New York, NY - Three-dimensional echocardiography is not new. It has been part of the diagnostic landscape for some 15 years, so it's possible that some cardiologists may have missed what's new about it these days. Technical developments over the past two to three years have meant that instead of images that are acquired in two dimensions and then reconstructed into a three-dimensional image using software, the images can be acquiredin three-dimensional volumes and displayed in real time.

This development, say those in the echo field, is expected to have a great impact on an increasing variety of clinical areas, including the assessment and management of valvular and congenital heart disease and in estimating cardiac volumes and left ventricular (LV) dyssynchrony, in the spotlight now since the advent of cardiac resynchronization therapy (CRT) for the growing population of patients with congestive heart failure.

Dr Linda Gillam (Source: Hartford Hospital

"Over the past 10 to 15 years, commercial interests in the technique and advances in the speed and agility of image processing, as well as advances in transducer technology, have gotten us to the point where there are commercially available systems—from more than one vendor at this point—that use transducers that are acceptably small and produce real-time 3D images of sufficient spatial and temporal resolution that they are able to be very helpful clinically," Dr Linda Gillam (Hartford Hospital, CT), current president of the American Society of Echocardiography, told heartwire.

Early 3D systems did not incorporate Doppler, a critical aspect for diagnosis of flow through leaking valves and shunts, she said. "It's really indispensable, and the fact that early 3D systems could look only at structure was a major limitation." Frame rates, the number of images acquired over a given period, have also improved, giving images that move smoothly, rather than the staccato "stop and go" images of early systems—providing the opportunity to evaluate not just cardiac structure but function.

There are three main clinical areas, she and other experts in this area noted, where the images provided by real-time 3D echocardiography are already making a difference.

Dr Roberto M Lang

One of these is the ability to quantify the function and structure of the heart in a much more accurate way, said Dr Roberto M Lang (University of Chicago, IL). "There are many studies showing that this new technology, compared with MRI, does exceedingly well in the calculation of volumes, ejection fraction, and left ventricular mass of the heart," Lang told heartwire. Several papers, including one from his own group,[1] have now validated this comparison, he said.

The main reason for this is that when measurements are made in two dimensions in the heart, certain geometrical assumptions are made. "If you want to measure cardiac volumes from a 2D image, you have to assume that the heart has a certain geometrical shape," he said. "Many times, these assumptions fail because of, for example, the presence of regional wall-motion abnormalities. But 3D echo does not assume the heart has a particular shape, because you see it as it is, and consequently quantification is much more accurate. That's where I see the major impact." Images are rapidly acquired and displayed, he adds. From this structural information, the 3D echo system can automatically calculate ejection fraction and left ventricular mass, making the results quantitative and therefore more reproducible and easily communicated, Lang said.

Online EF measurement from triplane imaging (Source: GE Healthcare)[Click on image for a larger view.]

The technology is also particularly suited to imaging the right ventricle, Gillam added, "a geometrically complicated chamber of the heart that has been relatively poorly evaluated with two-dimensional methods."

Another aspect of heart function of growing importance clinically is the ability to measure left ventricular dyssynchrony, or differences in wall motion and pumping action from one part of the ventricle to another, with this technology. Measuring the degree of LV dyssynchrony is useful in helping define which patients with heart failure will benefit from CRT with biventricular pacing, both Gillam and Lang pointed out.

For example, at the recent American College of Cardiology (ACC) 2005 Scientific Sessions, British researchers used real-time 3D echo to evaluate LV mechanical dyssynchrony in patients undergoing CRT. They showed that symptomatic improvement after CRT and reverse remodeling, defined as a reduction in LV end-diastolic volume of 20% or more, was predicted by an index of systolic dyssynchrony assessed using real-time 3D echo. This "may be useful in patient selection for CRT," Drs Stamatis Kapetanakis, Mark Monaghan (Kings College Hospital, London, UK), and colleagues concluded. They will soon publish a proposed Systolic Dyssynchrony Index that can be used to quantitate the degree of dyssynchrony and perhaps define more clearly who may benefit from CRT, Monaghan told heartwire.

Another area where real-time three-dimensional echo is of great interest is in visualization of heart valves, particularly the mitral valve. The main advantage of three-dimensional images in this application is they allow spatial orientation of structures and their relationship to each other, Lang said.

