End-systolic volume index is one of the most significant components of right ventricular stroke work penalized by ejection fraction (RVSWEF) in patients with worsening states of pulmonary arterial hypertension (PAH), according to a letter to the editor published in Pulmonary Circulation. For this reason, the authors suggested pressure-volume representation instead of combining end-diastolic volume index and pressure difference into RVSWEF.

This letter referenced a study performed by Yang and colleagues that investigated pediatric PAH. In that study, researchers identified a specific biomarker based on data from magnetic resonance imaging and right heart catheterization associated with clinical worsening, which led to better performance compared with other models. Follow-up lasted between 1 and 10 years after diagnosis, during which time the biomarker was found to have an upward trend associated with worsening. The authors proposed dividing stroke work by EF to derive penalized stroke work.

However, the letter’s authors pointed out that EF suffers from a comparable set of shortcomings as stroke work, as individual values are not unique and the same values can apply to individuals with different pathophysiology. This ratio actually leads to stroke volume canceling out, which makes it unlikely that the biomarker is a true reflection of stroke work.

The biomarker is derived from a pressure-volume rectangular area encompassing stroke work, which means the exact contours of the pressure-volume loop are rendered extraneous. Through increasing end-diastolic volume index and/or pressure difference, stroke work’s proportional importance to RVSWEF diminishes with time. Greater end-diastolic volume index and pressure difference values contribute to RVSWEF minus stroke work index equalling X. This means analysis and interpretation of the area X in RVSWEF is important.

The authors concluded that “…rather than the isolated value of [stroke work], even when obtained by a lumped parameter model, the [end-systolic volume index] is a dominant component of the proposed RVSWEF, especially in worsening PAH states. …We favor a representation in the [pressure-volume] domain, rather than the combination of [pressure difference] and [end-diastolic volume index] into a single number (namely RVSWEF) as created by multiplication.”

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Kerkhof PL Kerkhof, Li JK-J, Handly N. EXPRESS: Interpretation of a new biomarker for the right ventricle introduced to evaluate the severity of pulmonary arterial hypertension [published online January 14, 2019]. Pulm Circ. doi:10.1177/2045894019826945