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.