Gwangju (South Korea): Three-time champion Sun Yang survived a fright in the world 800 metres freestyle heats Tuesday, while American Katie Ledecky pulled out of the women's 1,500m freestyle final on "medical grounds".

Ledecky withdrew from the morning's 200m free heats in Gwangju and was assessed by doctors before deciding to also skip the 1,500m final later on Tuesday -- an event she has crushed at the last three world championships.