Changes in ventricular hemodynamics caused by a systemic-pulmonary shunt

Abstract

Systemic pulmonary shunts are both surgically created (Blalock-Taussig anastomosis) and obliterated (patent ductus arteriosus), but the effects of such a vascular communication on left ventricular hemodynamics have not been examined quantitatively. To study these effects, innominate arterial allografts were sutured between the descending thoracic aorta and the left main pulmonary artery in nine mongrel dogs. Left ventricular output (LVO) and shunt flow (SF) were monitored with electromagnetic flow probes while simultaneous phasic and mean pressures were recorded from the right atrium, aorta (AOP), and pulmonary artery. Data points (192) were analyzed while SF was varied between 0.02 and 5.5 liters/min using a variable-sized constricting band. Regression analysis showed increases ( P < 0.01) in LVO, stroke work (SW), and stroke volume (SV) in all dogs which were linearly related to SF ( r = 0.64–0.99). Increasing SF was also associated with decreases ( P < 0.01, r = 0.61–0.99) in resistance (RES) facing the left ventricle and in diastolic (D) AOP. To compensate for differences in allograft size and to quantify the effects of a patent shunt, the regression equations were used to compare the percentage change in all parameters at SF = 0 and SF = 1.5 liters/min. Increases occurred in SV (46 ± 20%), SW (32 ± 14%), and LVO (48 ± 21%), and decreases were present in DAOP (15 ± 12%) and RES (32 ± 13%). These data show that despite the decreases in pressure or the decreases in resistance facing the left ventricle in the presence of a systemic pulmonary shunt, a substantial increase in stroke work occurs. This supports early ligation of PDAs in premature infants who have minimal left ventricular reserve.