The rapid proliferation of catheter-mediated treatments for congenital heart defects has brought with it a critical need for cooperation and communication among the numerous physicians supporting these new and complex procedures. New interdependencies between physicians in specialties including cardiac imaging, interventional cardiology, pediatric cardiology, anesthesia, cardiothoracic surgery, and radiology have become apparent, as centers have strived to develop the best systems to foster success. Best practices for congenital heart disease interventions mandate confident and timely input from an individual with excellent adjunctive imaging skills and a thorough understanding of the devices and procedures being used. The imager and interventionalist must share an understanding of what each offers for the procedure, use a common terminology and spatial orientation system, and convey concise and accurate information about what is needed, what is seen, and what cannot be seen. The goal of this article is to review how the cardiovascular imaging specialists and interventionalists can work together effectively to plan and execute catheter interventions for congenital heart disease.
The variety of catheter-based interventions for congenital heart disease has dramatically increased over the past two decades, resulting in new interdependencies between interventionalists and imaging cardiologists. In the “old” paradigm, invasive cardiologists used fluoroscopy and angiography as the sole imaging modality for most procedures. The interventionalist controlled and interpreted the images, with little interaction with other imaging specialists. In the modern era, collaborative application of multiple imaging modalities is the foundation for success. The imager and the interventionalist must share an understanding of what each offers for the procedure, use a common terminology and spatial orientation system, and convey concise and accurate information. The purpose of this article is to review the expanding collaboration of cardiovascular noninvasive imaging specialists with interventionalists in the planning and execution of catheter-based interventions for congenital heart disease. We focus, intervention by intervention ( Table 1 ), on which specific imaging modalities are ideal at each of three critical stages: (1) patient selection and preprocedural planning, (2) intraprocedural monitoring, and (3) postprocedural evaluation and monitoring of long-term outcomes and late complications. The benefits and limitations of new and evolving three-dimensional (3D) imaging technologies are also presented.
| Interventional procedure | Key issues in procedural planning ∗ |
|---|---|
| 1. Pericardiocentesis | Do the images support the need for the procedure, and are they adequate to guide interventional technique? |
| 2. Defect closure | Are the images adequate for assurance that the device is indicated and can be deployed successfully with expectation of complete shunt obliteration? |
| a. Secundum ASD | |
| b. PFO | |
| c. Other defect closure (patent ductus arteriosus, VSDs, Fontan fenestrations, Coronary fistulae) | |
| 3. Defect creation | Do the images demonstrate special anatomic and/or physiologic features that affect the interventional technique? Do they suggest that a different treatment modality (surgery) might have greater success or fewer risks? |
| a. Transposition of the great arteries (balloon atrial septostomy) | |
| b. Pulmonary artery hypertension | |
| c. Patient on ECMO support | |
| d. Single ventricle (restrictive or intact septum in hypoplastic left heart syndrome or variant, hybrid stage 1 palliation, Fontan fenestration creation) | |
| 4. Valvuloplasty and vasculoplasty | Do the images confirm that the intervention is truly indicated? Are they adequate to draw the conclusion that catheter-mediated therapy is superior to a surgical approach? |
| a. Aortic stenosis | |
| b. Pulmonary stenosis | |
| c. Pulmonary valve perforation in pulmonary atresia with intact ventricular septum | |
| d. Pulmonary vein stenosis | |
| 5. Valve implantations | Has the best imaging technique been done to guide device selection and interventional technique? |
| a. Pulmonary valve | |
| b. Aortic valve | |
| c. Paravalvular leak closure | |
| 6. Stent procedures | Are the images adequate to ensure that the stent can be satisfactorily deployed with expectations that the obstruction will be effectively relieved? |
| a. Pulmonary artery stent | |
| b. Aortic stent |
∗ The key issues shown here are not the only issues of importance; refer to the text for a more comprehensive discussion.
Patient Selection and Preprocedural Planning
The first opportunity for collaboration between imagers and interventionalists is at the time of patient selection and procedure planning. Although the nature of the imaging information to be discussed will vary remarkably with the procedure under consideration, the discussion will generally need to address the following questions: (1) Do the images present clear and unmistakable indications for the procedure? (2) Before proceeding, are there relevant deficiencies in preprocedural diagnosis that require further imaging or different imaging modalities? (3) What sort of imaging will be necessary during the procedure? and (4) On the basis of the imaging available, what decisions can be made about the materials and means by which the intervention will be accomplished?
