Experimental fetal transesophageal and intracardiac echocardiography utilizing intravascular ultrasound technology

Extracorporeal Circulation in Ewe's Foetus: Towards a Reliable Foetal Cardiac Surgery Protocol a Comparison of two Cases

Foetal cardiac surgery is the ultimate goal in the treatment of congenital cardiac malformations. The aim of our research is to elucidate some of the features of the necessarily invasive experimental protocol to be used in an animal model of foetal cardiac surgery. In particular, we assessed the foetal placentar reactivity to prolonged cardiac bypass in steady-flow conditions.

Methods

Two cases were selected to show the outcome of prolonged (> 30 minutes) extracorporeal circulation (ECC) instituted without oxygenator under steady-flow assistance. Following the instrumentation of the animal (placement of pressure, flow and myocardial fiber length transducers) and the baseline recordings, a 60-minute bypass period was established with an axial turbopump (Hemopump 14 Fr), after systemic heparinisation and artero-venous cannulation. At the end of the circulatory assistance, the cannulae were removed and a 90 minute observation period followed. The cardiac function was assessed by means of indirectly obtained P-V loops.

Results

Case A showed a marked reduction in the end-systolic pressure-volume relationship (ESPVR) during ECC, corresponding to a rightward shift of the P-V loop, with a gradual recovery after the assisted circulation. On the contrary, case B was subjected to progressive placental dysfunction, as evidenced by haemogasanalytical data. Consequently, the haemodynamic data also outlined a negative outcome, with high ESPVR values after bypass.

Conclusions

The present study, while confirming the possibility of cardiac intervention in the foetus, underlines the critical role of minimally invasive protocol to limit both foetal stress and placental dysfunction.

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.

Factors affecting technical success of fetal aortic valve dilation

OBJECTIVE

We have reported previously that valve dilation enhances growth of cardiac structures and may prevent hypoplastic left heart syndrome (HLHS) in fetuses with critical aortic stenosis. We aimed to investigate maternal/fetal factors which may affect the technical success of fetal valvuloplasty, and to describe perinatal complications of the procedure.

METHODS

This was a descriptive series of 22 fetuses diagnosed with critical aortic stenosis developing into HLHS which underwent intervention by valvuloplasty. Initially this was attempted using a percutaneous approach; reassessment after our first five attempts, only one of which was successful, led to the introduction of the option of laparotomy. Technical success was defined as balloon inflation across the aortic annulus and a broader jet through the aortic valve as assessed by Doppler. Data collected included body mass index, demographic variables, ultrasound findings and postprocedure interventions.

RESULTS

Technical success increased significantly if maternal laparotomy was an option (83.3% vs. 20.0%, P = 0.017). Laparotomy was performed in 66.6% (12/18) of cases. There was a learning curve that showed an increase in success rate and decrease in need for laparotomy over the 3-year study period. Neither the need for laparotomy nor the chances of technical success were predictable by gestational age, body mass index or placental location. Tocolysis was limited to perioperative prophylaxis; one woman experienced wound infection and fluid overload. Postoperatively, three fetuses died and two delivered prematurely, 2 and 7 weeks after intervention.

CONCLUSION

Fetal aortic valvuloplasty can be performed with technical success, with low fetal loss rate and few maternal complications. While the need for laparotomy cannot be predicted, having it available as an option improves the technical success rate.

An initial application of transesophageal Doppler echocardiography in experimental small animal models

This study examined whether an intracardiac echocardiography catheter could be used for transesophageal echocardiography (TEE) examinations in normal rats, and intraoperative TEE in small animal models of disease. The study used 30 Sprague-Dawley normal rats, 10 rats undergoing coronary artery ligation, and 10 rats with experimentally induced mitral regurgitation. The rats were anesthetized with isoflurane and intubated. An intracardiac echocardiographic catheter was inserted into the esophagus. M-mode, 2-dimensional, and Doppler studies were performed in multiple views. TEE probe insertions were successful in all animals. Intraoperative TEE was safely performed in the rat models of myocardial infarction or mitral regurgitation. Mitral regurgitation was well assessed using color Doppler and pulmonary venous flow. This study demonstrates that TEE (including intraoperative TEE) can be safely performed in rats using an intracardiac echocardiographic catheter. It provides a new approach to the assessment of cardiac function and valvular regurgitation in small animals.

