Publications (3)10.78 Total impact
Article: A prospective study of an aggressive warfarin dosing algorithm to reach and maintain INR 2 to 3 after heart valve surgery.[show abstract] [hide abstract]
ABSTRACT: Good anticoagulation control in patients during the first months after heart valve surgery is important to prevent thrombotic complications. This is difficult to achieve, partly because the sensitivity to warfarin decreases progressively during approximately three months after valve surgery. A recently developed, simple but aggressive algorithm might improve anticoagulation control in this patient group. It was the objective of this study to evaluate the level of anticoagulation control when a specialised anticoagulation clinic changed from empirical dosing to the use of this new algorithm. In a before-and-after design, a cohort of consecutive patients managed with a new, aggressive dosing algorithm ('Algorithm cohort') was compared to a 'Retrospective cohort' of similar patients dosed empirically. Primary endpoint was individual time in therapeutic range (ITTR) during the first three months of warfarin therapy. Secondary endpoints included proportion of extreme International Normalised Ratio (INR) results, thrombotic and bleeding complications. Ninety-eight patients were included in the Algorithm cohort, 94 of whom were warfarin-naïve. Two hundred patients were included in the Retrospective cohort. Mean ITTR was 60.1% in the Algorithm cohort versus 48.7% in the Retrospective cohort (p <0.001). Patients in the Algorithm cohort spent 0.5% of time at an INR >5, versus 0.2 % in the Retrospective cohort. There was no major bleeding in either cohort; one patient in each cohort had a thrombotic complication. We demonstrate an improvement of the level of anticoagulation control with the use of a condition-specific, aggressive algorithm, as compared to standard dosing, in patients after heart valve surgery.Thrombosis and Haemostasis 02/2011; 105(2):232-8. · 5.04 Impact Factor
Article: Effect of a simple two-step warfarin dosing algorithm on anticoagulant control as measured by time in therapeutic range: a pilot study.[show abstract] [hide abstract]
ABSTRACT: The efficacy and safety of vitamin K antagonists for the prevention of thromboembolism are dependent on the time for which the International Normalized Ratio (INR) is in the therapeutic range. The objective of our study was to determine the effect of introducing a simple two-step dosing algorithm, as compared with dosing by anticoagulation clinic staffs on the basis of their experience, on time in therapeutic range (TTR) of warfarin therapy. We compared TTRs of all clinic patients before and after the introduction of a simple two-step dosing algorithm at a single anticoagulation clinic in Canada, between 1 August 2006 and 24 December 2008. TTR was calculated using the linear interpolation method of Rosendaal. We included 873 patients in the 'before' phase and 1088 patients in the 'after' phase. Introduction of the dosing algorithm significantly increased TTR of patients with a therapeutic INR range of 2-3 from 67.2% to 73.2% (P < 0.001), and that of patients with a therapeutic INR range of 2.5-3.5 from 49.8% to 63.8% (P < 0.001). The introduction of a simple two-step warfarin-dosing algorithm in place of dosing by experienced anticoagulation clinic staff significantly improved mean TTR for patients in a tertiary-care anticoagulation clinic. This inexpensive and widely applicable algorithm has the potential to improve warfarin control.Journal of Thrombosis and Haemostasis 10/2009; 8(1):101-6. · 5.73 Impact Factor
Article: Decreasing warfarin sensitivity during the first three months after heart valve surgery: Implications for dosing[show abstract] [hide abstract]
ABSTRACT: IntroductionVitamin K antagonists are prescribed to prevent thromboembolic complications after heart valve surgery. In our experience, patients often show a progressive decrease in sensitivity to warfarin after surgery making it difficult to reach and maintain a therapeutic International Normalized Ratio (INR).We sought to confirm our clinical impression and to gather data for the development of a guide to dosing these patients.Materials and methodsIn a large anticoagulation clinic, we retrospectively reviewed 200 patients who were on warfarin (target range of 2.0-3.0) during the first three months after valve surgery. Data on dosing and INR results were collected and time in therapeutic range (TTR) calculated. Controls were patients started on warfarin for atrial fibrillation.ResultsA steady increase in warfarin requirements was seen over the three months in patients with mechanical valves, bioprosthetic valves or valve repairs. The mean dose of warfarin increased by 26% while the mean INR decreased from 2.5 to 2.1. In contrast, both the mean dose of warfarin and the INR were stable in controls. TTR in patients after valve surgery was 48.5%, with 40.8% of time spent at an INR below 2.0. A dosing algorithm was modeled from the data in this patient group.ConclusionsPatients steadily become less sensitive to warfarin during the first months after heart valve surgery. This leads to subtherapeutic anticoagulation. A dosing algorithm that takes increasing requirements into account is proposed. This algorithm will need to be validated prospectively.Thrombosis Research.