Alterations to haemostasis following cardiopulmonary bypass and the relationship of these changes to neurocognitive morbidity

Combination of aptamer and drug for reversible anticoagulation in cardiopulmonary bypass

Unfractionated heparin (UFH), the standard anticoagulant for cardiopulmonary bypass (CPB) surgery, carries a risk of post-operative bleeding and is potentially harmful in patients with heparin-induced thrombocytopenia-associated antibodies. To improve the activity of an alternative anticoagulant, the RNA aptamer 11F7t, we solved X-ray crystal structures of the aptamer bound to factor Xa (FXa). The finding that 11F7t did not bind the catalytic site suggested that it could complement small-molecule FXa inhibitors. We demonstrate that combinations of 11F7t and catalytic-site FXa inhibitors enhance anticoagulation in purified reaction mixtures and plasma. Aptamer-drug combinations prevented clot formation as effectively as UFH in human blood circulated in an extracorporeal oxygenator circuit that mimicked CPB, while avoiding side effects of UFH. An antidote could promptly neutralize the anticoagulant effects of both FXa inhibitors. Our results suggest that drugs and aptamers with shared targets can be combined to exert more specific and potent effects than either agent alone.

Optical verification and in-vitro characterization of two commercially available acoustic bubble counters for cardiopulmonary bypass systems

Introduction:

Gaseous microemboli (GME) introduced during cardiac surgery are considered as a potential source of morbidity, which has driven the development of the first bubble counters. Two new generation bubble counters, introduced in the early 2000s, claim correct sizing and counting of GME. This in-vitro study aims to validate the accuracy of two bubble counters using monodisperse bubbles in a highly controlled setting at low GME concentrations.

Methods:

Monodisperse GME with a radius of 43 µm were produced in a microfluidic chip. Directly after their formation, they were injected one-by-one into the BCC200 and the EDAC sensors. GME size and count, measured with the bubble counters, were optically verified using high-speed imaging.

Results:

During best-case scenarios or low GME concentrations of GME with a size of 43 µm in radius in an in-vitro setup, the BCC200 overestimates GME size by a factor of 2 to 3 while the EDAC underestimates the average GME size by at least a factor of two. The BCC200 overestimates the GME concentration by approximately 20% while the EDAC overestimates the concentration by nearly one order of magnitude. Nevertheless, the calculated total GME volume is only over-predicted by a factor 2 since the EDAC underestimates the actual GME size. For the BCC200, the total GME volume was over-predicted by 25 times due to the over-estimation of GME size.

Conclusions:

The measured errors in the absolute sizing/counting of GME do not imply that all results obtained using the bubble counters are insignificant or invalid. A relative change in bubble size or bubble concentration can accurately be measured. However, care must be taken in the interpretation of the results and their absolute values. Moreover, the devices cannot be used interchangeably when reporting GME activity. Nevertheless, both devices can be used to study the relative air removal characteristics of CPB components or for the quantitative monitoring of GME production during CPB interventions.

Heparin monitoring during cardiac surgery. Part 1: validation of whole-blood heparin concentration and activated clotting time

There is limited published data on the agreement between techniques for monitoring heparin levels. The aim of this study was to validate the Hepcon/HMS, with particular focus on the agreement with laboratory anti-Xa assay. The performances of two ACT instruments - Hemochron and HemoTec - were also evaluated, including an assessment for interchangeability. Blood samples from 42 adult cardiopulmonary bypass (CPB) patients were analysed for activated clotting time (ACT), whole-blood heparin concentration (Hepcon/HMS) and anti-factor Xa (anti-Xa) plasma heparin concentration. Agreement between measures was determined using the method of Bland and Altman. Simple analysis of agreement between the Hepcon and anti-Xa heparin revealed the Hepcon has a mean bias of -0.46 U/mL, with the limits of agreement ±1.12 U/mL. The comparison between ACT instruments indicated a mean difference of -96 seconds for the HemoTec, with limits of ±265 seconds. The Hepcon/HMS instrument displayed satisfactory agreement with anti-Xa plasma heparin concentration, as the expected variation would not be expected to cause problems in the clinical setting. Agreement between the two measurements of ACT may be satisfactory, provided each is assigned a different target value.

