Thrombosis Research 127 (2011) 272–274

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Thrombosis Research

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Letter to the Editors-in-Chief

Aprotinin, but not tranexamic acid, is associated with increasedpulmonary microvascular fibrin deposition after cardiac surgery

Dear Editors,

We previously demonstrated that pulmonary microvascular fibrindeposition developed following cardiac surgery in aprotinin treatedpatients. Furthermore, the extent of microvascular fibrin depositionwas reduced with a pre-operative heparin infusion [1].

In the current study, we investigated whether the anti-fibrinolyticregimen used, to reduce post-operative bleeding, influenced theextent of pulmonary microvascular fibrin deposition.

Materials and methods

A case control study was undertaken. Allocation to the anti-fibrinolytic regimen was not randomised. Patients undergoingelective cardiac surgery with cardiopulmonary (CPB) were eligable.Patients were excluded if they were having re-do cardiac surgery,plasma creatinine greater than 250 μmol/L or age greater than 85.Cases: Six patients were not administered an anti-fibrinolytic agent, 4patients were administered tranexamic acid and 4 patients aprotinin.In these patients an open wedge biopsy of the lung was undertakenafter CPB and protamine administration. Controls: A lung biopsy wasalso undertaken in a further 4 patients before CPB to provide controllevels of pulmonary microvascular fibrin deposition. The patients thatdid not receive an anti-fibrinolytic agent or were administeredtranexamic acid were co-enrolled in the Aspirin and TranexamicAcid for Coronary Artery Surgery Trial [2]. The aprotinin patientscomprised the placebo arm of a study that assessed the effect of a pre-operative heparin infusion on pulmonary microvascular fibrindeposition following cardiac surgery [1]. These studies were approvedby the St. Vincent's Hospital Human Research Ethics Committee allpatients gave written informed consent.

Interventions: Tranexamic acid - was administered intravenouslyfollowing anaesthetic induction as a bolus of 100 mg/kg. Aprotinin -wasadministered intravenously following anaesthetic induction as a2 million U bolus, then infused at 0.5 million U/hr for the duration ofthe operation. An additional 2 million U was added to the pump prime.In the control subjects no heparin, anti-fibrinolytic agent, fresh frozenplasma, cryoprecipitate or platelets were administered prior to the lungbiopsy. In the case subjects no fresh frozen plasma, cryoprecipitate orplatelets were administered prior to the lung biopsy. Surgery: Prior toCPB all patients were administered approximately 300 U/kg of heparintomaintain an activated clotting time above 480 seconds (kaolin, ACT II,Medtronic Hemotec, Inc, Englewood CO). Protamine (~ 300 mg) wasadministered to all patients after discontinuation of cardiopulmonarybypass. Histological analysis of the lung biopsy was undertaken aspreviously described [1]. Statistical analysis: A unpaired permutationtest was used to compare groups [3]. Continuous variables are reportedat mean±standard deviation (SD) or median and (inter-quartile

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range), where appropriate. Differences were considered statisticallysignificant at pb0.05, after Bonferroni's correction for multiplecomparisons.

Results

The groups were similar with respect to baseline and operativecharacteristics (Table 1). Post-operative outcomes including durationof mechanical ventilation, intensive care and hospital stays were alsosimilar.

The extent of pulmonarymicrovascular fibrin deposition followingCPB was higher in the aprotinin group compared with pre-CPB bypasslevels (control group), 42 (33–57) vs 0.6 (0.1-9.4) deposits per mm2

of alveolar tissue, pb0.05. There was, however, no difference in theextent of pulmonary microvascular fibrin deposition following CPBbypass in the no anti-fibrinolytic and tranexamic acid groupscompared with pre-CPB bypass levels, 6.6 (0.6-11.3) p=0.4 and 0.5(0.2–3.0) p=0.7, respectively (Fig. 1). Post-hoc analysis demonstrat-ed that pulmonary microvascular fibrin deposition was higher in theaprotinin group compared with both the no anti-fibrinolytic andtranexamic acid groups, p=0.01 and p=0.02, respectively. Onhistological examination fibrin deposits typically did not totallyocclude the lumen but were layered on the capillary endotheliumforming a circumferential rim (Fig. 2).

Discussion

We found aprotinin, but not tranexamic acid, was associated withan increased number of pulmonary microvascular fibrin depositsfollowing cardiac surgery.