Basically, it can give a surgical view, he adds, providing surgeons planning to repair a valve with images very similar to what they will see at the time of surgery. It can also accurately measure the size of the orifice of certain valves, particularly the mitral valve, he added. In mitral valve stenosis, it has now been shown that real-time 3D echo is more accurate than other noninvasive modalities in measuring the mitral valve area, he said.

Lang and colleagues, led by Dr José Zamorano (Hospital Clinico de San Carlos, Madrid, Spain), published such a comparison in the European Heart Journal in 2004.[2] In an accompanying editorial, Drs Herman FJ Mannaerts, Otto Kamp, and Cees A Visser (VU University Medical Center, Amsterdam, the Netherlands) conclude, "This makes 3D echocardiography and especially real-time 3D echocardiography a new clinical standard, which offers more than the conventionally used ultrasound indices for assessment of the severity of mitral stenosis: a fast and reproducible technique with detailed anatomical information and orifice area assessment, relatively independent of confounding hemodynamic variables."[3]

Researchers, notably those led by Dr Robert A Levine (Massachusetts General Hospital, Boston), have used contrast with 3D echo to quantify regurgitation in both mitral and aortic valves.

As surgical and nonsurgical methods for repairing valves become more advanced, Gillam says, it becomes more critical to be able to define exactly what's wrong with the valve. "Again, I think we've done a reasonably good job with two-dimensional echo methods but, in effect, when you use two-dimensional methods it's the brain of the person looking at the echo images that translates that image into a three-dimensional construct of how the valve looks, how it's structured, and how it's working," she points out. "With three-dimensional echocardiography, people who aren't echocardiographers can appreciate valve anatomy and physiology in three dimensions. Surgeons tend to very much appreciate three-dimensional images because the echo image looks exactly like what they see when the heart is open."

Finally, smaller in numbers perhaps but nonetheless important, 3D echo is helping in the treatment of congenital heart disease, where the anatomy of tiny hearts can be highly unusual and differ from patient to patient. Over the past three years, real-time three-dimensional echocardiography has been an important addition to clinical care at Boston Children's Hospital, says Dr Gerald S Marx, senior associate in cardiology. "The most important aspect to the day-to-day use in pediatric patients is the rapid acquisition of three-dimensional images, even in infants and young children," he said. "Three-dimensional imaging provides a perspective on congenital heart defects that often cannot be realized by two-dimensional imaging."

Dr Gerald S Marx (Source: Boston Children's Hospital)

This information can help in devising a surgical approach to operations meant to correct these defects, he notes. "For example, for valve repairs, the specific regions of lack of leaflet coaptation can be appreciated. With the application of three-dimensional color-flow analysis, the specific regions of valve regurgitation can be defined."

Real-time three-dimensional imaging can also be applied to obtaining a more comprehensive anatomic delineation of complex congenital heart defects such as double outlet right ventricle. It is also being used to measure ventricular volumes in pediatric patients, he noted. Again, two-dimensional echocardiography must make assumptions about the geometry of the ventricle to calculate volumes. Three-dimensional echocardiography allows calculation of ventricular volumes without making such assumptions and inherently should provide more accurate calculations, he said.

"Certainly for the individual patient, three-dimensional echocardiography appears to provide important additional information to improve patient care," Marx said. "However, large-scale outcome studies will need to be undertaken to demonstrate the importance of this new technique. In the meantime, real-time, three-dimensional imaging is being widely accepted and utilized in pediatric centers throughout the world."

Gillam adds that as more and more children with congenital heart disease live to be adults, cardiologists who treat adults are also coming face to face with these complicated hearts in their practice. "Again, people have managed with 2D methods, but the skill required is really enormous," Gillam said. "Having a 3D approach doesn't obviate the need to have someone knowledgeable about the nature of heart disease, but it does make it a little bit easier for cardiologists and surgeons with these adult patients to understand what the structure and function of these sometimes-bizarre-looking hearts are."

While they may be impressive, the additional benefit of real-time three-dimensional images was questioned early on, even by some echocardiographers, who have worked effectively for years with 2D echo. "It's a lot easier to welcome new technology if there's something everybody appreciates as a limitation of existing technology," Gillam points out. "If the existing technology works very well, which it clearly does, especially in highly skilled hands, then there's always the sense that the technical 'new kid on the block' has to really prove that it's better."

