The importance of Time within Therapeutic Range (TTR)
TTR is the optimal measure of INR control, and has a significant relationship with
adverse outcomes in all studies1
- As a result:
- a 7% increase in TTR →1 less major haemorrhage/100 patient years
- a 12% increase in TTR →1 less thromboembolic event/100 patient years
- A 5% improvement in time in therapeutic range across UK anticoagulation clinics would prevent 400-500 strokes per year2
- In international studies, a marked benefit was found against stroke and total vascular events for patients who had mean TTRs ≥65%2
What can lead to low TTR?
- Lack of a clinical governance process to monitor and regulate the implementation of existing guidelines - medical practice is an important determinant of TTR3
- Lack of effective, ongoing dose adjustment1
- Patient non-compliance: compliance rates have been estimated at 50%- 60% for patients on long term medication4. Non compliance has been associated with poor treatment
1. Wan Y et al. Anticoagulation Control and Prediction of Adverse Events in Patients With Atrial Fibrillation. A Systematic Review. Circ Cardiovasc Qual Outcomes 2008; DOI: 10.1161/CIRCOUTCOMES.108.796185.
2. Connolly SJ et al. Depends on the Quality of International Normalized Ratio Control Achieved by Benefit of Oral Anticoagulant Over Antiplatelet Therapy in Atrial Fibrillation Centers and Countries as Measured by Time in Therapeutic Range. Circulation 2008; 118:2029-2037.
3. Anticoagulation for Atrial Fibrillation A simple overview to support the commissioning of quality services. NHS Improvement – Heart, 2011.
4. DiMatteo MR. Patient adherence to pharmacotherapy: the importance of effective communication. Formulary 1995; 30:596–8, 601–2, 605.