The fluid challenge for identification of pulmonary hypertension associated with left heart disease

Left heart disease (LHD) is the commonest cause of pulmonary hypertension (PH). The differential diagnosis between PH associated with LHD (PH-LHD) and pulmonary arterial hypertension (PAH) may be difficult. PH associated with LHD is causally related to chronically increased pulmonary artery wedge pressure (PAWP). However, PAWP may be "falsely" normal or high-normal at the time of diagnostic right heart catheterization.

Updated guidelines for step-by-step diagnosis of PAH and LHD leave nevertheless a proportion of patients with PH and diagnostic uncertainty. In these patients, several studies have shown that a PAWP >18 mmHg after a rapid infusion of 500 ml saline is associated with a high likelihood of LHD. Evidence has been accumulated that patients with PH, cardiovascular risk factors and a high-normal PAWP should have LHD excluded by a fluid challenge. Preliminary studies suggest that the test may be performed noninvasively by combining Doppler echocardiography and lung ultrasound showing respectively a ratio of trans-mitral flow E wave to mitral annulus tissue velocity e' (E/e') ≥12 and ≥5 B-lines.

A fluid challenge has a place in the step-by-step diagnostic work-up of patients referred for PH for the differential diagnosis between PH-LHD and PAH.