Is ectasia of the thoracic ascending aorta life threatening? if not, when is it a cause for concern? whats the treatment for this?

Ectasia is just another term for wider than expected. Its relevance in any situation can only be assessed by those with all your medical history, lab and exam findings. Treatment, if indeed any is needed would depend on the origin of the finding. It may be a variation of normal. Discuss this with your doc.

Widening of the ascending aorta is a serious matter. It could be a manifestation of Marfan syndrome that can result in rupture of aorta. It is imperative that you see a cardiologist at the earliest. Another cause is tertiary syphilis, though that is unlikely. Wish you good health!