Fig. 6.1
Transthoracic subxiphoid (subcostal) long-axis 2D image (a) of the atrial septum and a balloon atrial septostomy catheter (*) inflated in the left atrium. Immediately after septostomy pullback, the color Doppler image (b) shows laminar left-to-right shunting (arrow) and a negligible residual mean interatrial gradient of 1 mmHg (c). (RA right atrium)
Excluding these rare lesions transthoracic imaging remains the mainstay of ambulatory, preoperative assessment of congenital heart disease in all ages. The goal of the preoperative or preprocedural echocardiogram is complete delineation of the primary anatomic defect and physiology, identification of any coexisting lesions, and baseline cardiac function. For the past two decades transthoracic echocardiographic assessment has been deemed sufficient for a complete repair of even major congenital heart defects (Tworetzky et al. 1999). As such, this preoperative echocardiogram must achieve complete delineation of cardiac anatomy prior to entering the operating room. Conscious sedation can be necessary in young, noncooperative children; sedation risk assessment, including the American Society of Anesthesiology (ASA) score, can identify those at higher risk for sedation-related complications (Hoffman et al. 2002) to modify the sedation plan or appropriately refer for deep sedation if required for a complete echocardiogram. Cardiac MRI and MRA can be used selectively in patients in whom congenital lesions cannot be fully delineated by echocardiography. This includes patients with venous, arch, and other vascular anomalies but also quantifies valvular regurgitation and biventricular systolic function.
Transesophageal echocardiography (TEE) is rarely used as a diagnostic modality in pediatric-aged patients: thoracic imaging windows are frequently sufficient, and deep sedation, usually with anesthesia, is required to safely perform TEE in children. The vast majority of lesions can be adequately managed with less-invasive imaging, and TEE is often reserved for preoperative/preintervention imaging to further refine the diagnosis prior to the procedure. TEE can be superior to TTE for imaging valvular disease, atrial and ventricular septal defects, intracardiac vegetations or thrombus, and postsurgical anatomy when scar tissue can further compromise acoustic windows, typically in the older patient who can tolerate moderate sedation for a diagnostic study.
Once the decision is finalized to pursue surgery and/or transcatheter intervention, imaging plays a direct role in the procedural suite. As the modalities utilized vary somewhat between the procedural sites, they will be discussed under the respective locations.
Catheterization Laboratory
Numerous periprocedural imaging modalities are available to the interventionalist: intracardiac, transesophageal, and transthoracic echocardiography all have standard 2D and 3D options which complement fluoroscopy and 3D rotational angiography. The interventionalist acquires fluoroscopic and rotational angiography images and typically manipulates the intracardiac imaging probe. In many congenital programs, procedural echocardiographic imaging in the catheterization suite is performed and interpreted by a congenital imaging specialist. This is often a pediatric/congenital echocardiographer with specialized noninvasive imaging training, but can also be a cardiac anesthesiologist or any physician comfortable with the equipment and complexity of congenital heart disease. As such, the room configuration must account for the physical and viewing needs of all the participating providers. Echocardiographic images should display alongside fluoroscopic images, allowing the interventionalist to simultaneously gauge the status of his instruments and devices in the heart. Similarly, the imager must be able to view fluoroscopy to keep abreast of the ongoing procedure as he/she acquires images. A TEE probe can easily obscure a device at the most crucial point of the procedure; this is easily avoided if the imager has real-time access to fluoroscopic images.
The imager and interventionalist likely began a dialogue at the time of patient selection, well before meeting in the catheterization laboratory. A shared understanding of the characteristics of the lesion, expectations for the procedure, and open and timely communication throughout the case provide the best chance for a successful complex congenital intervention (Kutty et al. 2013).
