Capped Services

When I have multiple ekgs for the same date of service I have been billing with the number of units instead of a line for each ekg. I received a recommendation that as Medicare only covers three ekgs per date of service (capping the service at three) that I should be billing individually. I have never heard of this and there wasn't any material referenced for me to verify this information. What is the correct way to bill for multiple ekgs on the same date of service?
Thank you.