Cardiac function and dysfunction in the fetus

Left atrial strain in fetal echocardiography - could it be introduced to everyday clinical practice?

OBJECTIVES

Prenatal cardiology is a part of preventive cardiology based on fetal echocardiography and fetal interventional cardiology, which facilitates treatment of congenital heart defects (CHD) in pediatric patients and consequently in adults. Timely prenatal detection of CHD plays a pivotal role in facilitating the appropriate referral of pregnant women to facilities equipped to provide thorough perinatal care within the framework of a well-structured healthcare system. The aim of this paper is to highlight the role of left atrial strain (LAS) in prenatal evaluation of fetal heart and prediction of structural and functional disorders.

METHODS

We conducted a comprehensive literature review searching PubMed for articles published from inception up until August 2023, including the search terms "left atrial strain", "fetal echocardiography", and "prenatal cardiology" combined through Boolean operators. In addition, references lists of identified articles were further reviewed for inclusion.

RESULTS

Our review underscores the significance of LAS parameters in fetal echocardiography as a screening tool during specific gestational windows (starting from 11 to 14 weeks of gestation, followed by better visualization between 18 and 22 weeks of gestation). The left atrial strain technique and its parameters serve as valuable indicators, not only for identifying cardiac complications but also for predicting and guiding therapeutic interventions in cases of both cardiac and noncardiac pregnancy complications in fetuses. Evidence suggests establishment of second-trimester reference strain and strain rate values by speckle-tracking echocardiography in the healthy fetal cohort is essential for the evaluation of myocardial pathologies during pregnancy.

CONCLUSIONS

Finding of LAS of fetal heart is feasible and probably can have potential for clinical and prognostic implications.

Fetal Cardiac Inflow Characteristics in Response to Fetal Anemia: Based on Fetal Hemoglobin Bart's Disease at Mid-Pregnancy

OBJECTIVES

To identify the inflow (filling time fraction [FTF] and E/A ratio) characteristics of fetuses with anemia, and to evaluate the performance of the inflow markers in predicting the affected fetuses.

METHODS

Fetuses at risk of hemoglobin (Hb) Bart's disease at 17-22 weeks were prospectively recruited to undergo echocardiography before diagnostic cordocentesis. Cardiac Doppler images were digitally stored for off-line blinded measurements of FTF and E/A ratio.

RESULTS

A total of 428 fetuses at risk of Hb Bart's disease were analyzed, including 88 affected fetuses (20.6%). The mean gestational age at the time of diagnosis was 19.43 ± 1.5 weeks. The FTFs in both sides were significantly lower in the affected fetuses, whereas the E/A ratios of both sides were significantly higher in the affected group. According to the receiver operating characteristic curves, the performance of the FTF of the right side in predicting affected fetuses was slightly better than that of the left side (area under curve: 0.707 versus 0.680, P < .001). Likewise, the performance of the E/A ratio of the tricuspid valve was slightly better than that of the mitral valve. Also, FTF was superior to E/A ratio in predicting the affected fetuses.

CONCLUSIONS

New insights leading to a better understanding of the fetal cardiac response to anemia are: 1) the FTFs in both sides were significantly decreased, suggesting some degree of diastolic ventricular dysfunction; 2) the E/A ratios of both sides were significantly increased, indicating volume load; and 3) The inflow parameters may be useful as a new predictor of fetal anemia, especially among pregnancies at risk.

