Clinical study of optical coherence tomography in the diagnosis of peripheral pulmonary artery thrombus

Abstract

BackgroundPeripheral pulmonary artery thrombus (PPT) is common in the clinic. However, due to the lack of an ideal diagnostic tool, PPT cannot be quickly diagnosed and effectively treated at present. Optical coherence tomography (OCT) is a new intravascular imaging technique that is characterized by high image resolution. This technique is suitable for small vessel imaging and has the ability to distinguish red and white thrombi. ObjectiveThis study aimed to evaluate the value of OCT in the diagnosis of PPT and in identifying the nature of thrombi by comparing the difference in sensitivity between OCT and selective pulmonary angiography (SPA). MethodsHighly suspected PPT patients were enrolled in this study. Pulmonary ventilation/perfusion (V/Q) mismatch pulmonary segments or peripheral pulmonary arteries were chosen. SPA was performed first, followed by OCT imaging. The diagnostic standard of thrombus with SPA was an intraluminal filling defect. The procedure and criteria for OCT diagnosis of thrombus were previously introduced in intracoronary OCT thrombus images. The diameter of the imaging vessels was measured, and they were grouped according to diameter. The diameter was <2mm in the distal segment group, 2–3mm in the middle segment group, and >3mm in the proximal segment group. The recognition abilities of intravascular thrombus with the different diameters of these two techniques were compared. Patients with obvious clinical symptoms and more red thromboses revealed by OCT were given standardized anticoagulant therapy for half a year. The clinical symptoms, 6-minute walking test and changes in the thrombus in the OCT images of these patients before and after treatment were observed. ResultsA total of 22 patients with highly suspected PPT were suggested to undergo V/Q inspection. Finally, 12 patients were eligible for the study. SPA and OCT were performed in 61 peripheral pulmonary arteries in all 12 patients. The ideal SPA and OCT images obtained from a total of 76 blood vessel segments were suitable for comparative analysis. A total of 62 thrombi were found by SPA. Among these, eight thrombi were in the distal segment, 29 thrombi were in the middle segment, and 25 thrombi were in the proximal segment. A total of 81 thrombi were found by OCT, among which 22 thrombi were in the distal segment, 31 were in the middle segment, and 28 were in the proximal segment. There was a significant difference between two groups in the distal segment group (P=0.013), while there was no significant difference between two groups in the middle segment group or the proximal segment group (P>0.05). In addition to all the thrombi found by SPA, OCT found other thrombi that were missed by SPA. According to previous OCT images for determining the nature of thrombi, OCT revealed 81 thrombi, of which 48 (59%) were red thrombi and 33 (41%) were white thrombi. Then, seven patients who had obvious clinical symptoms and more red thrombi in the peripheral pulmonary artery were given anticoagulant therapy for six months. After treatment, these symptoms were improved, oxygenation indexes increased, and the six-minute walking test was extended in all these patients. After anticoagulation therapy, five patients underwent OCT review. These OCT images were matched and compared before and after anticoagulation therapy. The results revealed that most of the thrombi had disappeared, and a small amount of red thrombi turned white as the volume reduced. The mean lumen area before and after treatment was 2.05±1.03mm2 and 2.86±1.24mm2, respectively, and the difference was statistically significant (P=0.035). ConclusionOCT can clearly show the structure of the lumen and the wall of the peripheral pulmonary artery tube. The sensitivity of the diagnosis of PPT with a diameter of <2mm was higher than that of SPA. Moreover, OCT has the ability to distinguish between red and white thrombi, which is of guiding significance in anticoagulant therapy.