MD/PhD programs are primarily geared towards creating physicians who can function as medical research scientists. Generally most of that research is directed towards the biology related fields. Most of these MD/PhD positions are grant-funded, and may have restrictions on what kinds of PhD programs students are allowed to participate in.
If you can find a medical school associated with a university that has a biomedical engineering program (this will exclude a large number of medical schools right off the bat), and can convince the directors of the MD/PhD program to let you do the PhD portion of the in the biomed department (you would have to convince them this is a good thing), then you can probably do your MD/PhD(Eng). Surf the net and find a few promising schools, and then contact the program directors to see if a PhD(Eng) is a possibility.
The other alternative is to do a PhD(Eng), then get into a med school for your MD. A lot of physicians have ended up doing this kind of thing, deciding on a career change at some point in their life. I know a couple of MDs that started off with engineering or physics in their previous life and then went on to do an MD later.
The benefit of this approach is that you can choose a school with a strong Biomed program and then choose another school with a good MD program that fits your style. The other approach may get you a good program in one field but not so much in the other, or two mediocre programs.
Either route will end up taking up anywhere from 7-9 years of your life. And then there's a 4-5 year residency on top of that to consider when you're finished.
