A 60-year-old man presented with complaints of fatigue, headaches, and itching. Physical examination revealed a ruddy complexion and splenomegaly. Laboratory tests showed an elevated hematocrit, hemoglobin, and red blood cell count. A bone marrow biopsy confirmed polycythemia vera, a myeloproliferative disorder characterized by overproduction of red blood cells. Of the following, which is the most common complication and major cause of morbidity in patients with polycythemia vera?
