The use of mechanical circulatory assist devices is rapidly expanding. Patients in advanced stages of heart failure are implanted with support devices, allowing them to regain a fairly normal level of activity. Presently, more then 3,500 patients live with a left ventricular assist device (LVAD). The numbers of patients supported with biventricular assist devices or total artificial hearts is much smaller. The implantation of the total artificial heart is a quite extensive surgical procedure. Implantation of a left ventricular assist device, however, has become a routine intervention at experienced institutions. In both approaches, outcomes largely depend on the patient’s condition before surgery. As these patients are chronically ill, have significant heart failure, and have often secondary dysfunction of other organs, bleeding is a major concern during surgery. In addition, more and more patients with previous surgical interventions present for device implantation, posing another challenge in regards to bleeding complications. Patients often have been anticoagulated for prolonged periods because of stent implantation, valve replacements or arrhythmias. Patients may have been on milrinone therapy, which is known to cause platelet dysfunction. Finally, cardiac congestion with right sided failure leads to hepatic congestion, decreased hepatic function and dysfunction of the coagulation system.
As device implantation is usually performed using the heart lung machine, further impairment of the coagulation system is induced. The device itself, as it consists of artificial surfaces, leads to contact activation of the clotting system, which may manifest itself by consummation of fibrin products and platelets. Today’s devices exhibit a much more favourable biocompatibility compared to first-generation ventricular assist devices, however, contact activation and continuous mechanical trauma to blood components results in the destruction of cellular blood components as well as activation of platelets and still adds substantially to the challenge in managing bleeding problems during and after device implantation. Administration of systemic drugs promoting coagulation may cause clot formation in any area of the body but particularly inside the artificial heart pump. Pump thrombosis still forms a serious problem occurring in about 3–8 % of patients equipped with LVADs. Mostly this problem occurs early after implant, suggesting that medical interventions during the surgical procedure play a significant role in the event. Administration of intravenous agents, such as Factor VII can help with haemostasis in this high-risk group, but can pose additional complications including thrombotic events.1
A local haemostatic agent, that has no systemic effects, is extremely desirable in patients undergoing mechanical assist device implantation and transplantation surgery. In the past, we have been quite successful in leaving the chest open and packing the mediastinum with lap sponges after device implantation. This helps with local haemostasis and avoids right-heart compression.
Obviously, the administration of blood products and volume replacement in the situation of bleeding further puts significant stress on the right ventricle and should be avoided if possible. Therefore, local haemostatic measures are extremely valuable in this situation.2 Additionally, in the 2011 Society of Thoracic Surgeons update on blood conservation, topical haemostatic agents can provide local haemostasis at anastomotic sites and should be part of a multimodality blood management programme.3
Our approach to haemostasis, in this difficult patient population, relies on optimisation of the patient’s haemodynamic and metabolic parameters, the use of topical haemostatic agents and judicious use of delayed mediastinal closure.
Another concern in patients with implanted devices is infection. In particular, in these patients, whose life depends on the performance of the implanted heart assist device infection in the mediastinum would be a major catastrophe. Topical haemostats should not promote infection.
Cardiac Transplant Case
A 68-year-old male, post coronary bypass grafting, presented with progressive ischaemic cardiomyopathy and decompensated heart failure. He was listed urgently for heart transplantation and a donor organ became available. He underwent redo sternotomy and cardiectomy. There were multiple adhesions and intra-operative bleeding was severe and multiple blood product transfusion were required. Topical haemostatic agents were used on the surgical field including AristaAH® (Figure 1), which provided a thorough ‘covering’ of the surgical/mediastinal field. There was good local control of diffuse bleeding. The patient’s chest was kept open for 24 hours and he was returned to the operating room the following day for chest closure. He did well with no post-operative infection.
Discussion
Topical haemostats are important adjuncts that help control intra-operative bleeding. An ideal haemostat would be effective and rapidly metabolised, reducing the opportunity for post-operative fluid collection/swelling or infection. Our practice uses a number of haemostatic agents including oxidised cellulose and topical thrombin (bovine or recombinant human) with and without gelatin sponges. These agents have a long history of use but can be responsible for adverse advents and in the case of bovine derived thrombin, the induction of anti-bodies making future use potentially hazardous.
Fibrin sealants and polyethylene glycol polymer sealants are often used on anastomoses to assist in the control of higher pressure arterial bleeding. Sealants are very useful around the LVAD inflow and outflow cannula anastomoses. Glutaraldehyde and albumin based tissue adhesive is almost never used in our cases.
AristaAH (Microporous Polysaccharide Hemospheres) is a novel plant derived powdered haemostat with a history of use in cardiac surgery.4 This agent is used in almost all of our mechanical support implantation and cardiac transplant procedures. We apply this agent liberally. This agent provides rapid control of diffuse bleeding and has outstanding safety profile.
AristaAH (MPH) is an engineered microsphere formed from cross-linked polysaccharide chains. When applied to a bleeding wound it rapidly absorbs fluid and small molecular weight compounds. This molecular sieve action locally hyper-concentrates platelets and fibrinogen on the surface of the microsphere (Figure 2). The rapidly formed gel creates a mechanical barrier to bleeding and a fibrin clot rapidly forms. AristaAH is rapidly metabolised by amylase enzymes and is generally cleared in 48 hours. AristaAH may be used with cell salvage circuits as long as 40 micron filters are used.
Conclusion
The mechanical circulatory support and cardiac transplantation patient populations frequently have impaired coagulation profiles for many reasons. These patients frequently present with a prior cardiac surgical history and accompanying challenging surgical field. In our practice, we make use of a number of topical hemostats and surgical sealants, and delayed mediastinal closure to reduce blood transfusions and complications related to haemorrhage. Polyethylene glycol polymer sealant is used routinely around the LVAD cannulae. AristaAH, a novel polysaccharide haemostat, is an effective surgical adjunct with an exceptional safety record. It is used routinely in our mechanical support and cardiac transplantation procedures. It is important to note that we have not seen any infection in the mediastinum in our recent 100+ LVAD patients.
The use of local agents for haemostasis during LVAD implantation has shown very encouraging results. Application is easy and effective. Administration of substantial amounts of systemic blood products and clotting factors can be avoided or at least minimised. This has immediate positive consequences for right-heart performance after LVAD implantation or cardiac transplantation. Furthermore, the risk of sensitization through blood transfusion is reduced in patients implanted as bridge to transplant.