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Rapid Responses: Rapid Responses published:
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anticoagulation and prosthetic valves
- dr.manan vasenwala (26 November 2002)
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Anticoagulation for prosthetic heart valves perioperatively
- Kwok HO (27 November 2002)
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Anti-Thrombotic Therapy for Prosthetic Heart Valves in Pregnancy
- P Rachael James (19 December 2002)
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Correction
- Ira Goldsmith (20 December 2002)
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dr.manan vasenwala, consultant-cardiologist (non-invasive) k.k.heart center, aligarh.202002,INDIA
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previously recommended INR was very high. now it is lowered somewhat to remain between 2.5-3.0. higher INR are recommended for those with a high risk profile, like previous thromboembolism or AF, or for all valves in mitral position. aspirin alone, unlike with bioprosthesis, does not provide adequate protection in mechanical valves. however, the addition of aspirin to warfarin may reduce thromboembolism and should be given in all patients with prosthetic valves. acute thrombosis of prosthetic valve is an acute emergency. trial have been held for using thrombolytics in this situation. in some large series the success rate using streptokinase was 80%.in clinically stable patients with a stuck valve, a low thrombus burden,(less than 5 mm) thrombolysis is safe in primary episode as well as in recurrence. a large thrombus would mandate valve replacement. finally, prosthesis in tricuspid position is also a special situation. the incidence of thrombosis is highest here. as a result a bioprosthesis, which has a low thrombosis potential may be preffered to mechanical valve. also, there is less wear and tear in this position which confers a bioprosthesis an extra- durability. Competing interests: None declared |
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Kwok HO, Consultant Intensivist / Anaesthetist ICU, North Shore Hospital, Auckland 1309, New Zealand
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The recommendation made by the clinical review by Goldsmith et al. in this issue of BMJ did not elaborate on how to stratefy the risk of thromboembolism perioperatively. Stopping warfarin and admitting ALL patients with prosthetic heart valves to hospital for intravenous heparin a few days before surgery and after surgery seems not cost-effective, and maybe even not an evidence based recommendation. I am also not too sure whether we have enough data to support the use of low molecular weight heparin for prosthetic heart valves peri-operatively. According to the American Heart Association guidelines (1), 'the risk of increased bleeding during a procedure performed on a patient receiving antithrombotic therapy has to be weighed against the increased risk of thromboembolism caused by stopping the therapy. The risk of stopping warfarin can be estimated and is relatively slight if the drug is withheld for only a few days. Admission to the hospital or a delay in discharge to give heparin is usually unnecessary. Determining which patients are at very high risk of thrombosis and require heparin until warfarin can be reinstated may be difficult, and clinical judgment is required. Heparin can usually be reserved for those who have had a recent thrombosis or embolus (arbitrarily within 1 year), those with demonstrated thrombotic problems when previously off therapy, those with the Björk-Shiley valve, and those with 3 "risk factors." Risk factors are atrial fibrillation, previous thromboembolism, a hypercoagulable condition, and mechanical prosthesis; many would also include LV dysfunction (ejection fraction <0.30) as a risk factor. A lower threshold for recommending heparin should be considered in patients with mechanical valves in the mitral position, in whom a single risk factor would be sufficient evidence of high risk. Low-molecular-weight heparin is attractive as it is even more easily used outside the hospital; however, there are no data on patients with prosthetic heart valves, and low-molecular-weight heparins cannot be recommended at this time.' Reference: (1) ACC/AHA Practice Guidelines. Guidelines for the management of patients with valvular heart disease. Circulation 1998;98:1949-1984. Competing interests: None declared |
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P Rachael James, SpR Cardiology St Thomas' Hospital, SE1 7EH
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Goldsmith et al are correct in stating that women with heart valve replacements are at increased thrombolic risk during pregnancy[1] and all anticoagulant options are associated with potential risks to the mother and fetus. But the risk of thromboembolism is, in part, related to the type of valve replacement and the valve position (mital versus aortic). Anticoagulation with warfarin remains the safest option for the mother and may be the only option for those with older generation valves (e.g. Starr Edwards) in the mitral position, a combination which carries a higher thromboembolic risk. For some women, with newer generation mechanical valves in the aortic position, adjusted-dose heparin may provide sufficient anticoagulation. It should be recognised, however, that there are difficulties maintaining adequate levels of anticoagulation with heparin, especially in the third trimester[2]. Unfortunately, despite being the safest option, warfarin does cross the placenta and is associated with embryopathy and adverse fetal outcome[3]. This contrasts with both unfractionated and low molecular weight heparins which do not cross the placenta. Yet it is misguided to suggest that warfarin should be withdrawn when a woman is trying to conceive[1]. This would place her at unecessary thromboembolic risk. Warfarin embryopathy can be avoided if the drug is withdrawn by the sixth week of gestation and re-instituted after week twelve[3]. In addition, there is evidence of a dose related effect of the drug: the risk of warfarin embryopathy appears to be negated when the daily maternal dose is equal or below 5mg[4] and fetal outcomes are also improved when daily warfarin requirements are 5mg or less[5]. Any woman with a mechanical heart valve, who wishes to become pregnant, ideally should be seen for pre-pregnancy counselling and the risks discussed. 1. Goldsmith I, Turpie GG, Lip GYH. ABC of antithrombotic therapy. Valvular heart disease and prosthetic heart valves. BMJ 2002; 325: 1228- 1231 2. Brancazio LR, Roperti KA, Stierer R, Laifer SA. Pharmacokinetics and pharmacodynamics of subcutaneous heprain during the early thrid trimester of pregnancy. Am J Obstet Gynecol 1995; 173: 1240-1245 3. Chan WS, Anand S, Ginsberg JS. Anticoagulation of pregnant women with mechanical heart valves: a systematic review of the literature. Ann Int Med 2000; 160: 191-196 4. Cotrufo M, de Luca TSL, Calabro R, Mastrogiovanni G, Lama D. Coumarin anticoagulation during pregnancy in women with mechanical valve prostheses. Eur Heart J 1991; 5: 300-305 5. Vitale N, De Feo M, De Santo LS, Pollice A, Tedesco N, Cotrufo M. Dose-dependent fetal complications of warfarin in pregnant women with mechanical heart valves. J Am Coll Cardiol 1999; 33: 1637-1641 Competing interests: None declared |
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Ira Goldsmith, SpR Cardiothoracic Surgery B15 2TH
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Re authors and Ira Goldsmith: At present I am Specialist Registrar in Cardiothoracic Surgery at the Queen Elizabeth Hospital, Birmingham, UK. I will be grateful if you would make this necessary correction Many thanks Ira Goldsmith MD FRCS Competing interests: None declared |
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