In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: CONCLUSIONS : If ECG alone is used for specificity , the combination with dP / dtejc improved the sensitivity of the test and could be a cost - savings alternative to cardiac imaging or perfusion studies to detect myocardial ischemia , especially in patients unable to exercise .
### Output Text:
CONCLUSIONS : If ECG alone is used for specificity , the combination with dP / dtejc improved the sensitivity of the test and could be a cost - savings alternative to cardiac imaging or perfusion studies to detect myocardial ischemia , especially in patients unable to exercise . 