Platelet Function in Cardiopulmonary Bypass and Artificial Organs

Analysis of Platelet Function Testing in Children Receiving Aspirin for Antiplatelet Effects

Aspirin (ASA) remains the most common antiplatelet agent used in children. VerifyNow Aspirin Test® (VN) assesses platelet response to ASA, with therapeutic effect defined by the manufacturer as ≤ 549 aspirin reaction units (ARU). Single-center, observational, analysis of 195 children (< 18 years-old) who underwent first VN between 2015 and 2020. Primary outcome was proportion of patients with ASA biochemical resistance (> 549 ARU). Secondary outcomes included incidence of new clinical thrombotic and bleeding events during ≤ 6 months from VN in those who received ASA monotherapy (n = 113). Median age was 1.8 years. Common indications for ASA included cardiac anomalies or dysfunction (74.8%) and ischemic stroke (22.6%). Median ASA dose before VN was 4.6 mg/kg/day. Mean VN was 471 ARU. ASA biochemical resistance was detected in 14.4% (n = 28). Of 113 patients receiving ASA monotherapy, 14 (12.4%) had a thrombotic event and 2 (1.8%) had a bleeding event. Mean VN was significantly higher at initial testing in patients experiencing thrombotic event compared to those without thrombosis (516 vs 465 ARU, [95% CI: 9.8, 92.2], p = 0.02). Multivariable analysis identified initial VN ASA result ≥ 500 ARU at initial testing as the only significant independent risk factor for thrombosis (p < 0.01). VN testing identifies ASA biochemical resistance in 14.4% of children. VN ASA ≥ 500 ARU rather than ≥ 550 ARU at initial testing was independently associated with increased odds of thrombosis. Designated cut-off of 550 ARU for detecting platelet dysfunction by ASA may need reconsideration in children.

Platelet Count Trends and Prevalence of Heparin-Induced Thrombocytopenia in a Cohort of Extracorporeal Membrane Oxygenator Patients

OBJECTIVES

To assess the prevalence of heparin-induced thrombocytopenia and to study platelet count trends potentially suggestive of heparin-induced thrombocytopenia in a population of extracorporeal membrane oxygenator patients.

DESIGN

Retrospective cohort study.

SETTING

A total of 926-bed teaching hospital.

PATIENTS

Extracorporeal membrane oxygenator patients who survived longer than 48 hours from extracorporeal membrane oxygenator initiation between January 1, 2009, and December 31, 2013.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Demographic and clinical data were collected prospectively on all extracorporeal membrane oxygenator patients. Heparin-induced thrombocytopenia testing results and platelet count variables were obtained from the electronic medical record. We used our institutional algorithm to interpret the results of heparin-induced thrombocytopenia testing. Ninety-six extracorporeal membrane oxygenator patients met the inclusion criteria. Eight patients met the algorithm criteria for heparin-induced thrombocytopenia diagnosis and seven of those had documented thromboembolic event while on extracorporeal membrane oxygenator (prevalence of heparin-induced thrombocytopenia and heparin-induced thrombocytopenia related thrombosis, 8.3 and 7.3, respectively). Heparin-induced thrombocytopenia positive patients were younger; all underwent venoarterial extracorporeal membrane oxygenator; spent more hours on extracorporeal membrane oxygenator; had significantly higher heparin-induced thrombocytopenia enzyme-linked immunosorbent assays optical density; had a higher prevalence of thromboembolic events and reached platelet count nadir later. There was no difference in mortality between heparin-induced thrombocytopenia positive and negative patients. Comparison of platelet count trends revealed that there was no statistically significant difference between the predefined study groups.

CONCLUSIONS

Prevalence of heparin-induced thrombocytopenia and heparin-induced thrombocytopenia-related thrombosis among extracorporeal membrane oxygenator patients at our institution is relatively high. Using platelet count trends to guide decision to test for heparin-induced thrombocytopenia is not an optimal strategy in extracorporeal membrane oxygenator patients. Without a validated pretest probability clinical score, serosurveillance in a defined high-risk group of extracorporeal membrane oxygenator patients may be needed.

