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: There was marked QT prolongation greater than 0 . 55 s in 13 patients , bradycardia less than 40 beats / min in 6 patients , dizziness and general fatigue in 1 patient each .
### Output Text:
There was marked QT prolongation greater than 0 . 55 s in 13 patients , bradycardia less than 40 beats / min in 6 patients , dizziness and general fatigue in 1 patient each . 