The effects of high-dose heparin on inflammatory and coagulation parameters following cardiopulmonary bypass.

Systemic inflammation and the activation of the coagulation system following cardiopulmonary bypass (CPB) may contribute to postoperative complications. In vitro studies have demonstrated that heparin possesses anti-inflammatory properties. To ascertain the relative benefits of high versus low heparin doses, we studied the impact of varying heparin doses on the inflammatory response and coagulation system during and following CPB. Forty patients scheduled for elective coronary artery bypass surgery requiring CPB were randomized to either a low dose (300 U/kg) (Group L) or a high dose of unfractionated heparin (600 U/kg) (Group H). To evaluate the inflammatory response, proinflammatory cytokines [tumor necrosis factor-alpha and interleukin-6 (IL-6)] were measured at four different times: before CPB (T0), 30 min after the institution of CPB (T1), 30 min after cross-clamp release (T2), and 4 h after the end of CPB (T3). Thrombin-antithrombin complex, platelet factor 4 and anti-activated factor X heparin concentrations were also measured. Patients in Group H received greater heparin (44.934 U versus 27.741 U, P<0.001) and protamine (P=0.003) doses. Postoperative blood loss and blood products transfusions were not significantly different in the groups. At T1, mean heparin plasma concentration was higher in Group H (P<0.001). IL-6 was significantly lower in Group H compared with Group L (P=0.01) only at T1. Using a mixed-effects statistical model, tumor necrosis factor-alpha and IL-6 levels were comparable regardless of the heparin dose. Thrombin-antithrombin complex levels were lower in Group H (P=0.04) and platelet factor 4 levels were significantly lower in Group H at T2 (P=0.04). Higher heparin doses were associated with higher heparin concentrations during CPB. A high heparin dose achieved a better preservation of the coagulation system with less thrombin formation and platelet activation. The heparin dose had small influence on proinflammatory cytokines release.     

Recombinant hirudin for cardiopulmonary bypass anticoagulation: a randomized, prospective, and heparin-controlled pilot study

BACKGROUND: Lepirudin, a recombinant hirudin, is a direct acting thrombin inhibitor that has been used as a heparin alternative in patients with heparin-induced thrombocytopenia requiring on-pump cardiac surgery. To evaluate the efficacy, safety, and clinical utility of lepirudin as a cardiopulmonary bypass (CPB) anticoagulant, we compared lepirudin with heparin in a routine CPB setting. METHODS: Twenty patients were randomly assigned to receive lepirudin (0.25 mg/kg b. w. bolus and 0.2 mg/kg b. w. added to the CPB priming) or heparin (400 U/kg b. w. bolus) with protamine reversal. Lepirudin and heparin anticoagulation during CPB was monitored using the ecarin clotting time or ACT, respectively and additional lepirudin (5 mg) or heparin (5000 U) boluses were administered. RESULTS: The CPB circuit was performed in both groups without thromboembolic complications. Median blood loss during the first 36 hours was statistically higher ( P = 0.007) in the lepirudin group (1.226 +/- 316 ml) compared to the heparin group (869 +/- 189 ml). One patient of the lepirudin group developed pulmonary embolism 24 hours after surgery. This patient was tested homozygous for the FV-Leiden mutation. CONCLUSION: Lepirudin provides effective CPB anticoagulation but induces a higher postoperative blood loss than heparin. Lepirudin should be restricted to patients undergoing CPB who cannot be exposed to heparin.     

Neutralization of low molecular weight heparin by polybrene prevents thromboxane release and severe pulmonary hypertension in awake sheep

