Yuan S M, Chang Q, Guo Y R, Guo J Q
Department of Surgery, Fuwai Heart Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, People's Republic of China.
Kaohsiung J Med Sci. 1998 May;14(5):258-65.
Valved homograft conduits play an important role in the right ventricular outflow tract (RVOT) reconstruction for the surgical treatment of complex congenital heart disease. An excellent immediate rather than long-term outcome could be obtained. The hemodynamics for late failure, however, remained unclear. In vitro pulsatile flow visualization was not conducted before. A simplified right heart duplicator system was set up and driven under physiologic conditions. Polystyrene of 0.18 mm in diameter was applied as the tracing particle. Flow characteristics of models of normal pulmonary circulation as well as pulmonary artery atresia with the RVOT reconstructed utilizing valved and non-valved extracardiac conduits were observed. Flow patterns in the normal pulmonary circulatory model were mainly of axial flow associated with small scope of flow disturbances. A single vortex in the right ventricle was noted in diastole. In the pulmonary artery atresia model, a couple of vortexes were found in the right ventricle, a secondary flow in the main pulmonary artery, and a stronger secondary flow than in the normal pulmonary circulatory model in the two branches in both systole and diastole. A secondary flow was found in the proximal, an axial flow was observed in the distal portion of the extracardiac conduit with normal bioprosthetic valves and a secondary flow was observed in the entire conduit with stenotic bioprosthetic valves. The secondary flow intensity became stronger with the development of the stenosis. Severe insufficiency occurred in the bileaflet ceramic tilting-disc prosthesis during the entire cardiac circle, i.e., the prosthesis was in a maximum open position. Severe reverse flow could be found in the extracardiac conduit in the deceleration phase. Concavity of the crank shaft was found by examination to be filled with tracing particles and the prosthesis became stuck. Model of RVOT reconstruction with non-valved conduit yielded reverse flow inside the extracardiac conduit as well. Secondary flow may occur in normal or diseased extracardiac conduit for RVOT reconstruction. If micro-thrombus of over 0.18 mm in diameter attached in the concave of the crank shaft of a bileaflet tilting-disc prosthesis under a condition of resistance as occurred in the present study, the prosthesis may become stuck. Model of RVOT reconstruction with non-valved extracardiac conduit yielded reverse flow inside the conduit, of which the flow pattern was of greater energy consumption. Thus, a non-valved conduit should be avoided in clinical practice as far as possible.
带瓣同种异体移植管道在复杂先天性心脏病手术治疗的右心室流出道（RVOT）重建中发挥着重要作用。可获得良好的即刻而非长期效果。然而，晚期失败的血流动力学仍不清楚。此前未进行体外脉动流可视化研究。建立了一个简化的右心复制系统，并在生理条件下驱动。使用直径为0.18毫米的聚苯乙烯作为示踪颗粒。观察了正常肺循环模型以及采用带瓣和无瓣心外管道重建RVOT的肺动脉闭锁模型的血流特性。正常肺循环模型中的血流模式主要为轴向流，伴有小范围的血流紊乱。舒张期右心室内可见单个涡流。在肺动脉闭锁模型中，右心室内发现一对涡流，主肺动脉内有二次流，在收缩期和舒张期两个分支中的二次流均比正常肺循环模型中的更强。在心外管道近端发现二次流，在带正常生物瓣膜的心外管道远端观察到轴向流，在带狭窄生物瓣膜的整个管道中观察到二次流。随着狭窄的发展，二次流强度增强。双叶陶瓷倾斜盘式假体在整个心动周期中出现严重反流，即假体处于最大开放位置。在减速期的心外管道中可发现严重逆流。检查发现曲轴凹面充满示踪颗粒，假体卡住。无瓣管道重建RVOT模型的心外管道内也产生逆流。正常或病变的心外管道用于RVOT重建时可能会出现二次流。如果在本研究中出现的阻力条件下，直径超过0.18毫米的微血栓附着在双叶倾斜盘式假体的曲轴凹面，假体可能会卡住。无瓣心外管道重建RVOT模型的心外管道内产生逆流，其流动模式能量消耗更大。因此，临床实践中应尽可能避免使用无瓣管道。