Investigation of factors relating to neuropsychological change following cardiac surgery

Background. An analysis of neuropsychological impairment following cardiopulmonary bypass was performed in 55 patients undergoing elective coronary artery bypass grafting. Methods. Neurocognitive function was measured preoperatively using the MicroCog: Assessment of Cognitive Functioning computer-based testing tool. Testing was repeated in the postoperative period immediately prior to discharge from hospital. Analysis of significant score decline was performed using the standardised regression-based technique. A patient was classified as overall impaired when ≥20% of test scores were significantly impaired. The proposed marker of neurological damage S-100β was also used. Prothrombin Fragment 1+2 (F1+2) was measured as a marker of thrombin development to test the hypothesis that excessive haemostatic activation may lead to thromboembolic damage to the brain. Results and Conclusions. 32.7% of patients were classified as significantly impaired. No relationship was detected between F1+2 and any neuropsychological test score; however, the study was limited due to small sample size. F1+2 levels were higher in patients undergoing prolonged bypass times. Neuropsychological decline was significantly correlated with patient age, suggesting a degree of caution is warranted when operating on an elderly cohort. An unexpected relationship was detected between higher heparin concentrations and increased risk of neuropsychological impairment; however, this requires re-evaluation. Perfusion (2007) 22, 27—33.

Bivalirudin as an adjunctive anticoagulant to heparin in the treatment of heparin resistance during cardiopulmonary bypass-assisted cardiac surgery

Heparin resistance (unresponsiveness to heparin) is characterized by the inability to reach acceptable activated clotting time values following a calculated dose of heparin. Up to 20% of the patients undergoing cardiothoracic surgery with cardiopulmonary bypass using unfractionated heparin (UFH) for anticoagulation experience heparin resistance. Although UFH has been the "gold standard" for anticoagulation, it is not without its limitations. It is contraindicated in patients with confirmed heparin-induced thrombocytopenia (HIT) and heparin or protamine allergy. The safety and efficacy of the use of the direct thrombin inhibitor bivalirudin for anticoagulation during cardiac surgery has been reported. However, there have been no reports on the treatment of heparin resistance with bivalirudin during CPB. In this review, we report the favorable outcome of our single-center experience with the alternative use of bivalirudin in the management of anticoagulation of heparin unresponsive patients undergoing coronary artery bypass graft surgery.

Effect of cardiopulmonary bypass on thrombin generation and protein C pathway

OBJECTIVE

The purpose of this study was to evaluate the mechanisms of cardiopulmonary bypass (CPB)-induced dysregulation between thrombin and its regulatory anticoagulant activated protein C (APC).

DESIGN

A prospective observational cohort study.

SETTING

A tertiary care university hospital and associated research laboratory.

PATIENTS

Twenty patients undergoing elective coronary artery bypass surgery with (n = 10) or without CPB (n = 10).

INTERVENTIONS

Blood samples were collected at 7 time points: preinduction; after heparin; 1 hour after the institution of CPB (or the completion of distal anastomoses in off-CPB group); after protamine; and at 0, 4, and 18 hours in the Intensive care unit (ICU). Samples were analyzed for prothrombin fragments (F1+2), thrombin-antithrombin complexes, protein C (PC), APC, soluble thrombomodulin (sTM), and soluble endothelial protein C receptor (sEPCR).

MEASUREMENTS AND MAIN RESULTS

F1+2 levels increased significantly 1 hour after the initiation of CPB in comparison with baseline (2.7 ± 0.5 v 0.5 ± 0.2 nmol/L, p < 0.001) (mean ± standard deviation) and remained elevated until 4 hours after ICU admission (p < 0.001). In contrast, APC levels did not show any significant changes over time in either group. sEPCR, sTM, and PC levels did not change during CPB although sEPCR decreased significantly after the termination of CPB compared with baseline in the CPB group.

CONCLUSIONS

Exposure to CPB is associated with a distinct thrombin surge that continues postoperatively for 4 hours. The impaired ability to generate APC reflects a complex process that is not associated with increased levels of sEPCR and thrombomodulin during CPB. Further studies are required to evaluate the regulation of the host APC response in cardiac surgery.

