Blood flow velocity waveforms of the fetal pulmonary artery and the ductus arteriosus: reference ranges from 13 weeks to term

Maternal supplementation with docosahexaenoic acid does not cause constriction of fetal ductus arteriosus: randomized controlled trial

OBJECTIVE

Docosahexaenoic acid (DHA) is recommended routinely in pregnancy to promote fetal development. DHA has anti-inflammatory activity, but its effects on the fetal heart and circulation are unknown. This study aimed to investigate whether maternal DHA supplementation in the third trimester affects maternal prostaglandin levels and fetal ductus arteriosus flow dynamics.

METHODS

This was a double-blind randomized controlled trial with parallel groups conducted between 2018 and 2021. Pregnant women aged over 18 years with a normal fetus at 27-28 weeks' gestation showing no cardiac/extracardiac anomalies or ductal constriction were eligible for the trial. Women consuming substances with a known inhibitory effect on prostaglandin metabolism, such as non-steroidal anti-inflammatory drugs and polyphenol-rich foods, were excluded. The intervention group received oral supplementation of omega-3 with 450 mg/day of DHA for 8 weeks and the placebo group received capsules of soy lecithin for 8 weeks. Anthropometric measurements, assessment of polyphenol and omega-3 consumption, fetal morphological ultrasound examination, fetal Doppler echocardiographic examination and blood sample collection were performed at the start of the study and the latter two were repeated at follow-up. Prostaglandin E2 (PGE2) level and echocardiographic parameters were compared between the intervention and placebo groups and between baseline and follow-up.

RESULTS

A total of 24 participants were included in each group. After 8 weeks, there were no significant differences between the intervention and placebo groups in maternal serum PGE2 level or Doppler echocardiographic parameters of ductal flow. No case of ductus arteriosus constriction was observed. The expected intragroup changes in cardiac morphology, as a result of advancing gestation, were present.

CONCLUSIONS

Maternal DHA supplementation in the third trimester at a clinically recommended dose did not result in inhibition of PGE2 or constriction of the ductus arteriosus. These findings should be confirmed in postmarket surveillance studies with larger patient numbers in order to test the full safety profile of DHA and provide robust clinical reassurance. © 2024 International Society of Ultrasound in Obstetrics and Gynecology.

Recasting Current Knowledge of Human Fetal Circulation: The Importance of Computational Models

Computational hemodynamic simulations are becoming increasingly important for cardiovascular research and clinical practice, yet incorporating numerical simulations of human fetal circulation is relatively underutilized and underdeveloped. The fetus possesses unique vascular shunts to appropriately distribute oxygen and nutrients acquired from the placenta, adding complexity and adaptability to blood flow patterns within the fetal vascular network. Perturbations to fetal circulation compromise fetal growth and trigger the abnormal cardiovascular remodeling that underlies congenital heart defects. Computational modeling can be used to elucidate complex blood flow patterns in the fetal circulatory system for normal versus abnormal development. We present an overview of fetal cardiovascular physiology and its evolution from being investigated with invasive experiments and primitive imaging techniques to advanced imaging (4D MRI and ultrasound) and computational modeling. We introduce the theoretical backgrounds of both lumped-parameter networks and three-dimensional computational fluid dynamic simulations of the cardiovascular system. We subsequently summarize existing modeling studies of human fetal circulation along with their limitations and challenges. Finally, we highlight opportunities for improved fetal circulation models.

Cardiac Function Assessment in Fetuses With Ductus Arteriosus Constriction: A Two-Dimensional Echocardiography and FetalHQ Study

Background

Fetal ductal constriction (DC) is associated with excessive polyphenol-rich food (PRF) consumption during pregnancy. However, the effect of this hemodynamic change on fetal cardiac function still needs to be elucidated. Therefore, this study aimed to evaluate the cardiac function of fetuses with PRF-related DC and to describe serial observations of cardiac function changes.

Methods

We compared the traditional echocardiographic indices, including morphological, hemodynamic, and functional parameters, between study fetuses and controls. For global and segmental deformation analysis of the left and right ventricles, fetalHQ with the speckle-tracking technique was used to calculate sphericity index (SI), global longitudinal strain (GLS), fractional shortening (FS), fractional area change (FAC), etc. In addition, follow-up data were compared with the generalized linear model.

Results

A total of 60 DC fetuses and 60 gestational-matched controls were enrolled in our study, with 20 DC fetuses undertaking a follow-up echocardiogram after 2–3 weeks. Compared with controls, there was a distinct decrease in right ventricular GLS (RVGLS) (−13.39 ± 3.77 vs. −21.59 ± 2.51, p < 0.001), RVFAC (22.20 ± 9.56 vs. 36.01 ± 4.84, p < 0.001), left ventricular GLS (LVGLS) (−19.52 ± 3.24 vs. −23.81 ± 2.01 p < 0.001), and LVFAC (39.64 ± 7.32 vs. 44.89 ± 4.91, p = 0.004). For 24-segment FS analysis, DC fetuses showed lower FS in left ventricular (LV) segments 18–24, with no difference in LV segments 1–17. Right ventricular (RV) FS in segments 4–23 was also reduced in the DC group. The 24-segment SI analysis indicated significantly lower SI in DC than those in controls for LV segments 1–14 and RV segments 19–24. We found that the pulsatility index (PI) of ductus arteriosus (DA) was an independent variable for RVGLS (β = −0.29, p = 0.04). In 20 DC fetuses with follow-up echocardiograms, no obvious difference in myocardial deformation was found between the initial examination and follow-up data.

Conclusion

Left and right ventricular performances were both impaired in DC fetuses, along with a series of morphological and hemodynamic changes. Although the state of DA constriction improved on second examinations, cardiac function was not completely restored.

Fetal pulmonary hemodynamics: Doppler reference values in low risk pregnancies

OBJECTIVE

To investigate fetal pulmonary hemodynamics in normal pregnancy using pulsed and color Doppler ultrasonography and to define Doppler reference ranges values in the whole fetal pulmonary circulation during different gestational ages.

MATERIALS AND METHODS

A prospective observational study was conducted to evaluate 190 healthy singleton pregnancies between 20 and 38 weeks of gestation, including 10 cases for each gestational age. The main pulmonary artery, right pulmonary artery, left pulmonary artery, ductus arteriosus and pulmonary veins waveforms were evaluated. The waveform profile was studied for each pulmonary vessel investigated. We calculated the normal distribution of data of 12 Doppler parameters, their values were expressed as 5th, 25th, 50th, 75th and 95th centile.

RESULTS

We report several pulmonary hemodynamic changes with the progression of pregnancy. We focused on the hemodynamic values of the parameters most useful in clinical practice and that would better describe the hemodynamic events of this vascular district.

CONCLUSION

This study reports a complete description of the fetal pulmonary hemodynamics at different gestational ages. Many hemodynamic parameters show a typical change during gestation. The reference ranges described in this study may help in situations where is indicated to evaluate the pulmonary hemodynamics and to identify healthy fetuses from those affected by pathological conditions related mainly to fetal cardiovascular anomalies and/or feto-maternal pathologic conditions.

