Hyperviscosity syndrome revisited.

Secondary erythrocytosis occurs in cyanotic heart disease as a physiological response to chronic hypoxia, and this leads to hyperviscosity and various complications of the same. Microvascular stasis due to hyperviscosity results in symptoms including headache, fatigue, paraesthesia, and loss of vision. An important and dreadful feature of hyperviscosity is overt thrombosis in organ systems, resulting in cerebrovascular accident and myocardial infarction. Limited body iron store in a state of secondary erythrocytosis brings forth iron-deficient microcytic red cells; these being more rigid and less deformable than normocytic cells, further aggravate vascular occlusion. The management of hyperviscosity syndrome starts with intravenous hydration and correction of latent iron deficiency. However, therapeutic phlebotomy may be employed as a rescue measure if symptoms persist despite correction of dehydration and anemia. We present a series of four patients with uncorrected cyanotic congenital heart disease who presented with a spectrum of features of hyperviscosity and discuss pathophysiology, clinical features, and management of hyperviscosity in detail.