smartbands and/or APPs with FINE-detailed "heartrate" history.?

I currently have Sony smartband with heartrate

Inside APP i can view

1) active data to current seconds

2) history data down to minutes

I want to review data down to seconds. need it to better diagnosed medical (hard to diagnose need constant monitors just to hope to capture it)

I have Medical condition and need to review data after episodes. my problem is i caught/recorded health concern but need a greater detailed heartrate log. this it is a major tool (better than nothing when at DRs)

smartband RAM is only good for a day (data must be saved on APP or over-write)