Pericardiocentesis
Pericardiocentesis is commonly performed in emergent and nonemergent circumstances. The decision to perform pericardiocentesis is not solely image based or clinically based, so the imager and the interventionalist need to combine clinical and echocardiographic data to establish the need for the procedure. Echocardiographic findings, which by themselves may provide only borderline support for intervention, take on greater weight when coupled with ominous clinical features such as positional preference on the part of the patient, shortness of breath, chest pain, and pulsus paradoxus. Chronic pericardial effusions can gradually become quite large without provoking a clinical crisis, so the imager and interventionalist must have a shared understanding that effusion size alone ought not be the sole indication for intervention.
Two-dimensional (2D) transthoracic echocardiography (TTE) is the study of choice for the imager and interventionalist to review at the stage of patient selection and procedure planning. At this time, they confirm the need for intervention by evaluating in clinical context the size of the effusion (usually in millimeters of width between the pericardium and the epicardial surface), the character (fibrous strands or clots), the distribution and accessibility of fluid, and the hemodynamic effects (right atrial collapse or right ventricular diastolic collapse in early diastole, respiratory variation of ventricular filling, and excessive cardiac motion). The impact on cardiac output is documented with right heart compression and alteration of ventricular inflow patterns.
Defect Closure
Secundum Atrial Septal Defect (ASD)
At most large centers, 2D TTE is the primary preprocedural means for determining suitability for transcatheter ASD closure. At its most basic level, communication about ASD between the imager and interventionalist involves a shared understanding of the following: (1) the anatomic location (which must be confirmed as secundum, not primum or sinus venosus); (2) any multiple defects of fenestration; (3) the size of the ASD(s); (4) the adequacy of the surrounding tissue (in patients with suitable acoustic windows, 3D echocardiography or 2D TTE in additional planes can demonstrate the defect en face) ; and (5) any additional cardiac abnormalities that may affect the wisdom of pursuing catheter-mediated ASD closure, for example, other cardiac abnormalities that merit surgery, or hemodynamics such as elevated pulmonary artery pressure that may make device placement more risky. A shared, common vocabulary for naming the rims of the defect is one of the keys to effective communication. There are limits to the size of the rims around a defect that may be required for specific devices. Especially in small children, the actual length of the atrial septum may also be an important factor in determining whether a specific device can be used.
In some patients, the imager may recognize that not all of the critical anatomy can be delineated by 2D TTE, and in this circumstance, it is appropriate for the imager and interventionalist to consider together whether transesophageal echocardiography (TEE) can provide the necessary additional information. When an ASD appears likely but not certainly suitable for catheter-mediated closure, the discussion might lead to an arrangement in which TEE would be done in the catheterization laboratory immediately before a tentatively scheduled device ASD closure, with intent to proceed if appropriate or refer to surgery if not. Because TEE is commonly a guide for surgical repair, it will be useful either way.
Patient selection for catheter-mediated ASD closure also includes coming to a level of comfort that the defect is large enough to warrant closure. In general, ASD closure is indicated when the defect is large enough to allow sufficient left-to-right shunting to cause right heart enlargement over time. The preprocedural echocardiographic assessment should therefore very specifically address the presence of right ventricular enlargement. Some patients have poor transthoracic echocardiographic windows, and there may be few clues about whether a small or suspected ASD warrants closure, or the location of the ASD may be ambiguous. Frank discussion of this uncertainty between the imager and interventionalist may result in an appropriate decision to perform outpatient TEE (or cardiac magnetic resonance [CMR] imaging) before scheduling the laboratory at all.
Sometimes the diagnostic ambiguity is discordance between the small size of an ASD appreciated on 2D TTE and disproportionately severe right ventricular enlargement. This should raise suspicion for an additional source of shunt, such as a sinus venous defect, anomalous pulmonary vein, or systemic arteriovenous malformation. Imagers should alert interventionalists to such discordances and undertake measures such as TEE or CMR to resolve these long before reaching the catheterization laboratory.
Patent Foramen Ovale (PFO)
Catheter-mediated PFO closure remains controversial, and the indications for proceeding continue to be debated. Imagers and interventionalists ideally should share a philosophy regarding PFO closure indications and should approach patient selection with their common approach in mind. A large right ventricular volume load will be absent in simple PFO, but with a few considerations unique to PFO, patient selection and procedure planning considerations can be very similar to those outlined for secundum ASD. Far greater than with secundum ASD is the challenge of identifying confidently that a PFO exists using 2D TTE. When present, this diagnostic ambiguity must be discussed and resolved before embarking on a catheter intervention. Agitated saline contrast 2D TTE can be helpful, but sometimes TEE with contrast may be required.
