How 3-D Imaging Techniques Advanced Our Knowledge of Mitral Valve Disease
A new review paper looks at how 3-D echocardiography and other imaging methods have provided insights on the detailed physiology of this critical heart valve.
The mitral valve, also known as the bicuspid valve, consists of two flaps that lie between the left atrium and left ventricle of the heart. The most common type of mitral valve disease involves prolapse, a condition where the flaps bulge into the left atrium during the heart's contraction. This can cause blood to leak back into the atrium from the ventricle.
To better treat this condition, researchers are studying the detailed physiology of the mitral valve with the help of 3-D imaging techniques. In a review paper published Jan. 10 in Circulation: Cardiovascular Imaging, a team of physicians from the Mayo Clinic summarizes the new insights on this complex structure gathered by 3-D echocardiography, computed tomography, and cardiac magnetic resonance imaging.
“Before, there were measurements on the mitral valves of dogs and some low-quality measurements on humans -- it was low quality because we didn’t have the methods to do high-quality measurements,” said Maurice Enriquez-Sarano, a cardiologist at the Mayo Clinic and an author on the new paper. “But the technology of imaging has changed, and now with 3-D echocardiography, we can image the entire mitral valve.”
Previously, 2-D echocardiography could only visualize a single slice of the mitral valve. Later, a rotating transducer was used to create a 3-D reconstruction of the 2-D images, which identified the structure of the outer fibrous ring surrounding the valve -- the mitral annulus -- as having a saddle shape. However, in terms of diagnosing mitral valve disease, the reconstruction technique had a tendency to mislabel prolapse in patients who in fact had normal valves.
With the advent of 3-D echocardiography, each component in the mitral valve could be visualized and quantified in great detail. Researchers began to understand the patterns found in both humans with normal heart valves and those with mitral valve disease. Dynamic measurements of echocardiographic markers positioned along the mitral leaflets or annulus provide additional information, as physicians are able to witness the structural changes through the cardiac cycle.
“We have a much better understanding of the physiology of the normal valve, which has clinical implications for the treatment of mitral valve disease,” said Enriquez-Sarano.
In patients with degenerative mitral regurgitation, where blood leaks back into the atrium from the ventricle, the mitral annulus is enlarged, flattened, and more circular when compared to normal individuals. Dynamic 3-D measurements also show abnormalities in these patients, such as decreased annular area contraction and less of a pronounced saddle shape during systole, the phase of the heartbeat when the ventricles contract and pump blood into the arteries. While 3-D echocardiography remains the most cost-effective and simplest imaging modality, computed tomography and cardiac magnetic resonance imaging are alternatives that can also collect 3-D mitral valve data.
Alison Pouch, a research associate of radiology at the University of Pennsylvania who was not involved with the review paper, agrees that the mechanistic analysis of mitral valve disease has been quite rudimentary until recently.
“The morphological and functional distortions associated with degenerative mitral regurgitation are quite complex and challenging to characterize with conventional 2-D echocardiography alone,” said Pouch. “This complexity can make surgical planning quite challenging, especially for surgeons with less expertise in the subspecialized area of mitral valve repair.”
She believes that advanced image-based tools have the ability to identify patient-specific valve distortions and more individualized treatment plans. Because of the ease of use and portability of 3-D echocardiocraphy, Pouch predicts it will be the imaging modality most likely to lead these efforts.