Effects of circuit albumin coating on coagulation and inflammatory response for patients receiving aortic arch replacement: a randomized controlled trial

OBJECTIVE

To investigate whether human serum albumin coating before cardiopulmonary bypass (CPB) could improve platelet function and hemostasis and mitigate the inflammatory response among patients receiving aortic arch replacement with deep hypothermic circulatory arrest (DHCA).

METHODS

Sixty patients were included and randomized into two groups: the Control Group (CG, receiving 40 g human albumin 5 minutes after the initiation of CPB) and the Study Group (SG, circulating the prime with 40 g albumin for 5 minutes before CPB). Rapid thromboelastography, complete blood count, coagulation tests and cytokines (IL-1, IL-6, IL-10, TNF-α and PAF) were measured at two intervals: after anesthesia induction and before CPB (T1) and 10 minutes after heparin reversal before any blood product transfusion (T2).

RESULTS

Compared with T1, the fibrinogen and MA levels in both groups reduced significantly after heparin reversal and fell within the normal range for most patients. The platelet count reduction (ΔPLT) in the Study Group was significantly less than in the Control Group (p=0.031). Despite the inflammatory factor levels increasing after CPB (p<0.001), no differences were found between the Control Group and the Study Group. Fewer red blood cells were given in the Study Group, but this was not significant (p=0.05).

CONCLUSION

Most patients receiving aortic arch replacement with DHCA have normal platelet function and fibrinogen levels after heparin reversal. Albumin coating before CPB may mitigate the platelet count reduction, but not platelet dysfunction. There is a trend that the patients treated with albumin coating received less red blood cell transfusions.

Ambient hemolysis and activation of coagulation is different between HeartMate II and HeartWare left ventricular assist devices

BACKGROUND

Thromboembolic and bleeding events in patients with a left ventricular assist device (LVAD) are still a major cause of complications. Therefore, the balance between anti-coagulant and pro-coagulant factors needs to be tightly controlled. The principle hypothesis of this study is that different pump designs may have an effect on hemolysis and activation of the coagulation system. Referring to this, the HeartMate II (HMII; Thoratec Corp, Pleasanton, CA) and the HeartWare HVAD (HeartWare International Inc, Framingham, MA) were investigated.

METHODS

For 20 patients with LVAD support (n = 10 each), plasma coagulation, full blood count, and clinical chemistry parameters were measured. Platelet function was monitored using platelet aggregometry, platelet function analyzer-100 system ( Siemens, Marburg, Germany), vasodilator-stimulated phosphoprotein phosphorylation assay, immature platelet fraction, platelet-derived microparticles, and von Willebrand diagnostic.

RESULTS

Acquired von Willebrand syndrome could be detected in all patients. Signs of hemolysis, as measured by lactate dehydrogenase levels (mean, 470 U/liter HMII, 250 U/liter HVAD; p < 0.001), were more pronounced in the HMII patients. In contrast, D-dimer analysis indicated a significantly higher activation of the coagulation system in HVAD patients (mean, 0.94 mg/liter HMII, 2.01 mg/liter HVAD; p < 0.01). The efficacy of anti-platelet therapy using clopidogrel was not sufficient in more than 50% of the patients.

CONCLUSIONS

Our results support the finding that all patients with rotary blood pumps suffered from von Willebrand syndrome. In addition, a distinct footprint of effects on hemolysis and the coagulation system can be attributed to different devices. As a consequence, the individual status of the coagulation system needs to be controlled in long-term patients.

Biocompatibility assessment of a long-term wearable artificial pump-lung in sheep

