A new noninvasive evaluation method of pulmonary thromboembolism in rabbits—pulmonary transit time

Background and aim Pulmonary thromboembolism (PTE) is a common cause of cardiovascular death worldwide. Due to its nonspecific clinical symptoms, PTE is easy to be missed or misdiagnosed. Pulmonary transit time (PTT) is a noninvasive cardiopulmonary hemodynamic index, which is the time required for a blood sample to pass through pulmonary circulation. This study is aim to establish a rabbit PTE model using auto-thrombus, evaluating the dynamic changes in a rabbit’s heart structure and function at multiple time points before and after modeling by echocardiography and exploring the application value of PTT obtained by contrast enhanced ultrasound (CEUS) in evaluating a PTE model. Methods Twenty-four healthy rabbits were intubated by femoral vein puncture to establish the PTE model. Echocardiography was performed before embolization, 2 hours, 24 hours, 3 days, 5 days, and 7 days after embolization to obtain conventional ultrasonic parameters. Then, CEUS was performed to obtain the PTT. Results Seventh day after modeling, nineteen rabbits were alive. Compared with pre-modeling, right heart parameters and heart rate in echocardiography were significantly impaired in the acute phase (2 and 24 hours after modeling) and gradually returned to normal in the compensatory phase (3, 5, and 7 days after modeling). In contrast with conventional ultrasound parameters, PTT and nPTT revealed a gradually increasing trend at each time point. Receiver operating characteristic (ROC) curve analysis revealed with an extension of molding time, the area under the curve (AUC) of (n)PTT is larger and larger. Conclusions Right heart parameters obtained using conventional echocardiography can accurately indicate changes in the structure and function of the right heart during the acute phase of PTE, while (n)PTT measured by CEUS continues to extend during the acute and compensatory phases of PTE. Therefore, PTT (nPTT) obtained by CEUS is a useful clinical indicator for the diagnosis of PTE and can be utilized as a supplement to conventional echocardiography parameters.