Heart Disease in Sickle Cell Anemia

Sickle cell anemia is an inherited blood disorder primarily affecting groups with origins in endemic malarial areas, especially those of African descent. SCA results from one of two single amino-acid substitutions in beta-hemoglobin (Hb-S and Hb-C) that increases the propensity for hemoglobin to polymerize, thus distorting, sickling and hemolyzing red cells. Individuals homozygous for Hb-S (or double heterozygote Hb-S and Hb-C) develop sickle cell anemia (SCA), while heterozygotes have sickle cell trait. SCA is characterized by chronic anemia and crises of red cell sickling and ischemia that are often painful and affect several organs and tissue types. SCA confers considerable disability, morbidity and mortality. Annual mortality from SCA has been estimated at approximately 3%. As a significant number of these deaths are sudden, a cardiac cause has been suspected. However, no cardiac mechanism of sudden death (SD) has been clearly identified. Recently, it has been demonstrated that SCA patients with pulmonary hypertension (PAH) have a higher incidence of SD than those with normal pulmonary pressures. In many patients, PAH occurs in association with elevated pulmonary arterial wedge pressures and normal pulmonary arterial resistance, suggesting that the PAH develops as the result of left ventricular (LV) abnormalities. Furthermore, in other conditions in which PAH develops, SD occurs only at pressures considerably higher than those observed in SCA. These factors suggest that PAH in SCA is a surrogate marker for, rather than the cause of SD. Rather, an SCA cardiomyopathic process may provide a unifying mechanism that associates moderate degrees of PAH and high risk of SD from cardiac causes. We propose to describe the extent of cardiac involvement in SCA. Specifically, we will (1) describe the LV volume-pressure relations in SCA patients with and without pulmonary hypertension in order to determine how elevated pulmonary pressures are related to dynamic filling properties of the LV; and (2) determine whether cardiac arrhythmias are common in SCA patients with PAH and if they contribute to SD. Improved understanding of the etiology and mechanisms of SD in SCA may allow the development and testing of therapies for the primary prevention of SD.