Patient 4 is a 57-year-old female with end-stage nonischemic cardiomyopathy who underwent placement of an HVAD with a 20 mm PTFE graft covering. Antithrombotic management was based on oral anticoagulation (coumadin) targeted to INR 2.5–3.5 and aspirin (81 mg/day). On a scheduled follow-up visit 29 months after implantation, she was noted to have multiple episodes of suboptimal flows (2.5–3.0 L/min) despite optimization of her blood pressure and volume status. This problem worsened with low-flow levels of 1.8 L/min. She was otherwise asymptomatic, and her INR levels remained in the therapeutic range (2.5–3.5). A chest CTA revealed evidence of thrombus between the PTFE covering and outflow graft. This finding was subsequently confirmed by IVUS during invasive angiography. The patient underwent successful percutaneous stenting of the outflow graft with 7 overlapping LD Mega 12 mm × 36 mm stents with improvement in LVAD flows (2.5–3.0 L/min). She remains asymptomatic and with no recurrent complications after 7 months of follow-up.
There is no published data on the frequency of PTFE graft usage during LVAD implantation. Surgeons at our center frequently applied a PTFE graft over the entire length of the LVAD outflow graft to reduce adhesion formation and facilitate sternal reentry when LVAD explant was anticipated. Although this application of PTFE appears to be effective in reducing adhesions and facilitating reoperations, complications secondary to the use of PTFE have not been previously reported. Our first recognition of this unusual cause of outflow graft obstruction was during pump exchange. Despite the initial suspicion for a thrombus within the outflow graft, intraoperative examination of the outflow graft revealed the presence of white thrombus formation between the outflow and PTFE grafts. We deduce that this mechanism of white thrombus formation between the outflow and PTFE grafts is analogous to type IV endoleakage with stent endografting of aortic aneurysms. Seepage of blood components through the endograft material into the aneurysm sac leads to gradual aneurysm enlargement. This is a well-recognized phenomenon in endovascular surgery and is attributed to the inherent porosity of the endograft. Similarly with LVADs, the outflow graft is constructed of a knitted polyethylene terephthalate material that has its own inherent porosity permitting seepage of blood components that are then trapped in between the impermeable PTFE graft, thereby forming an extravascular thrombus. Gradual enlargement of this thrombus eventually leads to outflow graft impingement. Interestingly, these cases all developed in patients with therapeutic INR levels and without underlying hypercoagulable disorders as determined by preimplant hypercoagulable evaluation which included testing for protein C, protein S, lupus anticoagulant, antithrombin 3, G6PD, factor VIII, factor V, factor V by polymerase chain reaction (PCR), and rheumatoid factor. On the other hand, HVAD patients were managed with low dose aspirin. Indeed, our program is using 81 mg in an attempt to reduce the incidence of Gastrointestinal (GI) bleeding at our institution. Nevertheless, we believe that this thrombotic complication can occur despite therapeutic anticoagulation because of the intrinsic thrombogenicity of the extravascular space where stagnation of blood flow occurs and a milieu of thrombotic tissue factors prevail.
Since many of our LVAD patients have been previously implanted with a PTFE covering, we anticipate that we will continue to encounter cases of outflow graft obstruction from PTFE usage. As such, we have preemptively created a registry of patients implanted with PTFE and have begun performing surveillance CTAs to detect outflow graft obstructions before the onset of symptoms. Furthermore, given the potential for this complication, we have abandoned the use of PTFE grafts during LVAD implantation. Although leaving the LVAD outflow grafts bare is associated with increased adhesion formation, the shift towards intrapericardial pump usage at our institution (Heartware HVAD and Heartmate 3) has permitted the outflow grafts to be routed posteriorly along the diaphragmatic pericardium, thereby reducing the anterior adhesions that are problematic with sternal reentry. Additionally, with increased implementation of the mini-thoracotomy approaches to Heartware HVAD implantation, the anterior pericardium remains intact, also minimizing troublesome anterior adhesions. As such, we no longer appreciate a need to cover the outflow grafts on initial LVAD implantation.
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