Z-score of some pulsed-wave Doppler indices of right pulmonary artery segments of normal fetuses in the second and third trimestries

OBJECTIVE

To establish the Z-score equation of right pulmonary artery (RPA) segments for some valuable pulse-wave Doppler parameters (PWD) and estimate their reference ranges in normal fetuses.

METHODS

Two hundred and seventy-three normal singleton fetuses at 18-38 weeks were enrolled in this fetal echocardiography of a prospective cross-sectional study. The proximal, middle, and distal segments of RPA of pulsed-wave Doppler parameters, such as peak systolic velocity (PSV) and pulsation index (PI) were obtained by using fetal Doppler echocardiography. The mean and standard deviation (SD) of each parameter and gestational age (GA) were analyzed by regression, and the optimal model of Z-score was established.

RESULTS

There was a significant correlation between fetal pulmonary artery Doppler parameters and gestational age, during the whole pregnancy, PI showed a downward trend with the progress of gestational week, while PSV showed an upward trend. Whether it was the original data or the data converted for the normal distribution of Z-score, the model that best described the mean value of parameters was quadratic regression. The SDs for PSV of the middle segment was a linear equation, others were constants. From proximal to distal of RPA, PSV showed a decreasing trend while PI showed an increasing trend.

CONCLUSION

Z-score models and reference values for some PWD parameters of three segments of RPA were proposed against GA, which may quantitatively assess the flow dynamics of fetal RPA and quantitatively assess fetal lung circulation development and hemodynamic changes.

Management of fetal ductus arteriosus constriction with Digoxin and oxygen therapy

Constriction of the fetal ductus arteriosus is rare and usually attributed to medications or CHD. We describe a 24-year-old multigravida at 33 weeks 5 days gestation with echocardiographic findings of severe ductal constriction, a dilated, hypertrophied and hypocontractile right ventricle, and severe tricuspid regurgitation following BC powder® use. Treatment with Digoxin and oxygen resulted in a progressive 71% reduction in peak systolic ductal gradient, improved right ventricular function, and decreased tricuspid regurgitation.

Maternal low body mass index is a risk factor for fetal ductal constriction following indomethacin use among women undergoing fetal repair of spina bifida

OBJECTIVES

The objectives were to determine the prevalence of and to identify risk factors associated with constriction of the fetal ductus arteriosus (DA) following perioperative indomethacin use for fetal myelomeningocele (MMC) repair. Study design A retrospective chart review study included 100 consecutive fetuses who underwent fetal MMC repair between 2011 and 2018. All patients had fetal echocardiography (FE) on postoperative day (POD)#1 and 2 to detect constriction of the DA. All patients received indomethacin for tocolysis using a standardized protocol. Multivariate regression analysis was carried out to identify the predictors for fetal ductal constriction.

RESULTS

Eighty patients met our study eligibility criteria. Median gestational age at time of surgery was 25 (24-25) weeks. Constriction of the DA was detected in 14 fetuses (17.5%). In five fetuses, this was observed on POD# 1, in seven on POD# 2, and in two on both days. The only independent risk factor for predicting DA constriction was maternal body mass index (BMI) <25 kg/m² (P = .002).

CONCLUSION

Indomethacin therapy following fetal MMC surgery requires careful daily FE surveillance. The association of DA constriction and low BMI suggests that BMI-based dosing of indomethacin may be recommended for perioperative tocolysis in fetal MMC surgery.

Fetal umbilical, cerebral and pulmonary blood flow patterns in relation to lung function and asthma in childhood. The Generation R Study

BACKGROUND

Fetal growth restriction is associated with higher risks of childhood respiratory morbidity. Fetal blood flow adaptations might contribute to these associations. We examined the associations of fetal umbilical, cerebral, and pulmonary blood flow with wheezing patterns, lung function, and asthma in childhood.

METHODS

In a population-based prospective cohort study among 903 children, we measured fetal umbilical, cerebral, and pulmonary blood flow by pulsed-wave Doppler at a median gestational age of 30.3 (95% range 28.8-32.3) weeks. We obtained information about wheezing patterns until the age of 6 years by questionnaires. Lung function was measured by spirometry and information about current asthma was obtained by questionnaire at the age of 10 years.

RESULTS

Results showed a non-significant relationship between a higher umbilical artery pulsatility index (PI) and umbilical artery PI/cerebral artery PI ratio, indicating fetal blood flow redistribution at the expense of the trunk, with higher risks of early wheezing (OR [95% CI]: 2.07 (0.70-6.10) and 2.74 (0.60, 12.62) per unit increase, respectively). A higher pulmonary artery time velocity integral, indicating higher pulmonary vascular resistance, was associated with a higher risk of late/persistent wheezing (Z-score 1.14 [1.01-1.29]). A higher middle cerebral artery PI was associated with a higher FEV1 /FVC (Z-score [95% CI]: 0.21 [0.01-0.42]). Results did not materially change after additional adjustment for birth and growth characteristics.

CONCLUSION

Third-trimester fetal blood flow patterns might be related to childhood respiratory health. These findings should be considered as hypothesis generating and need further replication.

Transitional fetal hemodynamics and gas exchange in premature postpartum adaptation: immediate vs. delayed cord clamping

Background

Recent studies suggest that delayed cord clamping (DCC) is advantageous for achieving hemodynamic stability and improving oxygenation compared to the immediate cord clamping (ICC) during fetal-to-neonatal transition yet there is no quantitative information on hemodynamics and respiration, particularly for pre-term babies and fetal disease states. Therefore, the objective of this study is to investigate the effects of ICC and DCC on hemodynamics and respiration of the newborn preterm infants in the presence of common vascular pathologies.

Methods

A computational lumped parameter model (LPM) of the placental and respiratory system of a fetus is developed to predict blood pressure, flow rates and oxygen saturation. Cardiovascular system at different gestational ages (GA) are modeled using scaling relations governing fetal growth with the LPM. Intrauterine growth restriction (GR), patent ductus arteriosus (PDA) and respiratory distress syndrome (RDS) were modeled for a newborn at 30 weeks GA. We also formulated a "severity index (SI)" which is a weighted measure of ICC vs. DCC based on the functional parameters derived from our model and existing neonatal disease scoring systems.

Results

Our results show that transitional hemodynamics is smoother in DCC compared to ICC for all GAs. Blood volume of the neonate increases by 10% for moderately preterm and term infants (32-40 wks) and by 15% for very and extremely preterm infants (22-30 wks) with DCC compared to ICC. DCC also improves the cardiac output and the arterial blood pressure by 17% in term (36-40 wks), by 18% in moderately preterm (32-36 wks), by 21% in very preterm (28-32 wks) and by 24% in extremely preterm (20-28 wks) births compared to the ICC. A decline in oxygen saturation is observed in ICC received infants by 20% compared to the DCC received ones. At 30 weeks GA, SI were calculated for healthy newborns (1.18), and newborns with GR (1.38), PDA (1.22) and RDS (1.2) templates.

Conclusion

Our results suggest that DCC provides superior hemodynamics and respiration at birth compared to ICC. This information will help preventing the complications associated with poor oxygenation arising in premature births and pre-screening the more critical babies in terms of their cardiovascular severity.

