Time to threshold as a new indicator of circulatory state and prognosis in patients with pulmonary embolism

Background: Bolus tracking is commonly applied in computed tomography pulmonary angiography. The time that it takes for contrast to reach a predefined threshold in the pulmonary artery is called time to threshold (TTT). TTT could be associated with the circulatory state, and ultimately with prognosis in patients with PE. Aim: The purpose of the present study was to examine the correlation of TTT with embolus burden, radiological and clinical parameters of circulatory state, and ultimately with 30-day mortality. Methods: In a single-center, retrospective study 50 patients with pulmonary embolism and contrast administration via central venous line were included. The Mastora score was used to quantify embolus burden. Radiological parameters of circulatory state were the ratio of the short axes of the right and left ventricle diameter and the reflux of contrast medium into the inferior vena cava. Clinical parameters of circulatory state were arterial pH, systolic blood pressure, heart rate, and the Acute Physiology and Chronic Health Evaluation II: APACHE II. Survival was defined as surviving the following 30 days after the PE diagnosis. Results: TTT was significantly correlated with all radiological and clinical parameters of circulatory state and with 30-day mortality. However, TTT is dependent on device specific and protocol specific factors. Conclusions: Higher TTT is associated with worse prognosis in patients with pulmonary embolism.