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

Because of insufficient imaging by maternal transabdominal fetal echocardiography (TAE) in a human fetus with aortic atresia, imperforate atrial septum and progressive cardiac failure, we assessed the feasibility of fetal transesophageal echocardiography (TEE) as a monitoring tool during fetal cardiac intervention at 24 + 6 weeks of gestation. Percutaneous fetoscopic intraesophageal deployment of the ultrasound catheter was achieved and did not result in any maternal or fetal complications. Fetal TEE permitted substantially clearer definition of fetal cardiac anatomy and intracardiac device manipulations than conventional maternal TAE. Despite the employment of various devices, no sufficiently large opening could be achieved within the atrial septum. Although the fetus tolerated the procedure remarkably well and satisfactory fetoplacental flow could be documented at the end of the procedure, the fetus died from progressive cardiac failure 3 days after the intervention. Fetoscopic TEE is feasible in the human fetus and permits substantially clearer definition of fetal cardiac anatomy and intracardiac manipulations than conventional maternal TAE. Based on the observation of spontaneous closure of multiple iatrogenic perforations of the atrial septum, specialized devices are required in order to improve the technical success rate of septoplasty methods and hence the survival odds of these high-risk patients.

New fetal cardiac imaging techniques

Rapid advances in graphics computing and micro-engineering have offered new techniques for prenatal cardiac imaging. Some of them can be non-invasively applied to both clinical and laboratory settings, including dynamic three-dimensional echocardiography, myocardial Doppler imaging, harmonic ultrasound imaging, and B-flow sonography. With clinical constraints, a few others have been mainly used in laboratories, such as endoscopic ultrasound, magnetic resonance imaging and biomicroscopy. Appropriate use and co-use of these new tools will not only provide unique information for better clinical assessment of fetal cardiac disease but also offer new ways to improved understanding of cardiovascular development and pathogenesis.

Miniaturized transesophageal echocardiography in newborn infants

BACKGROUND AND METHODS

A miniaturized 5.5 to 10 MHz, phased-array, single longitudinal plane transducer mounted on a 3.3-mm diameter catheter (miniaturized transesophageal echocardiography [TEE]) may overcome mechanical limitations of standard pediatric transesophageal probes. We evaluated whether the miniaturized TEE probe could define clinically relevant anatomy in 17 infants who weighed less than 6 kg.

RESULTS

Twenty-two studies were performed in 17 infants without complication, weighing 2.1 to 5.6 kg. Twenty of twenty-two studies were diagnostic. Pediatric biplane TEE was not possible in 13 studies. Lack of horizontal plane imaging with miniaturized TEE made evaluation difficult in patients with atrioventricular septal defect.

CONCLUSION

Miniaturized TEE provided diagnostic intraoperative TEE in the majority of infants studied and may allow broader and safer application of TEE to neonates and small infants.

Intra-amniotic multimodal fetal echocardiography in sheep: a novel imaging approach during fetoscopic interventions and for assessment of high-risk pregnancies in which conventional imaging methods fail

During fetoscopic interventions, intraesophageal placement of intravascular ultrasound (US) catheters for fetal hemodynamic monitoring may result in esophageal injury in very small fetuses. Moreover, conventional fetal imaging by the transvaginal or transabdominal routes may be impossible in some high-risk pregnancies. The purpose of our study in sheep was to assess the potential of a phased-array intravascular US catheter for intra-amniotic fetal echocardiography. The catheter was percutaneously inserted into the amniotic cavity in seven pregnant ewes at between 78 to 98 days of gestation and permitted high-quality 2-D imaging of the fetal heart and multimodal Doppler assessment of fetal cardiovascular flows. Fetoscopic examination of intra-amniotic contents after intra-amniotic imaging was finished did not display any injury to intra-amniotic contents. The intra-amniotic imaging approach may provide an effective alternative in humans for monitoring during fetoscopic interventions, and to assess fetal anatomy and hemodynamics in high-risk pregnancies when sufficient images cannot be obtained by conventional routes.

Multimodal fetal transesophageal echocardiography for fetal cardiac intervention in sheep

BACKGROUND

The overall performance of available mechanical intravascular ultrasound catheters for fetal transesophageal echocardiography during fetoscopic fetal cardiac interventions in sheep has been limited by radioelectronic interference, low system frame rates, and low acoustic outputs. Therefore, a more reliable device is desired for human fetoscopic surgical procedures.

METHODS AND RESULTS

We assessed the potential of a newly available 10-French phased-array intravascular ultrasound catheter for multimodal fetal transesophageal echocardiography in 5 fetal sheep between 78 and 98 days of gestation (term, 145 to 150 d). The intravascular ultrasound catheter was easily inserted through the mouth into the esophagus in all 5 sheep fetuses (mean weight, 600 g), and it permitted high-quality 2D imaging of the fetal heart in vertical imaging planes that were validated by MRI. Color Doppler and pulsed Doppler imaging permitted clear assessment of fetal cardiovascular flows and recording of velocity-time integral tracings of the fetal heart and great vessels. The vertical imaging planes were particularly useful to demonstrate interventional material inside the fetal heart and great vessels.