Protamine reversal of heparin anticoagulation in patients is occasionally associated with life-threatening acute pulmonary hypertension. In a sheep model, we evaluated the effect on this adverse cardiopulmonary reaction of modifying the type of heparin (low molecular weight heparin compared with unfractionated heparin) and the type of heparin antagonist (polybrene compared with protamine). Protamine reversal of low molecular weight heparin (LMWH) and polybrene reversal of unfractionated heparin induced more than a 10-fold increase of plasma thromboxane B2 levels, a threefold increase of pulmonary vascular resistance and pulmonary artery pressure, and a 25% decrease of PaO2. A similar adverse reaction followed protamine reversal of conventional unfractionated heparin. However, with polybrene (1 mg/kg) reversal of LMWH (1 mg/kg), we measured neither pulmonary hypertension (pulmonary artery pressure was 22.6 +/- 3.6 mm Hg at 1 minute after polybrene reversal of LMWH compared with 47.9 +/- 4.2 mm Hg after protamine reversal of unfractionated heparin, p less than 0.005 groups differ), hypoxemia (PaO2 was unchanged 2 minutes after polybrene compared with a decrease of 26 mm Hg 2 minutes after protamine, p less than 0.05), nor acute release of thromboxane into arterial plasma (thromboxane B2 was 0.2 +/- 0.1 at 1 minute after polybrene compared with 3.7 +/- 1.7 ng/ml at 1 minute after protamine, p less than 0.005). The hemodynamic effects and mediator release were also benign after neutralization of larger doses of LMWH (3 mg/kg) by polybrene (3 mg/kg). The increases of activated clotting time and activated partial thromboplastin time due to both types of heparin were completely reversed with polybrene. Anti-Xa activity increased to more than 3 IU/ml 4 minutes after LMWH anticoagulation (p less than 0.01) but was only partially neutralized by polybrene. Various polyanion-polycation complexes that are formed when heparin anticoagulation is reversed induce thromboxane release and acute pulmonary vasoconstriction in awake sheep. Reversal of LMWH anticoagulation with polybrene does not elicit this adverse reaction.     

Comparison of recombinant hirudin and heparin as an anticoagulant in a cardiopulmonary bypass model.

Recombinant (r) hirudin is a potent thrombin-specific inhibitor originally derived from the natural hirudin of the leech (Hirudo medicinalis). We have studied the efficacy of r-hirudin compared to heparin in a dog model of cardiopulmonary bypass (CPB) surgery. Two administration regimens were used for r-hirudin: Group I received 1.0 mg/kg intracardiac (i.c.) bolus then intravenous (i.v.) bolus at 30 min (n = 10); Group II received 1.0 mg/kg (i.c.) bolus with 1.25 +/- 0.04 mg/kg/h (i.v.) infusion (n = 8). Group III was given heparin 1.66 mg/kg (i.c.) bolus (n = 9). Aspiration of blood from the chest cavity revealed no significant difference between the three groups. Measurement of fibrin deposits in the pump line filter revealed higher amounts in the r-hirudin groups (P = 0.02). Decreases in platelets, fibrinogen and haematocrit due primarily to haemodilution were the same in each group. The bleeding time was less prolonged for r-hirudin than for heparin (p less than 0.001). No antagonist for r-hirudin was used; however, due to its short half-life, all coagulation parameters returned to baseline within 30 min after CPB. Since r-hirudin has no effect on platelets, is a poor immunogen, does not require a plasma cofactor, and may not require an antagonist, it may provide an alternative anticoagulant to heparin in CPB. Additional studies are, however, needed to optimize the dose and to evaluate other clinical aspects of r-hirudin.     

A comparison of aminocaproic acid and tranexamic acid in adult cardiac surgery

We compared Aminocaproic acid with tranexamic acid, prospectively in 120 patients undergoing coronary artery bypass surgery on cardiopulmonary bypass. Patients were assigned to one of the 3 groups. Group A (n=40) did not receive any drug and acted as the control group. Group B (n=4) received aminocaproic acid 100 mg/kg each at anaesthetic induction, on bypass and after protamine reversal of heparin. group C (n=40) received tranexamic acid 10 mg/kg each at anaesthetic induction, on bypass and after protamine reversal of heparin. Postoperative blood loss at 24 hours, blood and blood product usage, and re-exploration rates were recorded, and tests for coagulation were performed at 6 hours postoperatively. It was found that blood loss in group A at 24 hours (780+/-120 mL) was significantly greater than Group B (360+/-90 mL) and Group C (215+/-70 mL). Plasma and platelet concentrate use in Group A (215+/-30 mL and 150+/-30 mL) was greater than Group B (190+/-20 mL and 75+/-30 mL) and Group C (185+/-20 mL and 80+/-30 mL). Re- explorations in Group A, 8/40 (20%) were greater than Group B, 2/40 (5%) and Group C, 2/40 (5%). Coagulation tests revealed better preservation of fibrinogen and lower levels of fibrin degradation products, in group B and C. These two groups were however statistically indistinguishable in respect to all the parameters studied, when compared with each other. It was concluded that both the antifibrinolytic agents in the doses studied were equally effective in reducing postoperative blood loss, blood and blood products usage and re-exploration rates. Coagulation parameters were better preserved as compared to the control group.     

