Shear wave elastography values of thrombus in patients with lower extremity deep vein thrombosis for pulmonary embolism detection: the ROC analysis

Rationale: Thrombosis of the iliac (IV) and femoral veins (FV) is one of the most common causes of pulmonary embolism (PE). Modern ultrasound scanners are equipped with the technology of shear wave elastography, which gives a quantitative assessment of thrombus stiffness by Young's modulus reconstruction. However, the lack of convincing data on the role of thrombus stiffness for clinical manifestations of PE hinders the active use of shear wave elastography to diagnose the risk of embolism. Aim: To determine the threshold values of the venous thrombus Young’s modulus for deep venous thrombosis (DVT) of the lower extremities complicated by massive PE and/or PE with acute cor pulmonale (ACP). Materials and methods: This was a single center cross-sectional study in 101 patients who were hospitalized with the diagnosis of acute (duration of less than 2 weeks) or subacute (from 2 weeks to 3 months) IV and FV thrombosis. Doppler ultrasound of the lower extremity veins and echocardiography were done in all patients. Forty eight patients with clinical signs of PE had chest computed tomography. The venous thrombus stiffness was assessed by shear wave elastography with the Young's modulus reconstruction. We performed the ROC analysis for mean values of the Young's modulus for proximal segments of IV and FV thrombi in patients with DVT and massive PE and ACP. Results: PE was diagnosed in 40.6% (26/64) of the patients hospitalized with acute DVT and in 54.1% (20/37) of those with subacute DVT. Echocardiographic signs of ACP in massive PE were found in 47.4% (9/19) of the patients, in submassive and minor PE in 55.6% (15/27). In DVT complicated with PE, the ROC analysis of the shear wave elastography results gave the following threshold values of the mean Young’s modulus for the proximal thrombus segment: for acute IV thrombosis + PE and ACP, ≤ 16.7 kPa (AUC 0.714, sensitivity 100%, specificity 42.1%), in subacute IV thrombosis + PE and APC, ≤ 23.7 kPa (0.939, 100 and 90.9%, respectively), in acute FV thrombosis + massive PE, ≥ 9.5 kPa (0.706, 100 and 50%, respectively), in subacute FV thrombosis + massive PE, ≥ 24.4 kPa (0.550, 60.0 and 68.8%, respectively). Conclusion: Shear wave elastography of deep vein thrombi of the lower extremities makes it possible to identify patients with PE and ACP during acute and subacute IV thrombosis and to determine massive PE in acute FV thrombosis.