Veins are under low pressure which causes slow bleeding.
Arteries carry blood from heart that transport the blood under the pressure of heart pumping action. It always flows . but in case of veins it carries from body parts .
So in Arteries pressure is very high when compared to veins , hence it is more dangerous .
In veins bleeding is steady and gushes . And venus bleeding is easier to control .

So, atrial bleeding is more dangerous than venous bleeding .