Mechanical Circulatory Support Devices: Is It Time to Focus on the Complications, Instead of Building Another New Pump?

In Vitro Assessment of Electric Currents Increasing the Effectiveness of Vancomycin Against Staphylococcus epidermidis Biofilms

Biofilms are communities of bacteria that can cause infections which are resistant to the immune system and antimicrobial treatments, posing a significant threat for patients with implantable and indwelling medical devices. The purpose of our research was to determine if utilizing specific parameters for electric currents in conjunction with antibiotics could effectively treat a highly resistant biofilm. Our study evaluated the impact of 16 μg/mL of vancomycin with or without 22 or 333 μA of direct electric current (DC) generated by stainless steel electrodes against 24-, 48-, and 72-h-old Staphylococcus epidermidis biofilms formed on titanium coupons. An increase in effectiveness of vancomycin was observed with the combination of 333 μA of electric current against 48-h-old biofilms (P value = 0.01) as well as in combination with 22 μA of electric current against 72-h-old biofilms (P value = 0.04); 333 μA of electric current showed the most significant impact on the effectiveness of vancomycin against S. epidermidis biofilms demonstrating a bioelectric effect previously not observed against this strain of bacteria.

Platelet activation after implantation of the Levitronix PediVAS in the ovine model

The Levitronix PediVAS is an extracorporeal magnetically levitated pediatric ventricular assist system with an optimal flow rate range of 0.3-1.5 L/min. The system is being tested in preclinical studies to assess hemodynamic performance and biocompatibility. The PediVAS was implanted in nine ovines for 30 days using either commercially available cannulae (n = 3) or customized Levitronix cannulae (n = 6). Blood biocompatibility in terms of circulating activated platelets was measured by flow cytometric assays to detect P-selectin. Platelet activation was further examined after exogenous agonist stimulation. Platelet activation increased after surgery and eventually returned to baseline in animal studies where minimal kidney infarcts were observed. Platelet activation remained elevated for the duration of the study in animals where a moderate number of kidney infarcts with or without thrombotic deposition in the cannulae were observed. When platelet activation did return to baseline, platelets appropriately responded to agonist stimulation, signifying conserved platelet function after PediVAS implant. Platelet activation returned to baseline in the majority of studies, representing a promising biocompatibility result for the Levitronix PediVAS.

Platelet activation in ovines undergoing sham surgery or implant of the second generation PediaFlow pediatric ventricular assist device

The PediaFlow pediatric ventricular assist device (VAD) is a magnetically levitated turbodynamic pump under development for circulatory support of small children with a targeted flow rate range of 0.3-1.5 L/min. As the design of this device is refined, ensuring high levels of blood biocompatibility is essential. In this study, we characterized platelet activation during the implantation and operation of a second generation prototype of the PediaFlow VAD (PF2) and also performed a series of surgical sham studies to examine purely surgical effects on platelet activation. In addition, a newly available monoclonal antibody was characterized and shown to be capable of quantifying ovine platelet activation. The PF2 was implanted in three chronic ovine experiments of 17, 30, and 70 days, while surgical sham procedures were performed in five ovines with 30-day monitoring. Blood biocompatibility in terms of circulating activated platelets was measured by flow cytometric assays with and without exogenous agonist stimulation. Platelet activation following sham surgery returned to baseline in approximately 2 weeks. Platelets in PF2-implanted ovines returned to baseline activation levels in all three animals and showed an ability to respond to agonist stimulation. Late-term platelet activation was observed in one animal corresponding with unexpected pump stoppages related to a manufacturing defect in the percutaneous cable. The results demonstrated encouraging platelet biocompatibility for the PF2 in that basal platelet activation was achieved early in the pump implant period. Furthermore, this first characterization of the effect of a major cardiothoracic procedure on temporal ovine platelet activation provides comparative data for future cardiovascular device evaluation in the ovine model.

Surface modification of a titanium alloy with a phospholipid polymer prepared by a plasma-induced grafting technique to improve surface thromboresistance

To improve the thromboresistance of a titanium alloy (TiAl(6)V(4)) surface which is currently utilized in several ventricular assist devices (VADs), a plasma-induced graft polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) was carried out and poly(MPC) (PMPC) chains were covalently attached onto a TiAl(6)V(4) surface by a plasma induced technique. Cleaned TiAl(6)V(4) surfaces were pretreated with H(2)O-vapor-plasma and silanated with 3-methacryloylpropyltrimethoxysilane (MPS). Next, a plasma-induced graft polymerization with MPC was performed after the surfaces were pretreated with Ar plasma. Surface compositions were verified by X-ray photoelectron spectroscopy (XPS). In vitro blood biocompatibility was evaluated by contacting the modified surfaces with ovine blood under continuous mixing. Bulk phase platelet activation was quantified by flow cytometric analysis, and surfaces were observed with scanning electron microscopy after blood contact. XPS data demonstrated successful modification of the TiAl(6)V(4) surfaces with PMPC as evidenced by increased N and P on modified surfaces. Platelet deposition was markedly reduced on the PMPC grafted surfaces and platelet activation in blood that contacted the PMPC-grafted samples was significantly reduced relative to the unmodified TiAl(6)V(4) and polystyrene control surfaces. Durability studies under continuously mixed water suggested no change in surface modification over a 1-month period. This modification strategy shows promise for further investigation as a means to reduce the thromboembolic risk associated with the metallic blood-contacting surfaces of VADs and other cardiovascular devices under development.

Total artificial heart--concepts and clinical use

End-stage congestive heart failure remains the leading cause of death in the United States. Despite advances in medical treatment, it also remains the most common reason for admission to the hospital. The gold standard of treatment for the failing heart, orthotopic heart transplantation, is limited by a shortage of donor hearts. There are also a significant number of patients who are not transplant candidates due to comorbid conditions and/or inability to tolerate immunosuppressive therapy. To meet the need for this latter group, the medical field has embraced ventricular assist device (VAD) therapy to extend survival and improve quality-of-life for the end-stage cardiac patient. This therapy, however, has been currently limited to the failing left ventricle and is still fraught with complications that limit long-term and widespread use. The total artificial heart, as currently available with two devices, is rapidly becoming the treatment of choice for biventricular failure.

Update on ventricular assist device management in the ICU

PURPOSE OF REVIEW

Mechanical circulatory support has a progressively increasing impact in the treatment of heart failure. The results of mechanical circulatory support are limited not only by the severity of the disease, which necessitated initiation of support, but also by the serious device-related adverse events. Optimized patient selection, improved patient management, and advanced device technology are interdependent key factors that contributed to the recently improved outcomes. The aim of this article is to summarize the current experience in application of mechanical circulatory support, focusing on the ICU management.

RECENT FINDINGS

Management should aim to prevent rather than treat serious complications and adverse events. Timing of intervention, optimization of the preimplantation patient status, patient and device management to ensure optimal hemodynamics, infection prevention, nutritional support, careful anticoagulation, and vigilance for early recognition and prompt treatment of 'minor' events before progression into major complications are essential elements of successful treatment.

SUMMARY

Critical patient care is a valuable adjunct to successful application of mechanical circulatory support, but it cannot counterbalance a late intervention, neither can it be fruitful in treating irreversible organ damage. Current management includes careful application of treatment protocols adjusted to recent experience, and also individualized care by a specialized team.