The Fall of the House of Usher and the Legend of Fafnir

In The Fall of the House of Usher the narrator reads from "The Mad Trist," in which a hero named Ethelred kills a dragon and takes the treasure that was guarded by the dragon. This reminded me of the story of Fafnir from Norse Mythology. When he was originally a dwarf, the gods accidentally killed his brother, and the gods paid his family a ransom of gold treasure. Fafnir then killed his father and kept the gold for himself, and eventually transformed himself into a dragon and poisoned the land around him to keep people away from his gold. Fafnir's last remaining brother later sent a mortal, Sigurd, to kill Fafnir and take the gold.

There are several connections between the Poe story and Fafnir. First, the narrator tells a similar story. Second, the grounds around the Usher mansion have decaying trees, as if the land was poisoned. Next, Sigurd digs trenches in the story of Fafnir, and the blood of Fafnir runs into them, which brings to mind the tarn in the Poe story. Finally, there are misdeeds against family members in both stories.

If Poe intended this comparison, then it raises the question of whether he meant to imply that the behavior of Fafnir characterizes the entire history of the Usher family. The Usher family tree never produced any separate branches. Perhaps Poe meant that someone from each generation killed off everyone else. Perhaps Poe meant to imply Roderick poisoned his sister with the help of the suspicious looking doctor.

I did some web searches to see if this connection with the story from Norse Mythology has been discussed before, but I couldn't find anything. Has anyone heard about this idea before, and does anyone have any thoughts on it?