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A novel cardiac chamber volume model is proposed for the assessment of left ventricular mechanical dyssynchrony.
The tool is potentially useful for assessment of regional cardiac function and identification of mechanical dyssynchrony
on MRI. Dyssynchrony results typically from a contraction delay between one or more individual left ventricular
segments, which in turn leads to inefficient ventricular function and ultimately heart failure. Cardiac resynchronization
therapy has emerged as an electrical treatment of choice for heart failure patients with dyssynchrony. Prior MRI
techniques have relied on assessments of actual cardiac wall changes either using standard cine MR images or
specialized pulse sequences. In this abstract, we detail a semi-automated method that evaluates dyssynchrony based on
segmental volumetric analysis of the left ventricular (LV) chamber as illustrated on standard cine MR images. Twelve
sectors each were chosen for the basal and mid-ventricular slices and 8 sectors were chosen for apical slices for a total of
32 sectors. For each slice (i.e. basal, mid and apical), a systolic dyssynchrony index (SDI) was measured. SDI, a
parameter used for 3D echocardiographic analysis of dyssynchrony, was defined as the corrected standard deviation of
the time at which minimal volume is reached in each sector. The SDI measurement of a healthy volunteer was 3.54%. In
a patient with acute myocardial infarction, the SDI measurements 10.98%, 16.57% and 1.41% for basal, mid-ventricular
and apical LV slices, respectively. Based on published 3D echocardiogram reference threshold values, the patient's SDI
corresponds to moderate basal dysfunction, severe mid-ventricular dysfunction, and normal apical LV function, which
were confirmed on echocardiography. The LV chamber segmental volume analysis model and SDI is feasible using
standard cine MR data and may provide more reliable assessment of patients with dyssynchrony especially if the LV
myocardium is thin or if the MR images have spatial resolution insufficient for proper resolution of wall thickness-features problematic for dyssynchrony assessment using existing MR techniques.
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