Reversible shear-mediated platelet dysfunction during cardiac surgery as assessed by the PFA-100 platelet function analyzer.

We undertook this investigation to assess alterations in shear-mediated platelet function during cardiac surgery and to determine the potential for the PFA-100 to predict post-operative bleeding. Platelet aggregation and PFA-100 closure times were determined in 18 adult patients at five intervals during cardiac surgery. Associations between post-operative bleeding and closure times were examined in an additional 58 patients. Statistical analysis consisted of Student's t, Wilcoxon signed rank, and Spearman correlation tests. All results are reported as mean +/- SEM. Collagen/epinephrine closure times were prolonged prior to and throughout surgery. Collagen/adenosine-5'-diphosphate (ADP) closure times were significantly prolonged by heparin administration, 141 +/- 15 s versus 115 +/- 10 s (P = 0.01), and subsequent initiation of cardiopulmonary bypass (CPB), 203 +/- 12 s (P= 0.0001); however, 15 min after protamine administration, closure times returned to near pre-operative values, 138 +/- 12 s (P = not significant). In contrast, platelet aggregation in response to ADP remained impaired in 17 of 19 patients after CPB. Neither ex vivo correction of sample hematocrits nor supplementation with Humate P affected closure times. Positive and negative predictive values for post-CPB collagen/ADP closure times to predict bleeding were 18 and 96%, respectively. These results suggest that factors both intrinsic and extrinsic to the platelet contribute to reversible shear-mediated platelet dysfunction during CPB, and that the PFA-100 may prove useful after CPB to identify patients unlikely to benefit from platelet transfusions.     

The importance of aprotinin and pentoxifylline in preventing leukocyte sequestration and lung injury caused by protamine at the end of cardiopulmonary bypass surgery

BACKGROUND: Protamine has adverse effects on pulmonary gas exchange during the postoperative period. The objective of this study was to investigate the importance of aprotinin and pentoxifylline in preventing the leukocyte sequestration and lung injury caused by protamine administered after the termination of cardiopulmonary bypass (CPB). METHODS: Participants (n = 39) were allocated into three groups at the termination of CPB: Group 1, (control group, n = 16); Group 2 (aprotinin group, n = 12), who received protamine + aprotinin (15,000 IU/kg); and Group 3 (Pentoxifylline group, n = 11), who received protamine + pentoxifylline (10 mg/kg). Leukocyte counts in pulmonary and radial arteries were determined after the termination of CPB and before any drug was given (t1), and 5 minutes (t2), 2 hours (t3), 6 hours (t4) and 12 hours (t5) after the administration of protamine. Alveolar-arterial O2 gradient (A-aO2) and dynamic pulmonary compliance were measured at t1, t2 and t3. RESULTS: In the control group, an increase in pulmonary leukocyte sequestration was observed 5 minutes and 2 hours after protamine administration, after which this difference disappeared. No significant degree of pulmonary sequestration was detected in any measurements after protamine was administered in the aprotinin and pentoxifylline (PTX) groups. Dynamic lung compliance was 50.1, 45.2 and 47.2 ml/cm H2O in the control group, 49.2, 61.1 and 56.3 ml/cm H2O in the aprotinin group, and 49.5, 54.5 and 50.4 ml/cm H2O in the PTX group. The A-aO2 gradient was 212.2, 263.3 and 254.3 mm Hg in the control group, 209.4, 257.1 and 217.3 mm Hg in the aprotinin group, and 211.3, 260.8 and 219.2 mm Hg in the PTX group. CONCLUSION: Aprotinin and PTX treatments have favourable effects on lung function by reducing protamine-induced leukocyte sequestration into lungs at the end of CPB.     

