Phlebotomy in cyanotic congenital heart disease with hyperviscosity syndrome
Phlebotomy is often resorted to in patients with cyanotic congenital heart disease (CCHD) and symptoms of hyperviscosity (hyperviscosity syndrome) due polycythemia which occurs in response to hypoxia which causes an increased erythropoietin level. In contrast, increased erythropoiesis in polycythemia rubra vera occurs with normal or low erythropoietin levels. Hemoglobin levels and hematocrit are important considerations while planning venesection in those with symptoms of hyperviscosity. Hyperviscosity syndrome is characterized by impaired tissue oxygen delivery with symptoms like headache, visual disturbances, loss of concentration, paresthesia, muscle weakness, and fatigue. It should be remembered that dehydration and iron deficiency may precipitate hyperviscosity symptoms and just hydration may relieve symptoms in some cases . Venesection in turn can lead to iron deficiency which can form a vicious cycle by increasing symptoms of hyperviscosity as the microcytes of iron deficiency (identified by lower mean corpuscular volume or MCV) are less deformable and can clog the microcirculation. This can also enhance the risk of stroke instead of reducing the risk. Hydroxyurea has been tried for reducing erythrocytosis in some refractory cases, though it has the risk of producing transient marrow suppression which responds to dose reduction . Though the aim of phlebotomy in polycythemia rubra vera is to maintain hematocrit below 45%, most clinicians phlebotomize patients with cyanotic heart disease and polycythemia only if the hematocrit is above 65%.
Mechanism of benefit with phlebotomy in hyperviscosity syndrome of CCHD
Phlebotomy works by reducing viscosity due to lower hematocrit, which in turn reduces peripheral vascular resistance and increases cardiac output. Oxygen transport is improved and hence the symptoms of hyperviscosity are ameliorated.
As mentioned above undue venesection has the potential of inducing iron deficiency and decompensated erythrocytosis, thereby defeating the very purpose of venesection.
- Rose SS et al. Cyanotic Congenital Heart Disease (CCHD) with Symptomatic Erythrocytosis. J Gen Intern Med. 2007; 22: 1775–1777.
- Reiss UM et al. Hydroxyurea therapy for management of secondary erythrocytosis in cyanotic congenital heart disease. Am J Hematol. 2007;82:740-3.