Other Defect Closure (Patent Ductus Arteriosus, Ventricular Septal Defects [VSDs], Fontan Fenestrations, Coronary Fistulae)
A ratio of left atrial to aortic dimension > 1.5 by 2D TTE is considered a marker for hemodynamic significance of a patent ductus arteriosus. This is based on the principle that the distensible left atrium will enlarge to accommodate the excessive pulmonary venous flow more than the less distensible aorta. In our experience, indexed left atrial volume and left atrial/right atrial volume ratio are useful additional markers of hemodynamic significance. Before catheterization, 2D transthoracic echocardiographic assessment of ductus morphology (long, short, tubular, or with multiple constrictions) and measurements of its minimal diameter, length, and ampulla size could be helpful in selecting the suitable method (coil vs device) of closure.
Currently, there are no devices approved in the United States with which to close perimembranous VSDs. In unusual circumstances when a variation from the classic surgical approach is felt to be advantageous, a percutaneous or hybrid perventricular approach of device closure has been used for hemodynamically significant muscular VSDs. Transcatheter VSD closure has also been successful for defects that occur as a complication of myocardial infarction when surgical options are limited. Should consideration of a catheter-mediated approach to VSD closure be clinically warranted, the imager and interventionalist should review the 2D transthoracic echocardiographic findings and discuss in clinical context the apparent hemodynamic impact of the VSD (left ventricular and left atrial size, degree of valve regurgitation, estimated pulmonary artery pressure), defect size and number, and rim size, especially those rims that border the atrioventricular valves, left ventricular outflow tract, and ventricular free wall.
Occasionally, an interventionalist is called upon to consider closing a fenestration between a Fontan channel and the atrial portion of the heart in the setting of palliated single ventricle. Careful collaborative review of the preprocedural imaging is necessary. Together, the imager and the interventionalist should discuss the following issues: (1) Does 2D TTE provide an adequate understanding of the size, location, and number of communications to be closed, or are other imaging modalities required to address this? (2) Does 2D TTE reveal any other features of this communication that would complicate its catheter-mediated closure (e.g., potential for the device to obstruct critical blood flow pathways, thrombus in the Fontan pathway)? (3) Do the images provide adequate guidance regarding the optimal catheter approach to the fenestration and the anticipated ideal type of device for its closure? and (4) Does 2D TTE reveal any problems that require surgical intervention, during which the fenestration could also be addressed?
Transcatheter closure of coronary artery fistulae is an established alternative to surgical methods. Before embarking on this procedure, however, the imager and interventionalist should review the relevant images together in clinical context to establish that intervention is truly indicated. Key points of discussion should include whether there is ventricular dysfunction or evidence of a substantial left-to-right shunt. The complexity of the fistulous origin(s) and point(s) of termination must be evaluated, and a judgment made as to whether catheter-mediated closure is likely to be safe and successful. On the basis of the anatomy, the risks and benefits expected with catheter closure should be compared with those expected with surgical methods.
Defect Creation
Balloon Atrial Septostomy in Transposition of Great Arteries
Although the enlargement of an ASD in d-loop transposition of the great arteries is often an urgent procedure, patient selection and procedure planning are still important. The imager and interventionalist should together make certain that the findings on 2D TTE are unambiguous and complete enough for confidence that the procedure is indicated and that there are no special features that should prompt a reconsideration of the standard approach (e.g., atrial septum intact, atrial septum exceptionally thick, left atrium extraordinarily small). Rarely, the right atrial appendage may be juxtaposed in transposition, and this anatomic feature may complicate the septostomy procedure. Two-dimensional TTE can identify the juxtaposed appendage that passes behind the great arteries to lie very close to the left atrium.
Atrial Septostomy in Pulmonary Hypertension
Because the procedure is done to treat individuals whose cardiac output is severely limited by pulmonary vascular resistance, it is impossible to select low-risk patients. In this high-stakes setting for atrial septostomy, the preprocedural data available through 2D TTE must be carefully evaluated by the imager and interventionalist to establish the following: (1) is the imaging sufficient to supply a complete understanding of the pathologic anatomy and physiology such that there is agreement that the septostomy is warranted (if not, a discussion should ensue to develop a strategy for safely obtaining the necessary images)? (2) Will the atrial septum require puncture, or does a small defect already exist? (3) Does the atrial septum exhibit thickening commonly present in this setting that would render a standard balloon catheter ineffective? and (4) Are there issues separate from the atrial septum that would require a surgery, during which the atrial septal obstruction could be relieved? Discussions will include consideration of the use of a blade catheter, cutting balloon, and/or stent to achieve an adequate atrial septal communication. With the standard balloon septostomy, the size of the created atrial septal opening is not precisely controlled. An overly large defect may cause severe hypoxemia from excessive right-to-left shunting. Therefore, placement of an atrial stent with a predetermined diameter could be beneficial.