Aprotinin is a unique anti-fibrinolytic, because unlike lysineanalogues, it also promotes coagulation activation through inhibitionof the endogenous anti-coagulant activated protein C. Aprotinincompetitively binds to the active site of activated protein C andinhibits it in a dose dependent manner [4–7]. Aprotinin may alsopromote thrombosis by preventing heparin binding to platelets [8].These actions may explain the increase in pulmonary microvascularfibrin deposition associated with aprotinin and may also explain thehistorical superiority of aprotinin in reducing post-operative bleedingcompared to lysine analogues [9]. Tranexamic acid did not increaselevels of pulmonary microvascular fibrin deposition. This finding mayreflect the relatively weak haemostatic action of tranexamic acid ormay be due to an anti-inflammatory effect. Randomised trials inpatients undergoing cardiac surgery found tranexamic acid reducedinterleukin-6 and plasminogen activator inhibitor-1 levels [10,11].

Pulmonary microvascular fibrin deposition is a potential patho-genic mechanism common to inflammatory conditions, includingsepsis, ischemia-reperfusion injury and trauma [12–14]. Inflamma-tion of the endothelium causes expression of tissue factor triggeringcoagulation activation and fibrin deposition [15]. Our results suggestthat inflammation in the lungs and administration of aprotinin maycombine to promote increased levels of pulmonary microvascular

Table 1Baseline and operative characteristics.

Control Cases

Lung biopsy before CPB(n=4)

Anti-fibrinolytic regimen

No anti-fibrinolytic(n=6)

Tranexamic Acid(n=4)

Aprotinin(n=4)

Age (years) 67.8±4.7 69.8±6.2 71.5±4.7 68.3±11.7Male n (%) 4 (100) 6 (100) 4 (100) 4 (100)Creatinine (umol/L) 107 (76-119) 93 (78-110) 141 (100-224) 93 (71-131)Left ventricle dysfunction‡ n (%) 1 (25) 0 0 0Diabetes n (%) 1 (25) 0 2 (50) 1 (25)Smoked n (%) 2 (50) 4 (67) 4 (100) 4 (100)Hypertension n (%) 3 (75) 5 (83) 3 (75) 3 (75)Statin n (%) 2 (50) 6 (100) 3 (75) 4 (100)Aspirin† n (%) 0 2 (33) 1 (25) 1 (25)Cardiopulmonary bypass (minutes) 136±42 144±26 158±41 112±41Distal grafts 3.5±0.6 3.7±1.4 3.0±1.4 4.0±1.2Aortic valve replacement n (%) 0 2 (33) 1 (25) 0

Data are presented as n (%) or median and (inter-quartile range) or plus-minus which denotes mean and standard deviation. ‡Left ventricle dysfunction denotes moderate or severeimpairment on pre-operative echocardiography. †Aspirin within 7 days of surgery. CPB denotes cardiopulmonary bypass.

273Letter to the Editors-in-Chief

fibrin deposition. Since our data are histological we can only speculateon the clinical significance of our findings. Our results, however,implicate a potential pathogenic mechanism that may be relevant tothe findings of The Blood Conservation Using Anti-fibrinolytics in aRandomised (BART) trial [16]. This trial, in high-risk patientsundergoing cardiac surgery, found a 2-fold increase in death ofpatients administered aprotinin as compared to lysine analogues. Theexcess deaths were due to cardiac causes with a 5-fold increase inright heart failure. Our results implicate excessive pulmonarymicrovascular fibrin deposition as a potential factor. This possibilityis supported by a case series that described patients administeredaprotinin undergoing cardiac surgery for end stage heart failure. Thesepatients developed fatal pulmonary hypertension. In each caseextensive pulmonary microvascular fibrin deposition was demon-strated on lung biopsy or at post-mortem. In one case, administrationof tissue plasminogen activator improved pulmonary pressures andcleared the microvascular thrombi [17,18].

Limitations: The study was small (due to the requirement of a lungbiopsy) and not randomised, these factors increase the possibility of atype II statistical error. Our study may have been strengthened byundertaking both pre and post-cardiopulmonary bypass lung biopsiesin the same patient. We, however, felt that the risk associated with 2lung biopsies was excessive.

Fig. 1. Microvascular fibrin deposits per mm2 of lung tissue. Pulmonary microvascularfibrin deposition was increased in aprotinin treated patients compared to pre-CPBbypass levels (pb0.05), but was not increased in patients not administered an anti-fibrinolytic (p=0.4) or patients administered tranexamic acid (p=0.7). Data shown asmedian and inter-quartile range. CPB denotes cardiopulmonary bypass.

