The Host Mary Agnes CareyKFF Health News @maryagnescarey Read Mary Agnes’ stories. Lawmakers in Washington this week held the first congressional hearing on the Change Healthcare cyberattack, a breach that sent shock waves through the health care system as payments for care ground to a halt and left some providers in financial trouble. Republicans and Democrats alike zeroed in on how big health care conglomerations — like Change’s parent company, UnitedHealth Group — are leaving patients vulnerable. And nearly 1 in 4 adults who lost Medicaid coverage in the past year are now uninsured, accordi…