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: An introducer sheath , a pacemaker , and sterile pacing wires were made readily available for the patients , should the need arise to terminate resistant cardiac dysrhythmias .
### Output Text:
An introducer sheath , a pacemaker , and sterile pacing wires were made readily available for the patients , should the need arise to terminate resistant cardiac dysrhythmias . 