Competing interests

The authors declare that they have no competing interests.

Acknowledgements

We would like to acknowledge and thank the patients whovolunteered to participate in this study.

Fig. 2. Immunohistochemical staining of fibrin (brown) in lung tissue following cardiacsurgery. Panels A (x 10 magnification) and Panel B (x 20 magnification) show fibrindeposits in alveolar capillaries (black arrows).

274 Letter to the Editors-in-Chief

Funding source: Supported by a grant from the St.Vincent'sHospital Research Endowment Fund.

References

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bypass: investigation of haemostatic parameters and the effect of aprotinin usingan ex vivo model. Perfusion Nov 2001;16(6):476–84.

[8] John LC, Rees GM, Kovacs IB. Reduction of heparin binding to and inhibition ofplatelets by aprotinin. Ann Thorac Surg May 1993;55(5):1175–9.

[9] Levi M, Cromheecke ME, de Jonge E, et al. Pharmacological strategies to decreaseexcessive blood loss in cardiac surgery: a meta-analysis of clinically relevantendpoints. Lancet Dec 4 1999;354(9194):1940–7.

[10] Jimenez JJ, Iribarren JL, Lorente L, et al. Tranexamic acid attenuates inflammatoryresponse in cardiopulmonary bypass surgery through blockade of fibrinolysis: acase control study followed by a randomized double-blind controlled trial. Critcare (Lond Engl) 2007;11(6):R117.

[11] Casati V, Della Valle P, Benussi S, et al. Effects of tranexamic acid on postoperativebleeding and related hematochemical variables in coronary surgery: Comparisonbetween on-pump and off-pump techniques. J Thorac Cardiovasc Surg Jul2004;128(1):83–91.

[12] Blaisdell FW. Pathophysiology of the respiratory distress syndrome. Arch Surg1974;108(1):44–9.

[13] Tanaka K. Specific inhibition of thrombin activity during cardiopulmonary bypassreduces ischemia-reperfusion injury of the lung. Fukuoka Igaku Zasshi Jan2001;92(1):7–20.

[14] Kojima M, Shimamura K, Mori N, Oka K, Nakazawa M. A histological study onmicrothrombi in autopsy cases of DIC. Bibl Haematol 1983;49:95–106.

[15] MulderAB, Hegge-Paping KS,Magielse CP, et al. Tumor necrosis factor alpha-inducedendothelial tissue factor is located on the cell surface rather than in thesubendothelial matrix. Blood 1994;84(5):1559–66.

[16] Fergusson DA, Hébert PC, Mazer CD, et al. A comparison of aprotinin and lysineanalogues in high-risk cardiac surgery. N Engl J Med May 29 2008;358(22):2319–31.

[17] Cooper Jr JR, Abrams J, Frazier OH, et al. Fatal pulmonary microthrombi duringsurgical therapy for end-stage heart failure: possible associationwith antifibrinolytictherapy. J Thorac Cardiovasc Surg May 2006;131(5):963–8.

[18] Gregoric ID, Patel V, Radovancevic R, et al. Pulmonary microthrombi during leftventricular assist device implantation. Tex Heart Inst J 2005;32(2):228–31.

Barry DixonDepartment of Intensive Care, St.Vincent's Hospital, Melbourne, AustraliaCorresponding author. Intensive Care, St. Vincent's Hospital, Melbourne,Victoria, 3065, Australia. Tel.: +61 3 9288 4488; fax: +61 3 9288 4487.

E-mail address: barry.dixon@svhm.org.au.

Ian NixonJames Kenny

Andrew E. NewcombAlexander Rosalion

Department of Cardiac Surgery, St.Vincent's Hospital, Melbourne, Australia

Kenneth OpeskinGeorgia Stamaratis

Department of Pathology, St.Vincent's Hospital, Melbourne, Australia

Brendan S. SilbertDepartment of Anaesethesia, St.Vincent's Hospital, Melbourne, Australia

S. SaidDepartment of Anaesethesia, St.Vincent's Hospital, Melbourne, Australia

John D. SantamariaDepartment of Intensive Care, St.Vincent's Hospital, Melbourne, Australia

Duncan J. CampbellSt.Vincent's Institute of Medical Research, Melbourne, Australia

2 September 2010