Prenatal Diagnosis of Fetal Heart Failure

Fetal heart failure (FHF) is a condition of inability of the fetal heart to deliver adequate blood flow for tissue perfusion in various organs, especially the brain, heart, liver and kidneys. FHF is associated with inadequate cardiac output, which is commonly encountered as the final outcome of several disorders and may lead to intrauterine fetal death or severe morbidity. Fetal echocardiography plays an important role in diagnosis of FHF as well as of the underlying causes. The main findings supporting the diagnosis of FHF include various signs of cardiac dysfunction, such as cardiomegaly, poor contractility, low cardiac output, increased central venous pressures, hydropic signs, and the findings of specific underlying disorders. This review will present a summary of the pathophysiology of fetal cardiac failure and practical points in fetal echocardiography for diagnosis of FHF, focusing on essential diagnostic techniques used in daily practice for evaluation of fetal cardiac function, such as myocardial performance index, arterial and systemic venous Doppler waveforms, shortening fraction, and cardiovascular profile score (CVPs), a combination of five echocardiographic markers indicative of fetal cardiovascular health. The common causes of FHF are reviewed and updated in detail, including fetal dysrhythmia, fetal anemia (e.g., alpha-thalassemia, parvovirus B19 infection, and twin anemia-polycythemia sequence), non-anemic volume load (e.g., twin-to-twin transfusion, arteriovenous malformations, and sacrococcygeal teratoma, etc.), increased afterload (intrauterine growth restriction and outflow tract obstruction, such as critical aortic stenosis), intrinsic myocardial disease (cardiomyopathies), congenital heart defects (Ebstein anomaly, hypoplastic heart, pulmonary stenosis with intact interventricular septum, etc.) and external cardiac compression. Understanding the pathophysiology and clinical courses of various etiologies of FHF can help physicians make prenatal diagnoses and serve as a guide for counseling, surveillance and management.

Comparisons of serum non-transferrin-bound iron levels and fetal cardiac function between fetuses affected with hemoglobin Bart's disease and normal fetuses

Objective

To compare the levels of Non-transferrin bound iron (NTBI) in fetuses with anemia, using Hb Bart's disease as a study model, and those in unaffected fetuses and to determine the association between fetal cardiac function and the levels of NTBI.

Patients and methods

A prospective study was conducted on pregnancies at risk of fetal Hb Bart's disease. All fetuses underwent standard ultrasound examination at 18-22 weeks of gestation for fetal biometry, anomaly screening and fetal cardiac function. After that, 2 ml of fetal blood was taken by cordocentesis to measure NTBI by Labile Plasma Iron (LPI), serum iron, hemoglobin and hematocrit. The NTBI levels of both groups were compared and the correlation between NTBI and fetal cardiac function was determined.

Results

A total of 50 fetuses, including 20 fetuses with Hb Bart's disease and 30 unaffected fetuses were recruited. There was a significant increase in the level of serum iron in the affected group (median: 22.7 vs. 9.7; p-value: 0.013) and also a significant increase in NTBI when compared with those of the unaffected fetuses (median 0.11 vs. 0.07; p-value: 0.046). In comparisons of fetal cardiac function, myocardial performance (Tei) index of both sides was significantly increased in the affected group (left Tei: p = 0.001, Right Tei: p = 0.008). Also, isovolumetric contraction time (ICT) was also significantly prolonged (left ICT: p = 0.00, right ICT: p = 0.000). Fetal LPI levels were significantly correlated inversely with fetal hemoglobin levels (p = 0.030) but not significantly correlated with the fetal serum iron levels (p = 0.138). Fetal LPI levels were also significantly correlated positively with myocardial performance index (Tei) of both sides (right Tei: R = 0.000, left Tei: R = 0.000) and right ICT (R = 0.013), but not significantly correlated with left ICT (R = 0.554).

Conclusion

Anemia caused by fetal Hb Bart's disease in pre-hydropic stage is significantly associated with fetal cardiac dysfunction and increased fetal serum NTBI levels which are significantly correlated with worsening cardiac dysfunction. Nevertheless, based on the limitations of the present study, further studies including long-term data are required to support a role of fetal anemia as well as increased fetal serum NTBI levels in development of subsequent heart failure or cardiac compromise among the survivors, possibly predisposing to cardiovascular disease in adult life.

The Association of Pulmonary Flow Characteristics With Cardiac Function in Tricuspid Valve Malformation Fetuses: Study With Two-Dimensional Speckle Tracking Echocardiography

OBJECTIVES

To explore the relationship between cardiac function and pulmonary flow characteristics in tricuspid valve malformation (TVM) fetuses by conventional and speckle tracking echocardiography.

METHODS

Eighty-eight TVM fetuses were retrospectively included and compared with 80 normal controls. TVM fetuses in each trimester were divided into two subgroups according to pulmonary flow characteristics: those with normal pulmonary flow (TVM-N) and those with reduced or absent pulmonary flow (TVM-R/A). Cardiac measurements, Celermajer index, and Simpson-Andrews-Sharland (SAS) score were obtained. Speckle tracking echocardiography was used to compute ventricular deformation parameters.