CONCLUSIONS

Our early experience with the phased-array intravascular ultrasound catheter indicates that multimodal fetal transesophageal echocardiography has now become possible in these smallest of patients.

Fetoscopic direct fetal cardiac access in sheep : An important experimental milestone along the route to human fetal cardiac intervention

BACKGROUND

Fetal cardiac interventions by direct ultrasound-guided approaches or open fetal cardiac surgery have been fraught with technical difficulties, as well as with significant maternal and fetal morbidity in humans. Therefore, the purpose of our study in sheep was to assess the feasibility and potential of fetoscopic direct fetal cardiac access.

METHODS AND RESULTS

In 15 anesthetized pregnant ewes (88 to 109 days of gestation; term, 145 days), 3 to 4 trocars were percutaneously placed in the uterus. Using videofetoscopic equipment, we assessed the feasibility of achieving direct fetal cardiac access. Minimally invasive direct fetal cardiac access by operative fetoscopy was achieved in 10 of the 15 fetal sheep. In 7 fetuses, the approach was successfully tested for fetal cardiac pacing (n=5) or antegrade fetal cardiac catheterization (n=2). Access was not achieved in 5 fetuses because of bleeding complications (n=2) or because the fetoscopic setup could not be established (n=3). All but 2 fetal sheep were alive at the end of the procedure. Acute fetal demise resulted from maternal hypotension or kinking of the fetal inferior caval vein by sternal suspension. Six ewes continued gestation; 3 of these went to term, with a normal fetal outcome. Two ewes died from septicemia 3 and 7 days after the procedure, and 1 ewe aborted 1 month after the procedure.

CONCLUSIONS

Minimally invasive direct fetal cardiac access by operative fetoscopy is feasible in fetal sheep. The fetoscopic approach carries important potential for fetal cardiac pacing, antegrade fetal valvuloplasties, and resection of fetal intrapericardial teratomas in human fetuses.

World experience of percutaneous ultrasound-guided balloon valvuloplasty in human fetuses with severe aortic valve obstruction

Prenatal alleviation of severe fetal aortic valve obstructions by percutaneous ultrasound-guided balloon valvuloplasty has been performed to improve the fate of affected fetuses. The purpose of this study was to analyze the current world experience of these procedures in human fetuses. Data from 12 human fetuses were available for analysis. The mean gestational age at intervention was 29.2 weeks (range 27 to 33). The mean time period between initial presentation and intervention was 3.3 weeks (range 3 days to 9 weeks). Technically successful balloon valvuloplasties were achieved in 7 fetuses, none of whom had an atretic valve. Only 1 of these fetuses remains alive today. Of the 5 remaining technical failures, 1 patient with severe aortic stenosis underwent successful postnatal intervention and remains alive. Six patients who survived prenatal intervention died from cardiac dysfunction or at surgery in the first days or weeks after delivery. Four fetuses died early within 24 hours after the procedure, 1 from a bleeding complication, 2 from persistent bradycardias, and 1 at valvotomy after emergency delivery. Thus, the early clinical experience of percutaneous ultrasound-guided fetal balloon valvuloplasty in human fetuses with severe aortic valve obstruction has been poor due to selection of severe cases, technical problems during the procedure, and high postnatal operative mortality in fetuses who survived gestation. Improved patient selection and technical modifications in interventional methods may hold promise to improve outcome in future cases.

Fetal transesophageal echocardiography utilizing a 10-F, 10-MHz intravascular ultrasound catheter--comparison with conventional maternal transabdominal fetal echocardiography in sheep

The purpose of our study in fetal sheep was to assess the measurement agreement between fetal transesophageal echocardiography (FTEE) and conventional maternal transabdominal echocardiography (CMTFE) by the Bland-Altman method. We performed our study in 11 fetal sheep between 95-103 days of gestation (term = 145 days). FTEE was performed by imaging the fetal heart in horizontal planes utilizing a 10-F, 10-MHz intravascular ultrasound catheter. CMTFE was carried out using a 5.0-MHz phased-array transducer replicating the FTEE imaging planes. We found close agreement between FTEE and CMTFE measurements of great vessel and cardiac valvar dimensions. Conversely, the variability between both techniques for measuring ventricular dimensions was inadequate. We conclude that FTEE permits measurement of great vessel and cardiac valve dimensions with high agreement with CMTFE measurements. This finding strengthens the applicability of FTEE as a monitoring tool during experimental open or fetoscopic fetal cardiac interventions.

