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Heart model provides realistic feedback

By Jennifer Durgin

Thub dub. Thub dub. A healthy heartuses a two-step motion—first relaxing, then contracting—to pump bloodthroughout the body. A failing heart,however, can't produce a strong, coordinated contraction—causing further dam-age to the organ and allowing blood topool in other parts of the body.

Problem: A technique called cardiac resynchronization therapy (CRT) can helpaddress this problem. But, so far, it has in-volved a lot of guesswork—guesswork that could be avoided, according to Justin Pearlman, M.D.

Pearlman, a Dartmouth cardiologist who's also trained as an engineer, and Heng Huang, a doctoral student in computer science, have created a computer-based model that represents "every littlebump and cranny" of an individual's heart, Pearlman says. Consisting of high-resolution MRI images, the model can simulate each heart's unique motion and the stresses and strains that every square inch experiences as it pumps.

Why is this important? In CRT, pace-maker leads—tiny wires—are placed on areas of the heart that are not contracting well. By transmitting small electrical impulses, the leads help coordinate the contraction. For the patient, successful CRT can mean the difference "between

Pearlman, left, and Huang view their 3D model.

being short of breath [while] lying in bed and being able to go shopping," Pearlman explains. But the key to optimizing the therapy lies in finding the best spots to place the leads.

Currently, cardiologists use two-dimensional or static three-dimensional reconstructions of patients' hearts to findthe best spots. But "measurements play avery small role" in that process, accordingto Pearlman. "With our model, we're measuring actual tissue properties, stresses andstrains," wall thickening,

ballistic motions, and many other factors. And Pearlman's model even allows physicians to try placing leads in various locations. So instead of "experimenting on patients," says Pearlman, "we can experiment on the computer copy of their heart."

System: Pearlman and Huang's model—which uses a new mathematical system that the two invented—is just one of several innovations by Pearlman. He's also developed ways to measure how much oxygen is getting to every part of the heart. "As a heart starts to fail," he explains, "tiny vessels can get plugged up and you can have microvascular disease. Clinically, we have no test for that." No test other than his, that is.

Word of Pearlman's inventions is spreading, and he is seeing more and more patients from Boston. He and Huang would like to continue testing and refining their heart model—as well as Pearlman's other creations—but they're worried that a gap in funding may halt their progress. "Frankly, we've been spending our energy on the model and the medicine," says Pearlman, "rather than on [a] sales pitch and traveling road show."

So they will now try to keep an eye on the flow of funding—as well as the flow of blood in ailing hearts.

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