Platelet aggregation during cardiopulmonary bypass evaluated by a laser light-scattering method

Perioperative platelet reduction after sutureless or stented valve implantation: results from the PERSIST-AVR controlled randomized trial

OBJECTIVES

Platelet count reduction is a common but not fully understood phenomenon after aortic valve replacement (AVR) with bioprosthesis implantation. The aim of the present study was to investigate the occurrence and the clinical impact of platelet count reduction in patients receiving the Perceval bioprosthesis compared to those receiving standard sutured stented bioprosthetic aortic valve in a randomized, controlled AVR study.

METHODS

PERceval Sutureless Implant versus STandard Aortic Valve Replacement is a prospective, randomized, adaptive, open-label trial. Patients were randomized (March 2016-September 2018) to AVR with a sutureless or stented valve. Ad hoc analyses have been performed to evaluate the occurrence of platelet count reduction and the clinical impact of the platelet variations in the 2 groups.

RESULTS

The Perceval group showed a higher platelet reduction than the control group (46% vs 32%). The phenomenon was transient in both groups, with a slow recovery of the platelet count by hospital discharge. No differences were observed between groups regarding need of transfusions, blood loss, major bleeding and stroke events.

CONCLUSIONS

The Perceval sutureless aortic bioprosthesis implantation is associated with higher rate of transient platelet reduction as compared to stented bioprostheses for AVR. However, the platelet count reduction is transient and the decline does not affect the patient's clinical outcomes. Current explanations for this phenomenon are speculative, and further investigations are required to elucidate it.

CLINICAL TRIAL REGISTRATION NUMBER

NCT02673697-ClinicalTrials.gov-4 February 2016.

Changes in MicroRNA Expression Level of Circulating Platelets Contribute to Platelet Defect After Cardiopulmonary Bypass

OBJECTIVES

Platelet defect mechanisms after cardiopulmonary bypass remain unclear. Our hypothesis microRNA expressions in circulating platelets significantly change between pre and post cardiopulmonary bypass, and consequent messenger RNA and protein expression level alterations cause postcardiopulmonary bypass platelet defect.

DESIGN

Single-center prospective observational study.

SETTING

Operating room of Kyoto Prefectural University of Medicine.

PATIENTS

Twenty-five adult patients scheduled for elective cardiac surgeries under cardiopulmonary bypass.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

In the initial phase, changes in microRNA expression between pre and post cardiopulmonary bypass underwent next generation sequencing analysis (10 patients). Based on the results, we focused on changes in mir-10b and mir-96, which regulate glycoprotein 1b and vesicle-associated membrane protein 8, respectively, and followed them until messenger RNA and protein syntheses (15 patients) using quantitative polymerase chain reaction and Western blotting. Seven microRNAs including mir-10b and mir-96 exhibited significant differences in the initial phase. In the subsequent phase, mir-10b-5p and mir-96-5p overexpressions were confirmed, and glycoprotein 1b and vesicle-associated membrane protein 8 messenger RNA levels were significantly decreased after cardiopulmonary bypass: fold differences (95% CI): mir-10b-5p: 1.35 (1.05-2.85), p value equals to 0.01; mir-96-5p: 1.59 (1.06-2.13), p value equals to 0.03; glycoprotein 1b messenger RNA: 0.46 (0.32-0.60), p value of less than 0.001; and vesicle-associated membrane protein messenger RNA: 0.70 (0.56-0.84), p value of less than 0.001. Glycoprotein 1b and vesicle-associated membrane protein 8 were also significantly decreased after cardiopulmonary bypass: glycoprotein 1b: 82.6% (71.3-93.8%), p value equals to 0.005; vesicle-associated membrane protein 8: 79.0% (70.7-82.3%), p value of less than 0.001.

CONCLUSIONS

Expressions of several microRNAs in circulating platelets significantly changed between pre and post cardiopulmonary bypass. Overexpressions of mir-10b and mir-96 decreased glycoprotein 1b and vesicle-associated membrane protein 8 messenger RNA as well as protein, possibly causing platelet defect after cardiopulmonary bypass.

