Transcatheter Tricuspid Valve Intervention and the Use of Three-Dimensional Intracardiac Echocardiography (ICE)
Can you tell us about your work and the types of structural heart interventions you perform?
I have been involved with large community of physicians investigating novel structural heart interventions, such as transcatheter aortic valve replacement (TAVR), mitral repair devices (MitraClip, Pascal, and Pipeline technologies), pulmonary valve replacement (S3 and Alterra technologies), and now tricuspid repair technologies (TriClip, Trialign, Cardioband, Forma, and Pascal devices). With all of these clinical research investigations, I have been fortunate to work with some very smart colleagues at academic centers and in industry, working together to move the field forward.
What are the challenges of visualizing the tricuspid valve?
The tricuspid valve sits on the right side of the heart and has often been referred to as the “forgotten” valve. For the most part, we don’t have any outstanding therapies, whether medical, surgical, or transcatheter therapies, to help patients struggling with tricuspid valve disease. Patients with tricuspid valve disease often have peripheral edema, swelling, fluid in their belly (ascites), and some degree of liver failure on top of their heart failure — a complicated set of issues.
The only standard medical therapy is diuretics, which does a relatively poor job. Surgical therapies involve either surgical replacement or repair, which involves placing a ring around the tricuspid valve. These are usually considered fairly high risk procedures and are not commonly done. It is a perfect storm for a transcatheter therapy to come in and find a home. Having said that, however, the tricuspid valve is complicated. It is intimately attached to the right ventricle, which itself is also a complex structure. Our ability to assess tricuspid valve function and size is relatively in its infancy. We tend to use echocardiography, because that is the mainstay of our tools for imaging different aspects of the heart. But the tricuspid valve, unlike the mitral valve, is not so easily imaged, in part because it is to the side and off axis from the esophagus, and thus is not well suited for standard transesophageal echocardiography (TEE), requiring transgastric TEE images which are not possible in every patient. We are still learning how to use other modalities to image the tricuspid valve, both intracardiac echo (ICE), computed tomography (CT) and magnetic resonance imaging (MRI). Certainly, there is a need to learn more about the tricuspid valve in terms of how to image it and how to treat regurgitation. Within that setting, we have been involved in a number of clinical trials, most recently with transcatheter tricuspid repair using a MitraClip, now called the “TriClip”, but essentially the exact same clip device used for the mitral valve. The still-progressing TRILUMINATE trial, sponsored by Abbott Vascular, uses a modified delivery system to deliver the TriClip and repair the tricuspid valve. We are still progressing in our abilities to get reliably good results with the system. In addition to the TRILUMINATE trial, I have been involved with three other Edwards Lifesciences devices: the Forma, Cardioband, and Pascal devices. All are in their infancy or in early feasibility studies. With all of these four devices, we have had some patients who have benefited dramatically, but we have had other patients and experiences that landed on the steep end of the learning curve.
What modalities are used to image the tricuspid valve?
Transesophageal echocardiography (TEE) has been the standard intraprocedural as well as preprocedural evaluation modality. TEE runs down the esophagus, which is midline and inline to the mitral valve, and therefore offers great mitral valve imaging, but the challenge in imaging the tricuspid valve is that TEE is at an oblique access or off-line position. Sometimes good tricuspid imaging can be obtained with TEE from a transgastric position, but this achievable in every patient, so we have been looking for ways to image the tricuspid valve more directly. Our early experience involved using standard, single-plane intracardiac echo, but what we really needed was multiplanar capability. Standard ICE probes only offer a single plane of imaging and full visualization of the three leaflets of the tricuspid valve requires imaging from multiple planes. We initially used some very outside-the-box approaches, including use of an infant TEE probe. We covered it in a sterile sleeve and used it like a multiplanar ICE catheter, putting it down the jugular vein into the right atrium. It allowed us to gain more experience placing MitraClips on the tricuspid valve and sometimes in using other annular technologies. We eventually had the opportunity to collaborate with our colleagues at Siemens to use a novel, wide field of view, three-dimensional intracardiac echo probe called the ACUSON AcuNav Volume ICE Catheter. We were first able to bring 3D ICE into the early feasibility trial experience with the Cardioband device, which involves six U.S. sites. We have been able to arrange collaborations with Siemens at every one of those sites and investigators are imaging with the ACUSON AcuNav Volume ICE Catheter in order to implant the Cardioband device around the tricuspid annulus. The ACUSON AcuNav Volume ICE Catheter is certainly a step up in our ability to visualize what we are doing and it is helping us significantly, but I would also add that all of us, whether we are working in imaging, intervention, clinical, or industry, are on the steep end of the learning curve. We are still learning how to obtain the necessary images and do the best job possible in treating tricuspid valve disease.
How long have you been working with the ACUSON AcuNav Volume ICE Catheter?
