Sickle cell disease: at the crossroads of pulmonary hypertension and diastolic heart failure.

Sickle cell disease (SCD) is caused by a single point mutation in the gene that codes for beta globin synthesis, causing haemoglobin polymerisation, red blood cell stiffening and haemolysis under low oxygen and pH conditions. Downstream effects include widespread vasculopathy due to recurring vaso-occlusive events and haemolytic anaemia, affecting all organ systems. Cardiopulmonary complications are the leading cause of death in patients with SCD, primarily resulting from diastolic heart failure (HF) and/or pulmonary hypertension (PH). HF in SCD often features biventricular cardiac hypertrophy and left ventricular (LV) diastolic dysfunction. Among HF cases in the general population, approximately half occur with preserved ejection fraction (HFpEF). The insidious evolution of HFpEF differs from the relatively acute evolution of HF with reduced ejection fraction. The PH of SCD has diverse origins, which can be pulmonary arterial (precapillary), pulmonary venous (postcapillary) or pulmonary thromboembolic. It is also appreciated that patients with SCD can develop both precapillary and postcapillary PH, with elevations in LV diastolic pressures, as well as elevations in transpulmonary pressure gradient and pulmonary vascular resistance. Regardless of the cause of PH in SCD, its presence significantly reduces functional capacity and increases mortality. PH that occurs in the presence of HFpEF is usually of postcapillary origin. This review aims to assemble what has been learnt from clinical and animal studies about the manifestation of PH-HFpEF in SCD, specifically the contributions of LV diastolic dysfunction and myocardial fibrosis, in an attempt to gain an understanding of its evolution.