Visualization of flow patterns from stents and stent-grafts in an in vitro flow-model

The authors determine flow characteristics and pressure gradients of different stents and stent grafts in an in vitro flow-model.

Five vascular stents (Memotherm, Cragg, two Palmaz P308, Strecker, and Wall) and one stent graft (Cragg EndoPro System 1), equal in length (60 mm) and diameter (10 mm), were deployed in a closed flow-model. The inner diameter of the tube measured 9 mm. Flow at 1.5 L/min, 6 L/min, and 10 L/min was simulated. Flow patterns were visualized by anionic particles illuminated with two Helium-Neon lasers. Laminary flow characteristics and pre-/poststent pressure gradients were determined in either expanded stent, 25% stenosis, or 50% stenosis.

Stent implantation induced a decrease of laminary flow compared with an unstented tube with and without concentric 25% stenosis (P < 0.01) at all flow rates and an increase of pressure gradients compared with an unstented tube for flow rates greater than 1.5 L/min (P < 0.01) (except for Cragg EndoPro System 1 stent, which revealed an increase of the pressure gradient at a flow rate of 1.5 L/min [P < 0.01]). Memotherm stent permitted maximum of laminary flow at all flow rates and stenoses (expanded: 79.50% at 1.5 L/min to 69.90% at 10 L/min; P < 0.01). Memotherm and Palmaz permitted lowest pressure gradients (P < 0.01). All of the endoprostheses demonstrated laminary flow at 50% stenosis.

The investigated stents and stent grafts showed different severity of flow disturbances and pressure gradients at different graded stenoses. Inadequate stent depolyment bears the risk of creating less laminary flow and pathologic pressure gradients. Because flow disturbances and pressure gradients may influence neointimal hyperplasia, stent design and completeness of stent unfolding are important regarding the appearance of postinterventional restenoses.