Warfarin: time in therapeutic range, a single centre study on patients using warfarin for stroke prevention in non-valvular atrial fibrillation and prosthetic heart valves.

Abstract

Background: There are various indications for the use of oral anticoagulants. Two common indications are in patients with atrial fibrillation and prosthetic heart valves. The quality of anticoagulation, determined by the time in therapeutic range, is less often evaluated and has important clinical implications in patient outcomes. Objectives: We sought to identify the indications for anticoagulation and determine the time in therapeutic range and the time out of range at a community-based and district level in patients attending the outpatient department at Mahatma Gandhi Memorial Hospital in KwaZulu Natal, South Africa. Further, we identified factors associated with the quality of anticoagulation and identified prevalence and contributors to thrombo-embolic and haemorrhagic events in anticoagulated patients with atrial fibrillation and prosthetic heart valves. Overview of thesis: Chapter 1 is a review of the literature and identifies the objectives of the study. Chapter 2 describes the study design and methodology. The sample population is described in Chapter 3. Chapter 4 and 5 evaluates the time in therapeutic range and Chapter 6 evaluates for associations thereof. Chapter 7 describes the findings of adverse events and the final chapter summarises the thesis with a general discussion and conclusion. Methods: We conducted a retrospective, descriptive and observational study with chart audits evaluating the anticoagulation control for the preceding one year for each patient. Descriptive statistics included mean and standard deviation for quantitative data and frequencies for categorical data. The variables demonstrated uniformity with linear plots and therefore comparisons of means was conducted by parametric testing. Analysis of variance was conducted for comparisons of variables with post hoc analysis for three groups. Confidence intervals were reported as 95%. Two-tailed p-values were conducted and any p-value less than .05 was considered significant. Results: TTR was poor for patients with atrial fibrillation and prosthetic valves (44.5% and 13.7% respectively). We identified older age, less frequent testing and high target ranges as significant factors associated with poorer outcomes. We demonstrated a high prevalence of adverse events (25.4%). Conclusion: Patients in this setting demonstrated poor quality of anticoagulation and had a high prevalence of adverse events.