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eComment: Anticoagulation for mechanical heart valves: a current assessment

Department of Cardiothoracic Surgery, University Hospital of Patras, 22500 Rion Patras, Greece

Mechanical aortic valve without anticoagulation for twenty-three years

Reading your case report [1], I realize that you neither focused on the responsible underlying mechanism of your patients normal valvular mechanics – by examining if he had traditional or non-risk factors for thromboembolism [2] – nor referred if your patient was under antiplatelet therapy after the discontinuation of anticoagulant due to allergic reaction. Furthermore, the guidelines you refer to are not updated (there are current guidelines – 10 years after yours). Also, you question the anticoagulation therapy following mechanical aortic valve replacement using data from the article of Andersen and Alstrup who recommend lifelong anticoagulation as the best postoperative treatment in isolated aortic valve replacement with a mechanical valve [3]. Cannegieter noted that, in the absence of oral anticoagulation, using antiplatelet therapy alone, there is an increase in both valve thrombosis and thromboembolism rates [2], fact that you do not mention despite the second reference in your article.

Generally, patients who undergo mechanical heart valve replacement require lifelong oral anticoagulants. Thromboembolism (TE), anticoagulation-related hemorrhage and a much rarer incidence of valve thrombosis are the major valve related events (VREs), which are the consequences of anticoagulation mismanagement, and account for more than 75% of all VREs [2]. These occur more frequently in the first 6 months following surgery, especially anticoagulant-related hemorrhage [2, 4]. Notably, VREs are less common in the aortic than in the mitral position while freedom from all VREs happens at approximately 8 years for mitral and 10 years for aortic valve prostheses [2, 4]. However, several long-term follow-up reports indicate that survival after valve replacement is due to patient-related factors rather than to the presence of the valve prosthesis itself. Recent data indicate this may be true for TE, as the rate of both major and minor TE will change depending on the risk factors in each individual patient [2].

Because of the fear of major TE events without a warfarin-based anticoagulation regimen and medical-legal implications of major events, antiplatelet therapy alone has not been pursued until recently. However, Garcia-Rinaldi is conducting a prospective non-randomized trial in which patients with mechanical aortic valves receive only aspirin and clopidogrel, loading immediately postoperatively when feasible [5]. The latest results indicate that one TE (cerebral vascular accident (CVA) at 48 h postop) and no valve thrombosis has occurred in 108 patients followed-up to 4 years, an average of 30 months postoperatively [2, 5]. TE and anticoagulant-related hemorrhage are not uncommon in the early postoperative period. Therefore, antithrombotic prophylaxis is recommended for at least 3 months for aortic valve replacement and chronically for mitral and tricuspid prostheses [2].

In conclusion, the use of antiplatelet agents alone currently can be recommended only if patients cannot take oral anticoagulation, yet low risk compliant patients would likely have a VRE rate at least equivalent to antithrombotic therapy [2]. The above prospective randomized trial in low-risk patients after AVR added to current medical advances is warranted and could provide evidence for substantive patient benefit [5].

	References

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1. Sharma S, McMurty K, Chalapathy N, Ameen A. Mechanical aortic valve without anticoagulation for twenty-three years. Interact CardioVasc Thorac Surg 2009;8:263–265.[Abstract/Free Full Text]
2. Emery RW, Emery AM, Raikar GV, Shake JG. Anticoagulation for mechanical heart valves: a role for patient based therapy. J Thromb Thrombolysis 2008;25:18–25.[CrossRef][Medline]
3. Andersen PV, Alstrup P. Long-term survival and complications in patients with mechanical aortic valves without anticoagulation. A follow-up study from 1 to 15 years. Eur J Cardiothorac Surg 1992;6:62–65.[Abstract]
4. Emery RW, Krogh CC, Arom KV, Emery AM, Benyo-Albrecht K, Joyce LD, Nicoloff DM. The St. Jude Medical cardiac valve prosthesis: a 25-year experience with single valve replacement. Ann Thorac Surg 2005;79:776–783.[Abstract/Free Full Text]
5. Garcia-Rinaldi R. Clopidogrel – ASA combination inhibits the thrombogenicity of St. Jude Medical mechanical aortic prosthesis. CTSNet Report, September 2004.

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