Estimating the rate of thrombin and fibrin generation in vivo during cardiopulmonary bypass

Our objective was to estimate the in vivo rates of thrombin and fibrin generation to better understand how coagulation is regulated. Studied were 9 males undergoing cardiopulmonary bypass (CPB). The rates of thrombin, total fibrin, and soluble fibrin generation in vivo were based on measured levels of prothrombin activation peptide F1.2, thrombin-antithrombin complex, fibrinopeptide A, and soluble fibrin, combined with a computer model of the patient's vascular system that accounted for marker clearance, hemodilution, blood loss, and transfusion. Prior to surgery, the average thrombin generation rate was 0.24 +/- 0.11 pmol/s. Each thrombin molecule in turn generated about 100 fibrin molecules, of which 1% was soluble fibrin. The thrombin generation rate did not change after sternotomy or administration of heparin, then rapidly increased 20-fold to 5.60 +/- 6.65 pmol/s after 5 minutes of CPB (P =.000 05). Early in CPB each new thrombin generated only 4 fibrin molecules, of which 35% was soluble fibrin. The thrombin generation rate was 2.14 +/- 1.88 pmol/s during the remainder of CPB, increasing again to 5.47 +/- 4.08 pmol/s after reperfusion of the ischemic heart (P =.000 08). After heparin neutralization with protamine, thrombin generation remained high (5.34 +/- 4.01 pmol/s, P =.0002) and total fibrin generation increased, while soluble fibrin generation decreased. By 2 hours after surgery, thrombin and fibrin generation rates were returning to baseline levels. We conclude that cardiopulmonary bypass and reperfusion of the ischemic heart results in bursts of nonhemostatic thrombin generation and dysregulated fibrin formation, not just a steady increase in thrombin generation as suggested by previous studies.     

不同负荷剂量氯吡格雷对血小板聚集率的影响

目的比较两种剂量氯吡格雷的起效时间及安全性,为急性冠状动脉（冠脉）综合征患者用药方案提供依据。方法60例急性冠脉综合征使用不同负荷剂量氯吡格雷患者随机分为A组（300mg）和B组（600mg）,均予氯吡格雷75mg／d后续治疗。以腺苷二磷酸（ADP）5μmol／L及20μmol／L作为诱导剂检测服药前及服药后2h和6h的血小板聚集率,并检测服药前及服药后第3天的血自细胞及血小板计数。结果在ADP20μmoL／L诱导的血小板聚集检测中,两组均显示服药后6h比服药后2h达到更高的血小板聚集抑制水平[A组（29．75±12．11）％比（43．63±14．31）％,P〈0．05;B组（28．86±10．24）％比（34．86±10．84）％,P〈0．05]。B组与A组相比,在服药后2h即起到更加明显的血小板聚集抑制作用[（34．86±10．84）％比（43．63±14．31）％,P〈0．05]。服药后3d内所有人选患者均无出血、自细胞减少及血小板减少等事件发生。结论氯吡格雷600mg作为负荷剂量较之300mg可以更快地达到较高水平的血小板抑制作用,且两者安全性相似。     

Hemostasis changes during cardiopulmonary bypass surgery

A number of hemostasis parameters were studied in a total of 63 patients undergoing cardiopulmonary bypass (CPB) for open heart surgery. In 33 patients fibrinogen, Factors II, V, VIII:C, X, XI, antithrombin, plasminogen, alpha 2-antiplasmin, and platelet counts were assayed before surgery, during maximal hypothermia, at the end of the bypass procedure, before and after protamine sulfate infusion, in the intensive care unit, and 48 hours postoperatively. All factors assayed decreased markedly when the patients were placed on the bypass machine, the drop fairly well paralleling the decrease in hematocrit. During bypass the factors remained low, although a slight tendency toward an increase was noted. Only platelet counts remained low with a decreasing trend until the end of bypass. In the intensive care unit a second decrease in fibrinogen, Factors II and V and antithrombin was noted. This drop was unrelated to four patients who experienced a greater blood loss during this time than the others. Forty-eight hours postoperatively, a marked increase could be found in all clotting factors and near normal levels were measured. Platelet counts remained low, however. The decrease in factors rarely dropped into a range where one would expect a compromised hemostasis (less than 30%). Although antithrombin levels decreased below 60%, no difficulties with heparinization were encountered. Several factors were assayed manually and by automated analyzer (Multistat III), and excellent correlations were found between both procedures. Also a good correlation was found between the activated whole blood clotting times and quantitative heparin assays. In 30 additional patients platelet function was studied before surgery, after thoracotomy, after heparin administration, after initiation of bypass, at maximal hypothermia, before and after protamine sulfate infusion, and 24 hours postoperatively. Platelet counts once again decreased as patients were placed on the CPB machine and remained low throughout the procedure. Mean platelet volumes were unchanged until protamine was given. At that time, a significant drop in mean platelet volume was recorded. Twenty-four hours postoperatively the volumes were normal again. Platelet aggregation studies were performed on a whole blood aggregometer using two concentrations of ADP, collagen, and ristocetin as aggregation inducers. A significant decrease in aggregability was seen when the patients were connected to the CPB apparatus.(ABSTRACT TRUNCATED AT 400 WORDS)     

