Background: Out-of-hospital treatment of patients with deep-vein thrombosis(DVT) is routine in many countries regardless of frequent concomitant asymptomatic pulmonary embolism(PE) in this group. However, patients with symptoms and verified PE are still regularly treated in hospital.The objectives were to test a model for outpatient tinzaparin therapy and to evaluate its safety andefficacy in patients with symptomatic, small or medium-sized PE using quantitative ventilation/perfusionscintigraphy (qV/P SCINT) for patient selection and follow up. Material/Methods: This prospective studyincluded 102 patients treated with tinzaparin and warfarin for 5 days at a patient hotel. PE was quantifiedscintigraphically as loss of perfusion with preserved ventilation at segmental or subsegmental levels(mismatch). Points were attributed to segments of reduced ventilation (RoVent) and perfusion (RoPer).A holistic principle of interpretation was applied. Patients were excluded if they had >14 RoPer points(7 segments) or >7 RoVent points. Clinical follow-up and scintigraphy were repeated at discharge in 100patients and after 13 months on average. Results: Embolism diminished by 44% after 5 days and demandingsymptoms declined. There was no thromboembolic mortality in the trial. At late follow-up, PE had notrecurred in patients with resolution after 5 days. In those with insufficient early response, persistentperfusion defects were usually observed. Conclusions: The results indicate the safety and efficacy ofoutpatient treatment of PE according to our model and merit larger, multicenter, controlled studies.

Keywords: Ambulatory Care, Fibrinolytic Agents - therapeutic use, Heparin, Low-Molecular-Weight - therapeutic use, Prospective Studies, Pulmonary Embolism - radionuclide imaging, Radiopharmaceuticals - diagnostic use, Technetium Tc 99m Pentetate - diagnostic use, Ventilation-Perfusion Ratio