Changes in platelet Bax levels contribute to impaired platelet response to thrombin after cardiopulmonary bypass: prospective observational clinical and laboratory investigations

Background

Anucleate platelets can undergo apoptosis in response to various stimuli, as do nucleated cells. Cardiopulmonary bypass (CPB) causes platelet dysfunction and can also activate platelet apoptotic pathways. We therefore evaluated time-dependent changes in blood platelet Bax (a pro-apoptotic molecule) levels and platelet dysfunction after cardiac surgery.

Methods

We assessed blood samples obtained from subjects having on-pump or off-pump coronary artery bypass graft surgery ( n =20 each). We also evaluated the in vitro effects of platelet Bax increase in eight healthy volunteers.

Results

Thrombin-induced platelet calcium mobilisation and platelet-surface glycoprotein Ib (GPIb) expression were lowest at weaning from CPB and did not recover on postoperative day one. On-pump surgery increased platelet expression of Bax, especially the oligomerised form, along with translocation of Bax from the cytosol to mitochondria and platelet-surface tumour necrosis factor-alpha (TNF-α)-converting enzyme (TACE) expression. In contrast, mitochondrial cytochrome c expression was reduced. While similar in direction, the magnitude of the observed changes was smaller in patients having off-pump surgery. In vitro , a cell-permeable Bax peptide increased platelet Bax expression to the same extent seen during bypass and produced similar platelet changes. These apoptotic-like changes were largely reversed by Bcl-xL pre-administration, and were completely reversed by combined application of inhibitors that stabilise outer mitochondrial membrane permeability and TACE.

Conclusions

CPB increases platelet Bax expression, which contributes to reduced platelet-surface GPIb expression and thrombin-induced platelet calcium changes. These changes in platelet apoptotic signalling might contribute to platelet dysfunction after CPB.

Clinical trial registration

UMIN Clinical Trials Registry (number UMIN000006033).

Off-pump coronary revascularization: A potential benefit for female patients?

Coronary artery disease is one of the leading causes of illness for both men and women. However, women are 3 times more likely to die for coronary artery disease as they are of breast cancer. There are an increasing prevalence of coronary artery disease in women and thus facing the need for surgical revascularization. It has long being accepted that women carry a high risk of coronary surgery than men. Many investigators have suggested that female itself is predictive of poor outcome after on pump coronary surgery. We thought to search the litlature to investigate whether women who undergo off-pump surgery receive any benefits compared with women undergoing on-pump surgery.

Evaluation of platelet count after isolated biological aortic valve replacement with Freedom Solo bioprosthesis

OBJECTIVE

The risk of thrombocytopenia in patients undergoing aortic valve replacement (AVR) with the Freedom Solo (FS) bioprosthesis is controversial. The aim of our study was to evaluate the postoperative evolution of platelet count and function after AVR in patients undergoing isolated biological AVR with FS.

METHODS

Between May 2005 and June 2010, 322 patients underwent isolated biological AVR. Of these, 116 patients received FS and were compared with 206 patients who received biological valves. Platelet count, mean platelet volume (MPV), and platelet distribution width (PDW) were evaluated at baseline (T0), first (T1), second (T2), and fifth (T3) postoperative days, respectively.

RESULTS

Overall in-hospital mortality was 1.5% with no difference between the two groups. Thirty-seven (11.5%) patients developed thrombocytopenia. FS implantation was associated with a higher incidence of thrombocytopenia compared with the control group (24.1% vs 4.4%, p<0.0001). Patients in the FS group showed a lower platelet count than the control group at T1 (99.4±38×10(3) μl(-1) vs 122.5±41.6×10(3) μl(-1), p<0.001), T2 (79.7±36.3×10(3) μl(-1) vs 122.5±43.3×10(3) μl(-1), p<0.001) and T3 (86.6±57.4×10(3) μl(-1) vs 158.4±55.8×10(3) μl(-1), p<0.001). Moreover, the FS group also had a higher MPV (11.6±0.9 fl vs 11±1 fl, p<0.001) and higher PDW (15.1±2.3 fl vs 13.9±2.1 fl, p<0.001) at T3. In a multivariable analysis, FS (p<0.0001), body surface area (p<0.0001), cardiopulmonary bypass time (p=0.003), and lower preoperative platelet counts (p=0.006) were independent predictors of thrombocytopenia.

CONCLUSIONS

The FS valve might increase the risk of thrombocytopenia and platelet activation, in the absence of adverse clinical events. Prospective randomized studies on platelet function need to confirm our data.