Microemboli detection on extracorporeal bypass circuitsa

Numerous authors have associated gaseous microembolization with adverse cerebral outcomes during cardiopulmonary bypass (CPB). The introduction to this review provides background on the connection between microemboli and adverse cerebral outcomes. This connection is often difficult to quantify, as outcomes depend on a number of factors, including the size of the bubble, where it passes through the patient, patient co-morbidities and other factors. Nonetheless, numerous studies have shown statistically significant differences in the mean number of cerebral emboli detected in patients that stroked and those that did not, as well as for patients with major cardiac complications and patients with a longer length of hospital stay. Our introduction is followed by case reports and laboratory studies showing how monitoring for gaseous microemboli (GME) can be used to reduce the embolic load delivered to the patient through the bypass circuit. These methods include improved qualification of bypass circuit design prior to surgery, modification of priming procedures to reduce air in the circuit at the start of surgery, new methods for injecting drugs into the circuit during surgery, and better detection of removal of sources of air during surgery. The review concludes with background on the ultrasonic detection of GME, comparing through-transmission gross air detectors and Doppler ultrasound technology with fixed-beam ultrasonic imaging of emboli, a new ultrasonic technique that images moving emboli in the blood using a single ultrasound transducer element in a fixed position. This overview is meant to shed light on why different ultrasonic detection technologies report widely varying counts and emboli loads, and why fixed-beam ultrasonic imaging represents an improvement in the ability to monitor, measure and quantitate embolic load during CPB.

Disposition of tissue factor pathway inhibitor during cardiopulmonary bypass

BACKGROUND

The tissue factor (TF) factor (F) VIIa complex activates coagulation FIX and FX to initiate coagulation, and also cleaves protease activated receptors (PARs) to initiate inflammatory processes in vascular cells. Tissue factor pathway inhibitor (TFPI) is the only specific inhibitor of the TF-FVIIa complex, regulating both its procoagulant and pro-inflammatory properties. Upon heparin infusion during cardiopulmonary bypass (CPB), a heparin releasable pool of endothelial associated TFPI circulates in plasma. Following protamine neutralization of heparin, the plasma TFPI level decreases, but does not return completely to baseline, suggesting that during CPB a fraction of the plasma TFPI becomes heparin-independent. We have investigated the structural and functional properties of plasma TFPI during CPB to further characterize how TFPI is altered during this procedure.

METHODS

We enrolled 17 patients undergoing first-time cardiac surgery involving CPB. Plasma samples were obtained at baseline, 5 min and 1 h after start of CPB (receiving heparin), 10 min after protamine administration (off CPB) and 24 h following surgery. Samples were analyzed for full-length and free (non-lipoprotein bound) TFPI antigen by enzyme-linked immunosorbent assay (ELISA) and for TFPI anticoagulant activity using an amidolytic assay. Western blot analysis was used to identify TFPI species of varying molecular weights in three additional patients. Dunnett's test for post hoc comparisons was used for statistical analysis.

RESULTS

The ELISA and Western blot data indicated that an increase in full-length TFPI accounted for most of the heparin releasable TFPI. Following heparin neutralization with protamine, the full-length TFPI antigen returned to baseline levels while the free TFPI antigen and the total plasma TFPI activity remained elevated. This was associated with the appearance of a new 38 kDa form of plasma TFPI identified by Western blot analysis. The 38 kDa form of TFPI did not react with an antibody directed against the C-terminal region of TFPI indicating it has undergone proteolysis within this region. All TFPI measurements returned to baseline 24 h following CPB.

CONCLUSIONS

During CPB the full-length form of TFPI is the predominant form in plasma because of its prompt release from the endothelial surface following heparin administration. Upon heparin neutralization with protamine, full-length TFPI redistributes back to the endothelial surface. However, a new 38 kDa TFPI fragment is generated during CPB and remains circulating in plasma, indicating that TFPI undergoes proteolytic degradation during CPB. This degradation may result in a decrease in endothelium-associated TFPI immediately post-CPB, and may contribute to the procoagulant and proinflammatory state that often complicates CPB.

Reinfusion of aspirated pericardial blood during CPB. Part II. Laparotomy sponges are hazardous parts of the CPB circuit?

