Differentiating pulmonary arterial and pulmonary venous hypertension and the implications for therapy.

Pulmonary arterial and pulmonary venous hypertension develop from distinctly different etiologies. Pulmonary arterial hypertension (PAH), or Group 1 pulmonary hypertension (PH), is a precapillary PH that arises idiopathically or as the result of a divergent array of causes, including connective tissue disease. Pulmonary venous hypertension (PVH), or Group 2 PH, primarily manifests as a postcapillary PH in the setting of left heart failure or valvular disease. A subset of PVH patients, however, develop a reactive precapillary component of PH that mimics PAH. These patients can be misdiagnosed as having Group 1 PH by 2-dimensional echocardiography and are sometimes treated as such, which leads to exacerbation of heart failure. Therefore, 2-dimensional or Doppler echocardiography alone cannot be used to differentiate between these two classifications of PH. This highlights the need for right heart catheterization in the clinical assessment and diagnostic work-up of PH. The combination of imaging and invasive hemodynamic assessment by right heart catheterization provides the best diagnostic approach to ensure proper delineation of pulmonary arterial and pulmonary venous hypertension, and in turn leads to appropriate treatment.