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,