WASHINGTON (Reuters) - U.S. Attorney General Eric Holder was treated for an elevated heart rate at a Washington, D.C., hospital on Thursday but later walked out of the hospital without needing assistance and was resting comfortably at home, his office said. Holder, 63, the chief U.S. law enforcement official, felt lightheaded and short of breath during a morning staff meeting, according to a statement from his office. He never lost consciousness, and stayed at the hospital for about three hours for tests. Although he was given medication to restore his heart rate to a normal level, doctors ruled out the...