The purpose of this study was to assess the biocompatibility of a newly developed long-term wearable artificial pump-lung (APL) in a clinically relevant ovine animal model. The wearable APL device was implanted in five sheep through left thoracotomy. The device was connected between the right atrium and pulmonary artery and evaluated for 30 days. Three sheep were used as the sham control. Platelet activation was assessed by measuring platelet surface P-selectin (CD62P) expression with flow cytometry and plasma soluble P-selectin with an enzyme-linked immunosorbent assay. Thrombotic deposition on the device components and hollow fiber membranes were analyzed with digital imaging and scanning electron microscopy. Surface P-selectin of the APL and sham groups changed significantly over the study period, but without significant differences between the two groups. Soluble P-selectin for the two groups peaked in the first 24 h after the surgery. Soluble P-selectin of the APL group remained slightly elevated over the study period compared to the presurgical baseline value and was slightly higher compared to that of the sham group. Plasma free hemoglobin remained in the normal ranges in all the animals. In spite of the surgery-related alteration in laboratory tests and elevation of platelet activation status, the APL devices in all the animals functioned normally (oxygen transfer and blood pumping) during the 30-day study period. The device flow path and membrane surface were free of gross thrombus. Electron microscopy images showed only scattered thrombi on the fibers (membrane surface and weft). In summary, the APL exhibited excellent biocompatibility. Two forms of platelet activation, surgery-related and device-induced, in the animals implanted with the wearable APL were observed. The limited device-induced platelet activation did not cause gross thrombosis and impair the long-term device performance.

Platelet activity before and after coronary artery bypass grafting

The normal response of the platelet can be altered either by increased pro-aggregatory stimuli or by diminished anti-aggregatory substances. Increased platelet activation occurs in the cardiovascular disease states of stable angina pectoris and acute coronary syndromes. Also, cardiac surgery involving cardiopulmonary bypass is associated with extensive contact between blood and synthetic surfaces and leads to a strong activation of platelets. Using light transmission aggregometry method, we tested platelet sensitivity to ADP and spontaneous activity in the platelet-rich plasma of patients before and after coronary artery bypass grafting (CABG). The median values of EC50 for ADP were significantly lower at days 3 and 5 after surgery (0.33 and 0.37 microM, respectively) than before surgery (0.65 microM). The medians percentages of spontaneous platelet aggregation were significantly higher after than before surgery (16 and 15% at days 3 and 5 after surgery, respectively, vs. 5% before surgery). Thus, there is a significant increase of spontaneous platelet aggregation and platelet hyperreactivity to ADP in patients after CABG compared with those before surgery.

Percutaneous Implantation of the CoreValve Self-Expanding Valve Prosthesis in High-Risk Patients With Aortic Valve Disease

BACKGROUND

The morbidity and mortality of surgical aortic valve replacement are increased in elderly patients with multiple high-risk comorbid conditions. Therefore, a prospective, single-center, nonrandomized study was performed in high-risk patients with aortic valve disease to evaluate the feasibility and safety of percutaneous implantation of a novel self-expanding aortic valve bioprosthesis (CoreValve).

METHODS AND RESULTS

Symptomatic high-risk patients with an aortic valve area <1 cm2 were considered for enrollment. CoreValve implantation was performed under general anesthesia with extracorporeal support using the retrograde approach. Clinical follow-up and transthoracic echocardiography were performed after the procedure and at days 15 and 30 after device implantation to evaluate short-term patient and device outcomes. A total of 25 patients with symptomatic aortic valve stenosis (mean gradient before implantation, 44.2+/-10.8 mm Hg) and multiple comorbidities (median logistic EuroScore, 11.0%) were enrolled. Device success and procedural success were achieved in 22 (88%) and 21 (84%) patients, respectively. Successful device implantation resulted in a marked reduction in the aortic valve gradients (mean gradient after implantation, 12.4+/-3.0 mm Hg; P<0.0001). The mean aortic regurgitation grade was unchanged. Major in-hospital cardiovascular and cerebral events occurred in 8 patients (32%), including mortality in 5 patients (20%). Among 18 patients with device success surviving to discharge, no adverse events occurred within 30 days after leaving the hospital.

CONCLUSIONS

Percutaneous implantation of the self-expanding CoreValve aortic valve prosthesis in high-risk patients with aortic stenosis with or without aortic regurgitation is feasible and, when successful, results in marked hemodynamic and clinical improvement.

A Prospective, Randomized Platelet-Function Study of Heparinized Oxygenators and Cardiotomy Suction

OBJECTIVE

The purpose of this study was to determine if substitution of a heparin-coated oxygenator and salvaged autologous blood for cardiotomy suction would improve platelet function.

DESIGN

A prospective, randomized trial.

SETTING

A large academic medical center.

PARTICIPANTS

Sixty adult patients undergoing coronary artery bypass graft surgery with cardiopulmonary bypass (CPB).

