Influence of respiration on systemic venous and pulmonary arterial flow pattern after Fontan operation : direct intravascular doppler analysis

Abstract

Background: The flow pattern and efficiency in the Fontan circuit vary according to the surgical modification of the Fontan operation. Sporadic studies have reported that cardiac and respiratory cycles have important influence on Fontan circulation, the details concerning the role of each component and/or interactions of respiration and heart beats according to surgical modification has been poorly appreciated. We assessed the flow patterns in the systemic veins and pulmonary artery during different respiratory and cardiac cycles by novel technique of direct intravascular Doppler assessment to evaluate the influence of heart beats, respiratory efforts and technical modifications on established Fontan circulation. Method: We surveyed 40 patients who had undergone a Fontan operation; 8 with an atriopulmonary connection (APC group), 22 with a total cavopulmonary connection with lateral tunnel (LTF group), and 10 with a total cavopulmonary connection with extracardiac conduit (ECF group). We used direct intravenous Doppler echocardiography with the Flowmap System (Medtronics, Minneapolis, MN, USA) and obtained Doppler measurements at the superior vena cava (SVC), inferior vena cava (IVC), hepatic vein (HV), left pulmonary artery (LPA) and Right pulmonary artery (RPA). We compared the average peak velocity (APV), velocity-time integral (VTI), net antegrade flow integral (NAFI), mean flow rate (MFR = Q), pulsatility index (PI), respiratory variability index (RVI) and inspiration/expiration MFR (IEQ) at each vessels among the three Fontan groups. The RVI and IEQ were also compared among vessels in each group.Results: On the comparison of VTI, APV and NAFI, the values in the ECF group showed tendency toward increase than those in the APC group, especially during inspiratory phase at the HV and both PAs (P<0.05) . However, in systolic phase during expiration, the VTI and APV at the HV were larger in APC group than other 2 groups (P<0.05). The PIs were significantly increased at all vessels in the APC group, regardless of the respiratory cycle (P < 0.05). The RVIs of APC group were significantly reduced at all vessels compared to those of other groups (P < 0.05). On comparison of RVIs among 5 vessels, the HV showed significantly increased RVIs in all 3 groups. Conclusion: Our findings provide integrated information concerning the influence of respiration and heart beats on the established Fontan circulation and its difference according to surgical modifications. Blood flow profiles shows superior efficiency in patients undergone ECF operation than in those with APC Fontan operation, and the flow efficiency is augmented during inspiratory phase. APC is associated with higher pulsatile flow mainly attributed to heart beats which pertains potential benefit of less endothelial dysfunction in long-term. Higher respiratory dependency of flow in the HV in all groups suggests the need of surveillance on their long-term effect on hepatic function and splanchnic circulation in post-Fontan patient.