The Length Versus Diameter Relationship and Radial Force Properties of the Amplatzer™ Vascular Plug Type IV: Observations for Oversizing.

BACKGROUND: In palliated single ventricle patients aortopulmonary collateralization is a cause for significant loss of cardiovascular efficiency. In larger vessels, device occlusion becomes an alternative to embolization with multiple coils. The physical characteristics of the Amplatzer ™ Vascular Plug Type IV (AVPIV) are potentially conducive to oversizing the device allowing coverage of a longer portion of vessel. Despite the widespread use of the AVPIV, little published data exists describing the behavior of the device as it is constrained in different vessel sizes. METHODS: 4-8 mm AVPIV devices were measured in glass tubing in diameters ranging from 1 to 8 mm internal diameter. Radial force was measured by constraining the devices to the desire diameters from 1 to 7 mm and measuring the force the device exerted to one of the constraining walls. This force vs. diameter relationship was evaluated for each device and compared across different devices. RESULTS: The devices range in length from 12.36 to 31.24 mm. The 4 mm device lengthened 3.44 mm from unconstrained to 1 mm diameter (12.36 to 15.80 mm), while the 8 mm AVP IV lengthened 14.74 mm from unconstrained to 1 mm diameter constraint (16.50-31.24 mm, 89% lengthening). The highest overall radial force (1.38 N), radial force at 50% compression (1.25 N), and average stiffness (0.95 N/mm) was found in the 5 mm diameter device. CONCLUSIONS: The AVP IV device has a reliable length for diameter relationship. A counterintuitive property of the AVP IV with regards to radial force for device size was found. The 5 mm AVPIV was found to exert the highest radial force and stiffness compared to the other devices. The 7 and 8 mm AVPIV devices were consistently found to exert less radial force. This property suggests that oversizing an AVP IV could be safe and effective, potentially decreasing total devices used, cost, and overall procedure time.

Hemolysis generation from a novel, linear positive displacement blood pump for cardiopulmonary bypass on a six kilogram piglet: a preliminary report.

BACKGROUND: Current blood pumps used for cardiopulmonary bypass generally fall into two different pump design categories; non-occlusive centrifugal pumps and occlusive, positive-displacement roller pumps. The amount of foreign surface area of extracorporeal circuits correlates with post-operative morbidity due to systemic inflammation, leading to a push for technology that reduces the amount of foreign surfaces. Current roller pumps are bulky and the tubing forms an arc in the pumping chamber (raceway), positioning the inlet 360 degrees from the outlet, making it very difficult to place the pump closer to the patient and to efficiently reduce tubing length. These challenges put existing roller pumps at a disadvantage for use in a compact cardiopulmonary bypass circuit. Centrifugal blood pumps are easier to incorporate into miniature circuit designs. However, the prime volumes of current centrifugal pump designs are large, especially for pediatric extracorporeal circuits where the prime volumes are too great to be of clinical value. METHOD: We describe a preliminary report on a novel, occlusive, linear, single-helix, positive-displacement blood pump which allows for decreased prime volume and surface area of the extracorporeal circuit. This new experimental pump design was used to perfuse a 6 kilogram piglet with a pediatric cardiopulmonary bypass circuit for two hours of continuous use. Blood samples were obtained every thirty minutes and assayed for plasma free hemolysis generation. CONCLUSIONS: The results from this initial experiment showed low plasma free hemoglobin generation and encourages the authors to further develop this concept.