Prolonged early antenatal indomethacin exposure is safe for fetus and neonate. J Matern Fetal Neonatal Med 2019;34:167-176. [PMID: 30905227 DOI: 10.1080/14767058.2019.1599351]

Objective: To evaluate fetal and neonatal safety of early-onset long-term antenatal indomethacin treatment (LIT) for short cervix.Methods: In this cohort study, women started LIT for short cervix (<25 mm) before completing 25 weeks. They followed a standardized regiment of oral indomethacin: 100 mg loading, 50 mg qid for 48 h, 25 mg qid until delivery or at 32 weeks gestational age (GA), whichever comes first. Weekly monitoring for oligohydramnios and ductus arteriosus (DA) constriction included confirmation of compliance with treatment/dose. This approach is established in our clinical practice. To identify LIT complications separate from prematurity, each neonate exposed to LIT were matched to two unexposed neonatal controls within ±3 days of GA of delivery and birth weight of ±10%. Odds ratios for neonatal variables included pulmonary hemorrhage, patent DA (PDA) requiring medical or surgical correction, necrotizing enterocolitis (NEC), spontaneous intestinal perforation (SIP), intraventricular hemorrhage (IVH) grade III-IV, other intracranial hemorrhage (ICH), neonatal mortality, calculated individually, and for total composite morbidity. Statistical determinants of neonatal morbidity were assessed using binary logistic regression. Exposure to LIT, maternal age, parity, BMI, GA at delivery, birth-weight (BW), neonatal gender, cord artery pH, and 5-min Apgar score were independent variables.Results: 166 LIT cases were matched with 332 controls. LIT median duration was 49 (3-108) days. Mean delivery GA was 34 weeks. LIT was stopped for 5 patients (2.9%) with oligohydramnios and 1 (0.6%) with DA constriction, without consequent morbidity. 71 cases (43%) completed LIT, stopping at 32 weeks. 95 stopped early for preterm premature ruptures of membranes (PPROM) (20%), active labor (11%) or patient choice (22%). Odds of any individual complication did not differ between treated cases and controls. LIT was not a statistical determinant of composite morbidity or any individual neonatal problem.Conclusion: Continuous early-onset indomethacin exposure, up to 15 weeks antenatally, did not increase fetal or neonatal complications. This level of safety is permissive to a randomized trial of indomethacin for the treatment of short cervix.

Z-score reference ranges for pulsed-wave Doppler indices of the cardiac outflow tracts in normal fetuses

To determine Z-score equations and reference ranges for Doppler flow velocity indices of cardiac outflow tracts in normal fetuses. A prospective cross-sectional echocardiographic study was performed in 506 normal singleton fetuses from 18 to 40 weeks. Twelve pulsed-wave Doppler (PWD) measurements were derived from fetal echocardiography. The regression analysis of the mean and the standard deviation (SD) for each parameter were performed against estimated fetal weight (EFW) and gestational age (GA), in order to construct Z-score models. The correlation between these variables and fetal heart rate were also investigated. Strong positive correlations were found between the twelve PWD indices and the independent variables. A linear-quadratic regression model was the best description of the mean and SD of most parameters, with the exception of the velocity time interval (VTI) of ascending aorta against EFW, which was best fitted by a fractional polynomial. Z-score equations and reference values for PWD indices of fetal cardiac outflow tracts were proposed against GA and EFW, which may be useful for quantitative assessment of potential hemodynamic alternations, particularly in cases of intrauterine growth retardation and structural cardiac defects.

Improving Prenatal Diagnosis of Coarctation of the Aorta

BACKGROUND

The purpose of the study was to evaluate the association between fetal echocardiographic measurements and the need for intervention (primary coarctation repair, staged coarctation repair, or catheter intervention) in prenatally diagnosed coarctation of the aorta.

METHODS

A single-centre retrospective cohort study (2005-2015) of 107 fetuses diagnosed with suspected coarctation of the aorta in the setting of an apex-forming left ventricle and antegrade flow across the mitral and aortic valves.

RESULTS

Median gestational age at diagnosis was 32 weeks (interquartile range, 23-35 weeks). Fifty-six (52%) did not require any neonatal intervention, 51 patients (48%) underwent a biventricular repair. In univariable analysis, an increase in ascending aorta (AAo) peak Doppler flow velocity (odds ratio [OR], 1.40 [95% confidence interval [CI], 1.05-1.91] per 20 cm/s; P = 0.03) was associated with intervention. No intervention was associated with larger isthmus size (OR, 0.23; P < 0.001), transverse arch diameter (OR, 0.23; P < 0.001), and aortic (OR, 0.72; P = 0.02), mitral (OR, 0.58; P = 0.001), and AAo (OR, 0.53; P < 0.001) z-scores. In multivariable analysis, higher peak AAo Doppler (OR, 2.51 [95% CI, 1.54-4.58] per 20 cm/s; P = 0.001) and younger gestational age at diagnosis (OR, 0.81 [95% CI, 0.70-0.93] per week; P = 0.005) were associated with intervention, whereas a higher AAo z-score (OR, 0.65 [95% CI, 0.43-0.94] per z; P = 0.029) and transverse arch dimension (OR, 0.44 [95% CI, 0.18-0.97]; P = 0.05) decreased the risk of intervention.

CONCLUSIONS

In prenatally suspected coarctation, the variables associated with intervention comprised smaller AAo and transverse arch size, earlier gestational age at diagnosis, and the additional finding of a higher peak AAo Doppler.

Variations in ductus arteriosus Doppler parameters in different sonographic views during the second half of gestation

The aim of the present study was to compare the Doppler parameters of the fetal ductus arteriosus (DA) measured in the traditional longitudinal ductal arch (LDA) view and the newly introduced three vessels and trachea (3VT) plane of the fetal upper mediastinum. The peak systolic velocity (PSV), end-diastolic velocity (EDV), time-averaged maximum velocity (TAMXV) and velocity-time integral (VTI) measurements were taken for 52 fetuses with normal growth (including 29 females). The pulsatility index (PI) and resistance index (RI) were calculated. All parameters for each fetus were measured three times by the same sonographer in the LDA and the 3VT view, and the averages were taken to obtain the final value. Differences in the above values obtained from the LDA and 3VT views were analyzed and the correlation between the differences of all indices and the gestational age (GA) was evaluated using Pearson's linear coefficient of correlation. All of the values were characterized as normally distributed continuous variables by homogeneity of variance analysis. Slight increases in the PSV, EDV, TAMXV and VTI determined in the LDA view were identified compared with those in the 3VT view (P<0.05). Furthermore, these increases were identified to be independent of the GA (P>0.05). However, no significant differences in the impedance indices PI and RI were observed between the two sonographic planes (P>0.05). In conclusion, the LDA view provides a better chance than the 3VT view to obtain higher values of velocity parameters (PSV, EDV, TMAXV and VTI) within the fetal DA, and the differences are independent of the GA. However, no significant variations in the impedance indices PI and RI were observed between these two sonographic planes.

