Group 2: Pulmonary hypertension due to left heart disease
Left-sided ventricular or valvular diseases may produce an increase of left atrial pressure, leading to a backward transmission of the pressure and a passive increase of pulmonary arterial pressure. Left heart disease, probably represents the most frequent cause of PH [60]. In this situation, PVR is normal or near normal (<3.0 Wood units) and there is no gradient between mean PAP and pulmonary wedge pressure (transpulmonary gradient <12 mm Hg). In the Dana Point classification, the increasing recognition of left-sided heart dysfunction with preserved ejection fraction leads to changes in the subcategories of Group 2 and now this group include three distinct etiologies: left heart systolic dysfunction, left heart diastolic dysfunction, and left heart valvular disease. In some patients with left heart disease, the elevation of pulmonary arterial pressure is out of proportion to that expected from the elevation of left arterial pressure (transpulmonary gradient >12 mm Hg), and PVR is increased to >3.0 Wood units (19–35% of patients) [60]. However, there is no widely accepted hemodynamic definition of transpulmonary gradient, and future recommendations may propose new definition and threshold of this gradient. Some patients with left heart valvular disease or even left heart dysfunction can develop severe PH of the same magnitude as that seen in PAH [61-63]. The elevation of PAP and PVR may be due to either the increase of pulmonary artery vasomotor tone and/or pulmonary vascular remodeling [64,65].