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: It discusses demographics , clinical characteristics and types of arrhythmia , postulated mechanisms of SIAT , and different treatment possibilities such as medications , surgery , and radiofrequency catheter ablation ( RFCA ) .
### Output Text:
It discusses demographics , clinical characteristics and types of arrhythmia , postulated mechanisms of SIAT , and different treatment possibilities such as medications , surgery , and radiofrequency catheter ablation ( RFCA ) . 