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: Thirty days after amiodarone discontinuation , His bundle electrograms showed atrial flutter without intra - Hisian or infra - Hisian delay .
### Output Text:
Thirty days after <span class="chemical">amiodarone</span> discontinuation , His bundle electrograms showed atrial flutter without intra - Hisian or infra - Hisian delay . 