The CEO of St. Louis University Hospital says that his health system is seeking the assistance of a third-party mediator to break an impasse in contract talks with a national health insurer. SLU Hospital Chief Executive Phillip Sowa said the hospital's parent company, Tenet HealthCare Corp. of Dallas, faxed a letter Friday to Anthem Blue Cross and Blue Shield of Missouri as well as HealthLink Inc., proposing that an "independent third party" help move contract talks forward. Both health insurers are owned by WellPoint Inc. of Indianapolis.