In praise of ventricular assist devices—mechanical bridge to virtual crossmatch for the sensitized patient

Management of Stroke in Patients with Left Ventricular Assist Devices

INTRODUCTION

The number of patients with left ventricular assist devices (LVAD) is rapidly growing in industrialized countries. While cerebrovascular events comprise a significant complication, data on stroke etiology, clinical management and functional outcome are scarce.

METHODS

Consecutive LVAD patients with ischemic or hemorrhagic stroke receiving treatment at an university stroke center between 2010 and 2018 were included into an institutional registry. Clinical characteristics, causes, management and functional outcome of stroke occurring within this cohort are reported. Acceptable functional outcome was defined as mRS 0-3.

RESULTS

N = 30 acute strokes occurred in 20 patients (77% ischemic, 23% hemorrhagic, mean age 57 ± 13 years, 10% female, 8 patients (40%) had more than one event). 87% of all events happened with non-pulsatile devices, on average 9 (IQR 3-22) months after the implantation. All patients used oral anticoagulation with a Vitamin-K antagonist in combination with anti-platelets. The international normalized ratio (INR)-values were outside the therapeutic range in 39% of ischemic strokes and in 57% of hemorrhagic strokes. Ischemic strokes were predominantly of cardioembolic origin (92%) and of mild to moderate clinical severity (median NIHSS 6 (IQR 4-10). None qualified to receive intravenous thrombolysis or intra-arterial endovascular therapy. 61% of IS-patients showed an acceptable functional outcome after three months. 4/7 patients with hemorrhagic stroke received immediate reversal of anticoagulation without any thrombotic complications.

CONCLUSION

The majority of LVAD patients with ischemic stroke had an acceptable functional outcome after three months. Future clinical research is warranted to improve therapeutic strategies for acute care and stroke prevention.

LVAD implant as a bridge to heart transplantation is associated with allosensitization as measured by single antigen bead assay

BACKGROUND

Left ventricular assist devices (LVAD) as a bridge (BTT) to heart transplantation (HTX) may be limited by the formation of anti-human leukocyte antigen antibodies. Whether sensitization occurs with continuous axial flow LVAD implant as assessed by single antigen bead (SAB) assay is unknown.

METHODS

Cytotoxic panel-reactive antibody (PRA) and SAB assays were analyzed in HTX recipients undergoing LVAD implant as a BTT. Sensitization was defined as peak anti-human leukocyte antigen antibody values of more than 2000 mean fluorescence intensity because these values have been found to correlate with flow cytometric crossmatch results.

RESULTS

LVADs were implanted as BTT in 30 patients. There were 7% (2 of 30) of patients before LVAD implant and no patients after LVAD implant with PRA more than 10%. However, 20% (6 of 30) of patients before LVAD and 53% (16 of 30) after LVAD were sensitized as measured by SAB (P=0.024). At HTX, 47% (14 of 30) of patients remained sensitized. A positive virtual crossmatch was observed in 28% (4 of 14) of the sensitized patients at HTX. There was no difference between the sensitized and nonsensitized groups (P>0.4 for all) in usage of blood products (6411 vs. 6339 units) and time to HTX (28,663 vs. 25,748 days), and 1 year after HTX, there were no differences in rejection (total rejection score 0.30 vs. 0.37) and survival (93% vs. 88%).

CONCLUSION

Allosensitization after LVAD is common despite cytotoxic PRA being negative. One year after HTX, this sensitization does not translate into increased acute cellular or antibody-mediated rejection or reduced survival.

Occurrence of Fatal and Nonfatal Adverse Outcomes after Heart Transplantation in Patients with Pretransplant Noncytotoxic HLA Antibodies

HLA antibodies (HLA ab) in transplant candidates have been associated with poor outcome. However, clinical relevance of noncytotoxic antibodies after heart transplant (HT) is controversial. By using a Luminex-based HLA screening, we retested pretransplant sera from HT recipients testing negative for cytotoxic HLA ab and for prospective crossmatch. Out of the 173 consecutive patients assayed (52 ± 13y; 16% females; 47% ischemic etiology), 32 (18%) showed pretransplant HLA ab, and 12 (7%) tested positive against both class I and class II HLA. Recipients with any HLA ab had poorer survival than those without (65 ± 9 versus 82 ± 3%; P = 0.02), accounting for a doubled independent mortality risk (P = 0.04). In addition, HLA-ab detection was associated with increased prevalence of early graft failure (35 versus 15%; P = 0.05) and late cellular rejection (29 versus 11%; P = 0.03). Of the subgroup of 37 patients suspected for antibody mediated rejection (AMR), the 9 with pretransplant HLA ab were more likely to display pathological AMR grade 2 (P = 0.04). By an inexpensive, luminex-based, HLA-screening assay, we were able to detect non-cytotoxic HLA ab predicting fatal and nonfatal adverse outcomes after heart transplant. Allocation strategies and desensitization protocols need to be developed and prospectively tested in these patients.

How to deal with presensitized candidates for heart transplantation?

PURPOSE OF REVIEW

With increasing utilization of assist devices and adoption of calculated panel-reactive antibody (cPRA), the number of presensitized patients being listed for heart transplantation is increasing. An effort to standardize identification and management of such patients is paramount and recently initiated in the heart transplant community. The current review describes the basic concepts of presensitization and details the most relevant work including the latest advancements in this area.

RECENT FINDINGS

More sensitive techniques in identifying presensitized patients have posed challenges in understanding the clinical relevance and implications of such testing. cPRA has been shown to benefit presensitized heart transplant patients. De-sensitization strategies have never been studied in a large clinical trial setting but a combination of plasmapheresis and intravenous immunoglobulin has been shown to be beneficial in small studies. Long-term positive outcomes of de-sensitization have been recently reported. Newer agents like alemtuzumab, bortezomib and complement inhibitors have been reported in case reports and series with promising results as de-sensitization strategy.

SUMMARY

Data specific to strategies and therapies in heart transplantation are sparse and most knowledge stems from other organ transplantation. Consensus efforts to standardize care and also advance research in this area were initiated recently with hope for improving care for these patients.

Humoral immunity and antibody-mediated rejection in solid organ transplantation

The humoral arm of the immune system provides robust protection against extracellular pathogens via the production of antibody molecules that neutralize or facilitate the destruction of microorganisms. However, the humoral immune system also provides a significant barrier to solid organ transplantation due to the antibody-mediated recognition of non-self proteins and carbohydrates expressed on transplanted organs. Historically, the presence of donor-specific antibodies (DSA) that recognize donor HLA molecules, incompatible ABO blood group antigens and other endothelial or xenogeneic antigens was considered a contraindication to transplantation. However, recent advances in antibody testing and immunosuppressive therapies have made it possible to cross certain antibody barriers successfully. In this article, we review our current understanding of antibody-mediated processes in solid organ transplantation and discuss the clinically available treatment options for preventing and treating antibody-mediated rejection.