Ductus arteriosus and fetal echocardiography: Implications for practice

The ductus arteriosus (DA) is a crucial part of the fetal circulation, both in the normal fetus and in critical congenital heart disease (CHD). It allows shunting between the pulmonary and systemic circulations. In physiological prenatal conditions, the DA lets the majority of right ventricular output bypass the fluid-filled, high-resistance lungs. The DA can cause hemodynamic compromise in the fetus and neonate when constricted or absent (in isolation or in patients with CHD) and may lead to pre- or postnatal sequelae within other systems when forming part of a vascular ring. In CHD, the DA can be interrogated by fetal echocardiography to infer information regarding severity of pulmonary outflow tract obstruction, adequacy of the sub-pulmonary ventricle to supply pulmonary blood flow, and to predict the likelihood of atrial septum restriction in transposition of the great arteries. A good understanding of the DA is crucial for fetal cardiologists.

Influence of perinatal low-dose acetylsalicylic acid therapy on fetal hemodynamics evaluated by determining the acceleration-time/ejection-time ratio in the ductus arteriosus

AIM

Acceleration-time/ejection-time ratio (At/Et ratio) of Doppler waveform is an established hemodynamic parameters that reflect proximal stenosis. Using this parameter, we evaluated whether perinatal low-dose acetylsalicylic acid (ASA) therapy could alter hemodynamics in the ductus arteriosus.

METHODS

Pulse Doppler measurements of the fetal ductus arteriosus were performed longitudinally from 20 to 37 gestational weeks in 106 healthy pregnant women (controls) and 65 pregnant women taking daily low-dose ASA (80 or 100 mg/day) because of a history of recurrent pregnancy loss. The At/Et ratio, pulsatility index (PI), and peak systolic velocity were evaluated and statistically analyzed.

RESULTS

The At/Et ratio significantly increased with gestational age in both the ASA group (r = 0.54) and the control group (r = 0.35), while the PI did not. Median peak systolic velocities also increased with gestational age in both the ASA group (r = 0.39) and the control group (r = 0.31). No significant differences in At/Et ratio, PI, or peak systolic velocity were observed between the ASA group and the control group.

CONCLUSION

Administration of low-dose ASA during pregnancy did not appear to alter hemodynamics in the fetal ductus arteriosus.

Retrograde lower body arterial reservoir discharge underlies rapid reversal of ductus arteriosus shunting after early cord clamping at birth in preterm lambs

Arterial reservoir (“windkessel”) function, whereby a part of left ventricular (LV) output is stored in elastic arteries during systole and discharged in diastole, is a well-established physiological phenomenon. However, its role in rapid reversal (to left-to-right) and a systolic-to-diastolic shift of shunting across the ductus arteriosus after birth is unknown. To address this question, ductal and aortic isthmus flows were measured with high-fidelity transit-time probes in six anesthetized preterm fetal lambs before and after cord clamping and subsequent early mechanical ventilation and for 30 min postbirth. Descending aortic flow was calculated as the sum of isthmus and ductal flows. Left-to-right ductal flow profiles were related to those of the isthmus and descending aorta, with upper body arterial reservoir discharge indicated by forward diastolic isthmus flow, and retrograde lower body arterial reservoir discharge by negative diastolic descending aortic flow. Left-to-right ductal shunting appeared immediately after cord clamping ( P < 0.001), due entirely to newly emergent retrograde lower body reservoir discharge, and rose with ventilation via increased lower body reservoir discharge ( P < 0.005), supplemented by upper body reservoir discharge after 45 s ( P < 0.025) and LV systolic flow after 3 min ( P = 0.025). The contribution of lower body reservoir discharge to left-to-right ductal shunting fell to 55 ± 8% at ≥15 min ( P < 0.001) but remained higher ( P < 0.002) than LV systolic flow (33 ± 8%) or upper body reservoir discharge (12 ± 5%). These results suggest that retrograde lower body arterial reservoir discharge plays a key role in rapid reversal and a systolic-to-diastolic shift of ductal shunting after cord clamping and early ventilation at birth.

Diagnosis and management of fetal ductus arteriosus constriction-closure

Pathognomonic features of in utero premature restriction/closure of the ductus arteriosus (DA) are increased right ventricular afterload, impaired right ventricular function, and consequently tricuspid regurgitation and right heart dilation. The most common reason for constriction-closure of DA is maternal administration of non-steroidal anti-inflammatory drugs (NSAIDs) during the 3rd trimester of gestation. The idiopathic form is a rare event and, maybe, an underestimated abnormality that, if it is not promptly recognized, may result in severe fetal-neonatal compromise. We describe a case of a 38-year-old woman presenting at 34+0 weeks of gestation with a normally grown male fetus whose fetal echocardiography had shown right ventricular hypertrophy, a tortuous S-shaped DA and a significant pulmonary hyperflow. All signs were consistent of an idiopathic severe constriction of DA with a significant fetal cardiac involvement. The patient was admitted to a tertiary care center equipped with Neonatal Intensive Care Unit (NICU), and delivered by cesarean section at 34+4 weeks with a good maternal and neonatal outcome. Based on our experience and a review of the Literature we propose a management algorithm to use when dealing with preterm or early term pregnancy complicated by this fetal hemodynamic malfunction.

Diagnosis and treatment of fetal cardiac disease: a scientific statement from the American Heart Association

BACKGROUND

The goal of this statement is to review available literature and to put forth a scientific statement on the current practice of fetal cardiac medicine, including the diagnosis and management of fetal cardiovascular disease.

METHODS AND RESULTS

A writing group appointed by the American Heart Association reviewed the available literature pertaining to topics relevant to fetal cardiac medicine, including the diagnosis of congenital heart disease and arrhythmias, assessment of cardiac function and the cardiovascular system, and available treatment options. The American College of Cardiology/American Heart Association classification of recommendations and level of evidence for practice guidelines were applied to the current practice of fetal cardiac medicine. Recommendations relating to the specifics of fetal diagnosis, including the timing of referral for study, indications for referral, and experience suggested for performance and interpretation of studies, are presented. The components of a fetal echocardiogram are described in detail, including descriptions of the assessment of cardiac anatomy, cardiac function, and rhythm. Complementary modalities for fetal cardiac assessment are reviewed, including the use of advanced ultrasound techniques, fetal magnetic resonance imaging, and fetal magnetocardiography and electrocardiography for rhythm assessment. Models for parental counseling and a discussion of parental stress and depression assessments are reviewed. Available fetal therapies, including medical management for arrhythmias or heart failure and closed or open intervention for diseases affecting the cardiovascular system such as twin-twin transfusion syndrome, lung masses, and vascular tumors, are highlighted. Catheter-based intervention strategies to prevent the progression of disease in utero are also discussed. Recommendations for delivery planning strategies for fetuses with congenital heart disease including models based on classification of disease severity and delivery room treatment will be highlighted. Outcome assessment is reviewed to show the benefit of prenatal diagnosis and management as they affect outcome for babies with congenital heart disease.

CONCLUSIONS

Fetal cardiac medicine has evolved considerably over the past 2 decades, predominantly in response to advances in imaging technology and innovations in therapies. The diagnosis of cardiac disease in the fetus is mostly made with ultrasound; however, new technologies, including 3- and 4-dimensional echocardiography, magnetic resonance imaging, and fetal electrocardiography and magnetocardiography, are available. Medical and interventional treatments for select diseases and strategies for delivery room care enable stabilization of high-risk fetuses and contribute to improved outcomes. This statement highlights what is currently known and recommended on the basis of evidence and experience in the rapidly advancing and highly specialized field of fetal cardiac care.

