Discerning Pulmonary Venous From Pulmonary Arterial Hypertension Without the Help of a Catheter

Pulmonary hypertension (PH) is an increasingly recognized cause of dyspnea and effort intolerance that may develop in response to 5 broad categories of disease.1 After excluding patients with hypoxic pulmonary disease, thromboembolism, and other systemic disorders, the differential diagnosis narrows to group I PH (or pulmonary arterial hypertension [PAH] due to abnormalities in the pulmonary arterial vasculature) and group II PH (due to pulmonary venous hypertension from left-sided heart disease). Group II PH is straightforward to diagnose noninvasively when obvious culprits such as left ventricular (LV) systolic dysfunction or valvular heart disease are identified by echocardiography.2 However, half of patients with left-sided heart failure have preserved ejection fraction (HFpEF),3 without significant valvular disease, and it can be challenging to distinguish this group of patients from those with PAH, who similarly have a normal EF, elevated pulmonary artery (PA) pressure estimates, and diastolic dysfunction on echocardiogram. The treatments and mechanisms underlying PAH and HFpEF are quite different, so distinction of one from the other is of obvious clinical importance.Article see p 257In the absence of shunts, the pulmonary and systemic circulations receive approximately the same amount of blood flow per minute, but this is where the similarities end. Pulmonary vascular resistance (PVR) is >10-fold lower than resistance in the systemic circulation, and the pressure in the venous bed draining the pulmonary arteries (pulmonary veins, left atrium) accounts for a much greater percentage of total PA pressure (40% to 60%) than the corresponding downstream venous pressure in the systemic circuit (right atrium, accounting for only ≈5% of systemic pressure). Because PA pressure is so heavily influenced by left heart filling pressures, it is not surprising that group II PH is the most common form of PH.2PH has traditionally been defined by mean PA pressure in …