INTERVENTIONS

Patients were randomized into 1 of 4 groups in a 2 x 2 factorial design by oxygenator (heparinized v nonheparinized) and blood salvage during CPB (cardiotomy suction v salvaged autologous blood).

MEASUREMENTS AND MAIN RESULTS

Primary outcome measures were platelet function, glass-bead retention, platelet dense-body adenosine triphosphate secretion, platelet-rich plasma (PRP) aggregometry, Plateletworks platelet-function analyzer (Helena Laboratories Corp, Allen Park, MI), and platelet count. Secondary outcome measures were chest-tube drainage and allogeneic blood transfusion requirements. All platelet-function tests except thrombin-receptor activator peptide-induced PRP aggregometry showed a reduction in platelet function during and immediately after CPB (all p < 0.05). The only statistically significant difference in platelet-function tests between the groups was the glass-bead assay at 5 minutes before discontinuation of CPB (p < 0.05). This difference resolved 10 minutes after protamine administration. There were no differences between the groups in the amount of blood transfused, chest-tube drainage, and routine laboratory test results.

CONCLUSIONS

The authors concluded that the effects of these changes to the CPB circuit were small and inconsequential in this cohort of patients.

Aprotinin restores the adhesive capacity of dysfunctional platelets

The post-operative coagulopathy associated with cardiopulmonary bypass (CPB) is known to be predominantly related to platelet dysfunction. The use of the serine protease inhibitor aprotinin dramatically reduces CPB associated hemorrhage and is thought to act primarily through the inhibition of plasmin without directly influencing platelets. Our data indicate that there is a direct effect of aprotinin on platelet adhesion, which has not been previously reported. We found that when aprotinin was added to blood samples with poorly adhesive platelets, platelet adhesion significantly increased as measured by the percent coverage of denuded arterial segments in the Baumgartner perfusion chamber. In preliminary experiments using expired platelet concentrates or fresh whole blood, the addition of aprotinin induced a positive increase of 22+/-7.5 and 14+/-6.2 percentage point in platelet adhesion, respectively. A simulated CPB model that recirculated a unit of anticoagulated whole blood for 2 h was used (n=14) to induce a platelet adhesion defect similar to that seen in clinical CPB. At initiation of recirculation, platelet adhesion was 55+/-9.5% but dropped to 13+6.5% coverage after 2 h simulated CPB. The addition of aprotinin to the post-recirculation samples induced a significant restoration of platelet adhesion back to 38+/-11% coverage. When epsilon amino-caproic acid with soybean trypsin inhibitor was added to post recirculation samples, there was no similar effect on adhesion scores. To compare these findings with surgical CPB, we collected one blood sample at the beginning and two at the end of CPB from each of seven open-heart patients. Aprotinin was added to one of each of the post-CPB samples. Platelet adhesion at the onset of surgical CPB was only 39+/-11% in this patient group but dropped to 7+/-7% by the end. Similar to the model, the addition of aprotinin post-CPB restored adhesion to 29+/-11%. These results suggest some action of aprotinin other than its antiplasmin effect, and that platelet adhesion in general can be promoted by aprotinin.

Biocompatibility of Trillium Biopassive Surface-coated oxygenator versus uncoated oxygenator during cardiopulmonary bypass

OBJECTIVE

To determine if the Trillium Biopassive Surface (Medtronic Cardiopulmonary, Minneapolis, MN) coating added to the cardiopulmonary bypass oxygenator reduces inflammatory mediators, blood loss, and transfusion requirements.

DESIGN

Prospective, randomized, and blinded human trial.

SETTING

Tertiary care academic medical center.

PARTICIPANTS

Thirty adult patients undergoing elective coronary artery bypass graft surgery.

INTERVENTIONS

Patients received visually identical coated or uncoated oxygenators.

MEASUREMENTS AND MAIN RESULTS

Hemoglobin, hematocrit, leukocyte count, platelet count, terminal complement complex, complement activation, myeloperoxidase, beta-thromboglobulin, prothrombin fragment 1.2, plasmin-antiplasmin, heparin concentration, activated coagulation time, and fibrinogen concentration were measured. Blood loss and blood product usage were recorded. In both groups, there were significant inflammatory alterations with the initiation of cardiopulmonary bypass. In the postprotamine samples, the coated oxygenator group had small but significant increases in hemoglobin, hematocrit, and leukocyte count. There were no differences in inflammatory mediators, blood loss, or transfusion requirements between the coated and uncoated groups.