Atrial Septostomy on Extracorporeal Membrane Oxygenation (ECMO)
A patient on ECMO with evidence of left ventricular dilation, left atrial hypertension, and the secondary pulmonary effects of pulmonary venous hypertension (pulmonary edema, pulmonary hemorrhage, or acute opacification of the lung fields on chest x-ray) may require an atrial communication to “unload” the left heart and improve cardiac and respiratory performance to optimize recovery. The imager and interventionalist must consider together if the clinical and imaging data support the hypothesis that clinical improvement will result from the creation of an atrial septal communication adequate to allow improved access for left atrial blood to the venous cannula of the ECMO circuit. Preprocedural planning requires that the imager and interventionalist also assess the adequacy of the available images, especially as it bears on the anatomic peculiarities of this undertaking (atrial septal thickness and its convexity toward the right atrium, the presence or absence of a small preexisting hole, and the likelihood that the right atrial cannula will be an impediment to catheter access to the atrial septum). On ECMO, there is potential for hemodynamic instability to result from worsening aortic regurgitation when the left ventricle is unloaded by ASD creation. Therefore, careful preprocedural evaluation for the presence and degree of aortic regurgitation is important. Discussions will also include consideration of the use of a blade catheter, cutting balloon, and/or stent to achieve an adequate atrial septal communication.
Atrial Septostomy in Single Ventricle
A newborn with single ventricle and an intact or severely restrictive atrial septum may do poorly regardless of the therapeutic approach, but emergent transcatheter intervention to decompress the left atrium may offer a better chance for survival. Balloon atrial septostomy in this setting carries a set of technical challenges for the interventionalist that can be mitigated to some extent by a thorough understanding of the cardiac images. These include (1) the small size and clinical instability of the patient, (2) the small left atrium, (3) the small size and unusual location of existing interatrial communications, and (4) the excessively thick interatrial septum and the convex configuration of the septum bulging toward the right atrium. Although time is limited for settling on a therapeutic approach for this critical problem, the imager and interventionalist should review the 2D transthoracic echocardiographic findings in light of these special anatomic and physiologic features when planning the procedure and weigh the pros and cons of this approach against surgical alternatives such as ECMO with a surgically created ASD. Because all urgent atrial septal procedures in single-ventricle patients are palliative until definitive surgery is performed, the interventionalist needs to decide the safest way to achieve an unrestrictive septum. Accurate sizing of the atrial communication is not essential in these patients, because the goal is to create an unrestrictive opening for most or all of the pulmonary venous return to cross the atrial septum. With the standard balloon atrial septostomy, spontaneous closure of the created opening may occur, necessitating additional procedure. Stenting of the atrial septum ( Figure 1 ) has been performed as an alternative to standard septostomy, given the thick and resistant nature of the septum. The stent can be inflated to a known diameter, with reasonable assurance of persistent patency. Suboptimal anatomy must be identified and discussed before the intervention to anticipate the risk for awkward stent positioning and instability, inadequate left atrial volume promoting thrombus formation with systemic embolic risk, or impingement of the stent on adjacent structures.
Late restriction of atrial septal communication is a rare complication after Fontan palliation. If a catheter-mediated treatment for this is being considered, the imager and interventionalist must discuss not only the usual considerations in ASD enlargement but also whether the imaging allows a good understanding of how access to the left atrium is to be obtained (is there a Fontan fenestration, and if so, is it adequate in size and orientation for the passage of the interventional equipment?) or whether retrograde access via the atrioventricular valve will be required for dilation of the atrial septum.
