You recently started work with Vanderbilt University Medical Center to help direct their structural heart program.
Yes, I have been at Vanderbilt about five months now as the director of interventional cardiology. I was previously with Houston Methodist, spending 5 days a week doing procedures, 50-60% of which were structural heart interventions. The opportunity at Vanderbilt was to revamp the structural heart program, which included an increase in my clinical volume to about 75% structural heart cases, plus administrative and leadership roles involving 1 to 2 days per week.
Can you describe the structural heart program at Vanderbilt?
As a group, we cover the entire spectrum of structural heart disease. The most common procedure we are doing right now is transcatheter aortic valve replacement (TAVR). One of our colleagues performs a high volume of left atrial appendage occlusion procedures. We are doing more and more mitral valve interventions including MitraClip (Abbott Vascular), mitral valve-in-valve, use of a perivalvular leak plug, and some mitral valvuloplasties. We are also doing a fair number of interatrial septostomies, which is creating a hole in the interatrial septum to vent the left ventricle and left atrium for a patient in shock, or to unload the left atrium for a patient with chronic heart failure who suffers from refractory heart failure and shortness of breath despite optimal medical therapy.
Finally, we are expanding our practice to start treating diseases of the right side of the heart, such as isolated tricuspid regurgitation for patients who do not have any good options, either medical or surgical. To address this population, we are evaluating various tricuspid transcatheter repair techniques.
What are some of the clinical challenges?
We all have great ideas, but when it comes to executing these ideas during a procedure, there can be significant challenges. First, the patient population we are treating for a specific clinical condition often has multiple comorbidities. It makes the risk of any procedure shift toward the higher end of the spectrum. Recovery from the procedure will often be slower than normally expected, and the expected outcomes to the procedure itself can be variable and even unpredictable. To further increase the difficulty, the primary technical challenge for the procedure is mainly due to limited visibility. Unlike surgery, where you have a direct visualization of the territory you are working or operating on, everything we do in the cath lab is guided by indirect imaging, meaning we rely on some sort of visualization by x-ray or fluoroscopy, ultrasound, echocardiography, or a combination therein. Therefore, to support the challenges with the imaging, there is a necessity for a unique skill set and expertise. We rely on interventional imagers, who are an essential part of the team in order to do more complex valvular procedures. If we can’t see the structure, we can only do so much. It takes skill to get adequate images and visualization, and a real-time assessment is required, whether or not the anticipated outcome — without any complications or other issues — has occurred. The last challenge would be the devices themselves. Many of them we are now attempting to use are fairly rudimentary. Furthermore, we are trying to use devices designed for specific purposes and indications, and apply them to other similar lesions or defects where they weren’t exactly designed to fit or move. There can be unpredictable responses to these procedures when we try to use these devices in alternative places.
Can you tell us more about how the operator and team interact with the interventional imaging specialist?
It is a relatively new field, and one of my partners in Houston really was one of the people who spearheaded it – Stephen Little. This role is a cardiologist or anesthesiologist with advanced training in echocardiography, who is also someone that has spent a lot of time in the cath lab guiding the procedures, understanding the vocabulary, the discussions, and the back-and-forth of what we are both looking at, so we are both speaking the same language. Just for simple things, such as when I say left versus right, we are talking about the same left and the same right. You’d be surprised at how often that simple orientation can be confusing. If we are not speaking with the same perspective, one of us can be inverted and thinking in the opposite direction. Developing the right skill set definitely takes a significant amount of time and effort, and has become crucial in order to do these procedures.
Can you tell us about the research relationship you had with Siemens Healthineers at Houston Methodist?
We were able to pilot the imaging software designed specifically for structural heart procedures, particularly advanced, real-time, 3D, echo-fluoroscopy and computed tomography (CT)-fluoroscopy fusion (CT Fusion, Siemens Healthineers), which quickly became essential for some of our structural heart procedures. CT Fusion is particularly useful when there is a specific target a device needs to reach, such as a valve. We take the pre-procedural CT scan, fuse the images over real-time fluoroscopy images, and generate landmark(s) on the screen so we don’t have to work very hard to get to the defect. If we are just going by plain fluoroscopy and echocardiography, which is how most of these procedures are currently performed, it becomes quite challenging to maintain focus on the target while looking back and forth at each set of images. Image fusion allows you to look at a single image with all the necessary information and clearly marked target(s).
