do I have a medical malpractice case?

My father has been suffering from a swollen and painful leg for over a year and has a history of blood clots. Within the past 6 months he saw a vascular surgeon who ordered a "blood flow test" and determined that my father has "good" blood flow to his left so this was not the cause of his swelling. Last week my father saw his cardiologist who ordered a sonogram and diagnosed my father with significant blockage in his artery behind his knee requiring bypass surgery and possibly amputation (we will know after the angiogram Thursday). My father has been for 3 previous sonogram of his leg in the past year and none of his doctors caught it.