As Real-Time 3D Echo Matures, It Finds a Clinical Niche

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Inadequate reimbursement could hamper widespread adoption of multi-dimension technique



 

With an aging population and the rise of obesity, cardiologists are seeing a tremendous increase in the growth of cardiovascular diseases, and noninvasive imaging is playing an increasingly critical role in diagnosis and management. Echocardiography typically has been the “go to” imaging modality for clinical cardiologists, despite a reputation that has dimmed in light of the exquisite three-dimensional images served up by cardiac CT and MRI. As the latest advancements brighten its reputation, 3D echocardiography is converting cardiologists and surgeons alike.

Real-time 3D transthoracic echo (TTE) not only brings understanding to 3D anatomy, but by depicting full volumes of the heart and quantifying ventricular global and regional function, it moves aesthetically and quantitatively closer to CT and MRI, says Randolph P. Martin, MD, director of the Emory University Hospital Echocardiographic Laboratory in Atlanta, Ga.

Historically, 3D echo was primarily a research tool because the data acquisition and processing was time-consuming. In the last several years, the technology has significantly improved and now four major ultrasound vendors—GE Healthcare, Siemens Medical Solutions, Toshiba America Medical Systems and Philips Medical Systems—offer some type of advanced real-time 3D TTE capability. Philips last year released the first version of a real-time 3D transesophageal echo (TEE) system.

“When a certain technique is embraced by vendors, it is the best signal that it’s here to stay,” says Roberto Lang, MD, vice president of the American Society of Echocardiography (ASE) and director of the Noninvasive Cardiac Imaging Labs at the University of Chicago Medical Center.

While only a handful of peer-reviewed studies can speak to the efficacy of the nascent 3D TEE technology, hundreds of studies have validated 3D TTE, Lang says. Among the findings, researchers have documented that 3D TTE is more accurate than 2D for calculating ventricular volumes; that it compares favorably with cardiac MRI, the gold standard for measuring ejection fraction; and that it has a lower intra- and interobserver variability than 2D, making it ideal for serial follow-up. Lang adds that the excellent intra- and interobserver variability of 3D echo make it ideal to study the effects of drugs because researchers would require fewer patients.

In a recent study, Il-Woo Suh, MD, and colleagues at the University of Ulsan College of Medicine in Seoul, South Korea, demonstrated that left atrial volume measured by real-time 3D TTE predicts clinical outcomes in patients with severe left ventricular dysfunction and in sinus rhythm. The study, published in the May 2008 issue of the Journal of the American Society of Echocardiography, is the first to use real-time 3D echo in this patient population, according to the authors.

The researchers prospectively evaluated the end-systolic, left atrial volumes of 108 patients with 3D TTE and 2D Doppler echo using the Sonos 7500 from Philips. Investigators found excellent interobserver agreement with the 3D approach, that 2D significantly underestimated volume, and that 3D measurement of volume and age were independent predictors of cardiac events.

Limitations to using real-time 3D TTE, according to the authors, include the extra time needed to store and analyze the 3D images compared to calculating volumes in 2D. In addition, 3D left atrial volume measurement could not be obtained from patients with atrial fibrillation or those who cannot hold their breath long enough to acquire a full-volume real-time 3D image. “Once these technical problems are solved, left atrial volume measurement in 3D can be easily measured in clinical practice,” they wrote.

Some of these limitations may already be solved. At the 2008 ASE meeting in Toronto, Siemens unveiled the Acuson SC2000 Volume Imaging Ultrasound System, which acquires full-volume 3D data pyramids—20 images per second—in a single heartbeat, compared to current systems that acquire partial data in a single heartbeat or full-volume data in four heartbeats. Acquiring a full pyramid in one heartbeat instead of four consecutive beats could be advantageous in that the data would not require any restitching, reanimation and regating, potentially saving time and improving throughput. Additionally, the patient could be imaged without any breath-holding, thereby avoiding artifacts through arrhythmias, Lang says.


To Doppler echo and beyond


With the advent of Doppler echo, interventional cardiologists were quick to adopt the technology for hemodynamic determination in aortic stenosis and intracardiac pressure determination. Now they are adopting live 3D TEE, specifically for aortic disease, endocarditis, left atrial disease and mitral valve disease—“everything in the posterior aspect of the heart,” says Emory’s Martin. He adds that 3D TEE has already become a standard tool for surgeons, having already encountered some who will not operate without pre-, intra-, and post-operative 3D TEE imaging, especially for valvular heart disease.

Lang and colleagues have routinely performed real-time 3D TEE (iE33 Echocardiography System, Philips) on more than 700 cases. One of the main advantages of live 3D TEE is its “surgeon’s eye” view of the cardiac anatomy, says Lang. He agrees that the technique is finding a niche in preoperative planning, particularly for percutaneous mitral valve repair, and as a guiding tool in the cath lab during percutaneous procedures such as atrial septal defect (ASD) closures.

