Investigation of Aortic Flow Patterns after Aortic Valve Replacement: Establishment of a New Ex Vivo 4D Flow MRI Model

Objectives: Recent evidence has shown that aortic flow patterns may be altered after implantation of conventional prosthetic valves in aortic position. In this study we aimed to establish a new ex vivo model to investigate aortic flow patterns using 4D flow MRI. The purpose of this model is to evaluate the influence of surgical procedures of the aortic valve, aortic root and ascending aorta on aortic flow patterns.

Methods: Fresh swine hearts including the aorta were obtained from a local butcher. The left ventricular outflow (LVOT) tract was dissected and all branches of the aorta were ligated. The LVOT and descending aorta were anastomosed to an MRI compatible mock circulation loop. The mock circulation can be perfused under standardized conditions, i.e., reproducible stroke volume and heart rate. The loop was perfused using 36.6% glycerine-saline to simulate blood viscosity. MRI scans were conducted on a 3 Tesla scanner and data were post-processed using GT flow to visualize and analyze aortic flow with regard to sinus vortices and secondary flow patterns. In the first step, aortic flow patterns were analyzed before (n = 2) and after transverse aortotomy (n = 1). Transverse aortotomy was performed distal to the right coronary artery, extending toward the non-coronary sinus on the right side and extending transversely to the left side. Aortotomy was closed using 4–0 Prolene and the Blalock technique. By the time of the conference we plan to have evaluated the aortic flow after aortic valve replacement using the Ozaki procedure and established biological and mechanical prostheses in this model.

Result: Aortic flow patterns in the native aorta before aortotomy showed similar flow patterns to healthy volunteers with vortex formation in the sinus of Valsalva and laminar flow throughout the entire aorta without relevant secondary flow patterns. On the contrary, aortic flow patterns after transverse aortotomy and closure using the Blalock technique showed more vortices in the aorta than before aortotomy.

Conclusion: We established a new ex vivo model to investigate aortic flow patterns using 4D flow MRI. Our results suggest that aortic flow patterns may be altered by performing a surgical aortotomy and closure thereafter. In the next step, we plan to investigate the influence of aortic valve substitutes (Ozaki procedure and conventional aortic valve prostheses) on aortic flow patterns.