A modified echocardiographic approach improves reliability of superior vena caval flow quantification.

OBJECTIVE: To assess accuracy and repeatability of a modified echocardiographic approach to quantify superior vena cava (SVC) flow volume that uses a short-axis view to directly measure SVC area and a suprasternal view to measure flow velocity, both at the level of the right pulmonary artery. SETTING: Three tertiary-level neonatal intensive care units. DESIGN: This was a multicentre, prospective, observational study. Accuracy of the traditional and modified approach was first assessed by comparing echo measurements according to both techniques with Phase contrast MRI (PCMRI) assessments, in a cohort of 10 neonates. In a second cohort of 40 neonates, intraobserver scan-rescan repeatability and interobserver analysis-reanalysis repeatability were assessed by repeated SVC flow echo measurements, according to both techniques. RESULTS: The traditional echocardiographic approach to assessment of SVC flow had a moderate agreement with PCMRI (r2 0.259), a scan-rescan intraobserver repeatability index (RI) of 37% (limits of agreement (LOA) -47/+51 mL/kg/min) and an interobserver analysis-reanalysis RI of 31% (LOA -38/+40 mL/kg/min). The modified approach showed a stronger agreement with PCMRI (r2 0.775), an improved intraobserver scan-rescan repeatability (RI 22%, LOA -24/+18 mL/kg/min) and improved interobserver analysis-reanalysis repeatability (RI 18%, LOA -18/+20 mL/kg/min). CONCLUSIONS: Echocardiographic assessment of SVC flow volume by tracing area from a short-axis view and measuring velocity-time integral from a suprasternal view offered an improvement in accuracy and repeatability, building on the traditional approach previously described.

Cardiovascular magnetic resonance of cardiac function and myocardial mass in preterm infants: a preliminary study of the impact of patent ductus arteriosus.

BACKGROUND: Many pathologies seen in the preterm population are associated with abnormal blood supply, yet robust evaluation of preterm cardiac function is scarce and consequently normative ranges in this population are limited. The aim of this study was to quantify and validate left ventricular dimension and function in preterm infants using cardiovascular magnetic resonance (CMR). An initial investigation of the impact of the common congenital defect patent ductus arteriosus (PDA) was then carried out. METHODS: Steady State Free Procession short axis stacks were acquired. Normative ranges of left ventricular end diastolic volume (EDV), stroke volume (SV), left ventricular output (LVO), ejection fraction (EF), left ventricular (LV) mass, wall thickness and fractional thickening were determined in "healthy" (control) neonates. Left ventricular parameters were then investigated in PDA infants. Unpaired student t-tests compared the 2 groups. Multiple linear regression analysis assessed impact of shunt volume in PDA infants, p-value ≤ 0.05 being significant. RESULTS: 29 control infants median (range) corrected gestational age at scan 34+6(31+1-39+3) weeks were scanned. EDV, SV, LVO, LV mass normalized by weight and EF were shown to decrease with increasing corrected gestational age (cGA) in controls. In 16 PDA infants (cGA 30+3(27+3-36+1) weeks) left ventricular dimension and output were significantly increased, yet there was no significant difference in ejection fraction and fractional thickening between the two groups. A significant association between shunt volume and increased left ventricular mass correcting for postnatal age and corrected gestational age existed. CONCLUSION: CMR assessment of left ventricular function has been validated in neonates, providing more robust normative ranges of left ventricular dimension and function in this population. Initial investigation of PDA infants would suggest that function is relatively maintained.

Validation study of the accuracy of echocardiographic measurements of systemic blood flow volume in newborn infants.