Enhanced ventricular pump function and decreased reservoir backflow sustain rise in pulmonary blood flow after reduction of lung liquid volume in fetal lambs

Although a reduction in lung liquid volume increases fetal pulmonary blood flow, the changes in central flow patterns that sustain this increased pulmonary perfusion are unknown. To address this issue, eight anesthetized late-gestation fetal sheep were instrumented with pulmonary trunk (PT), ductus arteriosus (DA), and left pulmonary artery (PA) micromanometer catheters and transit-time flow probes, with blood flow profile and wave intensity analyses performed at baseline and after withdrawal of lung liquid via an endotracheal tube. Reducing lung liquid volume by 19 ± 6 ml/kg (mean ± SD) augmented right ventricular power by 34% (P < 0.001), with distribution of an accompanying increase in mean PT blood flow (245 ± 63 ml/min, P < 0.001) to the lungs (169 ± 91 ml/min, P = 0.001) and across the DA (77 ± 92 ml/min, P = 0.04). However, although PT and DA flow increments were confined to systole and were related to an increased magnitude of flow-increasing, forward-running compression waves, the rise in PA flow spanned both systole (108 ± 66 ml/min) and diastole (61 ± 32 ml/min). Flow profile analysis showed that the step-up in PA diastolic flow was associated with diminished PA diastolic backflow and accompanied by a lesser degree of diastolic right-to-left DA shunting. These data suggest that an increased pulmonary blood flow after reduction of lung liquid volume is associated with substantial changes in PT-DA-PA interactions and underpinned by two main factors: 1) enhanced right ventricular pump function that increases PA systolic inflow and 2) decreased PA diastolic backflow that arises from a fundamental change in PA reservoir function, thereby resulting in greater passage of systolic inflow through the lungs.

Assessment of the ductus arteriosus in fetuses with tetralogy of Fallot and the implication for postnatal management

OBJECTIVE

To describe the antenatal and neonatal echocardiographic morphology and flow pattern of the ductus arteriosus in patients with tetralogy of Fallot.

PATIENTS AND METHODS

We included patients with a prenatal diagnosis of tetralogy of Fallot between January 2006 and December 2012.

RESULTS

Among the 52 fetuses with tetralogy of Fallot the severity of right ventricular outflow obstruction was considered mild in 32, moderate in 14, and severe in 6. In the mild right ventricular outflow obstruction group (n = 32) all had normal ductal morphology and flow pattern, eight (25%) elected for termination of pregnancy and two died in the neonatal period from extracardiac causes. In the moderate right ventricular outflow obstruction group (n = 14) the fetuses had a small ductus arteriosus with antegrade but abnormal flow velocity, one (7%) elected for termination of pregnancy. Immediately after birth the ductus arteriosus was very small or already closed at echocardiographic examination. Two out of 13 patients (15%) developed severe hypoxic spells and underwent modified Blalock-Taussig shunt during the neonatal period. Six fetuses were considered to have severe right ventricular outflow obstruction with flow reversal in the ductus arteriosus, three (50%) of whom elected for termination of pregnancy. The other three newborns underwent modified Blalock-Taussig shunt.

CONCLUSION

In fetuses with tetralogy of Fallot, ductal diameter can be reduced even up to prenatal closure. Prenatal ductal morphology assessment may be useful for improving management of patients with moderate right ventricular outflow obstruction and small ductus arteriosus who may become cyanotic at birth.

A case of progressive ductal constriction in a fetus

The ductus arteriosus is a normal and essential structure in fetal circulation. Since the introduction of fetal echocardiography, there have been reports of ductal constriction, many of which were related to maternal use of some medications. However, there have been some reports of idiopathic ductal constriction, which usually present in later gestation. Recently we experienced a case, which initially showed an S-shaped ductus with mild narrowing at 23 weeks and 27 weeks gestation and developed severe ductal constriction at 33 weeks. Soon after birth, ductus was searched for but no ductus was found in 2-D and color images. The neonate required mechanical ventilation with supplemental oxygen for 3 days. All echocardiographic abnormalities were normalized in 7 months. We report progressive ductal constriction in an S-shaped ductus and emphasize the importance of continuous follow up extending to the third trimester and even immediately after birth.

Maternal restriction of polyphenols and fetal ductal dynamics in normal pregnancy: an open clinical trial

BACKGROUND

We have recently demonstrated reversal of fetal ductal constriction after dietary maternal restriction of polyphenol-rich foods (PRF), due to its inhibitory action on prostaglandin synthesis.

OBJECTIVE

To test the hyphotesis that normal third trimester fetuses also improve ductus arteriosus dynamics after maternal restriction of polyphenols.

METHODS

Open clinical trial with 46 fetuses with gestational age (GA) > 28 weeks submitted to 2 Doppler echocardiographic studies with an interval of at least 2 weeks, being the examiners blinded to maternal dietary habits. A validated food frequency questionnaire was applied and a diet based on polyphenol-poor foods (<30 mg/100 mg) was recommended. A control group of 26 third trimester fetuses was submitted to the same protocol. Statistics used t test for independent samples.

RESULTS

Mean GA was 33 ± 2 weeks. Mean daily maternal estimated polyphenol intake (DMPI) was 1277 mg, decreasing to 126 mg after dietary orientation (p=0.0001). Significant decreases in systolic (SDV) and diastolic (DDV) ductal velocities, and RV/LV diameters ratio, as well as increase in ductal PI were observed [DSV = 1.2 ± 0.4 m/s (0.7-1.6) to 0.9 ± 0.3 m/s (0.6-1.3) (p = 0.018); DDV = 0.21 ± 0.09 m/s (0.15-0.32) to 0.18 ± 0.06 m/s (0.11-0.25) (p = 0.016); RV/LV ratio = 1.3 ± 0.2 (0.9-1.4) to 1.1 ± 0.2 (0.8-1.3) (p=0.004); ductal PI = 2.2 ± 0.03 (2.0-2.7) to 2.4 ± 0.4(2.2-2.9) (p = 0.04)]. In the control group, with GA of 32 ± 4 weeks, there were no significant differences in DMPI, mean SDV, DDV, PI and RV/LV ratio.

CONCLUSION

The oriented restriction of third trimester maternal ingestion of polyphenol-rich foods for a period of 2 weeks or more improve fetal ductus arteriosus flow dynamics and right ventricular dimensions.

Prenatal diagnosis and outcome of absent pulmonary valve syndrome: contemporary single-center experience and review of the literature

OBJECTIVE

To review the anomaly spectrum of prenatally detected absent pulmonary valve syndrome (APVS) and the outcome after diagnosis. Previous fetal studies reported survival rates of ≤ 25% for patients with intended postnatal care.

