HELP ME PLEASE!!! How not to send negative about a past employer?

So I have a few interviews lined up. And I'm trying to figure out ways to frame the response to, "why did you leave (my former position that I recently quit)"?

1. "It just wasn't a good fit". IMO this response is vague and leaves the next question of, "why wasn't it a good fit"? In which case I could have a five hour long conversation on the horrible pt outcomes of my former employer and how I felt my license was compromised everyday being thrown into independent practice situations because my preceptor was always too busy text messaging her boyfriend.

2. "The entire culture of the organization was not condusive to the positive development of the new grad". This is honestly how I feel but is also negative. Also leaves me open to a secondary line of questioning.

3. "When I interviewed, I was given the impression that I would be working in a cardiovascular ICU. However, when I started work, I quickly found out that the head cardiologist and his practice left the organization and I was only seeing tele overflow patients, and I am a critical care girl." Sounds negative'ish but leaves me open to the question of, "Well why didn't you transfer"? ...In which case I would talk about how the culture wasn't good for new grads.

The kicker here is that since I quit at the three month mark during the tail end of the orientation period, and because of this fact I am "not eligible for rehire". And I'm unsure whether to disclose this fact at the time of the interview.

Option B:

Pretend I never even worked at former organization aka hell hole and take the risk of potential employers finding out.

Argh!!! I'm so confused!