RESULTS

TVM fetuses demonstrated significantly lower global longitudinal strain (GLS) and strain rate for both ventricles than controls (all P < .05). When compared with TVM-N, left ventricular (LV) ejection fraction, LV fractional area change, right ventricular (RV) fractional area change, LVGLS, and RVGLS were significantly reduced (all P < .05), while the RV diameter Z-score, RV/LV diameter, SAS score, and Celermajer index were obviously increased in TVM-R/A in both trimesters (all P < .05). Both LVGLS and RVGLS correlated with cardiothoracic circumference ratio, RV diameter Z-score, RV/LV diameter, Celermajer index, and SAS score (all P < .01). There was a slow decline for LVGLS and RVGLS in TVM-N fetuses throughout the gestation. Conversely, these two parameters worsened rapidly in TVM-R/A group.

CONCLUSIONS

TVM fetuses present biventricular dysfunction by deformation analysis in the second and third trimester of pregnancy. TVM fetuses with reduced or absent pulmonary flow exhibit significantly greater impairment and more rapid deterioration of cardiac function, which may contribute to poor outcomes.

Retrograde flow in aortic isthmus in normal and fetal heart disease by principal component analysis and computational fluid dynamics

OBJECTIVES

Reverse flow Retrograde flow (RF) of blood in the aortic isthmus can be observed in different types of fetal heart disease (FHD), including abnormalities in heart structure and function. This study sought to investigate the relationship between RF and blood flow parameters, and develop a computational fluid dynamics (CFD) model to understand the mechanisms underlying this observation.

MATERIAL AND METHODS

A total of 281 fetuses (gestational age [GA] 26.6±.3 weeks) with FHD and 2803 normal fetuses (GA: 26.1±.1 weeks) by fetal echocardiography collected from May 2016 to December 2018. Principal component analysis (PCA) was performed to find the relationship and the CFD model reconstructed from 3D/4D spatio-temporal image correlation (STIC) images to simulate hemodynamics.

RESULTS

There was a significant difference in the percentages of RF between the study (80/201 (39%)) and control (29/2803 (1%)) groups (p < 0.05). The RF occur when the aorta flow rate (left heart) is reduced to 60% by CFD stimulation. Pearson correlation analysis showed significant correlations between flow rate and wall shear stress(WSS) (r = .883, p = 0.047) variables at the AI.

CONCLUSION

Volumetric flow rate of AO or left heart was the main component of the cause of RF. The hemodynamics of the cardiovascular system have highly complex behavior hinge on the turbulent nature of circulating blood flow.

Fetal Pulmonary Vein Pulsatility Index in the Third Trimester of Pregnancy as a Predictor of Small for Gestational Age

OBJECTIVE

This study aimed to establish whether the increased fetal pulmonary venous pulsatility index (PVPI) in late pregnancy can independently predict small for gestational age (SGA) and to verify its cut point value and efficacy.

METHOD

The PVPI was measured in women with singleton pregnancies between 25 and 39 gestational weeks. Maternal hypertension and diabetes, estimated fetal weight (EFW) and percentile of the corresponding weeks of pregnancy (USG_PER), gestational weeks at delivery, and birth weight and percentile of the corresponding weeks of pregnancy (BABY_PER) were reviewed. To assess whether PVPI was independently correlated with BABY_PER, Pearson's correlation analysis was performed. The cut point value of PVPI for the prediction of SGA was established using a receiver operating characteristic (ROC) curve.

RESULTS

A total of 129 mothers were included in this study. Both USG_PER and PVPI were significantly related to SGA, independently (P <.001 and P = .004, respectively). The cut point value of PVPI was found to be 1.13. The AUCs of PVPI and USG_PER were not significantly different (P = .624). The sensitivity of PVPI was 70.27%, and the specificity was 92.39%.

CONCLUSION

PVPI could predict SGA independently, and the efficacy was comparable to EFW during pregnancy.

