New test for heart disease

Building on years of research on the way that blood flows through the heart valves, researchers from the California Institute of Technology and Oregon Health Science University have devised a new index for cardiac health based on a simple ultrasound test.

The index is now ready for use, and provides a new diagnostic tool for cardiologists in searching for the very early signs of certain heart diseases.

In the April 18 issue of the journal Proceedings of the National Academy of Sciences (PNAS), the researchers show how ultrasound imaging can be used to create an extremely detailed picture of the jet of blood as it squirts through the cardiac left ventricle. Previous work by the Caltech team members has shown that there is an ideal length-to-diameter ratio for jets of fluid passing through valves, which means that any variation from this ratio is indicative of a heart that pumping in an abnormal manner.

According to Mory Gharib, Liepmann Professor of Aeronautics and Bioengineering at Caltech, the ideal stroke ratio for cardiac function is four. This means that the length of a jet of fluid is ideal in power efficiency if it is four times the diameter of the valve it is traveling through. Since pioneering the study of vortices in biological fluid transport, Gharib has worked at applying it to biomedical applications. The PNAS article presents the latest breakthrough.

"Vortex formation defines the optimal output of the heart," says Gharib. "The size and shape of the vortex is a diagnostic tool because the information can reveal whether a patient's heart is healthy or if there are problems that will lead to enlargement."

In vivo and in vitro images taken by the Caltech team and Oregon collaborators show that a healthy heart tends to form vortex rings in the blood as it passes through the left ventricle. If the valve is too large in diameter, the blood tends not to form strong vortices, and if it is too narrow, the heart has much less energy efficiency and must work harder in order to produce the effect of a healthy heart. In either case, the result of a non-optimal vortex formation is indicative of a malfunctioning heart.

The index that the researchers have created is a guide for cardiologists, who will be able to use a noninvasive ultrasound machine to image the heart, just as obstetricians use ultrasound devices to image developing fetuses. Thus, the technique can be used when the patient is at rest, unlike treadmill tests that can themselves pose a certain danger because they require patients to exert themselves.

"We're not saying that this technique replaces traditional diagnostic tools, but that it is another way of confirming if something is wrong," Gharib adds.

"We want to give people an earlier warning of disease with a new method that is non-invasive and relatively inexpensive," says John Dabiri, an assistant professor of aeronautics and bioengineering at Caltech and coauthor of the paper.

Continuing in vitro studies led by Arash Kheradvar, a medical doctor and graduate student in bioengineering at Caltech, are focused on correlating the new diagnostic index with specific symptoms of heart failure.

In addition to Gharib, the lead author, and Dabiri and Kheradvar, the authors are Edmond Rambod, a former postdoctoral researcher at Caltech, and David J. Sahn, a cardiologist at Oregon Health Science University.

The title of the PNAS paper is "Optimal vortex formation as an index of cardiac health."