Effect of fenestration on the sub-diaphragmatic venous hemodynamics in the total-cavopulmonary connection

To understand differences in the sub-diaphragmatic venous physiology between patients with fenestrated and non-fenestrated total-cavopulmonary connections (TCPC).

We studied the effects of respiration, retrograde flow, and gravity on the sub-diaphragmatic venous flows in 20 normal healthy volunteers (control), 25 Fontan patients with non-fenestrated TCPC, and 21 with fenestrated TCPC. Subhepatic inferior vena cava (IVC), hepatic vein (HV), and portal vein (PV) flow rates were measured with Doppler ultrasonography during inspiration and expiration in both supine and upright positions. The supine inspiratory-to-expiratory flow rate ratio was calculated to reflect the effect of respiration, the supine-to-upright flow rate ratio was calculated to assess the effect of gravity, and the magnitude of retrograde flow was evaluated with respect to total antegrade flow. Mean IVC, HV, and wedged hepatic venous (WHV) pressures were measured during cardiac catheterization in four TCPC patients before and after fenestration closure. The transhepatic venous pressure gradient (TVPG) was calculated as the difference between the HV and WHV pressure.

Compared with control, HV flow in TCPC was heavily dependent on respiration; this inspiratory capacity was greater in fenestrated than non-fenestrated subjects (inspiratory-to-expiratory flow ratio 1.7, 4.4, and 3.0, respectively P<0.001). Normal retrograde HV flow was diminished in TCPC patients, furthermore, fenestrated subjects had less flow reversal than non-fenestrated (retrograde as percent of antegrade flow 43, 19, and 30%, respectively P<0.001). Gravity decreased IVC and HV flows more in TCPC subjects than control, but this effect was not different between the two TCPC groups. Closure of the fenestration resulted in higher IVC and HV pressures (pre-closure versus post-closure pressures [mmHg]: 11.2 +/- 4.0 vs. 12.3 +/- 3.9, and 11.5 +/- 3.8 vs. 12.4 +/- 3.8, respectively P< or =0.001). The normal TVPG was reduced in fenestrated TCPC, and worsened after fenestration closure (0.9 +/- 0.3 and 0.7 +/- 0.4, respectively P < 0.04).

Fenestration of the inferior venous connection has important influences on sub-diaphragmatic venous return in TCPC patients. Although fenestration lowers venous pressures and partially restores TVPG, its beneficial effects on flow in TCPC patients are mediated primarily by an increase in inspiration-derived forward HV flow and reduced flow reversal. These observations suggest fenestration results in a more efficient and less congested splanchnic circulation in TCPC patients, and may have important implications in the early and late management of Fontan patients.