Distal anastomotic environment: the influence of intrinsic and extrinsic factors on flow structure

Abstract

Abstract Background Improved patency of the Miller cuff may be attributable to the modification of haemodynamics at the anastomosis inhibiting the accretion of myointimal hyperplasia. The influence of the distal anastomotic environment on flow patterns may therefore have important clinical significance. Methods Anastomotic models of Miller cuff, end-to-side (ETS) and precuffed grafts (Distaflo™, Impra, Tempe, AZ, USA) were perfused under physiological conditions. Visualization studies and Doppler colour flow mapping (P700, Philips Medical Systems, Reigate, UK) enabled qualitative flow analysis of the influence of anastomotic geometry, configuration and outflow distribution. Intraoperative flow distribution was measured with a Doppler transit time probe. Flow within in vivo precuffed grafts was analysed by means of colour flow mapping and velocity profiles. Results ETS anastomosis demonstrated a large area of flow separation at the graft toe, except when distal outflow approached 100 per cent, when laminar flow prevailed. The Miller cuff created a cohesive vortex within the proximal anastomosis, with reduced areas of flow separation. Outflow distribution had little effect upon the integrity of this vortex, although helical flow occurred in the distal vessel when proximal run-off was occluded. Cuff geometry, expressed as aspect ratio (cuff length: height) was important, with long and low cuffs demonstrating detrimental flow structures, including complex short-lived vortices and large areas of separation. The precuffed model produced a robust vortex, resistant to flow distribution. In vitro Doppler images of the vortex were reproduced accurately in 77 per cent of patients with precuffed grafts in situ (n = 32). Mean intraoperative flow distributions of 76 per cent distal: 24 per cent proximal in infragenicular grafts were significantly different from anticipated ratios of 50: 50 and 100: 0 (P < 0·001, single-sample t test). In above-knee grafts, however, distribution approached purely distal flow (mean 85: 15 versus 100: 0; P = 0·046). Conclusion Anastomotic flow structures are determined by the geometry of the anastomosis and the relative flow distribution proximally and distally in the recipient artery. A cuffed configuration of anastomosis is likely to be of most benefit when there is substantial flow proximally as well as distally in the run-off vessel, a situation that applies most often in infragenicular reconstruction. In addition, variable cuff geometry may detract from the full potential of the Miller cuff. A precuffed graft of optimum geometry may negate this concern, with the majority of patients demonstrating accurate replication of potentially beneficial flow patterns.