Platelet Functions in Cardiopulmonary Bypass Surgery

BACKGROUND

Haemorrhage after Cardio Pulmonary Bypass (CPB) Surgery is a well recognised complication that leads to significant morbidity and mortality. The incidence varies between 5-25% depending upon the clinical situation. Several factors are implicated as causative but none have been precisely proved.

METHODS

Our study was an attempt to evaluate the haemostatic defect with particular reference to platelet function abnormalities during cardio pulmonary bypass surgery, in order to reduce the morbidity and mortality associated with post CPB haemorrhage. Flow cytometric evaluation of different platelet glycoproteins like GPIb/IX, GPIIb/IIIa and GMP-140 was done.

RESULTS

The marker expression showed deregulation during surgery which returned to base after bypass was terminated. In contrast, the cases with bleeding showed significant variation. P-Selectin (GMP 140) expression decreased progressively till 3(rd) post-operative day showing lack of activation of platelets in cases of severe bleeding.

CONCLUSION

Longer duration of CPB initiates plasmin generation through heparin, which raises the PAI-1-tPA complex and thereby down regulating the functions of platelets. This suggests a link between duration of CPB, bleeding, platelet dysfunction and fibrinolysis. Hence serial estimations of the levels of GMP-140 and tPA can predict severe bleeding.

Coronary artery bypass grafting in an immune thrombocytopenic purpura patient using off-pump techniques

We performed an off-pump coronary artery bypass grafting (OPCABG) procedure on a 60-year-old woman with idiopathic thrombocytopenic purpura (ITP) whose platelet count was 42 x 10(3) per microliter on admission. She was treated with immunoglobulin G (IgG) (0.5 g.kg(-1).d(-1)) for 4 days, resulting in a platelet count rise to 187 x 10(3) per microliter. She subsequently underwent an uneventful OPCABG procedure without requiring any blood transfusions. The combination of OPCABG and preoperative IgG therapy appears to be an ideal strategy for ITP patients requiring coronary revascularization.

Neutrophil and platelet dynamics at organ level after cardiopulmonary bypass: an in vivo study in neonatal pigs

The aim was to investigate if organ dysfunction is a consequence of cell accumulation in the tissue and whether this accumulation is caused by the cardiopulmonary bypass (CPB) procedure. Twenty-six piglets were used in the sham group (sternotomy, n=12) or in the CPB group (sternotomy, CPB, n=14). Isotope-labeled autologous (99m)Tc-neutrophils (PMNs) and (111)In-platelets were infused and dynamically followed at organ level with a gamma camera before, during, and 4 h after termination of CPB. The CPB group showed a 49% increase in (99m) Tc-PMNs in the kidneys in the postoperative period compared to a decrease of 2% in the sham group. A less marked decrease was observed in the lungs and peripheral blood between the two groups. The increased radioactivity at organ level post-CPB could be due to changes in flow, extraction in the organ or accumulation of cells, especially in the kidneys and lungs, and might contribute to temporary organ dysfunction postoperatively.

Off-pump coronary artery bypass grafting: not a flash in the pan

During the past decade, technical improvements have made off-pump coronary artery bypass operations a routine procedure. During this time, off-pump coronary artery bypass has been audited against conventional techniques by many observational, case-matched, and prospective randomized studies. There is evidence in the literature suggesting that off-pump coronary artery bypass operations reduce postoperative morbidity, organ dysfunction, and costs, without compromising midterm outcome compared with conventional coronary operations. The available evidence also supports the view that high-risk patients might benefit the most from revascularization on the beating heart. High quality follow-up data are still needed to assess the impact of off-pump coronary artery bypass operations on long-term clinical outcome.

