Are normative values for LV geometry and mass based on fundamental imaging valid with use of harmonic imaging?

Abstract

Background: Multiple studies have reported echocardiographically determined normal reference values for left ventricular (LV) mass (LVM) derived using fundamental imaging (FI). Modern ultrasound systems now use harmonic imaging (HI) because of the improved LV endomyocardial definition. However, the 2005 American Society of Echocardiography (ASE) recommendations noted that the applicability of the reference values to HI-derived measurements has not been established.

Methods: LVM and LV end-diastolic volume, diameter, and wall thickness were determined using HI in healthy subjects (n = 251), including normal-weight (NW) (body mass index < 25 kg/m², n = 149, 68% women) and otherwise healthy, overweight (OW) (body mass index ≥ 25 and <30 kg/m², n = 102, 41% women) groups. Measurements were compared with ASE-endorsed reference values. The agreement between FI and HI was determined in a prospective cohort of 51 subjects.

Results: Two-dimensional (2D) derived LV volumes were similar between NW and OW subjects, although M-mode (MM)-derived LV diameters were slightly greater in OW subjects. 2D and MM-derived LVM was greater in OW compared with NW subjects, including after adjustment by height or height²·⁷; however, indexing to body surface area eliminated these differences. The partition values for abnormal 2D and MM-derived LVM were generally greater in NW and OW subjects of both sexes compared with the ASE-endorsed values (except MM-derived LVM in NW men). However, there were no significant differences in LVM determined by HI compared with FI in a prospectively studied cohort.

Conclusions: Reference values for LVM derived from NW and OW cohorts are generally higher than the ASE-endorsed referenced values. The difference between NW and ASE-endorsed values is unlikely to result from the use of HI rather than FI, because there is excellent agreement between these two imaging modalities. This study emphasizes the need to update normal reference values to reflect modern imaging methods.

Figure

Bland-Altman analysis of differences and 95% confidence intervals of subjects evaluated by both fundamental and harmonic imaging of 2D-derived LV mass (panel A), M-mode measurements of LV end-diastolic diameter (panel B), septal thickness (panel C), posterior wall thickness (panel D), M-mode-derived LV mass (panel E), and M-mode-derived relative wall thickness (panel F). Positive values on the y-axis reflect larger values measured with FI.