As a means to augment cardiac output or to treat protein-losing enteropathy, catheter-mediated creation or enlargement of a fenestration of the Fontan channel into the atrium proper is a consideration. Balloon or butterfly stent fenestration of a Fontan baffle is occasionally proposed in an effort to augment cardiac output in patients with chronically failing Fontan physiology. The imager and interventionalist must address the following questions: (1) Is the imaging sufficient to supply a complete understanding of the pathologic anatomy and physiology such that there is agreement that the opening a fenestration is warranted (if not, a discussion should ensue to develop a strategy for safely obtaining the necessary images)? (2) Is the puncture of the Fontan channel necessary, or does a small fenestration already exist? (3) Keeping in mind that the wall of the Fontan will not be like the atrial septum, and that this may require special strategies including blade catheters, cutting balloons, and stents, does the anatomy permit safety as such equipment is manipulated into position? and (4) Are there issues separate from the fenestration that would require a surgical revision, during which the atrial septal obstruction could be relieved?
Valvuloplasty and Vasculoplasty
Recently published reviews and a consensus statement have discussed the role of echocardiography in percutaneous aortic and mitral valve interventions, so these lesions are covered here only briefly. Patient selection for valvuloplasty requires a consensus that the imaging reveals (1) that the obstruction is severe enough to justify the intervention, (2) that the obstruction is truly at the level of the valve (i.e., not below or above the valve), and (3) that there are no contraindications to the procedure (e.g., an unacceptable preinterventional degree of valve regurgitation, other conditions present that require a surgical approach). Similar discussions are important in cases of vasculoplasty (e.g., balloon angioplasty for pulmonary vein stenosis). Procedure planning requires that the imager confirm with the interventionalist that the images are adequate not only for the purposes listed above but also to allow rational choice of balloon size. If they are not, a strategy must be developed to acquire the necessary information using an alternative imaging modality before proceeding ( Figure 2 ).
Valve Implantations
Pulmonary Valve Implantation
Patients with dysfunctional right ventricular outflow tracts that have previously undergone pulmonary valve surgery may be eligible for percutaneous pulmonary valve replacement. The Melody transcatheter pulmonary valve (Medtronic, Inc., Minneapolis, MN) has received US Food and Drug Administration approval under a humanitarian device exemption. The Edwards SAPIEN transcatheter heart valve (Edwards Lifesciences, Irvine, CA) remains in clinical trials at the time of this review. Valve dysfunction in these patients consists of stenosis, regurgitation, or both. If an increasing right ventricular outflow tract gradient is found on follow-up TTE (a 35 mm Hg mean gradient was used in the clinical trials), patients are often referred for diagnostic catheterization with possible valve implantation. Pulmonary regurgitation, and the resultant right ventricular dilation and dysfunction, have been more difficult to quantify with 2D TTE. With the ability to better quantify pulmonary regurgitation and right ventricular volumes, CMR imaging has been increasingly used in preprocedural evaluation for pulmonary valve replacement. It is important to review the measurements of the right ventricular outflow tract in the axial and sagittal planes, as well as the spatial relationship of coronary arteries to the outflow tract on CMR or CT. Anomalous coronary crossing the right ventricular outflow tract (e.g., in a patient with tetralogy of Fallot previously repaired with a right ventricle–to–pulmonary artery conduit or a patient with reimplanted coronary arteries after a Ross procedure) could create a potential risk for coronary compression during percutaneous pulmonary valve replacement. A recent report by Brown et al. describes useful echocardiographic markers (three-point pulmonary regurgitation and right ventricular apical diastolic area) in this setting. The authors suggested that echocardiography could be more useful for preprocedural screening and, in selected cases in which right ventricular systolic function is normal, could be considered as the only preprocedural imaging modality.
Transcatheter pulmonary valve implantation has also been described using a subxiphoid surgical approach with the assistance of intravascular ultrasound passed across the stenosed pulmonary outflow to guide positioning, coupled with TEE and fluoroscopy without angiography. Others have used an intracardiac echocardiographic catheter introduced under fluoroscopic guidance to the aortic isthmus to visualize the right ventricular outflow tract during pulmonary valve implantation.
Aortic Valve Implantation
Transcatheter aortic valve replacement is a treatment modality for patients with severe aortic stenosis deemed to be at high risk for conventional surgery because of advanced age and other comorbidities. For transcatheter aortic valve replacement, the Edwards SAPIEN valve (Edwards Lifesciences) is the only prosthesis currently approved for use by the Food and Drug Administration. This procedure is not currently recommended for children or young adults with aortic valve disease.
