Background: Left ventricular (LV) global longitudinal strain (GLS) and circumferential strain (GCS), and left atrial (LA) strain (LAS) are indicators of poor clinical prognosis. However, it is unclear how they relate to each other and to LV and LA geometry. The aim was to clarify these relationships to inform clinical and research applications. Methods: Patients referred for cardiovascular magnetic resonance imaging were retrospectively identified. Univariable and multivariable linear regression models evaluated associations between GLS, GCS, LAS, LV mass, the volumes and dimensions of the LV and LA, and mitral annular plane systolic excursion (MAPSE). Results: In patients (n=66, median [interquartile range] age 62 [53-72] years, 82% male, LV ejection fraction 48 [34-56]%, range 6-69%), GLS associated with both GCS (R2=0.86, p<0.001) and LAS (R2=0.51, p<0.001), and LAS associated with GCS (R2=0.42, p<0.001). GLS, GCS, and LAS were all univariably associated with MAPSE, LV mass, and the volumes and dimensions of the LV and LA (p<0.001 for all). In multivariable analysis, GLS associated with MAPSE and LV length (R2=0.85, p<0.001); GCS with MAPSE, LV end-systolic volume, and LV mass (R2=0.80, p<0.001); and LAS with LA end-diastolic volume and MAPSE (R2=0.67, p<0.001). Conclusions: MAPSE and LV length alone can accurately estimate GLS. GLS and GCS provide similar information. LV and LA strains can be understood as geometrically coupled composite measures of MAPSE, and the size, function, and dimensions of the LV and LA. The composite of these geometrical relationships likely explains the excellent prognostic strength of strain measures.