METHODS

Clinical data and echocardiograms of 12 cases with a fetal diagnosis of APVS between 2000 and 2010 were analyzed in this retrospective single-center study. Collected parameters included: gestational age at referral, associated fetal abnormalities, cardiothoracic ratio, maximum diameters of pulmonary annulus and main and branch pulmonary arteries, ventricular dimensions and function as well as ventricular Doppler flows. Karyotyping included fluorescence in-situ hybridization (FISH) analysis for microdeletion 22q11.2.

RESULTS

Median gestational age at diagnosis was 24 weeks. Three subtypes of APVS were observed: (1) with tetralogy of Fallot (TOF) and no arterial duct (n = 10; 83%); (2) isolated, with a large arterial duct (n = 1; 8%); and (3) with tricuspid atresia, right ventricular dysplasia and a restricted duct (n = 1; 8%). The cardiothoracic ratio and pulmonary artery dimensions were increased in all cases. The karyotype was abnormal in 70% of fetuses with TOF and their mortality rate was significantly higher due to pregnancy termination (n = 3) or perinatal demise (n = 2) (hazard ratio, 5; 95% CI, 0.87-28.9; P = 0.015). Of seven live births with active postnatal care, six children (86%) were alive without residual respiratory symptoms at a median follow-up of 4.7 (range, 2.1-10.6) years.

CONCLUSION

Outcome after fetal diagnosis of APVS was significantly better in this study compared with those of previous fetal series, with a low mortality rate for actively managed patients.

Reversal of fetal ductal constriction after maternal restriction of polyphenol-rich foods: an open clinical trial

OBJECTIVE

To test the hypothesis that maternal restriction of polyphenol-rich foods (PRF), which, like non-steroidal anti-inflammatory drugs (NSAID), inhibit prostaglandin synthesis in the third trimester, reverse fetal ductal constriction (DC).

STUDY DESIGN

An open clinical trial of 51 third trimester fetuses with DC with no history of NSAID intake was designed. All mothers were submitted to a food frequency questionnaire and were oriented to withdrawl PRF, being reassessed after 3 weeks. Doppler parameters were assessed before and after discontinuation of these substances. A control group of 26 third trimester normal fetuses, with no ductus arteriosus (DA) constriction, in which no dietary intervention was offered, was reviewed after 3 weeks. Student's t-test and Wilcoxon's test were used.

RESULT

Mean gestational age was 32±3 weeks (28 to 37 weeks). After discontinuation of PRF (≥3 weeks), 48/51 fetuses (96%) showed complete reversal of DC, with decrease in mean ductal systolic velocity (1.74±0.20 m s(-1) to 1.31±0.34 m s(-1), P<0.001), mean diastolic velocity (0.33±0.09 m s(-1) to 0.21±0.07 m s(-1), P<0.001) and mean right to left ventricular dimension ratio (1.37±0.26 to 1.12±0.17, P<0.001) and increase in mean ductal pulsatility index (PI) (1.98±0.36 to 2.46±0.23, P<0.001). Median daily maternal consumption of PRF was 286 mg per day and decreased after orientation to 0 mg per day, P<0.001. In the control group, with GA of 32±4 w (29-37 w), there was no significant differences in median daily maternal consumption of PRF, mean ductal systolic velocitiy, diastolic velocity, PI and right ventricular to left ventricular diameter ratio (RV/LV) ratio.

CONCLUSION

Reduction of maternal PRF intake during pregnancy, especially in the third trimester, is followed by complete reversal of DC (wide open DA), which may influence maternal dietary habits in late pregnancy.

Increased right ventricular output and central pulmonary reservoir function support rise in pulmonary blood flow during adenosine infusion in the ovine fetus

Although adenosine markedly increases fetal pulmonary blood flow, the specific changes in pulmonary trunk (PT), ductus arteriosus (DA), and conduit pulmonary artery (PA) flow interactions that support this increased flow are unknown. To address this issue, seven anesthetized late-gestation fetal sheep were instrumented with PT, DA, and left PA micromanometer catheters and transit-time flow probes. Blood flow profile and wave intensity analyses were performed at baseline and after adenosine infusion to increase PA flow approximately fivefold. With adenosine infusion, DA mean and phasic flows were unchanged, but increases in mean PT (500 ± 256 ml/min, P = 0.002) and the combined left and right PA flow (479 ± 181 ml/min, P < 0.001) were similar (P > 0.7) and related to a larger flow-increasing forward-running compression wave arising from right ventricular (RV) impulsive contraction. Moreover, while the increased PT flow was confined to systole, the rise in PA flow spanned systole (316 ml/min) and diastole (163 ml/min). This elevated PA diastolic flow was accompanied by a 170% greater discharge from a PT and main PA reservoir filled in systole (P < 0.001), but loss of retrograde blood discharge from a conduit PA reservoir that was evident at baseline. These data suggest that 1) an increase in fetal pulmonary blood flow produced by adenosine infusion is primarily supported by a higher PT blood flow (i.e., RV output); 2) about two-thirds of this increased RV output passes into the pulmonary circulation during systole; and 3) the remainder is transiently stored in a central PT and main PA systolic reservoir, from where it discharges into the lungs in diastole.

Enhanced central and conduit pulmonary arterial reservoir function offsets reduced ductal systolic outflow during constriction of the fetal ductus arteriosus

Constriction of the fetal ductus arteriosus (DA) has disparate effects on mean and phasic hemodynamics, as mean DA blood flow is preserved until constriction is severe, but DA systolic and diastolic blood velocities change with only mild constriction. To determine the basis of this disparity and its physiological significance, seven anesthetized late-gestation fetal sheep were instrumented with pulmonary trunk (PT), DA, and left pulmonary artery (PA) micromanometer catheters and transit-time flow probes. Blood flow profile and wave intensity analyses were performed at baseline and during mild, moderate, and severe DA constriction (defined as pulmonary-aortic mean pressure differences of 4, 8, and 14 mmHg, respectively), produced with an adjustable snare. With DA constriction, mean DA flow was initially maintained but decreased with severe constriction (P < 0.05) in conjunction with a reduction (P < 0.05) in PT flow (i.e., right ventricular output). By contrast, DA systolic flow fell progressively during DA constriction (P < 0.001), due to decreased transmission of both early and midsystolic proximal flow-enhancing forward-running compression waves into the DA. However, DA constriction was also accompanied by greater systolic storage of blood in the PT and main PA (P < 0.025), and increased retrograde diastolic flow from compliant major branch PA (P < 0.001). Transductal discharge of these central and conduit PA blood reservoirs in diastole offset systolic DA flow reductions. These data suggest that, during DA constriction in the fetus, enhanced central and conduit PA reservoir function constitutes an important compensatory mechanism that contributes to preservation of mean DA flow via a systolic-to-diastolic redistribution of phasic DA flow.

