INFLUENCE OF AGE AND LOW AFTERLOAD ON THE STRESS-VELOCITY RELATION OFTHE LEFT-VENTRICLE

The relation between systolic meridional wall stress (WS) and velocity of circumferential fiber shortening (VcFc) is widely accepted as a pr eload-independent index of contractility, with a linear relation in mo st subjects older than 2 y. However, this relation seems to become dif ferent in infants and after administration of inotropic agents. We dec ided to study the nature of the stress-velocity relation by a cross-se ctional assessment of the influence of age, low afterload, and increas ed contractility. Study subjects were 30 healthy infants, 32 healthy o lder children, and 35 asymptomatic older children after completion of anthracycline chemotherapy. WS and VcFc at rest were studied in these infants and children. WS and VcFc were also studied after dobutamine i nfusion in both groups of older children. Linear regression analysis o f the stress-velocity relation showed parallel slopes between the olde r children at rest. and the post anthracycline children after dobutami ne. The regression lines between the infants at rest and the healthy o lder children after dobutamine were also parallel, but with a differen t and steeper slope compared with the former groups. When comparing th e stress-velocity relation of the overall population at rest with the overall population after dobutamine, the resulting regression lines ar e curvilinear and parallel, with a steeper slope at low afterload. The stress-velocity relation in infants and after dobutamine, resulting i n low afterload is different compared with the stress-velocity relatio n in older children at rest and at higher afterload. Data of the overa ll population at rest and after dobutamine suggest a curvilinear relat ion.