Clinical Significance of Time in Therapeutic Range (TTR) During Unfractionated Heparin Therapy in Non-ST-Segment Elevation Myocardial Infarction

BackgroundUnfractionated heparin (UFH) is widely used in non-ST-segment elevation myocardial infarction (NSTEMI), but its narrow therapeutic window requires frequent activated partial thromboplastin time (aPTT) monitoring. Data on time in therapeutic range (TTR) in this setting are scarce.MethodsWe analyzed 1,553 consecutive patients with NSTEMI treated with UFH in a tertiary care intensive cardiovascular care unit between July 2019 and December 2025. TTR was calculated by linear interpolation over 72 hours. Associations with complications and 30-day and 1-year mortality were assessed.ResultsAmong them (mean age 67.1 ± 13.8 years, 73.9% male), only 325 (20.9%) reached the therapeutic range. Mean TTR was 12.5 ± 20.2%. An early invasive strategy predominated: 85.5% underwent coronary angiography, approximately 89% of them within 24 hours (mean time to angiography 14.4 ± 10.1 hours). Therapeutic-range attainment was not associated with mortality at 30 days (4.6% vs 4.0%, p=0.614) or 1 year (8.6% vs 9.3%, p=0.710), even after multivariable adjustment (adjusted OR 1.30, 95% CI 0.70-2.40 and 0.98, 95% CI 0.62-1.55, respectively). It was also not associated with in-hospital complications, including re-infarction, stroke, stent thrombosis, or bleeding.ConclusionsTherapeutic aPTT was achieved infrequently, and neither therapeutic-range attainment nor TTR was associated with clinical outcomes. These findings suggest that, using a contemporary approach to NSTEMI with a short time to angiography in the great majority of cases, TTR does not represent an optimal marker of anticoagulation quality, warranting evaluation of alternative strategies. Given the low event rate, confirmation in larger, adequately powered studies is required.