Real-time 3D echo beats 2D in predicting cardiac events

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South Korean researchers have demonstrated that left atrial volume measured by real-time 3D transthoracic echo 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 way, according to the authors.

Il-Woo Suh, MD, and colleagues at the University of Ulsan College of Medicine in Seoul, prospectively evaluated the end-systolic, left atrial volume of 108 patients with 3D transthoracic echo (TTE) and 2D Doppler echo using the Sonos 7500 from Philips Medical Systems.
Investigators found that 2D significantly underestimated volume compared to 3D. They also found excellent interobserver agreement with the 3D approach, consistent with other smaller studies, which, they said, suggests that 3D is more objective and less operator dependent than 2D.
After an analysis of the data, researchers found that 3D volume measurements and age were independent predictors of cardiac events.

Suh and colleagues determined that 3D left atrial volume of 100 mL was the best cut-off value for predicting adverse clinical outcomes during one year.

“This cut-off value would be a useful prognostic parameter for assessing the risks of intermediate-term adverse events in patients with severe LV dysfunction,” they wrote.

However, they also cautioned that the cut-off value for those in Western countries might differ as the Korean population in the study tended to be smaller than typical Westerners.

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 American Society of Echocardiography 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.

Current real-time 3D ultrasound systems acquire partial data pyramids in a single heartbeat or full-volume pyramids 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, said 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.

Lang added that using a system that acquires a full-volume pyramid in a single heartbeat would allow the patient to be imaged without any breath holding, thereby avoiding artifacts through arrhythmias.

3D Echo-Measured Volume Predicts Cardiac Events

Event-free survival curves of patients with large and small initial left atrial volumes determined by real-time 3-dimensional echocardiography.