For the services your office performs, you should report 93005 (Electrocardiogram, routine ECG with at least 12 leads; tracing only, without interpretation and report).
Although for many codes you would indicate performance of only a portion of the service by appending either modifier TC (Technical component) or 26 (Professional component), that method does not apply for ECGs.
Instead, this family of codes provides separate options depending on whether you perform the entire service (93000, ... with interpretation and report), the technical component only (93005), or the professional component only (93010, ... interpretation and report only).
Caution: Be sure payer agreements include the component codes (93005, 93010) in the payer fee schedule and not just the global code (93000).
Leesa A. Israel, BA, CPC, CUC, CMBS
Executive Editor, The Coding Institute
Manager, TCI Consulting & Revenue Cycle Solutions