Fetal transesophageal echocardiography: clinical introduction as a monitoring tool during cardiac intervention in a human fetus

Fetal Electrocardiogram Extraction from the Mother's Abdominal Signal Using the Ensemble Kalman Filter

Fetal electrocardiogram (fECG) assessment is essential throughout pregnancy to monitor the wellbeing and development of the fetus, and to possibly diagnose potential congenital heart defects. Due to the high noise incorporated in the abdominal ECG (aECG) signals, the extraction of fECG has been challenging. And it is even a lot more difficult for fECG extraction if only one channel of aECG is provided, i.e., in a compact patch device. In this paper, we propose a novel algorithm based on the Ensemble Kalman filter (EnKF) for non-invasive fECG extraction from a single-channel aECG signal. To assess the performance of the proposed algorithm, we used our own clinical data, obtained from a pilot study with 10 subjects each of 20 min recording, and data from the PhysioNet 2013 Challenge bank with labeled QRS complex annotations. The proposed methodology shows the average positive predictive value (PPV) of 97.59%, sensitivity (SE) of 96.91%, and F1-score of 97.25% from the PhysioNet 2013 Challenge bank. Our results also indicate that the proposed algorithm is reliable and effective, and it outperforms the recently proposed extended Kalman filter (EKF) based algorithm.

Fetal Cardiac Intervention in Critical Aortic Stenosis with Severe Mitral Regurgitation, Severe Left Atrial Enlargement, and Restrictive Foramen Ovale

OBJECTIVE

To assess the intrauterine course and outcome of fetal cardiac intervention (FCI) in fetuses with critical aortic stenosis (CAS), severe mitral regurgitation (MR), severe left atrial dilatation (LAD), and restrictive foramen ovale (RFO) or intact atrial septum.

METHODS

All fetuses with a prenatal diagnosis of CAS, severe MR, severe LAD, and RFO were retrospectively collected in one tertiary center for fetal medicine over a period of 10 years. Video recordings, pre- and postnatal charts were reviewed for cardiac and extracardiac anomalies, intrauterine course, and postnatal outcome.

RESULTS

Nineteen fetuses with CAS, severe MR, severe LAD, and RFO were diagnosed in the study period. In 5 cases, FCI was not considered as the parents either opted for expectative management or for termination. In the remaining 14 fetuses, 21 FCI were performed: 14 balloon valvuloplasties, 2 atrioseptostomies, and 5 fetal atrial stent insertions. Seven of 14 fetuses (50%) had fetal hydrops, 5 of 14 fetuses (36%) presented with intact atrial septum. Procedure-related death occurred in 5 fetuses after aortic valvuloplasty or concomitant atrioseptostomy but in none after fetal atrial stenting. Due to progressive hydrops, two terminations of pregnancy were performed. Among the 7 live births, 3 died in the neonatal period. The remaining 4 received single ventricle palliation, 2 following fetal aortic valvuloplasty and 2 after fetal atrial stent insertion.

CONCLUSIONS

CAS with severe MR, severe LAD, and RFO has a high overall mortality even in cases undergoing intrauterine intervention. Parameters that accurately predict the intrauterine and postnatal outcome have yet to be defined.

In utero intervention for severe congenital heart disease

The aim of foetal cardiac therapy is to treat an abnormality at the developmental stage so that the process of cardiac growth, which is complex and relies on the volume and direction of circulating blood as well as genetic determinants, can continue. In reality, most cardiac interventions are palliative; hence, major abnormalities are still present at birth. Nevertheless, tangible benefits following successful foetal intervention include improved haemodynamics and reduction in secondary damage leading to better postnatal outcomes. In cases of semilunar valve stenosis, or atresia, foetal valvuloplasty aims to achieve a biventricular, rather than univentricular, circulation. Opening and stenting a restrictive atrial foramen may preserve the pulmonary function in cases of hypoplastic left heart syndrome, thereby increasing the chances of successful postnatal surgery. More recent endeavours include percutaneous implantation of a miniaturised pacemaker to treat complete heart block and the promotion of left-sided heart growth by chronic maternal hyperoxygenation. The true clinical benefit of these interventions over natural history remains uncertain because of the paucity of appropriate randomised controlled trials (RCTs). Foetal cardiac therapy must now move from a pioneering approach to one that is supported by evidence, as has been done successfully for other foetal therapies.

