Eric Kruse, BS, RDCS, RVT

“The practice of echocardiography is always growing and changing, and the role of the cardiovascular sonographer has evolved with the profession. Today we find ourselves not only performing studies in echo labs but also participating in imaging procedures in cardiac catheterization labs and surgical suites. Transcatheter aortic valve replacement is a procedure where the role of the sonographer is changing, increasing, and becoming vitally important.” —Elizabeth F. McIlwain, MHS, RCS, FASE, Chair.

Transcatheter aortic valve replacement (TAVR) is a treatment option for patients with severe symptomatic aortic stenosis who are at high risk for cardiac surgery. In the past these patients had few options, but the recent evolution of TAVR has provided new therapeutic hope to many. As simple as the TAVR procedure may seem, it requires the interaction of cardiac and vascular surgeons, interventional and imaging cardiologists, anesthesiologists, and cardiac sonographers working as a team to ensure success.

The role of the sonographer in a TAVR procedure begins with the pre-procedure assessment and continues throughout the process. Although probe manipulation during transesophageal echocardiographic imaging is commonly performed by the imaging cardiologist, the role of the sonographer is vital.

The assessment prior to the procedure requires careful evaluation of aortic valve stenosis using either transthoracic (TTE) or transesophageal (TEE) echocardiography. The interrogation of the aortic valve provides information regarding the number of aortic valve cusps, resting transvalvular aortic gradient, and aortic valve area. The resting aortic gradient is used for comparison immediately after valve deployment. Utilizing two-dimensional or three-dimensional (3D) echocardiographic images, the sonographer measures the aortic valve area. Both parameters (area and gradient) should be obtained with the appreciation of a possible discrepancy between them due to low flow aortic stenosis. In this situation, a thorough quantification of left ventricular (LV) systolic function is warranted, including calculation of biplane ejection fraction, description of wall motion abnormalities, and a clear evaluation of the LV apex. Careful exclusion of an LV apical thrombus and aortic atherosclerosis are important to avoid complications during the procedure.

The aortic annulus diameter must also be measured. Communication with the imaging cardiologist is important in order to obtain an appropriate view that allows for a correct aortic diameter measurement. This measurement can be aided by 3D TEE imaging, which typically results in larger, more accurate and more reproducible measurements of the aortic annulus. Accuracy of this measurement is vital as it determines the size of the prosthesis to be inserted. An incorrect prosthesis size may result in transvalvular or perivalvular aortic regurgitation and/or device migration.

Currently, there are two devices approved by the US Food and Drug Administration: The edward’s SAPIEN and the Corevalve. It is imperative to choose the appropriate prosthesis based on the individual patient’s anatomy, as each have different characteristics. Complete understanding of the physical and mechanical properties of these prostheses by the sonographer results in improved echocardiographic guidance of the positioning and deployment of these devices.

The use of fluoroscopy combined with two-dimensional and 3D echocardiography can improve the confidence of correct prosthetic valve placement. The sonographer should repeatedly alternate between biplane and 3D live mode in the long-axis view to allow the interventional and imaging cardiologists to obtain a better understanding of catheter location. Prosthetic location can be improved by the imaging team (cardiologist and sonographer) attempting to visualize the ventricular and aortic edges of the prosthesis. In addition to identifying device edges, the imaging team should clarify the position of the device in relation to the surrounding structures. When the device is deemed to be in a correct position the prosthesis can be deployed. The sonographer should record the maximum number of loops during the deployment. During the actual deployment, the sonographer and cardiologist need to ensure that the prosthetic valve is deployed in the appropriate location and at the optimal angle.

Immediately after deployment of the prosthetic valve, the presence of perivalvular aortic regurgitation is assessed. It is important for the sonographer to display the aortic regurgitation using the biplane method with color in the long-axis view to distinguish between transvalvular and perivalvular jets. While assessment for perivalvular aortic regurgitation can be performed prior to catheter removal, assessment of transvalvular aortic regurgitation cannot be done until after the catheter is withdrawn.

Multiple complications, in addition to aortic regurgitation, may occur immediately before or concurrent with valve deployment. These include left main coronary artery obstruction ; prolapse of the prosthetic device into the left ventricular outflow tract or aorta; thrombus formation on catheter or prosthesis; and aortic root rupture. In the event of left main coronary artery obstruction, rapid diagnosis of a new wall motion abnormality by the imagers can make the team aware of this uncommon complication. The imaging team should obtain multiple views to assess for new ventricular wall motion abnormalities and, if possible, obtain a new ejection fraction using the biplane technique. Prolapsing of the prosthetic device can be first seen with echocardiography. This catastrophic complication may be avoided when the imaging team alerts the interventionalist prior to deployment that the device is misplaced or unevenly positioned. Identification of thrombus formation on the catheter or prosthesis assists in the prevention of complications due to a stroke. Aortic root rupture can also be rapidly identified by the imaging team. Prior to TEE transducer removal it is important to evaluate the aorta from the aortic annulus to the descending aorta to exclude an aortic dissection.

Finally, proper valve function should be confirmed. The sonographer should verify correct valve opening and closure of the prosthesis and obtain post-implantation transaortic gradients from the transgastric approach. Use of the biplane method will allow the sonographer to illustrate to the interventional and imaging cardiologist the correct functionality of the new valve.

In summary, a thorough evaluation by the imaging cardiologist and the sonographer using a combined transthoracic and transesophageal approach may greatly reduce complications. Communication among the experts in multiple disciplines is essential in all phases of the TAVR procedure. From the pre-TAVR assessment to the post-valve deployment, the sonographer’s responsibilities are vital for the success of the procedure.