BACKGROUND: The echocardiographic assessment of circulatory function in sick newborn infants has the potential to improve patient care. However, measurements are prone to error and have not been sufficiently validated. Phase-contrast magnetic resonance imaging (MRI) provides highly validated measures of blood flow and has recently been applied to the newborn population. The aim of this study was to validate measures of left ventricular output and superior vena caval flow volume in newborn infants. METHODS: Echocardiographic and MRI assessments were performed within 1 working day of each other in a cohort of newborn infants. RESULTS: Examinations were performed in 49 infants with a median corrected gestational age at scan of 34.43 weeks (range, 27.43-40 weeks) and a median weight at scan of 1,880 g (range, 660-3,760 g). Echocardiographic assessment of left ventricular output showed a strong correlation with MRI assessment (R(2) = 0.83; mean bias, -9.6 mL/kg/min; limits of agreement, -79.6 to +60.0 mL/kg/min; repeatability index, 28.2%). Echocardiographic assessment of superior vena caval flow showed a poor correlation with MRI assessment (R(2) = 0.22; mean bias, -13.7 mL/kg/min; limits of agreement, -89.1 to +61.7 mL/kg/min; repeatability index, 68.0%). Calculating superior vena caval flow volume from an axial area measurement and applying a 50% reduction to stroke distance to compensate for overestimation gave a slightly improved correlation with MRI (R(2) = 0.29; mean bias, 2.6 mL/kg/min; limits of agreement, -53.4 to +58.6 mL/kg/min; repeatability index, 54.5%). CONCLUSIONS: Echocardiographic assessment of left ventricular output appears relatively robust in newborn infant. Echocardiographic assessment of superior vena caval flow is of limited accuracy in this population, casting doubt on the utility of the measurement for diagnostic decision making.

Assessment of PDA shunt and systemic blood flow in newborns using cardiac MRI.

Patent ductus arteriosus (PDA) remains common in preterm newborns, but uncertainty over optimal management is perpetuated by clinicians' inability to quantify its true haemodynamic impact. Our aim was to develop a technique to quantify ductal shunt volume and the effect of PDA on systemic blood flow volume in neonates. Phase contrast MRI sequences were optimized to quantify left ventricular output (LVO) and blood flow in the distal superior vena cava (SVC) (below the azygos vein insertion), descending aorta (DAo) and azygos vein. Total systemic flow was measured as SVC + DAo-azygos flow. Echo measures were included and correlated to shunt volumes. 75 infants with median (range) corrected gestation 33(+6) (26(+4) -38(+6) ) weeks were assessed. PDA was present in 15. In 60 infants without PDA, LVO matched total systemic flow (mean difference 2.06 ml/kg/min, repeatability index 13.2%). In PDA infants, ductal shunt volume was 7.9-74.2% of LVO. Multiple linear regression analysis correcting for gestational age showed that there was a significant association between ductal shunt volume and decreased upper and lower body flow (p = 0.01 and p < 0.001). However, upper body blood flow volumes were within the control group 95% confidence limits in all 15 infants with PDA, and lower body flow volumes within the control group limits in 12 infants with PDA. Echocardiographic assessment of reversed diastolic flow in the descending aorta had the strongest correlation with ductal shunt volume. We have demonstrated that quantification of shunt volume is feasible in neonates. In the presence of high volume ductal shunting the upper and lower body flow volume are somewhat reduced, but levels remain within or close to the normal range for preterm infants.

Neonatal cardiac MRI using prolonged balanced SSFP imaging at 3T with active frequency stabilization.

UNLABELLED: Cardiac MRI in neonates holds promise as a tool that can provide detailed functional information in this vulnerable group. However, their small size, rapid heart rate, and inability to breath-hold, pose particular challenges that require prolonged high-contrast and high-SNR methods. Balanced-steady state free precession (SSFP) offers high SNR efficiency and excellent contrast, but is vulnerable to off-resonance effects that cause banding artifacts. This is particularly problematic in the blood-pool, where off-resonance flow artifacts severely degrade image quality. METHODS: In this article, we explore active frequency stabilization, combined with image-based shimming, to achieve prolonged SSFP imaging free of banding artifacts. The method was tested using 2D multislice SSFP cine acquisitions on 18 preterm infants, and the functional measures derived were validated against phase-contrast flow assessment. RESULTS: Significant drifts in the resonant frequency (165 ± 23Hz) were observed during 10-min SSFP examinations. However, full short-axis stacks free of banding artifacts were achieved in 16 subjects with stabilization; the cardiac output obtained revealed a mean difference of 9.0 ± 8.5% compared to phase-contrast flow measurements. CONCLUSION: Active frequency stabilization has enabled the use of prolonged SSFP acquisitions for neonatal cardiac imaging at 3T. The findings presented could have broader implications for other applications using prolong SSFP acquisitions.