Circulatory failure due to left-to-right shunts in children with congenital heart disease - Pathophysiology and therapeutic consequences

In children with large left-to-right shunts secondary to congenital heart d efects the imbalance between the pulmonary and systemic perfusion may lead to circulatory congestion with clinical signs similar to those of heart fai lure. The circulatory function in this state was evaluated by using the inv asive measurements performed during cardiac catheterisations in n = 64 youn g patients with ventricular septal defect (n = 56) or complete atrioventric ular septal defect (n = 8) aging 0.1 - 23.7 years (median 1.1 years). The m ean shunt ratio was Qp/Qs = 2-4 (range 1 - 8). With increasing shunt ratio the pulmonary perfusion raised (r = 0.84), but the systemic output dropped significantly (r = -0.77) while the total cardi ac output (Qp + Qs) increased slightly not exceeding 14 l/min/m(2). In infants, the systemic hypoperfusion affects the hemoglobin content: Hb = 14.9 - 1.01xQs, r = 0.63, p < 0.01. This may be due to the deminished oxyg en extraction reserve of 46%. With dropping systemic output, the vascular resistance increases and the me an aortic pressure (MAP) remains normal. The actual pressure values layed n ear to the curve of the normal aortic pressure calculated as MAP = QsxRs. T his pressure-flow-resistance diagram was used to interpret the effects of v asodilators established by 7 studies: ACE-inhibitors, Hydralazine, and Na-N itroprussid reduce the vascular resistance effectively but induce hypotensi on, because the systemic output fails to increase. In the chronic circulatory congestion secondary to a large intracardiac lef t-to-right shunt the pulmonary perfusion increases with the shunt ratio but the systemic output decreases and the total cardiac output is limited to a maximum of 14 l/min/m(2). In this state vasodilators cause systemic hypote nsion thus offering no acceptable therapeutic option.