Imaging risk in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a Janus-faced entity with, on one side, the pulmonary circulation and, on the other side, the right ventricle (RV). While the disease process is turned on at the site of the pulmonary resistive vessels, the patient symptomatology and prognosis are largely determined by RV structure and function adaptation to increased afterload. Yet, this important cardiac aspect of PAH pathophysiology remains insufficiently recognised. Combined measurements of TAPSE, TR and IVC outperformed other echocardiographic measurements previously shown to be predictors of outcome in PAH, such as right atrial (RA) surface area and pericardial effusion which are part of current guidelines recommendations for risk assessment. PAH is a progressive disease with high mortality. Indeed, combination treatment strategies and the option of probably most effective parenteral prostacyclin therapies would be prescribed to patients with the highest risk of deterioration and shorter survival. Risk assessment is thus essential to optimise treatment decisions aimed at slowing progression of the disease. 14 parameters were used to categorise patients into a low risk green zone (<5% 1-year mortality), an intermediate risk yellow zone (5–10% 1-year mortality) and a high risk red zone (>10% 1-year mortality). The inherent assumption of the approach was that treatments should be titrated or combined to move patients into lower risk zones and thereby improve survival. However, the majority of PAH patients remain in intermediate risk status or with overlapping risk assessments under a double combination of oral drugs, and there is little data offering support to the difficult decision of initial or sequential addition of parenteral prostacyclins. The echocardiographic examination of PAH patients generates many measurements which have been shown to be of prognostic relevance by rigorous univariate and multivariable analysis, though most of the time in limited size mono-centric studies. TAPSE is indeed a robust though load-dependent measure of contractility and IVC diameter a reflection of increased RV and RA pressure and dimensions. The RV adapts in severe PH by increased contractility to preserve its coupling to the pulmonary circulation and it is only after this basic homeometric mechanism is exhausted that Starling’s heterometric adaptation comes into play to preserve flow output, but at the price of increased dimensions and systemic congestion. Thus, the TAPSE (corrected for TR) reflects contractility adaptation and increased IVC dimension its failure. Echocardiography also allows for measurement of other load dependent indices of pump failure, such as RV fractional area change, and more load-independent measures of RV contractility, such as the maximum velocity of isovolumic contraction or longitudinal strain, and offers exploration of regional inhomogeneity of RV contraction which, alone or in combination with CPET, may also be prognostically pertinent.