Evaluation of endovenous radiofrequency ablation and laser therapy with endoluminal optical coherence tomography in an ex vivo model

BackgroundThis study evaluated the ability of endovascular optical coherence tomography (eOCT) to detect qualitative tissue alteration and quantitative changes of vein wall thickness and vein lumen diameter comparing endovenous radiofrequency ablation (RFA) and endovenous laser therapy (ELT) in an established ex vivo model.MethodsEndoluminal eOCT was performed by means of a new prototype rotating system (System M1, LightLab Imaging Inc, Boston, Mass) with automatic pullback of 1 mm/s. In the course of an eOCT examination of a 50-mm vein segment, 264 electronic cross section images with a spatial resolution of 15 to 20 μm are acquired. The eOCT scans were performed before and after treatment of each of 13 treated vein segments and of six control vein segments. Thirteen subcutaneous cow foot veins were reperfused in situ, and the defined 50-mm vein segments in the study were treated with RFA (n = 2) and ELT (n = 11). RFA followed the clinical VNUS-Closure protocol (VNUS Medical Technologies, San Jose, Calif) using a 6F 60-mm Closure-Plus catheter. ELT was performed using light of λ = 980 nm with a laser power of 3 (n = 2), 5 (n = 2), and 7 W (n = 4) with a paced pullback protocol with laser irradiation for 1.5 seconds every 3 mm, resulting in linear endovenous energy densities (LEED) of 15, 25, and 35 J/cm. Using 11 W (n = 3) with a continuous pullback protocol at 3 mm/s resulted in a LEED of 36.5 J/cm. Ten histologic cross sections of each treated and control vein segment were correlated with the corresponding eOCT cross sections to evaluate qualitative representation of vein wall layers and tissue alterations such as ablation and vein wall perforation. In addition, 26 eOCT cross sections of every treated vein segment before and after treatment and every control vein segment were analyzed to calculate quantitative changes in media thickness and vein lumen diameter.ResultsIn all specimens, qualitative analysis with eOCT demonstrated a clear match with histologic cross sections. A symmetrical, complete, circular disintegration of intima and media structures, without any transmural tissue defects, was shown after RFA. Pronounced semicircular tissue ablations (3 to 14 per 50 mm) and complete vessel wall perforations (0 to 16 per 50 mm) were detected after ELT. The quantitative analysis demonstrated a significant (P < .0001) increase in intima-media thickness after RFA (37.8% to 66.7%) and ELT (11.1% to 45.7%). A significant (P < .0001) reduction of vessel lumen diameter (36.3% to 42.2%) was found after RFA. Owing to the limited number of treated vein segments and inhomogeneous baseline vein lumen diameters, no linear correlation between laser energy level and effects on tissue such as ablation/perforation, media thickening, or vein lumen diameter could be identified.ConclusionsIn our ex vivo cow foot model, eOCT is able to reproduce normal vein wall structures and endovenous acute thermal alterations, such as tissue ablation and vessel wall perforations. Endovenous eOCT images can also be analyzed quantitatively to measure media thickness or vein lumen diameter. Endovascular OCT could become a valuable alternative tool for morphologic investigation of tissue alterations after endovenous thermal procedures.

Clinical RelevanceClinical data indicate that endovenous radiofrequency ablation (RFA) and laser therapy (ELT) can be performed safely; however, reports of recanalization, phlebitis, ecchymosis, and paresthesia indicate a certain potential for improving clinical results. Parallel with clinical trials, experimental studies could also help to identify certain treatment protocols that lead to effective collagen denaturation, vein wall thickening, and reduction of vein lumen diameter with minimal perivascular injury. This article reports the first results, to our knowledge, of a standardized experimental evaluation of endovenous radiofrequency and laser therapy using a newly developed ex vivo model. A new prototype endovascular high-resolution optical imaging procedure, endovascular optical coherence tomography (eOCT), was also used. The analysis of effects on tissue showed a pronounced and more reproducible collagen denaturation after RFA compared with ELT with a bare-tipped optical fiber. This report extends the understanding of tissue effects and offers suggestions for technical improvements especially for ELT. In the context of the endoluminal vein treatment presented, eOCT will mainly be used in experimental settings. When technical problems in this prototype device have been completely solved, eOCT could also be used in blood-filled vessels. EOCT might be considered for clinical trials investigating effects on tissue after RFA and ELT as an additional instrument alongside transcutaneous duplex ultrasound, but not in clinical routine. This new method could be of interest for investigating saphenous veins in situ to evaluate the suitability for venous bypasses or for intraoperative quality control of bypass anastomoses. Beyond that, the monitoring of percutaneous intra-arterial or of intravenous interventions such as balloon angioplasty and stent implantation should be possible.