CONCLUSION

This human trial of Trillium Biopassive Surface-coated oxygenators did not show clinical benefits or clinically important biochemical results.

Platelet glass bead retention predicts bleeding after cardiac surgery

OBJECTIVE

To determine if the platelet glass bead retention assay can predict bleeding after cardiac surgery.

DESIGN

Prospective, observational study.

SETTING

Large, tertiary care, academic medical center.

PARTICIPANTS

Forty-three adult patients scheduled to undergo elective cardiac surgery employing cardiopulmonary bypass (CPB).

MEASUREMENTS AND MAIN RESULTS

Whole blood samples were observed for platelet count, prothrombin time, and platelet (glass bead) retention assay. The platelet retention and prothrombin times were independent univariant and multivariant predictors of bleeding after CPB (r = 0.554, p = 0.0002 and r = 0.655, p = 0.00001).

CONCLUSION

The platelet glass bead retention assay measures dynamic platelet function and is sensitive to the CPB-induced adhesion and aggregation defect and correlates with postoperative blood loss. Modification of this platelet function assay used with the prothrombin time may provide a simple and effective diagnostic approach to bleeding after CPB.

Frequency, risk factors, and clinical outcomes of left ventricular assist device-associated ventricular thrombus

A retrospective, transesophageal study of 51 consecutive patients receiving a left ventricular (LV) assist device (AD) over a 2-year period showed that LVAD-associated LV thrombosis (16%) was predicted by acute myocardial infarction, atrial cannulation, and postimplantation bleeding, and was associated with a fourfold increased risk of stroke compared with patients without thrombosis. LV cannulation, when using short-term LVADs, may decrease the incidence of LV thrombosis, and early transition to Heartmate-LVAD support may improve outcome.

Changes in platelet activation associated with left ventricular assist system placement

BACKGROUND

Thromboembolic and hemorrhagic complications are common in patients after left ventricular assist system (LVAS) placement. Platelet physiology may be involved in these complications.

METHODS

Using flow cytometry, expression of CD62P and CD63 were analyzed as markers of platelet activation. Binding of annexin V was analyzed to determine platelet membrane asymmetry. Results from two patients who received a Novacor LVAS as a bridge to transplantation are reported.

RESULTS

Patients' platelets showed increased CD62P and CD63 expression, yet annexin V binding was not increased. They also revealed suppression of thrombin activation following LVAS placement, which approached normal after transplantation. Heparin suppressed thrombin activation, whereas aspirin or dipyridamole did not. Suppression was attenuated by protamine sulfate and heparinase.

CONCLUSIONS

Following LVAS placement, resting platelets demonstrate increased expression of activation markers.

Biocompatibility of a new cell separator studied by flow cytometry: analyses of platelet antigens during apheresis and storage

BACKGROUND

Alterations of platelet antigens are known to occur during cytapheresis and storage. These changes have been shown to be dependent on the biomaterials, techniques, and devices used. In this study, the influence of a new cell separator (AMICUS) and storage container (PL-2410) on platelet glycoproteins was analyzed.

STUDY DESIGN AND METHODS

During plateletpheresis and storage, the levels of platelet glycoproteins and binding of fibrinogen were determined by flow cytometry.

RESULTS

During apheresis, mean channel fluorescence intensity of CD41 a did not change significantly (p = 0.06). A small increase was evident in CD42b mean channel fluorescence intensity, which rose from a baseline level of 178.6 +/- 68.3 to 231.5 +/- 97.9 at the end of the procedure (p<0.05); in CD62p-positive platelets, which increased from 2.0 +/- 0.9 percent to 9.9 +/- 3.9 percent (p<0.05); in CD63-positive platelets, which increased from 1.7 +/- 0.7 percent to 7.9 +/- 2.6 percent (p<0.05); and in the binding of fibrinogen, which increased from 1.9 +/- 0.8 percent positive platelets to 10.5 +/- 2.6 percent (p<0.05). During storage, the mean channel fluorescence intensity of CD41a and CD42b, the percentage of CD62p- and CD63-positive platelets, and the binding of fibrinogen to platelets showed no significant change.

