Background Pulmonary artery hypertension (PAH) is common in newborn infants with hypoxia, infection and pulmonary mal-development. Clinical estimation of pulmonary artery pressure (PAP) is frequently performed echocardiographically by measuring the maximal velocity of the tricuspid regurgitation jet (TRmax) and/or flow in the patent ductus arteriosus (PDA). Challenges exist that may affect the accuracy of these methods.
Methods Prospective analysis of echocardiographic measurements from infants with PAH due to congenital diaphragmatic hernia, managed in a single surgical NICU. PAP was estimated by paired measurement of peak TRmax and PDA flow. TRmax was used to calculate RV systolic pressure (RVSP = 4(TRmax)2), and subsequently a ratio of RVSP to systemic blood pressure (RVSP:SBP). PDA flow was quantified by tracing the velocity time integer (VTI) to calculate a ratio of right-to-left:left-to-right flow, (PDARl:Lr). For both measures a ratio >1 indicates suprasystemic PAP, whilst a ratio <1 indicates PAP less than SBP. Correlation between RVSP:SBP and PDARl:Lr was assessed.
Results 213 echocardiograms were performed in 22 subjects. In 50 (23%) TR was not measureable, in 58 (27%) no PDA flow was present. Paired measures of TR and PDAflow were possible in 105 instances: median (range) RVSP:SBP was 0.81 (0.25–1.48), PDARl:Lr 0.90 (0.008.29). Correlation between paired RVSP:SBP and PDARl:Lr was poor: Spearman r = 0.33, P = 0.004.
Conclusions TR or PDA flow are frequently absent even in severe PAH, preventing PAP estimation. Poor correlation between TRmax and PDA flow indicates inaccuracy of these techniques. Accurate clinical quantification of PAP remains challenging. Assessment of other haemodynamic measures should be considered.
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