Rituximab in a risk‐adapted treatment strategy gives excellent therapeutic results in nodular lymphocyte‐predominant Hodgkin lymphoma

Heparin anticoagulation followed by protamine reversal is commonly used in cardiopulmonary bypass (CPB). As an alternative to protamine, a recombinant inactive antithrombin (riAT) was designed as an antidote to heparin and was previously shown to be as potent as protamine in‐vitro. In the present study, riAT was assessed for its ability to neutralize heparin after CPB in a rat model. After 60 min of CPB under heparin, rats received 5 mg/kg protamine, 37.5 mg/kg riAT or phosphate buffered saline (PBS) as placebo. Residual anticoagulant activity was assessed using the activated partial thromboplastin time assay before, and 10–30 min after reversion. Haemodynamic monitoring was performed and plasma histamine concentration was also measured. In this model, riAT appeared to be as efficient as protamine in neutralizing heparin. Ten minutes after injection, riAT and protamine both decreased heparin activity, to 1.8 ± 1.3 and 4.5 ± 1.4 u/ml, respectively (23.1 ± 5.1 u/ml in placebo group). Furthermore, evolution of mean carotid arterial pressure, heart rate and plasma histamine levels was comparable in rats treated with PBS or riAT, while protamine exhibited haemodynamic side effects and increased histamine plasma concentration. Thus, riAT could represent an advantage over protamine in CPB because it efficiently reverses heparin activity without negative effects on haemodynamic parameters and plasma histamine level.     

Complement activation from protamine sulfate administration after coronary angiography

The cause of hypotension after reversal of heparin by protamine has not been well defined. In this study we evaluated complement activation (C3a and C4a) by the heparin-protamine complex in 46 consecutive patients (40 received protamine sulfate to reverse heparin, and six did not) during and after coronary angiography. In patients receiving protamine sulfate, there was a significant increase in C3a over the value before protamine sulfate administration (P less than .001) or in patients who did not receive protamine sulfate (P less than .05): 807 +/- 100 ng/ml vs. 274 +/- 75 ng/ml. There were no significant changes in C4a after protamine sulfate administration. These results indicate that the alternate complement pathway is activated when protamine sulfate is administered after coronary angiography. This may induce hypotension as well as platelet aggregation and thrombus formation and may contribute to coronary instability. Therefore, in unstable patients, heparin reversal by protamine should not be done routinely.     

Heparin rebound phenomenon--much ado about nothing?

Significant postoperative bleeding following open-heart surgery is often ascribed to the so-called heparin 'rebound' phenomenon and as such is treated with additional empiric doses of protamine sulphate. However, inappropriate protamine administration has been reported to be associated with acute pulmonary hypertension. The efficacy of heparin reversal was investigated in 42 patients undergoing open-heart surgery. The standard heparin bolus of 3 mg/kg body weight (4.1 IU/ml blood) administered before cardiopulmonary bypass was countered at the end of bypass using an empirical equivalent (3 mg/kg) of protamine. This regimen resulted in complete heparin neutralization (measured by the Hepcon HMS [Hemotec Inc., Englewood, CO, USA]) 15 min after protamine administration in all 42 patients, but heparin levels (0.4 IU/ml) were transiently detectable (duration less than 1 h) in six (14%) of the 42 cases 2 h later. Twenty-four hour postoperative bleeding in these patients did not differ significantly from that seen in patients who did not exhibit heparin rebound. Similarly, the thrombelastographic profiles (at 15 min and 2 h post-operation) and coagulation screen (prothrombin time, activated partial thromboplastin time, activated clotting time and platelets) did not differ significantly from those of non-rebound patients. The significance, if any, of the phenomenon of heparin rebound following cardiac surgery remains to be elucidated, and, until such time, conservative administration of protamine in response to 'rebound' is recommended.     