Echocardiographic assessment of fetal cardiac function in the uterine artery ligation rat model of IUGR

BACKGROUND

Intrauterine growth restriction (IUGR) leads to cardiac dysfunction and adverse remodeling of the fetal heart, as well as a higher risk of postnatal cardiovascular diseases. The rat model of IUGR, via uterine artery ligation, is a popular model but its cardiac sequelae is not well investigated. Here, we performed an echocardiographic evaluation of its cardiac function to determine how well it can represent the disease in humans.

METHODS

Unilateral uterine artery ligation was performed at embryonic day 17 (E17) and echocardiography was performed at E19 and E20.

RESULTS

Growth-restricted fetuses were significantly smaller and lighter, and had an higher placenta-to-fetus weight ratio. Growth-restricted fetal hearts had reduced wall thickness-to-diameter ratio, indicating left ventricular (LV) dilatation, and they had elevated trans-mitral and trans-tricuspid E/A ratios and reduced left and right ventricular fractional shortening (FS), suggesting systolic and diastolic dysfunction. These were similar to human IUGR fetuses. However, growth-restricted rat fetuses did not demonstrate head-sparing effect, displayed a lower LV myocardial performance index, and ventricular outflow velocities were not significantly reduced, which were dissimilar to human IUGR fetuses.

CONCLUSIONS

Despite the differences, our results suggest that this IUGR model has significant cardiac dysfunction, and could be a suitable model for studying IUGR cardiovascular physiology.

IMPACT

Animal models of IUGR are useful, but their fetal cardiac function is not well studied, and it is unclear if they can represent human IUGR fetuses. We performed an echocardiographic assessment of the heart function of a fetal rat model of IUGR, created via maternal uterine artery ligation. Similar to humans, the model displayed LV dilatation, elevated E/A ratios, and reduced FS. Different from humans, the model displayed reduced MPI, and no significant outflow velocity reduction. Despite differences with humans, this rat model still displayed cardiac dysfunction and is suitable for studying IUGR cardiovascular physiology.

Biomechanics of Human Fetal Hearts with Critical Aortic Stenosis

Critical aortic stenosis (AS) of the fetal heart causes a drastic change in the cardiac biomechanical environment. Consequently, a substantial proportion of such cases will lead to a single-ventricular birth outcome. However, the biomechanics of the disease is not well understood. To address this, we performed Finite Element (FE) modelling of the healthy fetal left ventricle (LV) based on patient-specific 4D ultrasound imaging, and simulated various disease features observed in clinical fetal AS to understand their biomechanical impact. These features included aortic stenosis, mitral regurgitation (MR) and LV hypertrophy, reduced contractility, and increased myocardial stiffness. AS was found to elevate LV pressures and myocardial stresses, and depending on severity, can drastically decrease stroke volume and myocardial strains. These effects are moderated by MR. AS alone did not lead to MR velocities above 3 m/s unless LV hypertrophy was included, suggesting that hypertrophy may be involved in clinical cases with high MR velocities. LV hypertrophy substantially elevated LV pressure, valve flow velocities and stroke volume, while reducing LV contractility resulted in diminished LV pressure, stroke volume and wall strains. Typical extent of hypertrophy during fetal AS in the clinic, however, led to excessive LV pressure and valve velocity in the FE model, suggesting that reduced contractility is typically associated with hypertrophy. Increased LV passive stiffness, which might represent fibroelastosis, was found to have minimal impact on LV pressures, stroke volume, and wall strain. This suggested that fibroelastosis could be a by-product of the disease progression and does not significantly impede cardiac function. Our study demonstrates that FE modelling is a valuable tool for elucidating the biomechanics of congenital heart disease and can calculate parameters which are difficult to measure, such as intraventricular pressure and myocardial stresses.

Speckle-Tracking Echocardiography for the Assessment of Atrial Function during Fetal Life

INTRODUCTION

Speckle-tracking echocardiography has become a major tool in the evaluation of heart function. Atrial strain has emerged as an important component in the assessment of cardiac function, but there is a paucity of prenatal data. The aim of this study was to describe our initial experience of measurement of atrial strain in fetuses, with respect to both feasibility and the strain patterns observed.

