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ESSENTIALS OF DIAGNOSIS
Mean PA pressure of 25 mm Hg or more.
Dyspnea and often cyanosis.
Enlarged pulmonary arteries on chest radiograph.
Elevated JVP and RV heave.
Echocardiography is often diagnostic.
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GENERAL CONSIDERATIONS
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The normal pulmonary bed offers about one-tenth as much resistance to blood flow as the systemic arterial system. Experts recommend that a diagnosis of idiopathic pulmonary hypertension should be firmly based on a mean PA pressure of 25 mm Hg or more in association with a PCWP of less than 16 mm Hg at rest.
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The clinical classification of pulmonary hypertension by the Fourth World Symposium on Pulmonary Hypertension is outlined in Table 10–19. It is a complex disorder due to multiple causes.
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Group I includes pulmonary arterial hypertension (PAH) related to an underlying pulmonary vasculopathy. It includes the former “primary pulmonary hypertension” under the term “idiopathic pulmonary hypertension” and is defined as pulmonary hypertension and elevated PVR in the absence of other disease of the lungs or heart. Its cause is unknown. About 6–10% have heritable PAH. Clear genetic patterns have been identified that result in a derangement in one or more biologic pathways, and these result in so-called “heritable pulmonary hypertension.” A mutation in the BMPR2 gene (which encodes bone morphogenic receptor protein 2), a cell surface receptor for transforming growth factor-beta (TGF-beta), is the most common genetic abnormality known. Rarely, two other surface receptor genes have been identified including activin-like kinase-type (ALK-1) and endoglin (ENG). About 20% of idiopathic pulmonary arterial hypertension patients will have BMPR2 mutation. Pathologically, it is characterized by diffuse narrowing of the pulmonary arterioles. In addition, a novel channelopathy caused by a mutation of KCNK3 gene has been ...