Chapter 8. Pulmonary Arterial Hypertension (PAH)

Rebecca L. Attridge; Rebecca Moote; Deborah J. Levine

Clinical pathological definition: vasculopathy of the small pulmonary arteries which leads to ↑ pulmonary vascular resistance; may progress to right heart dysfunction & failure
Hemodynamic definition: mean pulmonary artery pressure (mPAP) ≥25mmHg at rest, AND pulmonary capillary wedge pressure (PCWP) or left ventricular end-diastolic pressure (LVEDP) ≤15mmHg measured by right heart catheterization
Established disease mediators: endothelin-1, prostacyclin, nitric oxide (J Am Cardiol 2009;53:1573)

Figure 8-1.

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Pulmonary arterial hypertensionpathophysiology. BMPR-2: bone morphogenetic protein receptor II; ALK1: activin receptor-like kinase 1; HTT: hydroxytryptamine transporter; ec-NOS: nitric oxide synthase; CPS: carbamyl phosphate synthase.

WHO Functional Classification of PAH

Table 8-1 WHO Functional Classification of Pulmonary Arterial Hypertension

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Table 8-1 WHO Functional Classification of Pulmonary Arterial Hypertension

Class

Description

Patients with PAH in whom there is NO limitation of usual physical activity; ordinary physical activity does NOT cause increased dyspnea, fatigue, chest pain, or presyncope

Patients with PAH who have mild limitation of physical activity; there is NO discomfort at rest, but normal physical activity causes increased dyspnea, fatigue, chest pain, or presyncope

III

Patients with PAH who have marked limitation of physical activity; there is NO discomfort at rest, but less than normal physical activity causes increased dyspnea, fatigue, chest pain, or presyncope

Patients with PAH who are unable to perform any physical activity at rest & who may have signs of right ventricular failure; dyspnea, &/or fatigue may be present at rest, & symptoms are increased by almost any physical activity

Etiology of PAH

(Group 1 of WHO Pulmonary Hypertension Classification) (J Am Cardiol 2009;53:1573)

Idiopathic (IPAH)
Heritable (BMPR2, ALK1, endoglin, unknown)
Drug or toxin-induced: fenfluramine, cocaine, toxic rapeseed oil
Associated with (APAH): connective tissue diseases, HIV infection, portal hypertension, congenital heart diseases, schistosomiasis, chronic hemolytic anemia
Persistent pulmonary hypertension of the newborn
Pulmonary veno-occlusive disease (PVOD) &/or pulmonary capillary hemangiomatosis (PCH)

Prognosis:

Dependent on WHO Functional Class, Hemodynamics, & Etiology of PAH

Diagnosis made hemodynamically by right heart catheterization (RHC) (Circulation 2006;114;1417)
- Establishes diagnosis & guides treatment decisions
- Evaluates pulmonary vasoreactivity
  - Use fast-acting, short-duration vasodilators (ex: epoprostenol, nitric oxide, adenosine) to determine extent of vasodilator response
  - Positive response: reduction of mPAP by at least 10mmHg to a value of 40mmHg or less; ↑ or unchanged CO
  - Negative response: should never receive trial of calcium channel blockers; move to PAH targeted therapy
Echocardiography: assess right heart function & right-sided chamber size, estimate pulmonary pressures; used primarily as screening tool & helpful in ruling out other cardiac processes
Evaluation of etiology of PAH: HIV test, serologies for connective tissue diseases, hepatitis panel, thyroid function tests, pulmonary function tests (to evaluate for restrictive or obstructive lung disease), evaluation for chronic thromboembolic ...

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