不同酸碱度对鱼精蛋白中和肝素的影响

目的:探讨心脏手术后患者不同酸碱度对鱼精蛋白中和肝素的影响。方法:我院2009年10月至2010年5月期间对352例心脏病患者行体外循环手术,麻醉后即测正常活化凝血时间(ACT)值,在打开心包后按2.5 mg/kg从中心静脉给予肝素,在体外循环结束时,鱼精蛋白的剂量从肝素的1.5倍开始在升主动脉根部给药,测量中和后的ACT值,并依此作为追加鱼精蛋白量的参考。按体外循环结束时其酸碱度不同分为3组,观察比较各组肝素与鱼精蛋白总量之比、中和后ACT值,并观测3组术后6 h、12 h及24 h引流量及术后总引流量。结果:在酸性环境下,鱼精蛋白中和肝素剂量及术后引流量高于其他2组,差异有统计学意义(P<0.05)。在非酸性环境下,鱼精蛋白和肝素比平均值为1.63∶1;在pH<7.31或剩余碱(BE)<-6时,鱼精蛋白的用量显著增加,鱼精蛋白和肝素比平均值为2.33∶1。结论:不同酸碱度对鱼精蛋白拮抗肝素有较大影响,酸性环境下鱼精蛋白的中和作用会减弱,鱼精蛋白用量增加,术后引流量也会增多。在体外循环结束时,测得pH<7.31或BE<-6时,建议纠正酸碱平衡的同时适量追加鱼精蛋白。     

Clinical effects of different protamine doses after cardiopulmonary bypass

The optimal dose of protamine needed to reverse the anticoagulant effect of heparin after cardiopulmonary bypass is still not known. In this retrospective cohort study, we investigated 3 different dose regimes in 300 patients undergoing coronary artery bypass grafting. Group A patients (n = 100) were given protamine in the ratio of 1.3 mg to 1 mg heparin, group B patients (n = 100) were given 0.75 mg protamine to 1 mg heparin, and group C patients (n = 100) were given protamine in fractionated doses of 1 mg + 0.15 mg + 0.15 mg to 1 mg heparin. The groups were comparable in all major clinical and operative variables. The heparin dose was almost identical in the groups. The rate of red cell transfusion was significantly higher in group B than in the other groups. A similar but nonsignificant trend was observed in the incidence of resternotomy for postoperative bleeding, mediastinal drainage, and postoperative hemoglobin loss. The study demonstrates that a single bolus dose of 1.3 mg protamine to 1 mg heparin is safe and efficient for neutralizing heparin after cardiopulmonary bypass.     

Reheparinisation requirements after cardiopulmonary bypass in patients treated with aprotinin.

OBJECTIVE--To determine reheparinisation requirements following protamine neutralisation after the discontinuation of cardiopulmonary bypass in a group of patients receiving "low dose" aprotinin compared with a control group. DESIGN--Randomised, placebo controlled study. SETTING--Regional cardiothoracic unit within a district general hospital. PATIENTS--20 patients were consecutively allocated to one of two groups. All patients had a primary elective aortocoronary bypass operation using standard anaesthetic techniques and no patient was withdrawn from the study. INTERVENTIONS--Aprotinin group patients (n = 9) received aprotinin (1 x 10(6) kallikrein inactivator units (KIU)) as an intravenous bolus after the induction of anaesthesia, and 1 x 10(6) KIU was added to the pump prime. Control group patients (n = 11) received 0.9% saline placebo. MAIN OUTCOME MEASURES--Activated clotting time (ACT), heparin concentration, and heparin dose response (HDR) measured before, during, and after bypass. The HDR is an accurate method to determine the patients' in vitro response to heparin and is used to predict the dose of heparin required to attain an ACT of 400 seconds. RESULTS--Activated clotting times were similar in the two groups for the duration of the study. Heparin concentrations were zero in all patients before heparin administration and after protamine neutralisation. During bypass there was no difference between the groups. The median heparin dose response was the same in the two groups before the administration of heparin, but after the neutralisation of heparin with protamine after the discontinuation of bypass the HDR was significantly higher in the aprotinin group for up to one hour (median of 2.9 IU/ml v 1.25 in the control group at 10 minutes after protamine neutralisation, P < 0.01; 2.5 v 1.45 at 30 minutes, P < 0.05; and 2.9 v 1.6 at one hour, P < 0.001). CONCLUSION--Heparin requirements were nearly doubled in patients treated with aprotinin, who required reheparinisation for up to one hour after protamine. This relative "heparin resistance" cannot be explained by the presence of excessive protamine. Aprotinin may be a substrate for the N-carboxypeptidase that destroys protamine, thus indirectly enhancing and prolonging the activity of protamine.     