Usually, cotton laparotomy sponges are discarded when they become blood soaked. During bypass surgery, however, they are often wrung out into the pericardial sac and the contents of the sac are aspirated into the cardiopulmonary bypass (CPB) circuit. After cardiopulmonary bypass, many patients give evidence of mental confusion, excessive bleeding, and systemic inflammatory response syndrome (SIRS). We believe that a possible cause is reinfusion of blood that has been activated by contact with laparotomy sponges and contains fibrin microemboli and thrombin. Thrombin production, soluble fibrin (SF) development, and fibrinogen disappearance were measured, over time, in model systems composed of increasing amounts (0-10-20 microL) of tissue factor (TF) in 4 ml of anticoagulated blood distributed through the interstices of a 49-cm(2) laparotomy sponge. Clotting occurred in all of the sponges. Clotting was accelerated by the presence of TF. Without TF, clotting occurred in an average of 28 min (range 17-39). With 10 and 20 microl TF, clotting occurred in 20 (range 11-27) and 13 (range 10-16) min, respectively. Thrombin at a level of approximately 16 NIHU/ml whole blood was present in several donors for 10-20 min after clotting was complete. If 120 ml of blood was to be wrung from a full-sized laparotomy sponge at this point in time, it could contain as much as 2000 units of thrombin.

The impact of cardiac ischemia and reperfusion on markers of activated haemostasis and fibrinolysis during cardiopulmonary bypass: comparison of plasma levels in arterial and coronary venous blood

INTRODUCTION

Activation of coagulation and fibrinolysis is common among patients undergoing cardiopulmonary bypass (CPB) surgery. Little is known, however, about the impact of myocardial ischemia and reperfusion on coagulation activation and fibrinolysis in this clinical setting.

STUDY DESIGN AND METHODS

We determined the levels of coagulation activation and fibrinolysis markers (CAFM) in 19 patients with severe coronary heart disease (CHD) during CPB surgery. FXIIa, tissue factor (TF), FVIIa, tissue plasminogen activator/plasminogen activator inhibitor-1 complexes (tPA/PAI-1), prothrombin fragments 1+2 (F1+2), D-dimers (DD) and plasmin-plasmin inhibitor complexes (PPI) were measured at baseline, prior to and after cardioplegic myocardial ischemia. Simultaneous blood samples were drawn from the aorta and the coronary sinus to evaluate arteriovenous CAFM plasma level gradients.

RESULTS

Myocardial ischemia induced significant increases in gradients of FXIIa and F1+2 levels across the coronary circulation without influencing systemic levels of these markers significantly. Systemic levels of FXIIa, tPA/PAI-1, F1+2, DD and PPI increased significantly during CPB operation. There was a significant linear correlation between FXIIa, FVIIa, F1+2, DD and PPI.

CONCLUSIONS

Myocardial ischemia induces contact activation and thrombin generation rather than release of tPA and might thus contribute to postoperative thromboembolic complications. Surgery itself and CPB cause activation of coagulation and fibrinolysis as already described. A significant association between FXIIa, FVIIa, F1+2, DD and PPI suggests a relationship between contact activation, thrombin generation, fibrin formation and fibrinolysis.

The response to activated protein C after cardiopulmonary bypass: impact of factor V leiden

Activated protein C (aPC) resistance is a recognized hypercoagulable phenotype that is associated with increased risk for thrombosis in multiple clinical settings. Factor V Leiden (FVL) represents a specific inherited cause of aPC resistance, but the perioperative thrombotic risk of FVL is unclear. In this investigation, we sought to quantify whether cardiopulmonary bypass produces alterations in aPC resistance in FVL carriers and noncarrier controls, testing the hypothesis that FVL is associated with a relatively hypercoagulable postoperative state. Two-hundred-five adult cardiac surgery patients were prospectively enrolled into a genetic registry whose purpose was to study the impact of genetic variables on clinical outcomes. For this study, 8 subjects heterozygous for FVL were identified (group L), as well as 2 control groups: group MC, matched controls, 18 matched subjects without FVL; and group UC, unmatched controls, 11 consecutive subjects without FVL. Plasma was sampled at the beginning of surgery, 10 min after protamine administration, and on postoperative day 1, and assayed for resistance to aPC (normal aPC ratio is >2.0). Both MC and UC groups exhibited normal aPC ratio at baseline (2.40 and 2.36, respectively), which increased significantly (to 2.76 and 2.75, P = 0.007 and 0.021, respectively) on postoperative day 1, indicating increased postoperative sensitivity to aPC. Conversely, group L subjects exhibited aPC resistance at baseline (aPC ratio 1.80), and did not change significantly postoperatively (P = 0.867). Patients without FVL therefore show laboratory evidence consistent with relative protection from postoperative thrombosis, whereas FVL carriers do not. These findings provide mechanistic support for previous speculations of increased postoperative thrombotic risk associated with FVL.

