Carolinas HealthCare System will collaborate with health insurer Aetna Inc. on a network to provide better-coordinated care for patients. The initiative will be based on what the health-care industry calls a "patient-centered medical-home model." Under that concept, care for patients will be coordinated throughout Carolina HealthCare's network of hospitals, outpatient facilities and specialists. Financial details of the arrangement, which began April 1, were not disclosed. Charlotte-based Carolinas HealthCare says it serves more than 20,000 patients who have Aetna coverage.