The Effect of Changing Afterload and Inotropic State on Inner and Outer Wall Thickening

To study the different behaviour of the inner (IH) and outer halves (OH) of left ventricular (LV) free wall during changing after load (40% increase in LV end-systolic pressure by aortic occlusion : AO) and inotropic state (dobutamine 3μg/kg/min iv (Dob), isoproterenol 0.1μg/kg/min iv (Isop), propranolol 2mg iv (Prop)), LV pressure (LVP : micromanometer), and transmural (TM) and OH wall thickness (WT : sonomicrometry) were measured in 11 anesthetized dogs. The IH-WT was led by subtracting OH-WT from TM-WT. Percent systolic wall thickening (%△WT) and fractional contribution (FC : a ratio of △WT of IH or OH to total △WT) were calculated. At rest, %△WT in TM, IH and OH were 22±1% (mean±SE), 33±3% and 13±2% (p<0.01), respectively. During AO, %△WT in IH was reduced to 22±2% (NS vs OH) and %△WT in OH was not changed (12±3%), while FC of IH (74±5%, at rest) and OH (29±4%, p<0.01 vs IH) were not significantly changed from control values by AO. During AO with Dob, %△WT (IH : 33±7%, OH : 16±5%) and FC (IH : 63±9%, OH : 33±7%) in each layer were not significantly reduced from the resting values after Dob. The same tendency was observed during AO with Isop. On the other hand, during AO after Prop, reduction of %△WT in IH (15±4%) was significantly greater than OH (12±3%, p<0.01), and FC in IH (51±13%) was not significantly different from OH (41±11%). Thus, non-uniformity of IH and OH wall thickening was maintained during increasing afterload with positive inotropic agents, while the non-uniformity was markedly attenuated by negative inotropic agent resulting from significant reduction of IH wall thickening.