Intracardiac Echocardiography
The emergence of intracardiac echocardiography (ICE) in 2006 was perfectly suited to the growing volume of device implantations. This technology places a miniaturized single-plane ultrasound element at the tip of a moderately flexible and drivable 8- or 10-French multiuse catheter (Fig. 6.2). The sheath is placed in the groin, either alongside the procedural sheath or in the contralateral groin. In a cooperative patient, the interventionalist can perform the entire procedure with local anesthetic injection and anxiolysis, rather than general anesthetic which is usually required for TEE. The catheter is guided, typically by the interventionalist, into the right atrium under fluoroscopy with the ability to rotate the catheter along its axis, flex and anteflex the tip, as well as tilt the catheter right and left. The small size of the catheter tip does not permit a biplane crystal to be utilized, so the operator uses a combination of the above maneuvers to orient the crystals into the ideal imaging plane to visualize the relevant structures. There is no thermistor on the probe as the continuous flow of blood prevents any risk of thermal injury from probe heating, permitting continuous imaging throughout the procedure.
Fig. 6.2
An 8-F AcuNav catheter (Siemens Inc., Erlangen, Germany) is shown with the tip in a flexed position. The catheter can be tilted in either the anteroposterior (AP) or left-right (LR) planes and rotated along the long axis by the operator. The catheter is predominantly used for intracardiac echocardiography but has also been used for transesophageal imaging
Atrial septal defect (ASD) closure is a primary indication for ICE (Assaidi et al. 2014). ICE is used to define the pulmonary venous return, the tricuspid and mitral valve regurgitation, and the ASD features: the number of defects, size of each, location, and integrity of the rims are all defined with the probe positioned in the right atrium. Balloon sizing, when performed, uses a compliant balloon inflated across the defect until there is no residual atrial shunting. The narrowest diameter, or “waist,” is measured by both fluoroscopy and ICE to select an appropriately-sized device. During device deployment, ICE is used to document disk capture of all defect rims, residual shunting, and stability of the device prior to and after device release. This entire procedure is typically performed with administration of local anesthetic and anxiolysis to the older patient, but under general anesthesia in the smaller child. Most operators will use ICE in children older than 2 years of age, or greater than 15 kg; in younger children, both sheath size and space in the heart for manipulation of the probe alongside intervention catheters can be challenging.
Another use for ICE in the catheterization laboratory includes assessment of the pulmonary valve in patients undergoing transcatheter valve replacement (Whiteside et al. 2015; Awad et al. 2014). The operator can steer the catheter into the right ventricle to provide images of the diseased pulmonary valve and the newly replaced valve. Angiographic assessment of pulmonary valve regurgitation can be confounded by exaggerated catheter-related regurgitation when an injection is performed in the main pulmonary artery. In contrast, ICE can be performed after removal of any devices and catheters that may disrupt the normal excursion and competence of the pulmonary valve. The post-procedural gradient and mechanism of residual stenosis can also be delineated by ICE (Whiteside et al. 2015). Similar preliminary interest and experience are present for transcatheter aortic valve (Bartel et al. 2015) placement in adults instead of TEE, which typically requires endotracheal intubation and deep sedation or anesthesia.
The ICE probe has also been used off-label as a transesophageal imaging solution when infant biplane probes cannot be passed due to their comparatively larger sizes (Fig. 6.3). Using a 10-F AcuNav catheter, 22 studies were performed in infants ranging from 2.1 to 5.6 kg with no hemodynamic compromise, airway resistance, or postoperative esophageal complication including insignificant heating of the tip (Bruce et al. 2002). It has also been used as an alternative to conventional TEE or ICE in adult patients with PFO (Mitchell-Heggs et al. 2010) to avoid the need for endotracheal intubation and deep sedation. The limitations of an ICE probe placed in the esophagus include lack of biplane imaging and difficulty in obtaining transgastric imaging due to limitations in probe flexion. With the advent of the micro-mini probe (Fig. 6.3b), a miniaturized biplane transesophageal probe, there is now rarely a need to use the ICE probe for this purpose.
