Commentary: Use fusion to avoid confusion

James A. DiNardo, MD

Central Message.

Rapid evolution of both hybrid approaches to treat complex cardiac lesions and advances in image fusion technology require that there be alignment of imaging technology with procedural requirements.

See Article page 146.

The use of a catheter-based hybrid procedure for the treatment of both congenital and acquired cardiac lesions has become commonplace. One of the challenges involved in the performance of these procedures is finding methods to visualize vital structures in a spatial orientation that is meaningful to the operator when direct open visualization is either compromised or nonexistent. X-ray fluoroscopy allows excellent visualization of catheters and implantable devices, but sole use of this modality alone may be associated with prolonged procedure times, a large radiocontrast load, and prolonged x-ray exposure. In addition, standard fluoroscopy provides only 2-dimentional imaging in real time and does not provide good soft-tissue delineation and detailed analysis of blood flow direction and velocity. These limitations can be mitigated by the simultaneous use of 3-dimentional transesophageal echocardiography (3D TEE); however, there are considerable logistical issues associated with this approach.

With standard simultaneous use of fluoroscopy and 3D TEE imaging, the proceduralist must work guided by spatial orientation that is obtained by continuous mental integration of images obtained by 2 different operators presented in disconjugate coordinate systems. Obviously, during complex procedures in which delayed or malpositioned device deployment can result in serious morbidity, this scenario is less than ideal. Fortunately, there exists robust technology in the form of echocardiography–fluoroscopy fusion (EFF) to fuse the 2 imaging modalities by “registering” the TEE probe with fluoroscopy. This technology allows the proceduralist to simultaneously manipulate the 2 imaging modalities in the same spatial orientation.¹ The utility of this technology during performance of high-complexity hybrid procedures has been well documented.1, 2, 3

In this issue of the Journal, Anselmi and colleagues⁴ describe use of fusion of 3D TEE and computed tomography (CT) images of the mitral valve in conjunction with conventional fluoroscopy. This technique was used to facilitate placement of a transcatheter mitral valve implantation using a transapically delivered, apically tethered, and self-expandable prosthesis (Tendyne device; Abbott Laboratories, Abbott Park, Ill) in a patient with severe mitral annular calcification.⁴ The purported advantage of this approach over EFF is that 3D CT fusion provides a more nuanced assessment of the extent and location of the mitral annular calcification than can be provided by EFF alone. Whether this is the best imaging modality in this situation remains to be seen, but the authors are to be congratulated for pursuing this innovative approach. Although not directly relevant to this case, one particular advantage of fusion of CT images with fluoroscopy and/or 3D TEE is the ability to precisely delineate coronary artery anatomy. This has been demonstrated to be useful in preventing inadvertent laceration of the left anterior descending coronary artery during percutaneous LV apical access.^5,6

In summary, although it is clear that fusion reduces confusion, it remains to be seen which fused images will best display complex spatial and structural information for the myriad procedures being performed in the rapidly evolving field of hybrid surgery. Sharing experiences as Amedeo and colleagues have done here is a first step toward aligning best practice in imaging technology with evolving hybrid techniques.