Stent Procedures
Patient selection for stent implantation procedures requires a consensus that the imaging reveals that (1) the obstruction is severe enough to justify the intervention, (2) the anatomy of the obstructed area is understood well enough to ensure that placement of a stent will not interfere with other cardiovascular flows of importance (to avoid jailing a pulmonary artery, for instance), (3) there are no anatomic features that require a special interventional approach (e.g., aneurysm or dissection), and (4) there are other conditions present that require a surgical approach regardless of the suitability of the lesion for stent arterioplasty. Procedural planning requires that the imager confirm with the interventionalist that the images are adequate not only for the purposes listed above but also to allow rational choice of balloon size. Many times, standard 2D TTE falls short of this standard, and a strategy must be developed to acquire the necessary information, perhaps by CMR or computed tomography (CT), before proceeding.
Intraprocedural Monitoring
Intraprocedural monitoring of a catheter intervention is perhaps the most obvious time during which collaborative communication between the imager and interventionalist is important, but the amount and nature of imaging support at the time of intervention varies widely by procedure. Indeed, whereas some interventions require continuous monitoring by TEE, others require only fluoroscopy.
Pericardiocentesis
The echocardiographer and interventionalist should both evaluate the pericardial effusion in terms of the procedure to follow, not just in defining that an effusion is present. Because the volume of the heart within the pericardial effusion changes as it empties and fills during the cardiac cycle, it is important to evaluate the minimum distance between the pericardium and epicardium at end-diastole (when the ventricles are maximally filled) and to communicate this clearly. In addition, it is important to consider the most appropriate path for the insertion of a needle and/or drainage catheter and the location where placement of the pericardiocentesis needle is least likely to cause cardiac injury as the process of pericardial drainage is initiated. With the patient supine, the transthoracic echocardiographic transducer should be moved in the chest, scanning from the subxiphoid to midaxillary and apical regions and in the anterior to posterior plane. This will enable delineation of the largest pocket of fluid for drainage, which often is apical and posterior. The standard approach for drainage is subxiphoid, but if the imager recognizes that the fluid pocket is not easily accessible from the subxiphoid location, this must be communicated to the interventionalist who might then approach from a nonstandard puncture location. Once the procedure begins, 2D echocardiography for live guidance of the procedure remains critical. Two-dimensional TTE usually remains feasible for imaging (placing a sterile sleeve over the transducer may be helpful to ensure sterile technique) simultaneously with the needle puncture. The imager conveys information about location, depth, and proper angle of approach for the needle. Proper location of the needle should be verified before exchanging for a larger system. Advancement of the guidewire will often satisfy both the imager and interventionalist that it is in the pericardial space, but if not, they might discuss whether small injections of saline contrast through the needle to document swirling bubbles in the pericardial space might help confirm proper location. Immediate 2D transthoracic echocardiographic evaluation allows the imager to confirm for the interventionalist that the pericardial drain is in place. The imager should provide confirmation that the effusion diminishes with the withdrawal of fluid and report any deterioration in ventricular function to the interventionalist.
Defect Closure
Secundum ASD and PFO
Periprocedural ultrasound imaging for ASD closure is most frequently obtained by TEE, but intracardiac echocardiography (ICE) or even TTE may sometimes be used. The limitations of each of these modalities must be well understood by both the imager and the interventionalist. To maximally assist the interventionalist, the imager must understand the structure of the various types of devices, their echocardiographic appearances, and the factors required for successful deployment.
The results of complete multiplane TEE, including careful inspection of the atrial septum and ASD and meticulous examination of all other intracardiac structures, must be successfully communicated to the interventionalist, especially those findings that may have an impact on successful catheter-mediated treatment (summarized above). Information about the rims of a secundum ASD is important in determining the suitability for closure and the type of device to be used. The rims are defined as aortic (anterosuperior), atrioventricular (anteroinferior), superior vena caval (posterosuperior), inferior vena caval (posteroinferior), and posterior (posterior atrial free wall). It is also important to ensure by imaging that all four pulmonary veins normally connect to the left atrium. TEE in the catheterization laboratory offers the opportunity for balloon sizing of the ASD; in each case, the imager and interventionalist should together consider the merits of gathering this information to aid in choice of type and size of device. In the early stages of the closure procedure, the interventionalist is primarily concerned with manipulating the catheter across the ASD, and the imager should therefore alert the interventionalist to the passage of the catheter into the left atrium ( Figure 3 ). Collaboration is key during balloon sizing to identify the moment at which shunt flow ceases, and the balloon diameter should be measured. The interventionalist and imager should have a common understanding of standards used for balloon waist measurement, transesophageal echocardiographic dimensions should be compared with fluoroscopic measurements, and significant differences should be reconciled if possible before selecting a device. Balloon sizing is also a time at which previously unappreciated secondary ASDs may be unmasked; the interventionalist will need to be made aware of these if they are discovered.
