Modeling of asynchronous myocardial contraction by effective stroke volume analysis.

Abstract

Left ventricular (LV) regional wall motion abnormalities (RWMA) are not easily quantified. We describe a model for quantifying RWMA by referencing regional amplitude and phase angle changes to global LV systole in eight anesthetized, open-chest dogs. Regional and total LV volumes (conductance catheter), regional shortening (epicardial piezoelectric crystals), and LV pressure were measured before, during, and after transient esmolol-induced apical RWMA. Regional phase angle (alpha) was defined as the relative distance, measured in degrees, that regional minimal volume differs from global end-systole. We compared maximal stroke volume (SV) with effective SV (that portion of regional SV contributing to total LV SV). Regional effective SV was also calculated from our model as the product of cosine alpha and regional maximal SV. Esmolol delayed apical end-systolic alpha (14.3 degrees +/- 11.4 degrees versus 35.7 degrees +/- 8.0 degrees baseline versus esmolol, P < 0.05) and decreased apical effective SV (2.4 +/- 0.3 versus 1.7 +/- 0.3 mL, P < 0.05), while apical maximal SV and total LV SV were not altered. Piezoelectric crystal dimension changes mirrored regional SV changes. We conclude that effective SV and phase angle analysis are more sensitive measures of regional myocardial dysfunction when RWMA exist than are measures of maximal regional SV. In a dog model of regional myocardial dyskinesis induced by esmolol, effective regional stroke volume and phase angle analyses are more sensitive measures of regional myocardial dysfunction than measures of maximal regional stroke volume that do not account for phase shifts.