Hirudin, heparin, and placebo during deep arterial injury in the pig. The in vivo role of thrombin in platelet-mediated thrombosis

Three dosages (0.3, 0.7, and 1.0 mg/kg) of recombinant hirudin, a specific inhibitor of thrombin, were compared with heparin (50 units/kg) and placebo for reducing thrombus formation in the carotid arteries of 50 pigs after deep injury by balloon dilatation. Each drug was administered as a bolus followed immediately by a continuous infusion of the same dose per hour. Major end points were quantitative indium-111-labeled platelet and iodine-125-labeled fibrinogen deposition and the incidence of mural thrombosis. This study showed that heparin, at a dose that prolonged the activated partial thromboplastin time (APTT) to twice the control time, did not prevent mural thrombosis or significantly reduce platelet deposition compared with placebo but did reduce fibrinogen deposition. Recombinant hirudin markedly reduced platelet and fibrinogen deposition in a dose-related manner and totally eliminated mural thrombosis at an APTT of two to three times that of control. Platelet deposition (x 10(6)/cm2, mean +/- SEM) in areas of deep arterial injury for the placebo, heparin, and 0.3, 0.7, and 1.0 mg/kg hirudin groups was 54 +/- 21, 33 +/- 9, 22 +/- 6, 8 +/- 1, and 7 +/- 1, respectively; electron microscopy showed a single layer (or less) of platelets at the two highest hirudin dosages. The incidence of macroscopic mural thrombosis was 76% with placebo, 57% with heparin, 46% with 0.3 mg/kg hirudin; there were no thrombi with 0.7 or 1.0 mg/kg hirudin (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Kistrin, a polypeptide platelet GPIIb/IIIa receptor antagonist, enhances and sustains coronary arterial thrombolysis with recombinant tissue-type plasminogen activator in a canine preparation

BACKGROUND. Kistrin is a 68-amino acid polypeptide from the venom of the Malayan pit viper Agkistrodon rhodostoma, which inhibits the platelet GPIIb/IIIa receptor. Its effect on thrombolysis, reocclusion, and bleeding associated with administration of recombinant tissue-type plasminogen activator (rt-PA) was studied in a canine model of coronary artery thrombosis. METHODS AND RESULTS. Coronary patency was monitored for 2 hours by ultrasonic flow probe and repeated coronary angiography. The rt-PA was given as 0.45-mg/kg bolus injections at 15-minute intervals until recanalization or to a maximum of four boluses. Four groups of four or five dogs were studied: a control group that received intravenous heparin (4,000-unit bolus and 1,000 units each hour) and three groups that received heparin and 0.48, 0.24, or 0.12 mg/kg kistrin, administered as a 10% bolus injection and an infusion during a 60-minute period. In the control group, reflow occurred in four of five dogs within 37 +/- 47 minutes but was followed by cyclic reflow and reocclusion. Kistrin at a dose of 0.48 and 0.24 mg/kg reduced the time to reflow to 6 +/- 5 and 10 +/- 3 minutes, respectively, and abolished reocclusion. With 0.12 mg/kg kistrin, reflow occurred in all four animals, within 27 +/- 23 minutes, and reocclusion occurred in two animals. Kistrin induced a dose-related prolongation of the template bleeding time: with 0.48 mg/kg kistrin, the bleeding time was prolonged from 3.8 +/- 1.3 minutes before infusion to 29 +/- 2 minutes during infusion, but it was shortened to 8.3 +/- 2.6 minutes at 90 minutes after the end of infusion. Kistrin also caused a dose-related inhibition of platelet aggregation with ADP and collagen: with 0.48 mg/kg kistrin, platelet aggregation was abolished during the infusion but had partially recovered toward the end of the observation period. Pathological examination of recanalized coronary arterial segments of dogs given 0.48 or 0.24 mg/kg kistrin revealed widely patent arteries with some platelets layered on the damaged intimal surface. CONCLUSIONS. Kistrin increases the rate and extent of thrombolysis with a reduced dose of rt-PA, and it prevents reocclusion. At an effective dose, it is associated with a transient prolongation of the bleeding time and inhibition of platelet aggregation. Kistrin may offer promise as adjunctive treatment to thrombolytic agents in patients with acute myocardial infarction.     