METHODS

Four-chamber Digital Imaging and Communications in Medicine loops were acquired prospectively for deformation imaging. Fifty-three normal fetuses with no morphologic or functional abnormalities were selected for analysis. The three strain components of atrial cycle for both left atrium (LA) and right atrium (RA) were acquired-reservoir (LAres or RAres), conduit, and contraction (LAct or RAct)-and are expressed as a percentage. Ratios of these components were calculated. Simple linear regression was used to analyze how the dependent variables changed according to gestational age and frame rate.

RESULTS

The median gestational age was 30 weeks (range, 23-35), and the frame rate was 74 frames per second (fps; range, 35-121). Left atrial strain was feasible in 48/53 (91%), and right atrial strain in 46/53 (87%) of cases. The onset of LA contraction could be identified on the strain curves in 32 of 48 (67%) cases, and of the RA in 17 of 46 (37%) cases. The values of RAres and RAct were higher compared with those of LAres and LAct (33.9% vs 30.3%, P = .014; and 21.5% vs 16.8%, P = .005), and the contraction:reservoir ratio was also higher for RA (0.63 vs 0.55 for LA, P = .003). Higher values for LAres, LAct, RAres, and RAct were associated with higher frame rate (P = .007, .020, .049, and .012, respectively). The onset of LA contraction was better identified with a higher frame rate (mean 77 vs 59 fps when not seen, P = .007). A higher LA contraction:reservoir ratio was associated with a lower gestational age (P = .042).

CONCLUSION

Measurement of atrial strain is feasible in the fetal heart. The values are influenced by gestational age and frame rate, so it is necessary to account for these variables. Comparison of left versus right atrial strain values contrasts with those observed postnatally. Atrial function merits further study during fetal life, to aid understanding of maturational changes and disease states.

Quantitative Assessment of Left Ventricular Dysfunction in Fetal Ebstein's Anomaly and Tricuspid Valve Dysplasia

BACKGROUND

Fetal Ebstein's anomaly and tricuspid valve dysplasia (EA/TVD) are associated with high perinatal mortality relative to pulmonary atresia with intact ventricular septum (PAIVS), despite both requiring redistribution of the cardiac output (CO) to the left ventricle (LV). LV dysfunction is suspected to contribute to adverse outcomes in EA/TVD.

OBJECTIVE

We sought to examine global and segmental LV function in fetal EA/TVD with comparison to normal controls and PAIVS. We hypothesized that LV dysfunction in EA/TVD is associated with abnormal LV remodeling and interventricular mechanics.

METHODS

We retrospectively identified 63 cases of fetal EA/TVD (40 with retrograde ductal flow) and 22 cases of PAIVS encountered from 2004 to 2015 and compared findings to 77 controls of comparable gestational age. We measured the combined CO and global LV function using two-dimensional, Doppler-derived, deformational (six-segmental vector velocity imaging) and dyssynchrony indices (DIs; SD of time to peak), and a novel global DI.

RESULTS

EA/TVD fetuses demonstrated abnormal LV global systolic function with reduced ejection fraction, fractional area change, and CO, while in PAIVS we observed a normal ejection fraction, fractional area change, and CO. PAIVS, but not EA/TVD, demonstrated increased LV sphericity, suggestive of remodeling, and associated enhanced radial function in the third trimester. In contrast, while EA/TVD fetuses had normal LV segmental longitudinal strain, there was abnormal radial segmental deformation and LV dyssynchrony with increased SD of time to peak and DI.

CONCLUSIONS

Fetal EA/TVD is associated with a lack of spherical remodeling and presence of mechanical dyssynchrony, which likely contribute to reduced CO and ejection fraction. Clinical monitoring of LV function is warranted in fetal EA/TVD. Further studies incorporating quantification of LV function into prediction models for adverse outcomes are required.

Introduction: From fetal echocardiography to fetal cardiology: A journey of over half a century

In this Special Issue of the Journal, 8 review articles that represent the new developments and applications of fetal echocardiography and fetal cardiology for diagnosis, prognosis, and treatment of fetal cardiovascular disease are included. The goal was to provide an updated review of the evidence for the current and emerging use of fetal echocardiography and cardiac magnetic resonance, improved diagnosis of challenging congenital heart disease, new tools for evaluation of fetal systolic and diastolic function, better prognosis and risk stratification of newborns with congenital heart diseases, and new and promising therapies for fetuses with cardiovascular disease.