Ductus arteriosus wave intensity analysis in fetal lambs: midsystolic ductal flow augmentation is due to antegrade pulmonary arterial wave transmission

In midsystole, fetal pulmonary trunk (PT) and arterial (PA) blood flows characteristically fall, despite pulmonary blood pressure increasing, while ductus arteriosus (DA) flow continues to rise to a delayed peak. Wave intensity (WI) analysis indicates that midsystolic fetal PT and PA flow reductions are related to a very large midsystolic PA backward-running compression wave (BCW(ms)), which originates in the pulmonary microvasculature and is partially transmitted into the PT. This study tested the hypothesis that midsystolic augmentation of DA blood flow was related to transmission of the PA BCW(ms) into the DA. DA, PT, and PA WI analysis was performed in eight anesthetized late-gestation fetal sheep instrumented with DA, PT, and left PA micromanometer catheters to measure pressure (P) and transit-time flow probes to obtain blood velocity (U). In a subgroup (n = 5), the main PA was briefly occluded to abolish wave transmission from the lungs. WI was calculated as the product of P and U rates of change. PA and PT WI profiles both contained a prominent BCW(ms), approximately 5-fold larger in the PA (P < 0.005), which increased P but decreased U. By contrast, the DA WI profile demonstrated a large midsystolic forward-running compression wave (FCW(ms)), which increased DA P and U, and occurred 5 ms after PA BCW(ms). Furthermore, both DA FCW(ms) and PT BCW(ms) were abolished by main PA occlusion. These results suggest that the fetal PA BCW(ms) undergoes retrograde transmission into the PT as a BCW(ms), but antegrade transmission into the DA as a FCW(ms) that augments midsystolic DA flow.

In vitro hemodynamic investigation of the embryonic aortic arch at late gestation

This study focuses on the dynamic flow through the fetal aortic arch driven by the concurrent action of right and left ventricles. We created a parametric pulsatile computational fluid dynamics (CFD) model of the fetal aortic junction with physiologic vessel geometries. To gain a better biophysical understanding, an in vitro experimental fetal flow loop for flow visualization was constructed for identical CFD conditions. CFD and in vitro experimental results were comparable. Swirling flow during the acceleration phase of the cardiac cycle and unidirectional flow following mid-deceleration phase were observed in pulmonary arteries (PA), head-neck vessels, and descending aorta. Right-to-left (oxygenated) blood flowed through the ductus arteriosus (DA) posterior relative to the antegrade left ventricular outflow tract (LVOT) stream and resembled jet flow. LVOT and right ventricular outflow tract flow mixing had not completed until approximately 3.5 descending aorta diameters downstream of the DA insertion into the aortic arch. Normal arch model flow patterns were then compared to flow patterns of four common congenital heart malformations that include aortic arch anomalies. Weak oscillatory reversing flow through the DA junction was observed only for the Tetralogy of Fallot configuration. PA and hypoplastic left heart syndrome configurations demonstrated complex, abnormal flow patterns in the PAs and head-neck vessels. Aortic coarctation resulted in large-scale recirculating flow in the aortic arch proximal to the DA. Intravascular flow patterns spatially correlated with abnormal vascular structures consistent with the paradigm that abnormal intravascular flow patterns associated with congenital heart disease influence vascular growth and function.

CURRENT ASPECTS OF FETAL CARDIOVASCULAR FUNCTION

Investigation of fetal cardiac function remains a challenging task. Although the response of the heart to changes in load is well-known in animal models and the adult human, the developmental changes in fetal cardiac response remain poorly characterised. However, quantitative evaluation of cardiovascular function is important to predict the clinical course and to manage the fetus optimally. To date, the routine evaluation of fetal cardio vascular function has relied largely on Doppler echocardiography which enables an estimate of haemodynamics; newer modalities such as measurement of myocardial velocities are employed less routinely. Fetal magnetic resonance imaging still lacks the resolution necessary to contribute significantly to morphological or functional assessment of the fetal cardiovascular system.

An echocardiographic study of diagnostic accuracy, prediction of surgical approach, and outcome for fetuses diagnosed with discordant ventriculo-arterial connections

Our aims were to examine the diagnostic accuracy of prenatal diagnosis of concordant atrioventricular and discordant ventriculo-arterial connections, the accuracy of predictions made concerning the postnatal surgical approach, and a description of the different subtypes related to outcome. All fetuses were evaluated at a tertiary centre for fetal cardiology between January, 1994, and December, 2003. In this period, we identified congenitally malformed hearts in 1,835 fetuses, of whom 56 (3%) met the criterions of inclusion. Of the total, 30 (54%) had an intact ventricular septum, 9 (16%) had an associated ventricular septal defect, 7 (13%) had a ventricular septal defect and pulmonary stenosis, 1 (2%) had pulmonary stenosis and an intact ventricular septum, 8 (14%) had a ventricular septal defect and aortic coarctation, and 1 (2%) had coarctation of the aorta with an intact ventricular septum. All the discordant ventriculo-arterial connections were correctly identified. For associated ventricular septal defects, the diagnostic sensitivity was 96%, with specificity of 88%, positive predictive value of 85%, and negative predictive value of 97%. For aortic coarctation, the sensitivity was 100%, specificity 96%, positive predictive value 82%, and negative predictive value 100%. The prediction of the surgical approach was accurate in 41 of 48 cases (85%). For those fetuses with pulmonary stenosis and ventricular septal defect, the ratio of the diameters of the pulmonary trunk was shown to be helpful in predicting the possibility of an arterial switch as opposed to the Rastelli type of repair. Of the 49 liveborn infants, 46 were alive at 30 days (94%, with 95% confidence intervals from 83 to 99%), and 43 at one year (88%, 95% confidence intervals from 75 to 95%). Deaths were mainly related to the anatomy of the coronary arteries, and associated cardiac lesions.

Prenatal diagnosis and outcome for fetuses with congenital absence of the pulmonary valve

OBJECTIVES

To analyze fetal echocardiographic findings of absent pulmonary valve syndrome (APVS), its association with chromosomal and extracardiac anomalies including nuchal translucency (NT) and the outcome after diagnosis.

METHODS

Data of 14 fetuses with confirmed APVS retrospectively collected in two tertiary referral centers between 1998 and 2004 were analyzed. The variables examined were: reason for referral, gestational age at diagnosis and associated abnormalities, including first trimester NT thickness. Cardiac evaluation included measurement of cardiothoracic ratio, diameter of pulmonary arteries and Doppler flow in the pulmonary trunk. Information was retrieved from clinical files, recorded videotapes and stored images. Karyotyping including examination for the 22q11 deletion was performed in all cases.

RESULTS

Mean gestational age at diagnosis was 28 weeks, with 5/14 (36%) diagnosed before 22 weeks. In 13/14 (93%) there was an associated ventricular septal defect (subaortic in 12 fetuses and inlet-type in one) and all 13 had tetralogy of Fallot. Enlargement of the central pulmonary arteries and cardiomegaly were present in all cases diagnosed after 22 weeks. Of the five fetuses in which APVS was detected before 22 weeks, four (80%) had a normal pulmonary trunk diameter, two (40%) had normal pulmonary branches and three (60%) had normal cardiac size. The arterial duct was absent in 11/14 (79%). A correlation between presence of the arterial duct and the size of the central pulmonary arteries or cardiomegaly could not be established. Increased NT was observed in 4/10 cases (40%) for which this information was available. 22q11 microdeletion was diagnosed in three fetuses (21%). There were five terminations of pregnancy, one intrauterine death, five neonatal deaths and one infant death. Of the six neonates with respiratory distress, only one (17%) survived and of the eight babies in whom there was an intention to treat, two survived (25%).

