MR tagging identifies LV torsion-to-shortening ratio in AS

By Radiology Review

March 4, 2004 -- (Radiology Review) Researchers at Maastricht University in the Netherlands have discovered an increased left ventricular (LV) torsion-to-shortening ratio (TSR) in children with valvular aortic stenosis (AS).

According to Dr. Tammo Delhaas and colleagues, there was impaired perfusion of LV subendocardium in patients with valvular aortic stenosis, which caused reduced subendocardial fiber contraction and increased LV torsion. This underperfusion may eventually lead to subendocardial infarction and other life-threatening structural changes.

To further evaluate this hypothesis, six asymptomatic children with valvular AS, five pediatric volunteers, and nine adult volunteers were investigated with echocardiogrraphy, ECT, exercise test and MR tagging (MRT). The children with AS were found to have a moderate to severe AS, and no or mild aortic valve insufficiency on echocardiography.

MRT was performed with a 0.5-tesla scanner using ECG gating. "Two parallel short-axis cross-section, located at about 2 and 4 cm below the base of the left ventricle, were determined," they reported. "Multiphase, single-slice, cine series as well as MRT image series were acquired from both the basal and apical slice."

The first MRT images were obtained 20 ms after the ECG trigger and the second images were obtained 130-160ms later. "LV torsion and natural strain of the inner diameter were determined from measured tag displacements in two short-axis slices of the LV."

Results were recently published in Magnetic Resonance in Medicine. Maximum LV torsion was significantly greater in children with valvular aortic stenosis and LV shortening was slightly larger, they found.

"The TSR is pediatric aortic stenosis patients was significantly higher than in both control groups," they wrote. It was found that the TSR was around 40% higher compared with both pediatric and adult volunteers. According to Dr. Delhaas, ECG and echocardiography did not demonstrate the increased TSR found on MRT in patients with aortic stenosis.

Increase in left ventricular torsion-to-shortening ratio in children with valvular aortic stenosis
Delhaas, Tammo, et. al.
Department of pediatrics, Cardiovascular Research Institute Maastricht, Maastricht University and University Hospital, Maastricht, the Netherlands
Magn Reson Med 2004 January; 51:135-139

By Radiology Review
March 4, 2004

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