CONCLUSION

These studies show that alterations in platelet antigens and platelet activation occur to a small degree during apheresis and storage. These findings demonstrate generally good biocompatibility of this new cell separator.

Platelets and cardiopulmonary bypass

Exposure of blood to an extracorporeal circulation, such as CPB, causes a variety of physiological responses. Haematological derangements are just one of many potential dangers to the patient who undergoes CPB. The paradox of CPB-related problems with the haematological system is that there are some factors tipping the balance towards a bleeding tendency, and others that favour a prothrombotic state. Both of these issues must be dealt with independently to create the safest environment for surgery. It has been demonstrated that platelets play a key role in both haemostatic dysfunction and thrombotic complications of CPB. Much has been achieved, both clinically and in the laboratory, in the understanding of the precise role platelets play in these events, but the exact mechanisms involved have yet to be completely identified. As research progresses, our understanding will increase, but until then clinical practice must be dictated by the current evidence available.

Alteration of platelet-associated membrane glycoproteins during extracorporeal apheresis of peripheral blood progenitor cells

In extracorporeal circulation, blood is affected by artificial biomaterials and shear forces. We investigated the effects of peripheral blood progenitor cell (PBPC) apheresis on the kinetics and level of platelet membrane antigen expression in 11 breast cancer and 13 testicular cancer patients. After mobilization with rhG-CSF, continuous-flow apheresis was performed. Expression of structural antigens CD41a and CD42b and activation-dependent antigens CD62p, CD63, and fibrinogen was analyzed by flow cytometry at fixed time intervals. Initial changes occurred in all of the antigens within minutes, followed by a progressive increase in the mean channel fluorescence intensities (MCFI) of CD62p from 26 +/- 8 (mean +/- SD) to 73 +/- 29 (p < 0.05), CD63 from 22 +/- 5 to 51 +/- 16 (p < 0.05) and antifibrinogen from 120 +/- 20 to 356 +/- 154 (p < 0.05). In contrast, CD41a and CD42b fluorescence decreased during apheresis (p < 0.05 for both). The more rapid sequestration of P-selectin-expressing platelets known to occur during extracorporeal PBPC apheresis suggests that platelet activation may be associated with the loss of platelets during this procedure. In addition, alteration of platelet surface antigens increases thrombogenic potential and may reduce the in vivo efficacy of the platelet hemostatic potential.

Flow cytometric analysis of platelet membrane antigens during and after continuous-flow plateletpheresis

BACKGROUND

The influence, extent, and duration of changes in platelet antigen expression caused by blood-biomaterial interaction in plateletpheresis were assessed.

STUDY DESIGN AND METHODS

Twenty-two apheresis donors were studied by using two automated continuous-flow apheresis devices. Blood samples were taken before, during, and for 4 days after extracorporeal circulation. The platelet surface expression of glycoproteins CD41a, CD42b, CD62p, and CD63 was analyzed by flow cytometry.

RESULTS

Over the course of plateletpheresis, there was a significant increase in mean channel fluorescence intensity (MCFI) of CD62p, from 25.1 +/- 7.9 (mean +/- SD) to 50.4 +/- 28.9, and of CD63, from 22.3 +/- 6.5 to 33.3 +/- 13.2. There was a significant decrease in CD41a expression as measured by the MCFI, from 1129.8 +/- 125.0 to 1066.6 +/- 102.2, and in CD42b MCFI, from 329.6 +/- 49.4 to 321.4 +/- 52.0. The two apheresis devices showed different platelet activation kinetics, but the overall MCFI of CD62p and CD63 did not significantly diverge after 60 minutes of apheresis. CD62p and CD63 expression as measured by the MCFI returned to preapheresis levels during the follow-up period in 25 and 25 of 44 procedures, respectively, within 24 hours; in 10 and 13 of 44 procedures after 48 hours; in 7 and 3 of 44 procedures after 72 hours; and in 2 and 3 of 44 procedures on Day 5.

