AFTERLOAD REDUCTION BY HYDRALAZINE IN CHILDREN WITH A VENTRICULAR SEPTAL-DEFECT AS DETERMINED BY AORTIC INPUT IMPEDANCE

Hydralazine was administered at cardiac catheterization to eight child ren with a ventricular septal defect (age: 2.2-8.8 years), and the ext ent of afterload reduction was determined using aortic input impedance and wall stress. The pulmonary to systemic blood flow ratio decreased from 2.2 +/- 0.8 to 1.8 +/- 0.4 (p < 0.05) and the pulmonary systemic resistance ratio increased from 0.11 +/- 0.08 to 0.13 +/- 0.10 (p < 0 .05) after hydralazine administration. Hydralazine reduced mean aortic pressure and the amplitude of the late systolic peak of the aortic pr essure wave. Peak flow velocity in the descending aorta increased from 62 +/- 14 to 81 +/- 24 cm/sec (p < 0.05). Peripheral resistance decre ased significantly from 13.3 +/- 5.9 to 6.6 +/- 3.7 10(3) dyn sec/cm(3 ) (p < 0.05). The modulus of the first harmonic, indicating pulse wave reflection, decreased from 1196 +/- 575 to 815 +/- 382 dyn sec/cm(3) (p < 0.05). The characteristic impedance, indicating aortic stiffness, did not change. End-systolic wall stress decreased significantly from 54.4 +/- 16.7 to 34.8 +/- 10.2 g/cm2 (p < 0.01). Hydralazine acutely achieved afterload reduction by reducing both peripheral resistance an d pulse wave reflection, and increased stroke volume.