I was in the same position as many of you last year, anxiously awaiting for interview offers. I matched at a Midwest university program. I applied to ~ 25-30 programs, and received ~ 10 interviews (3 pittsburgh programs, 3 ohio programs, 2 programs in Michigan, and 2 programs out west). I applied almost exclusively in the Midwest secondary to family considerations.
Currently, chief resident (I only applied as a 3rd year resident) of community hospital (with university affiliation), poster presentation at AHA meeting, multiple poster and oral presentations at local/state meetings, 1st author on manuscript, good letters of rec...
I did not receive my first interview offer (ohio state) until early February. I received 2-3 rejections in January, but the vast majority of programs I applied to did not offer interviews/send rejections until February and March. Three of the programs I interviewed at did not notify applicants of offers until early/mid March, and the interviews were held at the end of April for these programs. Therefore, do not worry if you have not heard from many programs yet. I too agree with the above re: the selection criteria. After meeting/talking to many of the applicants along the way, I realized that there are a wide range of criteria (and not just one) that programs use when selecting applicants to interview. The MAJORITY of places I interviewed at had selected applicants with a wide range of credentials (2nd year residents, 3rd year residents, residents with post grad training in imaging/heart failure/etc., residents with lots of research, residents with minimal research but from well known programs...you get the picture). There were a few programs that many of the interviewees were from within the program. Good luck with the interview process. If anyone has any questions, please feel free to email me.