Asymmetric prototypes for mitral valve replacement

The heart's valves, which guarantee the unidirectional flow of blood from one chamber to another, are asymmetrical. For example, the two flaps of the heart's mitral valve - which regulates blood flow between the left atrium and the left ventricle - vary in size by up to 70 percent. This arrangement, says fluid mechanicist Marija Vukicevic from the University of Trieste (now a researcher at Clemson University), naturally drives blood flow along the lateral wall of the ventricle; from there, blood takes a smooth turn creating a large vortex that redirects the blood toward the aorta (the main blood vessel of the heart), through which it exits out into the body.

Mechanical heart valves, however, are symmetric in design - with both flaps of a mitral valve replacement of identical size - and that, Vukicevic and colleagues have found, disrupts the flow of blood. "Blood flow in the left ventricle is characterized by a physiological vortex that disappears when a symmetric mechanical prosthesis is implanted," she says. With such prostheses, which are implanted into an estimated 60,000 patients each year in the United States, blood flows across the ventricular chamber then hits the opposite side instead of taking a turn, leading to a higher effort in the heart muscle and a disruption in its regulatory mechanism.

To see if a more naturally asymmetric design could improve blood flow, Vukicevic, along with Gianni Pedrizzetti of the University of Trieste and colleagues created aluminum models of asymmetric valves, similar in size to the valves of an adult human heart. The valves were tested in a mock ventricle, made of silicon, through which the researchers could visualize fluid flow. The pattern and rate of flow through the valves, the researchers found, closely matched that of a healthy heart. "We recommend that industries test asymmetric prototypes for mitral valve replacement," she says.

Vukicevic will discuss the findings in a talk at the APS Division of Fluid Dynamics Meeting, which will take place Nov. 20-22, 2011, at the Baltimore Convention Center in the historic waterfront district of Baltimore, Maryland.