Fig. 6.3
This image demonstrates a sample of the various probe sizes that can be used for transesophageal echocardiography (TEE). Probe a is the 8-F AcuNav catheter (Siemens Inc., Erlangen, Germany) also depicted in Fig. 6.2. The remaining probes b through e are Philips medical probes designed for transesophageal use: probe b is a micro-TEE S8-3 t TEE probe, approved for use in babies >2.5 kg; probe c is a mini-TEE S7-3 t sector array probe for infants >5.0 kg, d is an adult omniplane probe, and e is the 3D X7-2 t adult xMATRIX array TEE probe
Transthoracic Echocardiography
Transthoracic echocardiography has little utility in the operating room unless being used for epicardial imaging. There is similarly limited utility in the catheterization suite; nonetheless, we always keep a machine and probe available. An urgent pericardial effusion evaluation is best performed with TTE, rather than struggling with the ICE catheter or emergently placing a TEE probe. Also, in our experience, the catheterization lab can be an excellent opportunity to perform a complete transthoracic study on a toddler to avoid duplicate sedation, both to confirm the referral diagnosis and exclude any additional lesions.
In our experience, there are two ideal uses for transthoracic-guided catheterization intervention: balloon atrial septostomy and closure of the hemodynamically significant ductus arteriosus in neonates. Both of these procedures are performed in very small patients, where passage of a TEE probe may not be possible and certainly comes with increased risk. TTE is thus ideally suited to both interventions and can be performed either bedside or in the catheterization suite.
In patients with transposition of the great arteries or other cardiac defects that require unrestrictive atrial mixing, transthoracic subcostal/subxiphoid imaging delineates the plane of the interatrial septum (Fig. 6.1). The interventionalist passes a balloon atrial septostomy catheter from the femoral or umbilical vein into the heart. Under continuous TTE guidance, the balloon catheter is visualized crossing the restrictive atrial septum (Fig. 6.1a). After balloon inflation and confirmation of positioning in the left atrium, a vigorous “pull-back” septostomy is performed to tear the thin septum primum and allow unrestrictive mixing of blood in these cyanotic patients (Fig. 6.1b, c). Occasionally, transthoracic echocardiography will also be used to guide static balloon dilatation and stent placement in thicker atrial septums where a conventional septostomy cannot be performed.
We have recently published our experience with transcatheter closure of patent ductus arteriosus (PDA) in neonates, including premature infants, ranging from 700 gm to 4000 gm. While this technique has been used for decades in older children and adults, neonates have been historically excluded due to concerns about damage to groin access vessels, and device obstruction to pulmonary or aortic blood flow. Surgical ligation has been the mainstay of treatment for the persistent and hemodynamically important ductus arteriosus in the premature infant but comes with important morbidity and mortality (Roze et al. 2015; Hamrick and Hansmann 2010). We have found that TTE combined with judicious use of fluoroscopy allows us, in real time, to visualize device placement and impact of the device on descending aortic and left pulmonary artery flow (Zahn et al. 2015). We have had a procedural success of 88 % with no complications and no mortality and excellent midterm follow-up (pending publication).
Transesophageal Echocardiography
Despite the advent of new technology, TEE retains a firm footing in the catheterization laboratory. TEE provides excellent delineation of the entirety of the intracardiac anatomy, without compromising the sterile field. The operator remains at the head of the bed, often performing a complete anatomic study at the onset of the case, and can then provide real-time feedback throughout the intervention including information about cardiac function and pericardial effusion. Guidelines for TEE performance, indications, contraindications, etc. were recently published as a joint statement from the American Society of Echocardiography and the Society of Cardiovascular Anesthesiologists (Hahn et al. 2014). The pediatric patient with congenital heart disease presents unique indications for TEE, safety issues, and technical considerations necessitating additional operator training for TEE compared with adult TEE (Ayres et al. 2005). Commercially available TEE probes (Fig. 6.3) range from micro-TEE probes which are approved for use in babies >2.5 kg, mini-TEE probes approved for weights >5.0 kg, and adult probes, including 3D-TEE probes, for patients >18–25 kg. Adverse events related to TEE are more prevalent in smaller children (Stevenson 1999); fortunately, the safety profile and image quality of the micro-TEE probe (Zyblewski et al. 2010; Pavithran et al. 2014) have allowed this probe to be used successfully in neonates and small infants.
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