Impact of Systole Phase on Ventricular Outflow Tract Diameter and Cardiac Output Calculation in Infants Born Preterm: A Clinical Validation Study.

Abstract

Objective: To investigate systolic phase-related variation in measurements of right ventricular outflow tract diameter (RVOTd) and left ventricular outflow tract diameter (LVOTd) and calculated right ventricular ouput (RVO) and left ventricular output (LVO) on targeted neonatal echocardiography (TNE) and examine their clinical applicability.

Study design: Based on the hypothesis that clinically reliable methods would yield RVO equal to LVO in the absence of cardiac shunts, allowing for predefined margin of ±15% mean difference (MD%), RVOTd/LVOTd were retrospectively measured at early systole (ES), mid systole (MS), and late systole (LS) to calculate corresponding RVOs/LVOs, for neonates who had a TNE without detectable shunt over a 6-year period (1 TNE/patient). Percent variability related to the systolic phase at measurement were compared between right- and left-sided measures and between different pairs. MD% (95% CI) were calculated for 9 paired RVO/LVO combinations, and absolute MD (95% limits of agreement) were identified using Bland-Altman analysis (BA).

Results: Fifty-six neonates were included. Overall, variables varied significantly based on the choice of systolic phase at measurement, greater for the right ventricle (RVOTd vs LVOTd 13.8±6.5% vs 7.5±4.3%, p <0.01; RVO vs LVO 25.3 ± 11.0% vs 14.3 ± 7.9%, p<0.01). A stepwise reduction occurred in all measurements though systole (ES>MS>LS). Of the 9 RVO/LVO pairs, only RVO-LS/LVO-ES showed MD%< ±15% [5.3% (-3.9%,14.6%)] and lowest MD on BA but wide LOA [38 (233, -158) ml/min/kg].

Conclusions: The choice of systolic phase at RVOTd/LVOTd measurement is an important source of variability, needing standardization during output calculations on TNE. RVOTd-LS/LVOTd-ES pair may provide clinically acceptable performance for output calculation in neonates.