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: Persistent atrial fibrillation ( 7 . 9 % vs 2 . 3 % , P = 0 . 020 ) and renal failure ( 9 . 7 % vs 1 . 7 % , P = 0 . 002 ) were also more common in Group T , in the primary valve surgery subgroup .
### Output Text:
Persistent atrial fibrillation ( 7 . 9 % vs 2 . 3 % , P = 0 . 020 ) and renal failure ( 9 . 7 % vs 1 . 7 % , P = 0 . 002 ) were also more common in Group T , in the primary valve surgery subgroup . 