Fig. 7.1
Photograph of a 3D model of D-transposition of the great arteries status post-Mustard atrial switch with pulmonary venous baffle obstruction. a View of the model from the patient’s right side. Three right pulmonary veins (asterisks) are seen entering the pulmonary venous atrium posteriorly. The stenosis (arrows) sits between the dilated posterior pulmonary venous atrium (to left) and the much larger anterior atrial chamber (to right). b View of the stenotic orifice (arrows) as seen through a cutaway in the anterior atrial wall. The 3 right pulmonary veins (asterisks) can be seen entering the posterior atrial chamber. c View of the stent in the stenotic orifice as seen through a cutaway in the anterior atrial wall. Adapted with permission from International Journal of Cardiology
ASD Model Creation and Post-processing
In such cases, where 3D models will be created to guide the management of complex atrial septal defects, source images for the model may come from any of the three imaging modalities; 3D echo, cardiac magnetic resonance or cardiac computed tomography. For source images derived from 3D echo, the goal is to set the field of view as large as possible to mitigate disorientation from a narrow imaging field. Setting the gains to create little noise in the blood pool helps to make post-processing of the model easier. Obtaining late systolic or early diastolic imaging datasets is best, so that the defect is viewed when the atria and the interatrial septum are at their largest. Finally, if an interventional procedure is being planned, the model may need to show systemic venous connections, so that an approach to the defect can be fully visualized. If a complex surgical procedure is being planned, again, the pulmonary and systemic veins should be segmented and included in the model.
For source images derived from CT or MR, these datasets should be segmented, paying particular attention to the region of the septal defect (see Fig. 7.2). Typically, a segmentation of the blood pool is created, and then the inside is subtracted so that a thin (1–2 mm) layer at the blood pool–myocardial border is left for optimal display of the defect. Again, systemic and pulmonary venous information should be included in the model whenever relevant to the repair.
Fig. 7.2
Digital 3D cardiac model of a moderate, retroaortic secundum atrial septal defect derived from multi-detector cardiac computed tomography (MD-CCT) data. a shows an anterior–posterior view, b shows a superior–inferior view, looking into the atria from above. In this case, a model was created to help guide decision-making about the appropriateness of device closure with minimal retroaortic septal rim. ASD atrial septal defect, RA right atrium, RV right ventricle, LA left atrium, LV left ventricle
VSD
Ventricular septal defects (VSDs) are the most common congenital heart defects, with a prevalence of 1/700 live births for muscular defects to 1/1300 live births for perimembranous defects [1]. There are generally four types of VSDs according to the Society of Thoracic Surgeons (STS) classification—muscular, perimembranous, inlet-type (or atrioventricular canal VSDs), and outlet-type (or conoseptal hypoplasia/supracristal defects) [6]. VSDs can also be associated with a malaligned conal septum and are frequently seen in conjunction with conotruncal defects, such as double outlet right ventricular or transposition of the great arteries. For the purposes of this chapter, we will consider isolated VSDs and allow for discussion of more complex defects in other chapters.
Current Imaging of VSD
Similar to ASDs, the majority of imaging of uncomplicated VSDs is currently carried out by transthoracic echocardiogram in children with both 2D and 3D imaging [7]. Occasionally, CMR may be used to create a 3D reconstruction, particularly if an intervention is being planned in the management of the defect, or if views are limited from the transthoracic echo [8]. Finally, when multiple or complex defects are seen, MD-CCT is occasionally used in adults to delineate VSDs, particularly in post-myocardial infarction defects where patients may be too sick to undergo CMR or transesophageal echocardiography. In each of these defects, it is important to note the extent of the defect and which regions of the interventricular septum are involved.
Value Added by 3D Cardiac Model of VSD
Uncomplicated perimembranous VSDs rarely require additional imaging beyond standard transthoracic echocardiography prior to management decision-making. However, before undertaking the management of unusual types of VSDs such as large or multiple muscular defects, malalignment VSDs, or post-infarction VSDs [9], a 3D model can be helpful in visualizing complex anatomic relationships of the defect to its surrounding structures (Figs. 7.3 and 7.4).