Laser-light scattering, a new method for continuous monitoring of platelet activation in circulating fluid

We evaluated a novel technique of laser-light scattering (LLS) to detect platelet-volume changes continuously, reflecting platelet aggregation in circulating fluid. Carotid arteries from 20 dogs were mounted in a dual perfusion chamber. Balloon angioplasty (BA) was performed and arteries perfused with platelet-rich plasma (PRP). A He-Ne laser beam was passed through cuvettes connected to tubing draining the arteries. From the angle of incidence, the average volume of aggregates was measured by the ratio of scattering light at 1 to 5 degrees' spread on the diode array of a multichannel analyzer. Platelet volume varied linearly with the scattered light ratio at 1 to 5 degrees (y = -24.2 + 27.6 x [y = particle size, microm(3); x = scattered light ratio at 1/5 degrees]). For comparison, we used an electronic particle counter (Coulter counter) to measure platelet volume. P-selectin expression was measured to confirm platelet activation. Comparing 10 uninjured and 10 BA-injured arteries, we found that platelet volume as measured with LLS increased from 21.6 +/- 4.1 to 52.1 +/- 12.5 microm(3) (P < .003); as measured with the Coulter counter, it increased from 29.9 +/- 2.4 to 62.3 +/- 7.0 microm(3) (P < .005). Six BA-injured arteries perfused with PRP and aspirin (0.2 mg/mL) were compared with six arteries treated with BA alone. The aspirin decreased platelet volume as measured with LLS from 56.2 +/- 11.8 to 40.2 +/- 12.7 microm(3) (P < .01); the Coulter counter revealed a decrease from 51.9 +/- 18.5 to 38.8 +/- 14.2 microm(3) (P < .001). Coulter counter and LLS results were correlated: r = 0.74, P < .05. The peak of P-selectin expression coincided with peak platelet volume. These data demonstrate that increases in circulating-platelet size stimulated by endovascular injury can be reliably and continuously monitored with the use of LLS.

Does off-pump coronary surgery reduce morbidity and mortality?

OBJECTIVE

To compare hospital outcomes of on-pump and off-pump coronary artery bypass surgery.

METHODS

From 1997 to 2000, primary coronary artery bypass grafting was performed in 481 patients off pump and in 3231 patients on pump. Hospital outcomes were compared between propensity-matched pairs of 406 on-pump and 406 off-pump patients. The 2 groups were similar in age (P =.9), left ventricular function (P =.7), extent of coronary artery disease (P =.5), carotid artery disease (P =.4), and chronic obstructive pulmonary disease (P =.5). However, off-pump patients had more previous strokes (P =.05) and peripheral vascular disease (P =.02); on-pump patients had a higher preoperative New York Heart Association class (P =.01).

RESULTS

In the matched pairs the mean number of bypass grafts was 2.8 +/- 1.0 in off-pump patients and 3.5 +/- 1.1 in on-pump patients (P <.001). Fewer grafts were performed to the circumflex (P <.001) and right coronary (P =.006) artery systems in the off-pump patients. Postoperative mortality, stroke, myocardial infarction, and reoperation for bleeding were similar in the 2 groups. There was more encephalopathy (P =.02), sternal wound infection (P =.04), red blood cell use (P =.002), and renal failure requiring dialysis (P =.03) in the on-pump patients.

CONCLUSIONS

Both off- and on-pump procedures produced excellent early clinical results with low mortality. An advantage of an off-pump operation was less postoperative morbidity; however, less complete revascularization introduced uncertainty about late results. A disadvantage of on-pump bypass was higher morbidity that seemed attributable to cardiopulmonary bypass.

Subsystem organ function during coronary surgery

Conventional coronary artery bypass grafting (CABG) carries a mortality rate of 1% to 2% in elective patients. However, despite advances in perfusion, anaesthetic, and surgical techniques cardiopulmonary bypass (CPB) is still associated with subsystem dysfunction. Off-pump coronary artery bypass grafting (OPCAB) has recently gained popularity as a potentially more physiological method to maintain the functional integrity of major organ systems. The review of observational reports, case-matched studies and prospective randomized trials seems to suggest that OPCAB surgery reduces postoperative subsystem organ dysfunction when compared with conventional coronary revascularisation.