A lack of indications and inadequate reimbursement for 3D echo are stumbling blocks for wholesale adoption. Medicare currently pays for two indications: estimation of the mitral valve orifice area and preoperative planning of mitral valve surgery. Lang would like to see the quantification of left ventricular ejection fractions and volumes added to the list. He says the ASE is working with the government to secure adequate reimbursement and additional indications for 3D echo.

Lang and others are quick to point out that 2D echo remains the first line of investigation in most cases. Three-dimensional studies are done only when cardiologists believe they can get added information.


Not just your father’s probe


Henry Issenberg, MD, director of the Pediatric Echocardiography Laboratory at the Maria Fareri Children’s Hospital at Westchester Medical Center in Valhalla, N.Y., has been performing real-time 3D TTE with the Philips system for about one year He says the journey from 2D echo with color flow to 3D echo “gives us more information to spatially look at the heart in ways we had never been able to do except in the post-mortem laboratory with the heart in your hand.”

Pediatric cardiac diseases are mostly congenital structural malformations. One example where 3D TTE delivers superior clinical data over 2D echo is for ASD repairs, Issenberg says. With conventional 2D echo or x-ray angiography, ASDs often look circular, with equal diameters. Even in the operating room, the defect in the relaxed heart can look circular. In a normally beating heart, however, the defect is often oval in shape and real-time 3D echo accurately shows the shape. This realization gained through the use of live 3D echo explains the fairly high failure rate of percutaneous repair with closure devices. “You would put a round device into an oval hole and end up with portion of it not closed,” Issenberg says.

One can extrapolate the potential benefits of real-time 3D TTE to other congenital heart diseases, such as complex malformations of the mitral or tricuspid valves involving both the annulus and the leaflets or the subvalvular apparatus. “To be able to see the relationships of those structures in multiple dimensions and in real-time has totally expanded our understanding of cardiac anatomy,” Issenberg says.

3D echo also is much more helpful than 2D when there are multiple congenital malformations that have to be corrected simultaneously in the operating room. For example, a mitral valve may straddle a ventricular septal defect (VSD). With 2D echo, it is difficult to determine how much of the valve is over the VSD. Without this knowledge, a surgical patch over the VSD could interfere with the valve function. With 3D echo, surgeons can clearly see the movement of the leaflet of the mitral valve and determine how much—if any—interference the repair will cause, according to Issenberg. “The technology has evolved to the point where 3D TTE has to be integrated into our day-to-day evaluation of children with congenital heart diseases,” he says.

It is easy enough to post-process and manipulate the 3D images on the Philips’ machine or on a workstation with Philips’ proprietary software, but Issenberg does not like that he cannot download many of the post-processed images into the hospital PACS. “They end up in the resident archive on the workstation or remain within the platform of the echo machine,” he says. “It’s a matter of getting a DICOM standard and then having the archiving companies collaborate and adopt the standard.”


Frontier modality


John Erwin, senior staff cardiologist at Scott and White Memorial Hospital and Clinic in Temple, Texas, calls 3D echo “an exciting frontier, but still a frontier modality.” He cautions that if good images are not obtained with 2D echo, 3D imaging will not be helpful either. Erwin uses the GE Vivid 7 Dimension 3D TTE system, as well as the Philips 3D TEE system.

Erwin is convinced of the clinical benefits of real-time 3D TEE, particularly to determine the complex geometry of the mitral valve. “Over the last decade, we’ve been leaning towards repairing the mitral valve rather than replacing it. The 3D technique helps us tremendously with repair, which has a lower rate of morbidity and mortality,” he says.

Real-time 3D TEE allows cardiac surgeons to see how the two leaflets of the mitral valve interface with each other and determine with more certainty which scallop is having the most difficulty, or if the problem is related to the mitral annular plane. “Sometimes you see that the supporting fibrotic structure of the valve is dilating too much, which calls for a particular repair, a Dacron ring sewn into the annulus to improve the competency of the valve,” Erwin says.

Martin calls 3D TEE “revolutionary,” but also cautions to be careful with the first-generation product. “It’s not a simple plug and play,” he says. “One has to learn how to display and crop the complex anatomy.” Whereas 3D TTE has data points to help orient oneself in space, 3D TEE does not and getting oriented requires skill.

For the 3D modalities to take hold among rank-and-file cardiologists, there needs to be improvements in image quality and throughput, Martin says. Additionally, reimbursement will have an impact as well. “You want the most accurate diagnostic and prognostic information from an echo test, but you also have to realize the economics of throughput and reimbursement,” he says. “If there is a technique that is more labor intensive but reimburses inadequately, the only reason to adopt it is because it aids in your diagnosis and in your competitive stance.”