Esmolol-induced regional wall motion abnormalities do not affect regional ventricular elastances

The effect of regional wall motion abnormalities (RWMA) on regional and global left ventricular (LV) elastances has not been defined. To induce RWMA, we infused esmolol (9 mg) into the left anterior descending coronary artery in eight anesthetized open-chest canine preparations. Global and regional stroke volumes and end-systolic pressure-volume relationships (LV conductance catheter) and pressure-length relationships (sonomicrometer crystals) were measured in dysfunctional (apical) and normal (basilar) LV regions at baseline, during esmolol infusion, and after treatment with a systemic dobutamine infusion (4 microg. kg(-1). min(-1)) and combined dobutamine-esmolol. Esmolol induced apical dyskinesis, as evidenced by reduced effective apical stroke volumes and stroke work, a parallel right-shift of the apical regional, global end-systolic pressure-volume relationships, and increased regional and global LV volumes (P < 0.05). However, global and regional elastances remained unchanged. Dobutamine increased global and apical regional elastances, but did not increase regional volumes. During the infusion of combined esmolol-dobutamine, apical elastance and volumes increased compared with baseline (P < 0.05), but apical regional stroke work decreased. Thus, esmolol-induced RWMA were associated with cardiac dilation but not with decreased regional or global elastances.

Regional and global elastances and maximal stroke volumes may not identify esmolol-induced left ventricular regional dysfunction in dogs. The primary effect of asynchrony of regional contraction is global cardiac dilation. Systemic dobutamine infusion increases regional and global left ventricular elastances but does not reverse regional wall motion abnormality-induced cardiac dilation.