Platelet damage caused by the centrifugal pump: laser-light scattering analysis of aggregation patterns

Platelets are damaged by shear force during centrifugal pumping; however, the mechanism of this damage has not been fully investigated. A new laser-light scattering (LS) assay method enables quantification of real-time changes in the number of platelet aggregates of different sizes. Using this method, we assessed the kinetics of platelet damage caused by the centrifugal pump from the standpoint of platelet aggregation capacity. Conventional optical density (OD) and LS methods were used to measure platelet aggregation with a Kowa AG-10 aggregometer. Platelet aggregation in fresh human blood was evaluated in a mock circuit for 3 h under a flow rate of 5.0 L/min and a pressure head of 100 mm Hg. Test samples were obtained before pumping for control, and at 1, 2, and 3 h after the start of pumping. The test series was begun 8 times. Aggregation after stimulation by 2.0 microg/ml collagen was determined; small (9 to 25 microm), medium (25 to 50 microm), and large (50 to 70 microm) aggregates were counted by the LS method. OD measurement at hourly intervals showed significant reduction in platelet aggregation. The LS method showed that generation of small and medium aggregates was not suppressed during pumping, but that generation of large aggregates was significantly reduced at 2 and 3 h of pumping. Platelet aggregation is significantly suppressed during centrifugal pumping, and the resulting platelet dysfunction is due mainly to inhibited development of small aggregates into larger aggregates.

Reduced postoperative blood loss and transfusion requirement after beating-heart coronary operations: a prospective randomized study

OBJECTIVE

Coronary artery bypass grafting on the beating heart through median sternotomy is a relatively new treatment, which allows multiple revascularization without the use of cardiopulmonary bypass. A prospective randomized study was designed to investigate the effect of coronary bypass with or without cardiopulmonary bypass on postoperative blood loss and transfusion requirement.

METHODS

Two hundred patients with coronary artery disease were prospectively randomized to (1) on-pump treatment with conventional cardiopulmonary bypass and cardioplegic arrest and (2) off-pump treatment on the beating heart. Postoperative blood loss identified as total chest tube drainage, transfusion requirement, and related costs together with hematologic indices and clotting profiles were analyzed.

RESULTS

There was no difference between the groups with respect to preoperative and intraoperative patient variables. The mean ratio of postoperative blood loss and 95% confidence interval between groups was 1.64 and 1.39 to 1.94, respectively, suggesting on average a postoperative blood loss 1.6 times higher in the on-pump group compared with the off-pump group. Seventy-seven patients in the off-pump group required no blood transfusion compared with only 48 in the on-pump group (P <.01). Furthermore, less than 5% of patients in the on-pump group required fresh frozen plasma and platelet transfusion compared with 30% and 25%, respectively, in the on-pump group (both P <.05). Mean transfusion cost per patient was higher in the on-pump compared with that in the off-pump group ($184.8 +/- $35.2 vs $21.47 +/- $6.9, P <.01).

CONCLUSIONS

Coronary artery bypass grafting on the beating heart is associated with a significant reduction in postoperative blood loss, transfusion requirement, and transfusion-related cost when compared with conventional revascularization with cardiopulmonary bypass and cardioplegic arrest.

Platelet activation and aggregation during normothermic cardiopulmonary bypass

OBJECTIVE

The usefulness of heparin-bonded circuits under normothermic cardiopulmonary bypass has not been elucidated. We studied platelet activation and aggregation differences between heparin-bonded and nonheparin-bonded circuits in patients undergoing surgery involving normothermic cardiopulmonary bypass.

METHODS

Eight patients underwent coronary artery bypass grafting with non heparin-bonded circuits (controls) and 7 the same with heparin-bonded circuits (heparin group). Heparin bonding was applied to the blood contact surface of our system, including the oxygenator and connecting tubes. Patient body temperature was kept between 36 and 37 degrees C. Beta-thromboglobulin and platelet factor 4 were measured before, during, and after cardiopulmonary bypass, and platelet aggregation was evaluated by laser-light scattering.

RESULTS

Changes in beta-thromboglobulin and platelet factor 4 during and after cardiopulmonary bypass were similar in both groups. Small particle formation was the primary aggregate induced during and after cardiopulmonary bypass in both groups, and serial changes in particle formation up to 24 hours after cardiopulmonary bypass were similar in both groups.

CONCLUSIONS

Our results indicate that in 2-3 hours of normothermic cardiopulmonary bypass, heparin-bonded circuits are similar to nonheparin-bonded ones in platelet compatibility.

Heparin-induced platelet dysfunction and cardiopulmonary bypass

BACKGROUND

Cardiopulmonary bypass is associated with impaired platelet macroaggregation. Heparin contributes to platelet dysfunction before extracorporeal circulation. In vitro heparinization of whole blood does not impair macroaggregation. Heparin releases several endothelial proteins; thus heparin may inhibit macroaggregation indirectly.