However, across all areas of medicine, there is a demand for new technologies and treatments to demonstrate incremental value in their effect on outcomes, she said. "What I think you see reflected now is that people are going through that exercise and identifying the areas where it will definitely make a difference."

She is confident, though, that real-time 3D echo is finding its place. The major competing technology with 3D-imaging capability is MRI, she said, but MRI doesn't offer real-time imaging and frame rates are lower, so temporal resolution is not as good. In addition, MRI is still not widely available, is relatively expensive, and cannot be used portably. Three-dimnensional echo, on the other hand, is commercially available at "I would say modest incremental cost over state-of-the-art two-dimensional imaging," Gillam added. The machines are also portable and radiation-free.

Lang feels this technology provides some of its most useful added value in the quantification. "It's not only the pictures, but it provides you with truly accurate information that we could not obtain otherwise."

For his part, Marx says that since their work is mostly with cardiac surgeons, the value of real-time 3D imaging is not questioned. The biggest investment for the general cardiology community is becoming accustomed to these new images, he says. "The added true expense and time really comes down, I think, to the learning phase."

The major cardiology meetings now regularly dedicate several abstract sessions to novel and developing uses of real-time 3D echo, a signal that it is moving out of the research arena and into clinical utility. Although it may still be below the radar for most cardiologists, Gillam feels that will change. "The next generation of cardiologists and echocardiographers will, in effect, 'grow up' on three-dimensional echocardiography, and in the same way that 2D echocardiographers today can't imagine how people managed with M-mode, I think you're going to find that the next generation is going to say 'how did we manage with 2D?'

"It's certainly cutting edge, but my prediction is it will become mainstream in a few years."

At the ACC meeting held recently in Orlando, FL, several sessions were dedicated to ongoing investigation of novel and developing uses for 3D echo. Some of the areas where this modality is being tested include:

Atrioventricular septal defects (AVSD):Researchers at the Medical University of South Carolina, Charleston, assessed patients studied with 2D and real-time 3D echocardiography at their institution to see whether the information gained by 3D echo was additive (resulting in a new finding or a changed diagnosis), useful (no new findings but useful information was obtained), or not useful. They found that 3D echo provided useful and additive information in unrepaired balanced AVSD, repaired AVSD with residual lesions, and unbalanced AVSD under consideration for biventricular repair.

Useful information included precise characterization of mitral regurgitation and cleft leaflet, substrate for subaortic stenosis, valve anatomy, and the presence and location of additional septal defects, the researchers, with first author Dr Anthony M Hlavacek, conclude. Hlavacek told heartwire they are doing similar studies looking at the usefulness of 3D echo in patients with mitral or aortic valve abnormalities, aortic arch abnormalities, and intracardiac devices, as well as validating 3D Doppler color-flow measurements in quantifying cardiac output and regurgitant fractions.

Guiding intervention: Researchers at the University of Maryland, Baltimore, reported their experience using real-time 3D echo to guide performance of biopsies of the right ventricle of transplant patients, sampling for signs of rejection, and examined differences in biopsy quality compared with biplane fluoroscopy. Real-time 3D echo "is a new method to facilitate rapid placement and accurate localization of the bioptome in transplant patients, providing comparable-quality right-ventricle biopsies to biplane fluoroscopy," Dr Monica Aggarwal and colleagues conclude.

Real-time 3D echo during 2D dobutamine stress echo: Researchers reported a complementary role for the 3D method used during 2D dobutamine stress echo, acquiring images at peak stress by rapidly switching from one transducer to another. Technically satisfactory images were obtained with both methods, and there was good overall agreement between 2D and 3D echo in the assessment of ischemia, the researchers, with first author Dr Masood Ahmad (University of Texas Medical Branch at Galveston, TX), report, but the 3D method had a higher sensitivity and detected a greater number of ischemic segments than the 2D method. The visualization of the left ventricle from multiple vantage points by 3D, they conclude, "offers advantages in estimating the extent of ischemia."

Kawasaki disease: In a separate report, Japanese researchers compared real-time 3D imaging with 2D imaging for evaluating coronary artery morphology in patients with Kawasaki disease. Dr Michio Miyashita (Nihon University, Tokyo) and colleagues concluded that the three-dimensional method was superior for visualizing the coronary arteries, particularly in evaluating the right coronary artery and circumflex branches. "Since coronary artery diameters can be measured three-dimensionally when analytical software is used, this system is expected to improve the screening of coronary arteries and the throughput of the test."