Can the CT by-product Time to threshold be a prognostic factor in patients with acute pulmonary embolism?

Bolus tracking is 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). Our purpose was to analyse possible associations between TTT and circulatory state and prognosis in patients with acute pulmonary embolism (PE).

In a single-centre, retrospective study 138 patients with PE and contrast administration via peripheral venous line were included. Clinical parameters of circulatory state were arterial pH, systolic blood pressure, heart rate, sPESI score, Wells score and GENEVA score. Survival was defined as surviving the following 30 days after the PE diagnosis.

Time to threshold was only weakly correlated with Fi02 (r = 0.26, P = 0.04), pH (r = -0.22, P = 0.009), venous base excess (r = -0.18, P = 0.04) and venous lactate (r = 0.21, P = 0.01). TTT did not correlate with clinical parameters/scores and mortality. There were weak associations between TTT and blood gas analysis parameters. There were no associations with clinically relevant prognosis scores and overall survival.

Therefore, albeit TTT is an easily assessable parameter of CTPA, the potential use in clinical routine is limited for prognosis stratification in patients with PE.