CONCLUSIONS

APVS can be accurately diagnosed by fetal echocardiography but screening ultrasound in the mid-second trimester is likely to have a low detection rate, probably due to the incomplete expression of the disease at this point. Many fetuses with APVS have an increased NT in the first trimester and this may help an earlier recognition of the defect. The most common associated karyotype anomaly is 22q11 microdeletion. Enlargement of the central pulmonary arteries is mainly related to the gestational age at diagnosis. Our results confirm that the outlook for these patients is extremely poor.

Three-dimensional and four-dimensional fetal echocardiography: a new frontier

PURPOSE OF REVIEW

One of the difficulties of conventional two-dimensional cardiac imaging is the inability to examine fetal cardiac anatomy from multiple angle planes. Three-dimensional and four-dimensional ultrasound allows the fetal examiner to more accurately accomplish this task. Currently, multiple disciplines may be involved in the examination of the fetal heart (pediatric cardiologists, obstetricians, maternal-fetal medicine specialists, and radiologists). The three-dimensional and four-dimensional imaging equipment used by these specialty physicians varies greatly. The purpose of this communication is to review techniques using three-dimensional and four-dimensional imaging that the pediatric cardiologist may not be exposed to in the clinical environment, however, in consulting with colleagues needs to have an understanding of these imaging modalities.

RECENT FINDINGS

The reconstruction of cardiac structures using this technology allows the examiner to view cardiac anatomy in a manner that was limited by previous two-dimensional imaging. Volume datasets are obtained in the three-dimensional static mode (no cardiac motion) or using four-dimensional - the three-dimensional heart is observed contracting during one or multiple cardiac cycles. Therefore, the fourth dimension is time. Using either three-dimensional or four-dimensional technology datasets are acquired, followed by image reconstruction. The image reconstruction enables the examiner to evaluate a two-dimensional image using multiple views, evaluate intracardiac anatomy at different depth planes, and recreate casts of blood flow of the chambers and great vessels.

SUMMARY

This new technology has enhanced the ability of the examiner to identify normal and complex fetal heart anatomy during the early second to the late third trimesters of pregnancy.

Noninvasive assessment of fetal pulmonary blood flow in experimental pulmonary hypertension in the fetal lamb

The aim of this study was to assess pulmonary arterial blood flow changes induced by the creation of a systemic arteriovenous fistula (120 d gestation) in the fetal lamb using Doppler technique. Doppler echocardiographic assessment of the pulmonary artery blood flow performed 1, 6, and 14 d after surgery showed that mean pulmonary arterial blood flow in the left or right pulmonary artery was 224 +/- 58 mL/min at day 1 in the fistula group, significantly higher than in the control group (113 +/- 22 mL/min; p < 0.01, ANOVA test) whether no difference was found at days 6 and 14. The mean inner diameter of the left pulmonary artery measured on postmortem lung arteriograms compared favorably to the one measured on day 14 at the same level on ultrasound. The mean left pulmonary arterial blood flow, measured at birth on day 14 after surgery, using ultrasonic flow transducer, was not statistically different from the one measured by Doppler on day 14. Our data demonstrate that echocardiography allows accurate assessment of pulmonary arterial blood flow in utero, providing evidence suggesting transient high pulmonary blood flow that did not last >6 d after the creation of a systemic fistula.

Echocardiographic evaluation of cardiac function in the fetus

The development of high-resolution ultrasound has allowed detailed examination of the fetal heart. The accuracy of fetal echocardiography in the diagnosis of malformations of the fetal heart has been established in the second trimester and, more recently, at a much earlier stage in gestation (Allan et al., 1980; Allan et al., 1981; Simpson, 2000; Huggon et al., 2002). Confirmation of structural abnormalities has usually been by autopsy or by postnatal investigation. This is certainly sufficient for confirmation of structural malformations, but functional evaluation of the fetal heart is far more difficult to validate. Post-mortem studies, by their very nature give little insight into cardiac function and postnatal studies, whilst permitting functional evaluation of the heart, do so under entirely different conditions compared to the circulation in utero. Prior to the advent of ultrasound, fetal data was drawn from invasive animal studies (Pohlman, 1909; Dawes et al., 1954; Barcroft, 1936; Rudolph, 1985). There have been very few invasive studies in the human fetus including some conducted on exteriorised fetuses undergoing termination by hysterotomy (Nyberg and Westin, 1962; Rudolph et al., 1971). Pressure data has been obtained from the human fetus for normal human hearts and in cardiac disease (Johnson et al., 2000; Johnson et al., 1992; Johnson, 1992). However, the vast majority of cardiac functional data in the human fetus has been obtained by non-invasive means, which has almost exclusively been by echocardiography. This article will review some of the techniques that may be used to evaluate fetal cardiac function and will also emphasise some of the limitations of such techniques.

Repeatability of echocardiographic measurements in the human fetus

OBJECTIVES

To determine the repeatability of cross-sectional, M-mode and Doppler echocardiographic measurements in the human fetus.

METHODS

This was a prospective echocardiographic study of 10 normal fetuses, involving measurement of 32 different echocardiographic variables in each. The intra- and interobserver error of measurements were quantified. The median (range) gestational age was 23 (17-34) weeks.

RESULTS

Cross-sectional echocardiography: for left ventricular end-diastolic volume the intraobserver coefficient of variation was 13% and the interobserver limits of agreement were a ratio of 0.46-2.19. For left ventricular ejection fraction the repeatability was +/- 8.8% and the interobserver limits of agreement were +/- 20%. M-mode echocardiography: the coefficient of variation for left ventricular end-diastolic dimension was 10%, and the interobserver limits of agreement were a ratio of 0.74-1.70. The intraobserver repeatability of left ventricular fractional shortening was +/- 8.8%, and interobserver limits of agreement +/-15%. Limits of agreement for M-mode-derived left ventricular end-diastolic volume were wide, intraobserver coefficient of variation 32% and interobserver limits were a ratio of 0.44-4.36. Doppler echocardiography: the intra- and interobserver errors were high for Doppler variables such as acceleration time, acceleration slope, stroke volume, cardiac output and vessel dimension. There was less error associated with measurements such as maximum Doppler velocity, velocity time integral, ejection time and heart rate.

CONCLUSIONS

The repeatability of most echocardiographic measurements in the fetus is poor. This applies particularly to volumetric data such as ventricular volumes and volume flow estimations. Interobserver errors are consistently higher than intraobserver errors, confirming that when sequential measurements are clinically important, the same observer should be used.

Fetal hemodynamics

Starting in the left cardiac ventricle the reader is taken on a guided tour on a fetal erythrocyte as measured by Doppler ultrasound. Up in the ascending aorta we move through the aortic isthmus to the descending aorta and the internal umbilical arteries, which fuse around the umbilical cord. With fresh oxygen from the placenta our erythrocyte moves in an accelerating continuous flow along the umbilical vein to the ductus venosus. After having reached the left ventricle again it now passes through a coronary artery to the right atrium and eventually the ductus arteriosus or the pulmonary circulation. Concepts of pulsatility, impedance and resistance are presente in the context of their clinical applicability in Doppler waveforms of various fetal vessels.