Three-dimensional imaging adds a needed perspective to cardiac procedures. Nowhere is this more pronounced than in the field of valvular interventions.
While still a young field, 3D echocardiography has become an important tool to give physicians a better look at annulus, leaflets and other structural problems along with providing volumetric measurements on blood flow and regurgitation. Unlike other 3D techniques, the upgraded transducers found in 3D echocardiographic machinery allow for real-time assessment and unlike older 2D echo, the added dimension provides better understanding of structures that would otherwise have been harder to view.
“Echo is, I think, inherent and absolutely critical for [the evaluation of] valve disease,” says Mani A. Vannan, MBBS, director of noninvasive services in the department of cardiovascular medicine at Ohio State University in Columbus. Vannan has been involved in a number of studies using 3D echo to model mitral and aortic valves. While he noted that echo needn’t be used exclusively to assess a patient, it was the one modality he couldn’t work without. “I cannot think of a valve disease in which echo is dispensable, but I can certainly think about a valve disease in which MR or CT are entirely dispensable.”
A number of imaging modalities have been used in the past to help cardiologists better understand the nature of a patient’s valvular problem. MR imaging and CT angiography can provide some of the picture and be used to create 3D images, but while they may be clear, the gated technique takes several heartbeats to acquire a full image. Some modalities like CT expose a patient to more contrast, while others like MRI are not feasible if a patient is claustrophobic or cannot fit into a machine.
Meanwhile, 2D echocardiography is a flat image and while vital to treating valve disease, it doesn’t capture all of the angles of the problem. With 3D echo, physicians have the ability to better quantify what’s wrong. In studies, 3D echo outshined its older counterpart in detecting widths and gaps (Am J Cardiol 2013;111:588-594). These and other findings don’t discount 2D echo; on the contrary, cardiologists can look at 2D images from the 3D image. It just doesn’t work the other way around.
“[Y]ou only have what you acquired because 2D [echo] is 2D data. You can’t go back later and try to get more information which you did not acquire. It’s not possible with 2D,” Vannan says.
Having this noninvasive 3D technique means “we can help the evolution and fashion the further development of transcatheter-based valve therapies,” he says. “That’s why 3D echo is important, because it’s able to look at blood flow and structure simultaneously in 3D in real time.”
Vannan notes that both transthoracic and transesophageal echo make 3D echo very “doable.” He also notes that 3D echo imaging is automated.
In addition to blood flow, annulus and valve area data, number of clips needed and so on, Vannan says, “For all of these, to put it in a nutshell, the fact that we can do quantitative, real-time volume color Doppler echocardiography by transthoracic or transesophageal echocardiography has become an important, absolutely critical, necessary part of evaluation of patients with valve disease in 2015, especially if intervention is being considered in these patients. So, 99.9 percent of valve questions can be answered by echo, and 3D echo is an important component of that assessment, especially for transcatheter valve therapies.”
Familiarity meets clarity
With 3D echo as part of a wave of technological and procedural innovations in the cath lab, cardiologists and industry are working together to improve how physicians are able to view modalities.
“There’s definitely a learning curve to really understanding true three-dimensional anatomy when traditionally cardiologists and interventional cardiologists have trained and practiced in a two-dimensional world, both in two-dimensional echo but also in two-dimensional x-ray imaging,” says Michael S. Kim, MD, director of the Structural Heart Disease Program at the University of Colorado Denver in Aurora. Kim and colleagues have been working with a process that combines the advanced imaging of 3D echo with the benefits of x-ray. “Bringing in that three-dimensional aspect is something that is becoming more commonplace these days.”
Both echo and x-ray have long been part of cath labs and many cardiologists are more familiar with how to use x-ray to guide their procedures than they are with 3D echo. There are also limits to what’s visible in either modality. Soft tissue is not as clear on an x-ray image and echo may fall short in other ways.
“You don’t see interventional equipment quite as well, because interventional equipment, wires, catheters, etc., were designed to be seen under x-ray,” Kim says. “They weren’t necessarily designed to be seen under ultrasound.”
There are drawbacks to using x-ray alone as well. “It’s very difficult to orient yourself in three dimensions when using x ray procedures,” says Roberto M. Lang, MD, head of the Valve Clinic at University of Chicago Medicine. Both he and Kim find fusion imaging, which brings together x-ray and 3D echo, better for orienting in three dimensions while retaining all of the benefits of both imaging styles. “The best of all worlds,” as Kim says.
He notes that combining the techniques allows cardiologists to “get a better understanding of what you’re doing and positively impact patient care, procedural success, etc., and obviously, long-term, better outcomes.”
Three-D echo alone and fused 3D echo/x-ray imaging add to costs, though. Just examining 3D echo, the costs include upgrading transducers from the 2D echo set up to provide the speed for real-time 3D imaging. When combining 3D echo and x-ray imaging, costs accrue through physicians and techs on hand to perform and evaluate the imaging. Added, further, are the costs of upgraded software needed to resolve the data coming in from the 3D echo and, if combined with x-ray, overlay the picture into something usable.
General anesthesia also carries costs when patients are undergoing prolonged valve procedures with transesophageal 3D echo. “It definitely adds costs both from time and a resource utilization standpoint,” says Kim.
However, the benefits in valve disease are recognized globally. “Three-D echo is definitely something that has been accepted worldwide,” says Lang. “You can go to remote places and 3D echo from a transesophageal point of view is being used. In Africa. In Asia. In the Middle East. And it is used because it is very, very practical. The clinical benefits are obvious [otherwise] people would not have adopted them.”
These sentiments are echoed by Lang’s colleagues, especially Vannan. “If any lab is involved with the assessment of valve disease in 2015 or any lab that’s involved in the assessment and helping with interventions such as transcatheter aortic valve or mitral clip… I don’t think you can do it without 3D echo,” Vannan says.
Lang points out that all of the major ultrasound vendors have come on board with 3D echo. “And when any new modality is being adopted by all of the vendors, it is here to stay.”