REN and hydrops fetalis: Plasma Renin Activity (PRA). The prognostic role of PRA as a specific neurohumoral biomarker of the RAAS and sympathetic activation pathways in HF was assessed in a population of 996 patients with HFrEF on optimal therapy treatment (LVEF < 50%, mean age 65 ± 13 years), who were followed up for a median 36 months (range 0 to 72) for CV death and appropriate implantable cardioverter device (ICD) shock [95].