METHODS

Patients undergoing operations using cardiopulmonary bypass and ABO blood group compatible volunteers were studied. Whole blood impedance aggregometry assessed macroaggregation in response to collagen (0.6 microg ml(-1)) in blood diluted either with normal saline or with platelet poor plasma, obtained from patients at different stages of cardiopulmonary bypass.

RESULTS

Before heparinization, blood diluted with its own platelet poor plasma recorded an impedance change of 13.0 (4.7 to 15.6) Ohms. Platelet poor plasma obtained after heparinization or during extracorporeal circulation reduced this response to 3.7 (1.1 to 8.4) and 2.0 (1.1 to 3.3) Ohms, respectively (both p < 0.0001 versus pre-heparin; n = 13). Macroaggregation in blood from volunteers was similarly inhibited by patients' platelet poor plasma (n = 30). The macroaggregatory response in blood sampled after heparinization for cardiopulmonary bypass, decreased gradually from 11.4 (8.2 to 15.9) Ohms immediately after sampling to 1.7 (1.4 to 4.1) Ohms 2 hours later (p < 0.0001; n = 11).

CONCLUSIONS

In vivo heparinization induces plasma changes that inhibit platelet macroaggregation. This is an indirect, delayed inhibition that is transferable in vitro to normal platelets.

Heparin, platelet aggregation, neutrophils, and cardiopulmonary bypass

Cardiopulmonary bypass (CPB) is associated with both neutrophil activation and failure of platelets to form large stable aggregates. We aimed to determine the effects of heparin and of neutrophil activation on platelet aggregation in whole blood. Fourteen patients undergoing routine aortocoronary bypass grafting and NSAID-free for over 7 days were studied before and after heparinisation, and at end-CPB. Whole blood, anticoagulated with rHirudin, was stirred for 3 minutes, and macroaggregation in response to collagen (0.6 microg. mL(-1)) or the neutrophil stimulant fMLP (10(-7)M) was determined by whole blood impedance aggregometry. Microaggregation was measured by counting unaggregated single platelets (corrected for haemodilution). The blood of volunteers was studied in vitro.

PATIENTS

Before CPB, heparin effectively abolished platelet macroaggregation induced by collagen (20.5 to 1.4 Ohms) or fMLP (3.9 to 0 Ohms (p<0.0001). CPB had no additional effect. Heparinisation also reduced the platelet count from 127 (110-170) to 95 (64-117). The inhibition of macroaggregation could not be reversed by ex vivo heparinase.

VOLUNTEERS

In vitro, the same heparin concentration, as measured in vivo (4 micromL(-1)), inhibited collagen-induced macroaggregation (20.3 to 14.7 Omega), but this effect was less than that observed ex vivo and was reversed by heparinase. In vitro heparin promoted fMLP macroaggregation (2.9 to 8.6 Omega). The inhibition of macroaggregation resulted from heparinisation, per se, rather than CPB and was insensitive to heparinase. There was less inhibition by in vitro heparin, which was reversible by heparinase, indicating a direct effect of heparin in vitro. The disparate findings are suggestive of an indirect action by heparin in vivo on macroaggregation, although heparin had a small direct stimulatory action on microaggregation.

Refractoriness to platelet transfusion following double valve replacement in an ITP patient who had undergone splenectomy

Reports of patients with idiopathic thrombocytopenic purpura (ITP) undergoing cardiac surgery are rare, and almost all of the reported cases required platelet transfusion. ITP patients, especially those having a history of splenectomy or a history of heavy bleeding, may have to undergo multiple platelet transfusions. Such transfusions may induce alloimmunization against the human leukocyte antigen (HLA) and result in refractoriness to subsequent platelet transfusions. We report a case of a 63-year-old female with ITP, with a history of splenectomy and multiple platelet transfusions, who underwent aortic and mitral valve replacement. Although corticosteroid administration, high-dose immunoglobulin therapy, and repeated platelet transfusion led to a temporary increase in platelet count and successful hemostasis, refractoriness to platelet transfusion occurred postoperatively because of the presence of the anti-HLA antibody. In addition, the patient showed complications of pyothorax. Corticosteroids might have exerted an inhibitory influence on the occurrence of pyothorax.