Abstract 15074: Application of the AHA 17 Segment Model: Evaluation of Relative Segmental Mass of the Left Ventricle by Cardiac MRI

Abstract

Background: The division of the left ventricle (LV) into 17 segments consisting of 6 basal, 6 mid, 4 apical and an apical cap has entered into widespread use. The individual segments are a priori considered to have equal mass, assigning the basal ring 35%, mid wall ring 35%, and apical ring and apex 30% of total left ventricular mass. Autopsy studies demonstrate relative masses of the basal, mid and apical rings at 42%, 36%, and 21% respectively. Segmental mass determination in vivo has not previously been evaluated. We defined the relative contribution to left ventricular mass of each of the 17 segments in normal volunteers using cardiac MRI imaging.

Methods: Steady-state free precession short axis cine stacks of the left ventricle containing approximately 13 slices were evaluated for mass in 27 normals. Relative mass of each segment was determined using multiple wall thickness measurements between endocardial and epicardial borders at end diastole. The apical cap was not included in the mass analysis due to limitations of this technique. Segments were defined using the AHA segmentation model using right ventricular anterior and inferior insertion points on a radial long axis with automated division into the 16 segments. Data was analyzed using CVI42 advanced cardiac imaging software.

Results: The mean LV mass was 129g. The mean relative mass of the basal ring (segments 1-6) was 28.9% (SD 6.65, 95%CI 26.3-31.5), of the mid ring (segments 7-12) was 46.8% (SD 3.31, 95% CI 45.5-48.1), and of the apical ring (segments 13-16) was 24.3% (SD 5.36, 95% CI 22.2-26.4). With exclusion of papillary muscles, the mean relative mass of the basal ring was 30.1% (SD 6.79, 95%CI 27.4-32.8), of the mid ring was 44.7% (SD 3.41, 95% CI 43.4-46.1), and of the apical ring was 25.1% (SD 5.24, 95% CI 23.1-27.2). The mean relative mass of the mid ring segments were significantly greater than the basal ring and the apical ring (both p<0.005). This difference persisted even with the papillary muscles excluded (both p<0.005).

Conclusion: When the 17-segment model was applied to the LV of normal hearts, the mid ventricular segments were found to have a higher relative mass than the basal and apical segments. These findings have implications when using the 17-segment model for myocardial jeopardy scoring.