A potentially curative fetal intervention for hypoplastic left heart syndrome

Hypoplastic left heart syndrome (HLHS) encapsulates a spectrum of complex congenital cardiovascular malformations involving varying degrees of underdevelopment of the left-sided heart structures. However, despite improved survival rates since the introduction of staged surgical reconstruction, treatment options for HLHS remain palliative rather than curative. A major limiting factor in the development of definitive curative therapy for HLHS is an incomplete understanding of its pathogenesis. Currently, the aetiology HLHS is best conceptualised by the 'flow theory' of cardiogenesis, which states that normal cardiac development is reliant on the interrelationship of normal flow patterns of blood through the developing heart, and appropriate growth of the cardiac valves and myocardium. Thus, congenital cardiac malformations, such as HLHS, are thought to arise when these two processes are incorrectly coupled in utero. The rationale for the hypothesis proposed herein rests upon the flow theory of cardiogenesis. Morphological studies of HLHS indicate that, although underdeveloped, all left-sided cardiac structures are present and anatomically correct. Further, of the various structural abnormalities that can occur within the spectrum of HLHS, the presence of a ventricular septal defect (VSD) is rare. The rarity of a VSD within the morphological spectrum of HLHS suggests the syndrome may not develop in the presence of a functionally significant VSD. Presumably, the presence of a functional VSD establishes a communication between the two ventricles during cardiac development, and preserves the normal pressure-flow-dependent growth of the left ventricular (LV) myocardium, despite inflow/outflow valve defects. It is proposed that surgical creation of a VSD in utero will 'rescue' the LV of hearts with left-sided valvular deformities that render them susceptible to the development of HLHS later in gestation. In evaluating this hypothesis, potential techniques for surgical creation of a VSD in utero are offered. These techniques are based on already established catheter-based in utero interventions, and conventional postnatal percutaneous procedures for VSD creation. Further discussion is also offered on techniques to avoid, and manage, potential complications (i.e. conduction system damage) of the proposed technique(s). Finally, if VSD creation in utero is indeed practically feasible, and successfully establishes the hypothesised hemodynamic and myocardial growth normalisation within the abnormally developing LV, the clinical implications are profound. This procedure may hold a potential cure for almost every sub-type of HLHS.

Foetal therapy: what works? Closed interatrial septum

Hypoplastic left-heart syndrome and critical aortic stenosis with severely restricted or intact foramen ovale are associated with high neonatal mortality and poor long-term outcome. Despite accurate foetal diagnosis and successful postnatal catheter-based and surgical intervention, the 1-month survival rate is about 33%. Changes in pulmonary vascular architecture resulting in pulmonary hypertension result in important long-term morbidity. Prenatal relief of left atrial and pulmonary hypertension may promote normal pulmonary vascular and parenchymal development and improve short- and long-term outcomes. Foetal atrial balloon septostomy, laser perforation, and stenting of the foetal interatrial septum are the current options for foetal therapy. This paper provides an overview of foetal diagnosis, selection of patients for foetal intervention, and interventional techniques, and also reviews the current status of foetal and postnatal outcomes after intrauterine intervention.

Update in fetal cardiac intervention

The severity of fetal heart disease progresses during gestation and may lead to significant in utero or postnatal morbidity and mortality. Fetal echocardiography allows us to detect heart disease early enough in pregnancy to perform fetal cardiac intervention that may change the natural history of some diseases. The principal aims are the prevention of hydrops due to congenital heart disease, recruitment of hypoplastic ventricles, remodeling of the fetal pulmonary vascular bed, or creation of a two-ventricular circulation after birth without risk to the mother. The initial fetal interventions for valvuloplasty and atrial septostomy showed a high mortality and did not achieve significant change in the final outcome of patients. Nevertheless, some technique modifications have improved the outcome of these patients, making fetal cardiac intervention a promising treatment for congenital heart disease. Conversely, different assessment tools for selection of the correct patient have been studied in some series to improve the success of these procedures and thus the survival odds. We believe that percutaneous procedures with local anesthesia are preferable.

Current applications of fetal cardiac imaging technology

PURPOSE OF REVIEW

Over the last few years, great progress has been made in imaging technology, which is changing the way prenatal visualization of the fetal heart is used for diagnosis and therapy.