Is the target set in advance?
Yes, the target is identified on the CT and then it is overlaid onto the periprocedural fluoroscopic images. Generally there is a radiopaque marker that we use to fuse the CT onto the fluoroscopy screen.
What are the obstacles that make image fusion essential?
When the CT image is side by side to fluoroscopy, it can’t be translated to anything meaningful or helpful, unless the two images are fused. Sometimes the CT might be a 3D-rendered image, but still not applicable in terms of offering a target during the procedure, and/or it might not be able to be placed in the plane we are imaging in the cath lab. Historically, a diagnosis was made based on the CT and then we would struggle in the cath lab to deliver the intended treatment modality. Now we can not only use the CT for diagnostic purposes, but during the actual therapeutic procedures. With visibly enhanced targets via image fusion, we have a higher success rate in our procedures as well as shorter procedural times.
How are advances in echocardiography helping structural heart procedures?
We are excited about a new intracardiac echocardiography (ICE) catheter that allows 4D echo in real time and will help us for guidance during right-sided procedures. One of the challenges on the right side of the heart is visualization, as fluoroscopy alone has limited capabilities. We have had some success with CT fusion, but it is still challenging on the right side. Transesophageal echocardiography (TEE) is challenging and limited, even in the hands of an experienced echocardiographer. ICE, however, allows us to put the probe directly in the right atrium, look down on the tricuspid valve, and identify exactly where we need to put a device, such as the MitraClip. We can assess the valve in real time to make sure there is adequate tissue before releasing the clip safely to treat a regurgitant valve. ICE catheters have the same capabilities as TEE, with either pulse wave or continuous wave Doppler, so that we can get a hemodynamic and semi-quantitative assessment of our result and compare it both pre- and post-intervention. I think that ICE, with either 3D or 4D probes, will become the modality of choice because it is able to guide us so well for right-sided interventions. The issue is going to be providing imagers enough expertise, because for the most part, ICE is used only for simple image acquisition, but now we are going to need more comprehensive and higher resolution images.
What do you envision for the structural heart program at Vanderbilt?
We are very excited because one of the things we will be doing within the next 12 to 18 months is opening two more hybrid ORs. These new rooms are currently shells that have been in limbo; now, our needs dictate that we take advantage of the space and build out these rooms, since we are doing structural heart cases 5 days a week. We have Siemens’ equipment at Vanderbilt, as well as a good partnership with our top-notch radiology department, which does our CT scans and is very engaged in our structural heart program. This week alone, we did 12 structural cases among the team, so we are quickly approaching capacity even though the volume increase has occurred over the past few months. As a result of the clinical research and data coming out, we anticipate further increases in our structural heart procedures. Adding two additional hybrid ORs we can access 5 days a week means we will be able to run two rooms with structural procedures every day. It is very exciting, and I think follows the current direction of growth in interventional cardiology and cardiovascular disease treatment.
From a clinical and imaging perspective, what would you like to see happen in the future?
In the structural heart space, we still need some fine-tuning and advanced programming of fusion imaging. For example, the current fusion imaging is accurate, which is great, but the images are not dynamic. The heart, obviously, is beating while we are working on it, but we can only fuse or label the target using a static image. As a result, we will pick whether we tag something in systole or diastole, or whatever phase of the cardiac cycle, but that marker will stay still on our screen, which is contrary to what is happening. Therefore, the technology needs to advance to the point where fusion of the images is both 3D and dynamic. We could then utilize the CT scan in a dynamic way so the selected target is moving and beating on the screen, synchronized with the cardiac cycle. Additionally, the speeds of transferring and acquiring images could also benefit from enhancements. Physiologic assessments would be another thing to add, particularly to CT. We can get some idea of coronary perfusion, but it would be nice to get and really know physiologic assessments with stenotic or regurgitant structural lesions, which are dependent now on echocardiography or invasive measurements. It is exciting to think about all the opportunities to enhance our imaging modalities, thereby moving forward our abilities to treat more complex conditions and patients.
Disclosure: Dr. Barker reports he is part of the Advisory Board for Medtronic and Boston Scientific.
Colin M. Barker, MD, can be contacted at email@example.com.