Hi Osvaldo,
SmartStor tools is possibly your best option
The "prune" option will find agents that have no historical data in SmartStor and then remove the associated metadata.
The src data directory remains unchanged while the dest data directory contains the pruned data (which you can just discard).
To get what you need the output of the prune command will list what has been pruned to standard out/console so if you redirect it to a file that will give you a list of metrics that have been pruned i.e. the metrics which are empty/have no data.
Configure and Manage SmartStor Data - CA Application Performance Management - 10.5 - CA Technologies Documentation
How do I cleanup SmartStor data? - CA Knowledge
Hope that helps.
Regards,
Lynn