Scott Thompson, an on-air personality who co-owned and managed the ESPN-Radio affiliate 1570-AM in Louisville, Ky., and who assisted in Kentucky Derby coverage for more than 20 years for the Mutual Broadcasting Network and other major outlets, died of a heart attack at his Louisville home early Saturday. He was 45. Thompson was a major booster of local racing coverage by airing up-to-date results, on-site feature-race coverage, and other racing programming on his station. Thompson is survived by his wife, Sue, and two teenage children.