Correlation between Time in Therapeutic Range (TTR) and Prognosis in patients with Pulmonary Embolism Treated with Unfractionated Heparin

Introduction: Pulmonary embolism (PE) is a life-threatening condition often treated with unfractionated heparin (UFH) in high-risk patients. Activated Partial Thromboplastin Time (aPTT) is used to monitor UFH efficacy. We sought to evaluate the correlation between time in therapeutic range (TTR) and prognosis in patients with pulmonary embolism treated with unfractionated heparin.

Methods: A prospective cohort study included 203 patients admitted to a tertiary care center between July 2019 and August 2024 with a confirmed diagnosis of PE treated with UFH. TTR was calculated based on aPTT values during the first 72 hours of hospitalization. The correlation between TTR and mortality rates was assessed.

Results: Out of the 203 patients, 116 (57%) patients were in therapeutic range at least once. Of them, the mean TTR was 43.1% (±22.4) (median 39%). Nevertheless, the mean TTR of all patients was only 24.6% (±27.3) (median 18.8%). During the study period 27 (13.3%) patients have died, of them 9 (4.4%) within 30 days and 16 (7.9%) during the first year. Patients with higher rates of TTR demonstrated lower 30-day (p=0.051) and one-year (p=0.045) mortality rates. ROC analysis identified a TTR cutoff of 21.5% for predicting one-year mortality, yielding a high negative predictive value (NPV) of 96.8%, despite a low positive predictive value (PPV) of 12%.

Conclusions: Patients with acute PE who had higher TTR had better outcomes at 30 days and at 1 year. However, only a quarter of patients had sufficient TTR values.