I have been working with Siemens for the past 18 months. It is a project in evolution. We have learned that we can, to a much greater degree, image the tricuspid annulus with the ACUSON AcuNav Volume ICE Catheter, but trying to see finer details at higher resolution as well as at the higher temporal speeds needed for tricuspid leaflet interventions is still challenging. We are working to find the best way to obtain that information.
What other interventional procedures are enhanced by the use of ICE?
Standard single-plane ICE has been commonly used for the past few years in closing atrial septal defects (ASDs) and patent foramen ovales (PFOs). ICE has been experimented with in left atrial appendage (LAA) closure, but the standard, single-plane ICE is probably inadequate. Along with one other center, we have been using the ACUSON AcuNav Volume ICE Catheter to guide left atrial appendage closure. I think 3D ICE potentially has a real role, but we are just learning at this point.
Can you talk more about your imaging protocol for tricuspid procedures? Do you ever use CT fusion with fluoroscopy?
Our imaging protocol is that we try everything! We are still in our infancy of understanding how best to image and treat tricuspid disease. Every patient will undergo a transthoracic echo and a transesophageal echo, if possible, with 3D reconstruction of the tricuspid valve. Patients also undergo a computed tomography (CT) scan to help us better sort out the annular anatomy. Sometimes the patient will also get a cardiac MRI, because the tricuspid valve is intimately connected with the right ventricle and a right ventricular myocardial process could be playing a role in the disease. Many different imaging modalities go into helping us preplan the intervention or simply learn how best to help the patient. Imaging fusion is one aspect we aren’t yet ready to utilize for tricuspid valve intervention, however. A fair bit of work has been done to overlay different imaging modalities, either CT or MRI, with fluoroscopy in order to guide certain interventions. However, we don’t know enough yet about how well that works for tricuspid valve disease. We are still determining how best to use image fusion with mitral valve disease and so haven’t yet begun to use it with tricuspid valve disease.
What are your thoughts on partnering with industry?
We are in the earlier stages of learning about imaging and how to offer certain less invasive therapies. We all have to work collaboratively. We have seen how physicians in different fields, from non-invasive imaging to surgical to interventional cardiology, needed to learn to work together to further advances in treating structural heart disease. The same idea is behind collaborations between industry and academia. We are attempting to treat complicated disease processes faced by our patients. The idea is to bring an understanding of new technologies and new methods of imaging to the forefront. We don’t have easy answers and the only way we are going to get answers is via a collaborative approach.
How did the partnership get started originally?
I knew I had a problem — imaging the tricuspid valve. I reached out to the head of Siemens ultrasound for North America and was put in touch with the ACUSON AcuNav Volume ICE Catheter program. The ACUSON AcuNav Volume ICE Catheter program is the only research program we have going with Siemens. Everything else is done clinically.
How do you see your use of ICE developing in the future?
The future is bright. Many of the limitations regarding imaging have to do with processing power, which is something that can be technologically overcome with time. We need to better image the heart from the interior, and in doing so, we have the potential to eliminate some of the other aspects of imaging, such as transesophageal imaging. To put an ultrasound probe down a patient’s esophagus requires them to be anesthetized and intubated, which adds to the morbidity of the procedure, the expense, and the complexity of recovery at times. The availability of less invasive options, like a 3D, wide field of view ICE probe, has the potential to make the overall procedural experience less complex and less invasive for patients.
Who is in charge of ICE during procedures?
It is vital that the people whose hands are on the ICE probe be experienced in imaging the heart. That experience can come in a variety of different ways. Certainly there could be a scenario where the echo-cardiologist, experienced with imaging using TEE, scrubs in and runs the ICE probe. If the interventionalist has experience imaging with ICE, they also could be the ones with their hands on the echo probe. At our center, in addition to myself and another of our interventionalists with intracardiac echo experience, we also have echo technicians, who can scrub in and assist us in acquiring these images. They are able to help drive the catheter to different views in the heart. It comes back to the idea of collaboration between interventionalists, surgeons, and echo imaging specialists, whether echo technicians or echo cardiologists.
Any final thoughts?
In whatever intervention we are performing, whether for mitral or tricuspid valve disease, we are still trying to push the envelope, and do things that are novel and complex. Using a variety of different imaging modalities to visualize what we are doing opens up an exciting future. We cannot provide therapy to patients suffering tricuspid valve disease — or any other heart disease — without comprehensive imaging. It is even more important for complicated disease states, such as severe tricuspid regurgitation, that we be able to image the disease and how we are going to impact that disease. I commend my colleagues at Siemens and other imaging companies for taking on this challenge and helping us in this way. It is about offering something better to our patients.
Disclosure: Dr. Lim reports that his institution receives funding for clinical research on tricuspid valve interventions from Abbott Vascular, Edwards Lifesciences, Siemens Healthineers, and Mitralign.
Dr. Scott Lim can be contacted at SL9PC@virginia.edu.
