Medtronic Inc., the world’s largest maker of heart-rhythm devices, said it has completed half of its planned 1,000 job cuts in an effort to save $100 million to $125 million a year. The Fridley-based company had eliminated about 500 of the identified 1,000 positions as of July 27, according to a filing Wednesday with the U.S. Securities and Exchange Commission. The remaining job cuts are expected to be finished by the end of the 2013 fiscal year, Medtronic said in the filing.