VALIDATING THE USE OF PULMONARY ARTERY ACCELERATION TIME IN ESTIMATING PULMONARY PRESSURE IN NEONATES
Authors: Bhattacharya Soume , McNamara Patrick , Jain Amish , Ye Philip , McNamara Karl 
Published: May 2018

Abstract

BACKGROUND
Estimation of right ventricular peak systolic pressure (RVSP) or pulmonary pressure using echocardiography is crucial in neonates with acute or chronic pulmonary hypertension. Conventionally in echocardiography, the maximal velocity of the Tricuspid Regurgitant jet (TR Vmax) is used to estimate the RVSP. However, TR jet can often be absent or unmeasurable in neonates, resulting in a need to search for alternative echocardiographic measures of pulmonary pressure in neonates. Pulmonary Artery Doppler Waveform Parameter known as Pulmonary Artery Acceleration Time (PAAT) has been investigated in adults and older children and found to be reliable in estimating pulmonary pressure. To date, no such validation study exists for neonates.Hence we designed this study to explore the role of Pulmonary Artery Acceleration Time in estimating pulmonary pressures in neonates.

OBJECTIVES
To identify the pulmonary artery doppler waveform parameter that most closely reflects pulmonary pressure and analyse the impact of baseline variables and measurement techniques on this relationship.

DESIGN/METHODS
This was a retrospective cohort analysis conducted at two tertiary neonatal intensive care units. All neonates who underwent Targeted Neonatal Echocardiographic(TnECHO) assessments over May 2014-May 2017 were assessed for eligibility. Neonates whose echocardiography revealed a complete, measurableTR jet were included. Baseline characteristics such as gestational age, chronological age at echo, weight, blood pressure, ventilation and diagnosis were collected. Echocardiographic parameters such as TR Vmax, Pulmonary artery doppler waveform parameters such as Right Ventricular Ejection Time (RVET) and Pulmonary Artery Acceleration Time (PAAT) were measured by a single expert operator. Pulmonary Vascular Resistance Index (PVRI) was calculated as a ratio between RVET and PAAT. Correlation between pulmonary artery waveforms and RVSP estimated from the TR jet was examined using Pearson or Spearman analysis as appropriate. Univariate and multivariate regression analysis was used to further explore the influence of relevant factors on this relationship. Ethical approval was obtained from the institutional ethic board.

RESULTS
678 neonates with 1767 echocardiographic studies were screened for eligibility of which 201 scans were included. Mean gestational age of this cohort was 30.5+/-5.7 weeks with mean birthweight of 1635 +/-1115 grams. Pulmonary Vascular Resistance Index (ratio of RVET to PAAT) also known as indexed PAAT, measured by Pulsed Wave Doppler at the level of the main pulmonary artery was found to have the strongest correlation with RVSP estimated from TRVmax. [r=0.45,P<0.05]. Using regression analysis, we could generate an equation to estimate systolic pulmonary artery pressures(ESPAP) directly from PVRI. [ESPAP= 25.53 + 3.97xPVRI, p<0.0001]. At the multivariate level, factors such as the Systolic Blood Pressure at time of echocardiogram and the presence or absence of PDA were found to have a statistically significance influence on this relationship. Pulmonary Vascular Resistance Index could be measured on all eligible scans. Inter-observer and intra-observer reliability assessment completed on a random subset of 30 showed excellent reliability for PVRI. [ICC =0.88, P<0.000]

CONCLUSION
This important validation study shows that PAAT indexed to right ventricular ejection time(PVRI) has statistically significant correlation with pulmonary pressures as measured by TR jet in neonates. However the strength of correlation in neonates is moderate at best. The measurement is feasible with good interobserver agreement and potentially can play an important role in serial monitoring of pulmonary pressures in neonates without any demonstrable TR jet on echocardiography.