Anticoagulation with heparin during cardiac catheterization and its reversal by protamine

The duration of effective anticoagulation with heparin during cardiac catheterization and angiography was determined in 201 patients. Effective anticoagulation was defined as prolongation of the activated partial thromboplastin time (APTT) by 2 or more times the upper limit of normal. When the procedure was completed within 40 min of heparin administration, all patients were anticoagulated adequately. The incidence of inadequate anticoagulation ranged from 9% to 25% as the time from heparin administration increased to 89 min. Procedures completed more than 90 min after heparin administration had a 58% incidence of inadequate anticoagulation. A protocol to estimate the appropriate protamine dose was developed based on experience accumulated in the first 78 patients and tested subsequently in 101 consecutive patients. Clotting studies returned to the normal range in 92% of the patients. The mean APTT decreased from 84.1 +/- 19.4 to 27.4 +/- 2.5 sec (p less than .001) after protamine. Patients who did not correct to normal after protamine remained only 2.8 +/- 1.4 sec (range 0.7-5.5 sec) above normal. These data provide an estimate of the duration of anticoagulation during cardiac catheterization and angiography and demonstrate the feasibility of a simple and reliable method to reverse the effects of heparin.     

Hirudin interruption of heparin-resistant arterial thrombus formation in baboons

To determine the role of thrombin in high blood flow, platelet-dependent thrombotic and hemostatic processes we measured the relative antithrombotic and antihemostatic effects in baboons of hirudin, a highly potent and specific antithrombin, and compared the effects of heparin, an antithrombin III-dependent inhibitor of thrombin. Thrombus formation was determined in vivo using three relevant models (homologous endarterectomized aorta, collagen-coated tubing, and Dacron vascular graft) by measuring: (1) platelet deposition, using gamma camera imaging of 111In-platelets; (2) fibrin deposition, as assessed by the incorporation of circulating 125I-fibrinogen; and (3) occlusion. The continuous intravenous infusion of 1, 5, and 20 nmol/kg per minute of recombinant hirudin (desulfatohirudin) maintained constant plasma levels of 0.16 +/- 0.03, 0.79 +/- 0.44, and 3.3 +/- 0.77 mumol/mL, respectively. Hirudin interrupted platelet and fibrin deposition in a dose-dependent manner that was profound at the highest dose for all three thrombogenic surfaces and significant at the lowest dose for thrombus formation on endarterectomized aorta. Thrombotic occlusion was prevented by all doses studied. In contrast, heparin did not inhibit either platelet or fibrin deposition when administered at a dose that maximally prolonged clotting times (100 U/kg) (P greater than .1), and only intermediate effects were produced at 10-fold that dose (1,000 U/kg). Moreover, heparin did not prevent occlusion of the test segments. Hirudin inhibited platelet hemostatic function in concert with its antithrombotic effects (bleeding times were prolonged by the intermediate and higher doses). By comparison, intravenous heparin failed to affect the bleeding time at the 100 U/kg dose (P greater than .5), and only minimally prolonged the bleeding time at the 1,000 U/kg dose (P less than .05). We conclude that platelet-dependent thrombotic and hemostatic processes are thrombin-mediated and that the biologic antithrombin hirudin produces a potent, dose-dependent inhibition of arterial thrombus formation that greatly exceeds the minimal antithrombotic effects produced by heparin.