Pharma thinks it's found the next frontier in preventing heart attacks.  Novartis , Amgen and Eli Lilly are among the drugmakers betting that slashing levels of a particularly bad form of cholesterol could deliver the next blockbusters in cardiology. All three of the pharmaceutical giants are in late-stage trials to test whether drugs that cut Lp(a) can protect people from heart attacks. If they can, the opportunity could be massive: an estimated one in five people worldwide have elevated Lp(a), and there's not much they can do to lower it. Evidence from human genetics suggests the idea could work, but drugmakers don't know for sure. That makes the first late-stage trial results from Novartis, expected later this year, important for the entire pipeline.  "History has taught us you can't make assumptions," said Dr.…