Axillary artery cannulation for cardiopulmonary bypass reduces cerebral microemboli

BACKGROUND

Aortic cannulation for cardiopulmonary bypass (CPB) is linked to cerebral microemboli emanating from the ascending aorta. Aortic calcification or disease requiring replacement precludes aortic cannulation. Clinical experience with axillary artery cannulation led to the hypothesis that axillary cannulation may be cerebroprotective.

METHODS

Five mongrel dogs underwent a median sternotomy and isolation of the right axillary artery. The canine bicarotid brachiocephalic trunk was reconfigured by grafting the origin of the left carotid to the proximal left subclavian artery. Microspheres were injected into the ascending aorta during 4 conditions: before and after reconfiguration, CPB with aortic cannulation, and CPB with axillary cannulation. Brain, kidneys, and skeletal muscle were analyzed for microsphere distribution.

RESULTS

Each animal served as its own control for comparison of aortic and axillary cannulation. No significant differences were documented in microsphere deposition for prereconfiguration and postreconfiguration. In the right middle cerebral artery distribution, 2300 +/- 710 microspheres per gram were deposited during aortic cannulation, compared with 540 +/- 110 during axillary cannulation (P <.05). In the left middle cerebral artery region, 2030 +/- 330 microspheres per gram with aortic cannulation were reduced to 1320 +/- 240 with axillary cannulation (P <.05). Axillary cannulation resulted in 73% fewer microspheres in the right brain and 40% fewer microspheres in the left compared with aortic cannulation (P <.05).

CONCLUSIONS

Axillary artery cannulation for CPB is cerebroprotective. Altered blood-flow patterns during axillary cannulation may produce retrograde brachiocephalic artery blood flow and competing intracerebral right-to-left collateral blood flow, deflecting emboli from the ascending aorta and arch toward the descending aorta. Expanded use of axillary artery cannulation during cardiac operations could decrease the incidence of stroke.

Different effects of abciximab and cytochalasin D on clot strength in thrombelastography

Maximum amplitude (MA) in thrombelastography (TEG) consists of a plasmatic and a platelet component. To assess the magnitude of the plasmatic component, pharmacological approaches have been proposed to eliminate the platelet component. We evaluated the individual and combined effects of abciximab and cytochalasin D on the MA of TEG. Whole blood, platelet-rich plasma (PRP) and homologous platelet-poor plasma (PPP) from 20 healthy volunteers were spiked with abciximab or cytochalasin D or a combination of both and TEGs performed. Abciximab and cytochalasin D decreased MA in all samples. MA of whole blood (18.6 +/- 3.1 mm) and PRP (33.7 +/- 3.5 mm) spiked with abciximab or cytochalasin D alone (15.0 +/- 2.9 mm and 25.0 +/- 4.0 mm) were significantly higher when compared with abciximab and cytochalasin D combined (10.4 +/- 3.0 and 20.2 +/- 3.5 mm). While MA of PRP and homologous PPP were significantly (P < 0.001) different after individual administration of abciximab and cytochalasin D, combination of both abolished this difference (20.2 +/- 3.5 mm and 20.4 +/- 3.7 mm, P = 0.372). In whole blood of critically ill patients or patients undergoing major surgery there was also a significant difference of MA between abciximab alone and in combination with cytochalasin D (16.5 +/- 11.3 mm and 11.3 +/- 7.7 mm, P < 0.001). This indicates that in contrast to individual administration of abciximab or cytochalasin D, a combination of both compounds eliminates the platelet-specific effect on MA of TEG tracings.

Management of heparin resistance during cardiopulmonary bypass: the effect of five different anticoagulation strategies on hemostatic activation

OBJECTIVE

Attenuation of hemostatic activation is a central goal during CPB. However, this poses a problem in patients insensitive to heparin. The present investigation was performed to assess different strategies of managing patients with heparin resistance during CPB.

DESIGN

A randomized, prospective clinical investigation.

SETTING

A major European heart center.