RECENT FINDINGS

This paper reviews recent clinical research using these new techniques, namely dynamic three-dimensional (4D) echocardiography, myocardial Doppler imaging, B-flow ultrasonography, endoscopic ultrasound, and magnetic resonance imaging. Of them, 4D echocardiography is the most significant development and is discussed in greater detail. This includes real-time volumetric data acquisition using matrix-array transducer technology, motion artefact elimination using spatio-temporal image correlation, and various display options. The advantages and limitations of each are also addressed.

SUMMARY

These techniques can provide (1) sequential assessment of the entire heart using a full 4D dataset, (2) 4D delineation of trabeculation patterns on the ventricular walls, en-face dynamic shapes of ventricular septal defects and spatially complex malformations, (3) derivation of cardiac indices to myocardial contractility and strain rate by Doppler tissue imaging, and/or (4) the use of transoesophageal ultrasound to guide in-utero cardiac intervention. All of these techniques expand our ability to evaluate the morphology and function of the in-utero heart.

Controversies of fetal cardiac intervention

Remarkable advances in ultrasound imaging technology have made it possible to diagnose fetal cardiovascular lesions as early as 12-14 weeks of gestation and to assess their physiological relevance by echocardiography. Moreover, invasive techniques have been developed and refined to relieve significant congenital heart disease (CHD), such as critical aortic and pulmonary stenoses in the pediatric population including neonates. Recognition of the fact that certain CHDs can evolve in utero, and early intervention may improve the outcome by altering the natural history of such conditions has led to the evolution of a new fetal therapy, i.e. fetal cardiac intervention. Two entities, pulmonary valvar atresia and intact ventricular septum (PA/IVS) and hypoplastic left heart syndrome (HLHS), are associated with significant morbidity and mortality even with postnatal surgical therapy. These cases are believed to occur due to restricted blood flow, leading to impaired growth and function of the right or left ventricle. Therefore, several centers started the approach of antenatal intervention with the primary goal of improving the blood flow through the stenotic/atretic valve orifices to allow growth of cardiac structures. Even though centers with a reasonable number of cases seem to have improved the technique and the immediate outcome of fetal interventions, the field is challenged by ethical issues as the intervention puts both the mother and the fetus at risk. Moreover, the perceived benefits of prenatal treatment have to be weighed against steadily improving postnatal surgical and hybrid procedures, which have been shown to reduce morbidity and mortality for these complex heart defects. This review is an attempt to provide a balanced opinion and an update on fetal cardiac intervention.

Fetal intervention for cardiac disease: the cutting edge of perinatal care

Fetal cardiac valvuloplasty has been proposed for progressive cardiac disease with a poor prognosis, such as critical aortic stenosis and pulmonary atresia with intact ventricular septum and balloon atrial septostomy for hypoplastic left heart syndrome, or simple transposition of the great arteries with closed or restrictive inter-atrial communication. It is anticipated that early rescue of ventricles or the pulmonary veins from an unfavourable environment may promote healthier ventricular and vascular growth and improve postnatal outcomes. While close collaboration between the fetal medicine specialist and perinatal cardiologist may optimize the chances of technical success, obstacles to progress include the relative rarity of suitable cases and late referral for therapy. In common with other interventions in fetal medicine, there is a learning curve, and it would benefit progress if the procedures were initially concentrated in just a few centres to enable them to develop skills and experience. Following careful evaluation, it may then be desirable to train further centres and roll out best practice models.

In-utero intervention for severe congenital heart disease

The concept of fetal therapy is well established for many disorders diagnosed before birth but practical issues regarding its introduction into clinical practice are more difficult. Cardiac malformations are common, with major lesions affecting about 3.5 per thousand pregnancies; however, only a small proportion of these is likely to benefit from an intrauterine intervention. In addition, there are no good animal models of human cardiac disease and our knowledge of the underlying mechanisms is at best sketchy. This combination of factors has resulted in slow progress in developing effective therapies for the intrauterine management of cardiac disease. Recent research and clinical developments have included percutaneous valvuloplasty for severe aortic and pulmonary stenosis, perforation of the closed or restrictive inter-atrial septum and pacing for complete heart block. Progress in these endeavours has been variable but - overall - shows promise for treatment of the human fetus.