As I was reading the posts for this, I don't remember seeing anyone say the science behind the "new" ACLS changes (they are also coming out with new guidelines this year as well folks), for the AHA. It was the largest study done, certainly by the AHA (possibly ever) and encompassed medicine from literally all over the world. What was discovered was that because the coronary arteries are "filled" on the "back pressure" from the aorta, it does take a significant amount of time and energy (in this case energy=compressions) to bring the perfusion of the myocardium to a state where the muscle is more "accepting" of an electrical charge. Another reason that they are saying "don't stop compressions for LONGER than 10 SECONDS" is because they found that the cardiac output during compressions is at BEST 1/3 of a normal contraction, and the assumption was that it was higher than that prior to the release of the studies. That being said, there really is no reason that you should stop compressions for longer than 10 seconds, especially with the availability of alternative airways. I would prefer the combi-tube or something similar instead of an LMA, but the reality is either will work.
As an addendum to the AHA studies, they found that for every 10 second stop (2 minutes or 5 cycles of 30 compressions and 1 breath-BVM, non-secured airway) it takes about 15-20 compressions to bring that perfusion level in the myocardium back up to the point where it was before the 10 second stop. So, in essence, even with only a 10 second stop, at least 1/2 of the compressions of the next "round" are just used to bring the perfusion back up and not a maintenance.