The emerging role of the contractile and vascular reserves in pulmonary arterial hypertension

We agree with our colleagues J.C. Grignola and E. Domingo on the importance of measurements of both right ventricular (RV) and pulmonary vascular reserve in patients with pulmonary arterial hypertension, and that further studies are needed to define the most relevant variables and optimal methodology [1]. They have a point that isometric-phase measures of RV systolic function, such as isovolumic myocardial acceleration, may be preferable, as they are less load-dependent than more commonly assessed indices, such as the S ′ wave, tricuspid annular plane systolic excursion, fractional area change or ejection fraction. Isometric-phase measurements best correlate with the gold-standard end-systolic elastance in intact experimental animals [2]. The maximum velocity of isovolumic contraction has been shown to be a stronger predictor of outcome than a number of other echocardiographic measurements of RV function in patients with severe pulmonary hypertension [3]. However, what matters in the end is how RV contractility increases in a fashion adapted to afterload [4]. This may be disclosed by simpler surrogate measurements of contractile reserve such as changes in RV peak systolic pressure during exercise [5]. Clinical utility and optimal indices of RV contractile reserve in PAH remains an open question