PARTICIPANTS

Five groups with 20 patients each were investigated.

INTERVENTIONS

The groups were handled as follows: (1). maintenance of a target ACT, (2). maintenance of the target unfractionated heparin (UFH) level and supplementation of a UFH level-based strategy with (3). AT III, (4). the direct thrombin inhibitor r-hirudin, or (5). the short-acting platelet glycoprotein (GP) IIb/IIIa antagonist tirofiban. Platelet count and generation of contact factor XIIa, thrombin, and soluble fibrin were assessed. Samples were obtained before CPB and after CPB before protamine infusion.

MEASUREMENTS AND MAIN RESULTS

There were no differences observed in the generation of factor XIIa. The UFH-based strategy and supplementation with AT III, r-hirudin, and tirofiban resulted in significantly reduced (p < 0.05) thrombin generation compared with ACT management. A significant reduction of fibrin formation was seen only in patients who received AT III, r-hirudin, or tirofiban supplementation to the UFH. The administration of tirofiban resulted in a significant preservation of the platelet count compared with the other groups. There were no significant differences in the postoperative blood loss.

CONCLUSIONS

Activation of hemostasis during CPB in heparin-resistant patients most likely has to be attributed to stimulation of the tissue factor pathway. Even the sole use of high concentrations of UFH does not effectively inhibit this activation. Therefore, in these patients anticoagulation during CPB with UFH should be supplemented with either AT III, a short-acting direct thrombin inhibitor, or a short-acting platelet glycoprotein IIb/IIIa antagonist.

Predictors of ARF after cardiac surgical procedures

BACKGROUND

In a pilot study, a low preoperative serum ferritin level predicted increased risk for acute renal failure (ARF) after cardiopulmonary bypass. It was hypothesized that this may reflect a decreased ability to bind free iron and defend against oxidative stress. However, the pilot study was performed in a small number of patients (n = 30) operated on by a single surgeon. The purpose of this study was to validate whether the serum ferritin level predicts ARF in a larger sample.

METHODS

The present study evaluated 120 patients who underwent procedures performed by eight surgeons at another tertiary referral center. Data were collected prospectively and included patient characteristics, laboratory studies, procedure types, and postoperative course. ARF was defined as a 25% or greater increase in creatinine level 48 hours after surgery.

RESULTS

The frequency of ARF was 42%, but no patient required dialysis therapy. Preoperative serum ferritin levels did not differ in the groups with and without ARF (158 +/- 119 and 163 +/- 125 ng/mL, respectively), and rates of ARF did not differ when examined by ferritin quartiles. ARF was more frequent in those who underwent valve surgery (54% versus 35% in patients who did not undergo valve procedures; P = 0.044). The odds ratio for ARF after valve surgery was 2.58 (95% confidence interval, 1.06 to 6.29; P = 0.037), adjusted for longer times of surgery and aortic cross-clamp. Most excess ARF occurred in those who underwent aortic valve replacement (AVR; 62%; P = 0.014 versus nonvalve procedures).

CONCLUSION

Low preoperative serum ferritin level was not confirmed to predict ARF after cardiac surgery. Valve procedures, particularly AVR, increased the risk for ARF.

Five year clinical follow up of patients who have had off pump coronary artery bypass grafting

BACKGROUND

Off pump coronary artery bypass (OPCAB) has become a common technique for conducting coronary artery surgery. There has been some concern that the anastomoses might not be conducted as effectively on the beating heart, which could lead to poor long-term results. The aim of the present study was to follow up all patients who had undergone OPCAB at our institution to determine clinical outcomes up to 5 years postoperatively.

METHODS

All living patients who had undergone OPCAB up until December 2000 were telephoned. For those who could be contacted, a detailed questionnaire was completed and the data were analysed.

RESULTS

The technique of OPCAB was carried out on 312 patients. Thirteen of these patients died, five perioperatively. Actuarial survival at 5 years was 94.6% and freedom from cardiac related events was 92.1%. There were only two patients with angina worse than class I. Patients showed a high rate of compliance with risk factor management. Forty per cent of patients claimed to have had psychological problems related to the surgery.

CONCLUSIONS

Mid-term results of OPCAB are very satisfactory, but randomised trials are needed to see whether they are different from the results of conventional coronary artery bypass grafting.