Incorporating Ventricular Geometry into the Myocardial Work Index: A Proof-of-Concept Study

Background: Mechanical work is traditionally defined by the pressure-volume loop, but its invasive nature limits routine clinical use. The myocardial work index (MWI) has emerged as a non-invasive alternative, combining strain and estimated pressure to assess cardiac performance. However, MWI does not account for ventricular geometry and treats the ventricle as a dimensionless chamber. According to Laplace's law, wall stress and the true myocardial load depend on both pressure and ventricular geometry. Therefore, this study aims to develop and evaluate a geometry-informed myocardial work framework that provides a more physiologically representative estimate of mechanical energy expenditure. Method: In this proof-of-concept study, mechanical work was calculated using the one-fiber model of the left ventricle (LV) with Laplace-based geometric correction, integrating fiber stress over strain to derive the tension-adjusted myocardial work (TAMW) model. Strain was obtained from speckle tracking echocardiography along with pressure data while LV volumes and wall geometry were obtained from cardiac MRI. Two acute myocarditis patients with compact and dilated ventricles were analyzed, comparing cumulative and instantaneous work between MWI and TAMW. Performance gaps were quantified as the percentage difference in peak cumulative work. Results: Conventional MWI differed substantially between two cases (2576 vs. 1795 mmHg%, performance gap: 33.3%) whereas TAMW reduced this discrepancy to 7.5% (10,806 vs. 9789 mmHg%). TAMW also highlighted differences in temporal distribution of instantaneous work relative to MWI, reflecting the influence of ventricular geometry on contraction dynamics. Conclusions: TAMW incorporates the influence of geometry in the myocardial work framework revealing a more physiologically consistent reflection of myocardial effort across different ventricular geometries.