One salient feature of Poe's narrators is their unreliability. And, this unreliable narrator for whom divisions between rationality and irrationality, mind and spirit, and self and other are often blurred is more prevalent in American Gothic literature than in European Gothic literature.
The internal dialogue of the irrational narrator who plunges the reader into the questionable mind is distinctly Poe. For, often his narratives commence with the narrator's disturbed thoughts. In "The Cask of Amontillado," for example, Poe's narrator declares,
Thethousand injuries of FortunatoI hadborne the best I could, but when he ventured upon insult, I vowed revenge....
and in "The Tell-Tale Heart," the narrator begins
True!--nervous--very,very nervous I had been and am; but, why will you say that I am mad?
In addition to immersing the reader immediately into the mind of the unreliable narrator, Poe enhances the high, overwrought emotionalism of the plot and the dialogue through his use of what he termed arabesques. These are turnings and returnings to ideas and phrases and actions, a looping that confuses again the lines between reality and unreality, rationality and irrationality.
The Gothic genre is defined by setting, tone, hauntings, mysteries, high emotionality, supernatural events or personages, darkness, death, decay, terror, castles (or other old dilapidated structures), madness, and a few other such things as these. In The Tell-Tale Heart, reputed as one of the classics of American Gothic literature, there is no castle, this is true, but the narrator's diction is of an antiquated sort ("How, then, am I mad? Hearken!" "I arose and argued about trifles, in a high key and with violent gesticulations;" "Why would they not be gone?") from which we can surmise an older--even dilapidated, if you will--structure. The basis of the story is stark terror and madness. The resolution of the story occurs because of the haunting of the heart, "louder—louder—louder!" It is certainly a mystery as to why the poor fellow is so tormented and the event poses a mystery to the "gentlemen." The heart audible under the floorboards may also be construed to represent the supernatural. The story is told almost exclusively in darkness and it definitely leads to death brought about by the narrator's frenzy of extremely high emotion, although the heart doesn't decay soon enough for the narrator.... All in all, I'd say that this analysis of The Tell-Tale Heart in relation to the definition of the Gothic genre establishes conclusively that Poe's tale is American Gothic.