This is a poll from the Public Policy Poll, a firm with Democratic leanings.  However, even putting a thumb on the scale is not going to yield a result of 22% approval rating.  Heller is definitely in trouble, and his actions in the health care debate/votes in the Senate seem the most likely culprit.

http://thehill.com/blogs/blog-briefing-room/344771-poll-hellers-approval-rating-in-nevada-drops-to-22-percent