Improvements in the Cuff and Graft Interface with a Total Artificial Heart

Abstract

Research Question: Our initial question was: are there TAH-graft interface irregularities which could lead to blood flow disruption?

Background and Significance: Our objective was to evaluate design improvements of the inlet cuff-port and outlet graft-port interface of a Total Artificial Heart (TAH) on pannus formation. The orifice size, interface, blood flow path geometry, blood flow velocity, materials, surface finish, and hematologic parameters (such as anti-coagulants and anti-platelets) all contribute to the hemocompatibility of the TAH inflow and outflow. The focus of this work is the blood flow path geometry and material change. Practical application of this research involves progression of TAH as a method of treatment of potentially definitive treatment of heart failure, and as an extended bridge therapy until heart transplantation.

Materials and Methods: The performance of progressive inflow and outflow design iterations of a rotary total artificial heart operated in continuous and pulsatile outflow were evaluated in Corriente calves for durations of 30 days. Design modifications included a smoother blood flow port transition, geometrical improvements to the diameter and tangent angle to the polyurethane connector/pump interface, and methods of securing the connection including a titanium ring on the cuff with biospan rings and PEEK zip ties on both the cuffs and grafts. The graft flow path includes a circumferential hump which allows the titanium outflow port to seat against this hump and eliminate a void which could be a source of thrombus or emboli. Additionally, the cuff and port materials were changed. Subjects were 6-12 month old calves with weights ranging from 82 kg to 108 kg, while conditions such as pump flow, pressures and anticoagulants were closely monitored. The TAH was run in pulsatile mode for most of the studies. At necropsy, photos of the cuff and graft interface to the pump were analyzed and any tissue samples were sent for histological evaluation.

Results: A titanium ring on the cuff prevented the cuff from pulling away from the titanium port at the ostium and prevented the cuff from being pulled too far onto the port during surgical installation. Pannus formation at the interface of the cuff and graft to the titanium ports was graded from Absent (0) to Extreme (5), (Extreme equals >75% area reduction). In earlier design iterations, pannus formation at the inflow cuff or outflow graft interface ranged from (2) mild to (5) extreme. After implementing the design improvements, pannus was (0) absent in all inflow cuff interfaces. One graft that was not fully installed on the port had moderate buildup and the remainder had (0) absent to (1) minor at the outflow graft interface despite minimal anticoagulation.

Conclusion: Improvements to the inflow cuff/outflow graft-port interface significantly reduced pannus and thrombus formation in chronic animal implants treated with limited anticoagulation.