LETTER TO THE EDITOR
The optimal intensity of vitamin K antagonists in patients with mechanical heart valves: A meta-analysis
Hugh O. O'Kane, FRCS
9 Malone Park, Belfast BT9 6NH, Northern Ireland
(Email: hugh{at}doctors.org.uk).
I enjoyed the article by Vink et al. (1), which again revisits an old and most important clinical chestnut, but I have serious misgivings about their conclusions. Some years ago, we did a detailed and comprehensive analysis of 1,134 patients who had received St. Jude prosthetic valve(s) over a 13-year period (2). The follow up was 100% complete—4,936 patient years—and the study had a 60% post-mortem examination rate for early deaths.
The recommendation we made as the result of our analysis, namely that the INR should be kept between 2.5 and 3.0, is at complete variance with that of the authors. I believe that the problem arises from the fact that the target international normalized ratio (INR) range on which the authors focused may have no bearing whatsoever on the INR at the actual time of the anticoagulant-related complication. In contrast, we based our recommendations on the INR measured at the actual time of the anticoagulant-related complication, which we had in 88% and 58% of the major thromboembolic and hemorrhagic complications, respectively. Furthermore, in a more recent study (3), we found that at any given time 21.8% to 32.5% of patients were outside the target INR set for them; indeed, other authors have found an even greater number of patients (up to 52%) outside the target INR range (4).
It is essential therefore to base any recommendation regarding anticoagulation on an analysis of INR readings at the actual time of the anticoagulant-related complications rather than the target INR range, which is the ideal rather than the reality.
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References
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1. Vink R, Kraaijenhagen RA, Hutten BA, et al. The optimal intensity of vitamin K antagonists in patients with mechanical heart valves: a meta-analysis J Am Coll Cardiol 2003;42:2042-2048.[Abstract/Free Full Text]
2. Ibrahim M, O'Kane H, Cleland J, et al. The St. Jude Medical prosthesisA thirteen-year experience. J Thorac Cardiovasc Surg 1994;108:221-230.[Abstract/Free Full Text]
3. Sidhu P, O'Kane HOSelf-managed anticoagulation: results from a two-year prospective randomized trial with heart valve patients. Ann Thorac Surg 2001;72:1523-1527.[Abstract/Free Full Text]
4. Horstkotte D, Piper C, Wiemer M. Optimal frequency of patient monitoring and intensity of oral anticoagulation therapy in valvular heart disease. J Thromb Thrombylysis 1998:5 Suppl 1:S19–24..
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