatseriessample https://developer.apple.com/documentation/healthkit/hkheartbeatseriesquery

And this related WWDC video session is very useful for understanding this new API: https://developer.apple.com/videos/play/wwdc2019/218