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Right heart adaptation to pulmonary arterial hypertension: physiology and pathobiology.

J Am Coll Cardiol. 2013 Dec 24;62(25 Suppl):D22-33

Authors: Vonk-Noordegraaf A, Haddad F, Chin KM, Forfia PR, Kawut SM, Lumens J, Naeije R, Newman J, Oudiz RJ, Provencher S, Torbicki A, Voelkel NF, Hassoun PM

Abstract
Survival in patients with pulmonary arterial hypertension (PAH) is closely related to right ventricular (RV) function. Although pulmonary load is an important determinant of RV systolic function in PAH, there remains a significant variability in RV adaptation to pulmonary hypertension. In this report, the authors discuss the emerging concepts of right heart pathobiology in PAH. More specifically, the discussion focuses on the following questions. 1) How is right heart failure syndrome best defined? 2) What are the underlying molecular mechanisms of the failing right ventricle in PAH? 3) How are RV contractility and function and their prognostic implications best assessed? 4) What is the role of targeted RV therapy? Throughout the report, the authors highlight differences between right and left heart failure and outline key areas of future investigation.

PMID: 24355638 [PubMed - in process]

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Pulmonary hypertension (PH) is defined by a mean pulmonary artery pressure ≥25 mm Hg at rest, measured during right heart catheterization. There is still insufficient evidence to add an exercise criterion to this definition.

The term pulmonary arterial hypertension (PAH) describes a subpopulation of patients with PH characterized hemodynamically by the presence of pre-capillary PH including an end-expiratory pulmonary artery wedge pressure (PAWP) ≤15 mm Hg and a pulmonary vascular resistance >3 Wood units. Right heart catheterization remains essential for a diagnosis of PH or PAH. This procedure requires further standardization, including uniformity of the pressure transducer zero level at the midthoracic line, which is at the level of the left atrium. One of the most common problems in the diagnostic workup of patients with PH is the distinction between PAH and PH due to left heart failure with preserved ejection fraction (HFpEF). A normal PAWP does not rule out the presence of HFpEF. Volume or exercise challenge during right heart catheterization may be useful to unmask the presence of left heart disease, but both tools require further evaluation before their use in general practice can be recommended.

Early diagnosis of PAH remains difficult, and screening programs in asymptomatic patients are feasible only in high-risk populations, particularly in patients with systemic sclerosis, for whom recent data suggest that a combination of clinical assessment and pulmonary function testing including diffusion capacity for carbon monoxide, biomarkers, and echocardiography has a higher predictive value than echocardiography alone.

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Registries of patients with pulmonary arterial hypertension (PAH) have been instrumental in characterizing the presentation and natural history of the disease and provide a basis for prognostication. Since the initial accumulation of data conducted in the 1980s, subsequent registry databases have yielded information about the demographic factors, treatment, and survival of patients and have permitted comparisons between populations in different eras and environments. Inclusion of patients with all subtypes of PAH has also allowed comparisons of these subpopulations.

We describe herein the basic methodology by which PAH registries have been conducted, review key insights provided by registries, summarize issues related to interpretation and comparison of the results, and discuss the utility of data to predict survival outcomes. Potential sources of bias, particularly related to the inclusion of incident and/or prevalent patients and missing data, are addressed. A fundamental observation of current registries is that survival in the modern treatment era has improved compared with that observed previously and that outcomes among PAH subpopulations vary substantially. Continuing systematic clinical surveillance of PAH will be important as treatment evolves and as understanding of mechanisms advance.

Considerations for future directions of registry studies include enrollment of a broader population of patients with pulmonary hypertension of all clinical types and severity and continued globalization and collaboration of registry databases.