CONCLUSION

The varying kinetics of expression, as measured by the MCFI, of platelet antigens CD62p, CD63, CD41a, and CD42b during extracorporeal circulation may be useful for biocompatibility testing. Activated platelets continue to circulate in donors for several days after cytapheresis, which suggests that a sufficient interval between apheresis procedures is necessary to avoid the collection of activated platelets.

Preoperative platelet dysfunction increases the benefit of aprotinin in cardiopulmonary bypass

BACKGROUND

This study was designed to determine the benefit of aprotinin therapy in reducing bleeding during and after cardiopulmonary bypass in patients with preoperative platelet dysfunction. Platelet function involvement in the mechanism by which aprotinin acts was also investigated.

METHODS

In a double-blind, randomized study, patients received high-dose aprotinin (n = 54) or placebo (n = 52). Whole blood aggregation was measured preoperatively. Platelet function and activation in both groups were assessed intraoperatively and postoperatively at five times.

RESULTS

Aprotinin significantly reduced perioperative bleeding and postoperative blood transfusion. Placebo-treated patients with reduced preoperative platelet aggregation bled more postoperatively, but aprotinin reduced the bleeding in patients with normal or reduced platelet function to similar levels. Any cardiopulmonary bypass-induced changes in platelet aggregation, platelet activation as measured by P-selectin expression, and von Willebrand factor antigen and function were similar in aprotinin-treated and placebo-treated groups.

CONCLUSIONS

The mechanism by which aprotinin reduced bleeding was independent of any effect on platelet function. However, aprotinin produced a greater reduction in bleeding among patients whose condition was hemostatically compromised by preoperative platelet dysfunction.

Low thromboembolic risk without anticoagulation using advanced-design left ventricular assist devices

BACKGROUND

A major limitation of cardiac assist devices has been the high incidence of thromboembolic events and their requirement for systemic anticoagulation. The Thermo Cardiosystems HeartMate 1000 IP left ventricular assist device (LVAD) employs a design that may reduce thromboembolic risk and obviate the need for systemic anticoagulation.

METHODS

Two hundred twenty-three patients with nonreversible heart failure were supported with the HeartMate LVAD as a bridge to heart transplantation. All patients were monitored prospectively for thromboembolic events. Anticoagulation regimens and occurrence of subclinical thromboembolic events, including those seen by transcranial Doppler examinations in selected patients, were also recorded.

RESULTS

Total time of LVAD support use was 531.2 patient-months. Twenty-three patients (10%) received warfarin postoperatively for 42.4 patient-months (8.2% of total support time). Six patients (2.7%) had thromboembolic events, representing 0.011 events per patient-month of device use.

CONCLUSIONS

The thromboembolic complication rate associated with this LVAD is acceptably low despite the minimal anticoagulation employed in this series, allowing consideration of long-term device use for the treatment of heart failure.

Time for new concepts about measurement of complement activation by cardiopulmonary bypass?

Fifty-one patients admitted for routine coronary bypass operations were randomized to cardiopulmonary bypass with a membrane oxygenator (Capiox) or a bubbler (Polystan or William Harvey). Complement activation was measured using enzyme immunoassays for concentrations of C3 activation products and the terminal complement complex. From 5.8 to 8.1 arbitrary units (AU)/mL (medians), the plasma concentrations of C3 activation products increased by 119.9 AU/mL (Capiox), 124.6 AU/mL (Polystan), and 79.5 AU/mL (William Harvey) to a peak at closure of the sternum (not significant when related to baseline concentrations). The increase in C3 activation products and baseline C3 activation were linearly correlated (R2 = 0.30; p less than 0.0001). From 5.5 to 6.1 AU/mL, the plasma terminal complement complex concentrations increased by 45.2 AU/mL (Capiox), 15.4 AU/mL (Polystan), and 17.4 AU/mL (William Harvey) to a peak before termination of cardiopulmonary bypass. Maximal terminal (C5-C9) activation was significantly higher in the membrane oxygenator group (p less than 0.0001) and showed no relationship to C3 activation. Measurement of C3 activation only gives no information about C5-C9 activation. At present, terminal complement complex quantitation is probably the best index of C5-C9 activation during cardiopulmonary bypass.