Background: We hypothesized that the splanchnic circulation protects against diastolic steal through a systemic-to-pulmonary arterial shunt by reducing its resistance. To test the hypothesis we compared the basal and postprandial mesenteric blood flow velocities and vascular resistance in infants after shunt palliation for their underlying cyanotic heart disease with those in nonshunted infants.
Methods: The basal and postprandial superior mesenteric arterial (SMA) time-average flow velocity (TAMV), end-diastolic flow velocity (EDFV), and relative resistance were assessed in 23 infants with congenital heart disease. The findings in the 9 shunted infants (group I) were compared with those in 14 nonshunted ones (group II).
Results: In group II, TAMV (0.25 +/- 0.07 versus 0.33 +/- 0.09 m/s, p < 0.001) and EDFV (0.08 +/- 0.04 versus 0.11 +/- 0.04 m/s, p = 0.003) increased, while SMA relative resistance decreased (297 +/- 121 versus 198 +/- 73 mm Hg/ms(-1), p < 0.001) postprandially. Similarly, in group I, TAMV (0.35 +/- 0.13 versus 0.48 +/- 0.19 m/s, p = 0.008) increased, while SMA relative resistance decreased (182 +/- 61 versus 116 +/- 38 mm Hg/ms(-1), p = 0.005) after feeding. However, whereas basal and postprandial diastolic flow was antegrade in group II, absent or retrograde diastolic flow was characteristic of group I (preprandial, -0.10 +/- 0.07 m/s; postprandial, -0.13 +/- 0.06 m/s). Furthermore, group I had significantly lower SMA relative resistance both before (p = 0.02) and after (p = 0.006) feeding.
Conclusions: Profound disturbance of splanchnic perfusion occurs in infants palliated with a systemic-to-pulmonary arterial shunt. Their basal and postprandial SMA diastolic blood flow is either absent or reversed. The lowering of basal and postprandial resistance of the splanchnic circulation probably represents an adaptive mechanism to counteract such diastolic steal.