Feasibility study: transesophageal echocardiography with a 10F (3.2-mm), multifrequency (5.5- to 10-MHz) ultrasound catheter in a small rabbit model

Transesophageal echocardiography (TEE) is useful in children with congenital heart defects. However, because of available probe size (>/=7 mm diameter), its use is limited to patients weighing more than 3 kg. The aim of this study was to determine the feasibility of TEE in a small animal model by using a 10F (3.2-mm) intravascular ultrasound tipped catheter with a monoplane (longitudinal) 5.5- to 10-MHz phased vector array transducer. Ten New Zealand White rabbits (400 to 3400 g; mean 1580 g) underwent TEE. With animals under general sedation, the probe was blindly introduced into the esophagus. All intracardiac and extracardiac structures were examined, and the images were stored and independently reviewed. All pertinent intracardiac and extracardiac structures were identified except in the 3 smallest rabbits (400 to 600 g). Doppler hemodynamics and color Doppler were possible in each animal. Frequency agility (5.5 to 10 MHz) facilitated optimization of image resolution and penetration. Certain transgastric, 4-chamber, and short-axis views were limited because of the monoplane array. No overt adverse effects were associated with the procedure. Diagnostic TEE can be performed in a small animal model with a 10F, 5.5- to 10-MHz phased vector array ultrasound catheter. Our study suggests that this system has potential in performing diagnostic TEE safely in small, even premature, neonates.

Transesophageal echocardiography in rats using an intravascular ultrasound catheter

In vivo assessment of cardiac structure and function in small animals is an important experimental goal, but currently available techniques have significant limitations. A commercially available intravascular ultrasound (IVUS) system was adapted to perform transesophageal echocardiography (TEE) in rats. Twelve Sprague-Dawley rats (270-370 g) were anesthetized with intraperitoneal pentobarbital sodium. A 4.3-Fr, 30-MHz or an 8-Fr, 20-MHz IVUS catheter was inserted into the esophagus to obtain long-axis views of the aortic arch, short-axis views of the ascending aorta, and long-axis views of the pulmonary artery. A preshaped, 8-Fr, 20-MHz catheter was used to obtain short-axis images of the left ventricle (LV) at the midpapillary muscle level, which were used to measure LV diastolic and systolic dimensions (diameters) and to calculate LV mass and fractional shortening. Measurements by TEE were compared with those obtained by transthoracic echocardiography in 6 of 12 rats. Postmortem, the LV was weighed to determine actual LV mass. The correlation coefficients between TEE- and transthoracic echocardiography-calculated LV mass and actual LV mass were 0.94 and 0.88, respectively, and had a good agreement with actual LV mass. Inter- and intraobserver variability of TEE measurements was <10%. IVUS instrumentation may offer an alternative technique for the accurate, serial assessment of LV dimensions, mass, and systolic function and a means of imaging the great vessels in small laboratory animals.

Fetoscopic and open transumbilical fetal cardiac catheterization in sheep. Potential approaches for human fetal cardiac intervention

BACKGROUND

Shortening the prenatal disease course of severe aortic and pulmonary stenoses by balloon valvuloplasty may diminish their postnatal expression. The purpose of this study in fetal sheep was to assess the feasibility of fetoscopic and open transumbilical fetal cardiac catheterization guided by fetal transesophageal echocardiography to provide alternative approaches for human fetal cardiac intervention.

METHODS AND RESULTS

We studied a total of nine fetal sheep (95 to 103 days of gestation; term = 145 to 150 days) and performed transumbilical fetal cardiac catheterization by a minimally invasive fetoscopic (n = 6) or an open fetal surgical approach (n = 3). Monitored by fetal transesophageal echocardiography, with an 8F or 10F, 10-MHz intravascular ultrasound catheter we placed guidewires and interventional catheters via the umbilical arterial route into the fetal heart. In three of the fetuses, we created supravalvar pulmonary artery stenosis by open fetal cardiac surgery After fetal and maternal recovery, we exteriorized these fetuses and performed open transumbilical fetal cardiac catheterization with successful pulmonary arterial angioplasty in two. Three fetuses survived fetoscopic transumbilical catheterization for 1 or 2 days and died most likely of blood loss after sheath dislodgment (n = 1) or removal (n = 2). By securing the sheath insertion site with a suture, we prevented sheath dislodgment and minimized bleeding during sheath removal in three fetuses. These fetuses then survived fetoscopic transumbilical fetal cardiac catheterization for 1 to 2 weeks before being killed.

CONCLUSIONS

This study in fetal sheep demonstrates that fetoscopic and open transumbilical fetal cardiac catheterization are feasible and, guided by fetal transesophageal echocardiography, provide potential alternative approaches for human fetal cardiac intervention.