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: Phase 2 early afterdepolarization as a trigger of polymorphic ventricular tachycardia in acquired long - QT syndrome : direct evidence from intracellular recordings in the intact left ventricular wall .
### Output Text:
Phase 2 early afterdepolarization as a trigger of polymorphic ventricular tachycardia in acquired long - QT syndrome : direct evidence from intracellular recordings in the intact left ventricular wall . 