Recognizing Declining Right Ventricular Reserve in Pediatric Pulmonary Arterial Hypertension: A Clinical Framework for Discordant Multimodal Findings

Right ventricular (RV) failure is a major determinant of clinical deterioration in pediatric pulmonary arterial hypertension (PAH), yet loss of RV reserve is difficult to recognize before overt low-output failure. Pulmonary artery pressure may remain stable or fall as RV pressure-generating capacity declines. Other commonly followed variables may also diverge: tricuspid annular plane systolic excursion can remain preserved despite worsening RV free-wall strain or cardiovascular magnetic resonance (CMR)-derived ejection fraction; natriuretic peptides may rise before conventional echocardiographic changes; and symptoms may deteriorate while estimated pressure appears unchanged. This focused narrative review integrates pediatric evidence with selected physiologic data to examine the interpretation of such discordance. We distinguish three clinical states—maintained adaptation, suspected loss of reserve, and overt decompensation—without proposing a new risk score. Assessment is organized around the clinical question left unanswered after the initial review. Signal quality and serial comparability are checked first, followed by transient modifiers of loading conditions and biomarker concentration. CMR helps resolve uncertainty about RV volume or global function, whereas right-heart catheterization directly defines pulmonary vascular load, filling pressure, and forward output when these measurements will affect management. Direct pediatric evidence supports serial assessment of RV and right atrial remodeling, myocardial deformation, CMR-derived function, natriuretic peptide trajectories, right atrial pressure, cardiac index, and mixed venous oxygen saturation, but no isolated variable has been validated as an independent treatment threshold. Concordance, direction, and rate of change across domains may improve recognition of declining RV reserve while limiting escalation driven by measurement noise.