Feasibility and Safety of the Second-Generation, Frequency Domain Optical Coherence Tomography (FD-OCT): A Multicenter Study
- Volume 24 - Issue 5 - May 2012
- Posted on: 4/26/12
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Abstract: Objectives. This study sought to assess the effectiveness and safety of the second-generation frequency-domain optical coherence tomography (FD-OCT) system. Background. The second-generation FD-OCT was recently developed, with simplified imaging technique and faster acquisition time compared to the first-generation time-domain OCT. However, the safety and effectiveness of the FD-OCT has not been evaluated, and this study was conceived as a pre-approval study for Food and Drug Administration clearance for clinical use in the United States. Methods. A total of 50 patients were enrolled from 3 institutions. Following stent implantation, the FD-OCT was performed with contrast injection through the guiding catheter to acquire pullback images with the pressure-triggered automatic pullback device. The primary endpoint was to achieve a median clear image length of more than 24 mm. Serious procedure-related or postprocedural adverse events (death, myocardial infarction, or ventricular arrhythmia) were recorded to assess safety of the device. Results. The primary endpoint of obtaining >24 mm of median clear image length (CIL) was achieved in 94% of the subjects (47 out of 50), with measured CIL of 43.2 mm. In 5 patients (10.6 %), a second attempt was necessary due to suboptimal image quality of the first pullback. In 36 patients (76.6%), a full stent length was obtained during the first attempt. There were no serious procedure-related or postprocedural adverse events. Conclusions. The new second-generation FD-OCT system provides fast and reliable resolution images of the coronary artery. The pullback can be safely performed over long segments of the artery without serious adverse events.
J INVASIVE CARDIOL 2012;24(5):206-209
Key words: frequency domain OCT, FD-OCT, feasibility, safety
Intracoronary optical coherence tomography (OCT) is a high-resolution imaging modality that uses near-infrared light to visualize coronary artery structures and geometry. Since its first use for in vivo coronary artery evaluation in 2002,1 it has been widely accepted as a reliable tool for assessing the structures of coronary arteries. With OCT, it is possible to visualize pathologic changes in microstructures of the coronary artery, as well as evaluate the adequacy of stent deployment due to its higher resolution (10 µm) compared to intravascular ultrasound (IVUS; resolution, 100 µm).1
One limitation of OCT compared to IVUS is the requirement for blood to be displaced in order to obtain images of the artery wall. The techniques for blood displacement in the conventional time-domain OCT (TD-OCT) require either the combined use of a small imaging catheter and a compliant occlusion balloon (occlusive technique) or an infusion of an iso-osmolar viscous solution through the guiding catheter (non-occlusive technique).2 These techniques have been proven to be safe, but require extra time to perform and may not be feasible in clinically unstable patients.3,4 Additionally, the TD-OCT has a slow pullback rate of about 0.5-3 mm/s, with 10-30 seconds of occlusion or flush to image a 30-mm long coronary artery, which may lead to myocardial ischemia.4
The second-generation frequency-domain OCT (FD-OCT) system has recently been developed for clinical use. It employs a rapid-exchange design non-occlusive catheter, which minimizes the possible ischemic effect caused by occlusion of coronary arteries. The FD-OCT system provides faster acquisition time with a pullback speed of 20 mm/s that can scan up to 50 mm of an artery in about 3 seconds.5 Additionally, there is increased penetration depth6 and a higher sampling line density per frame with the FD-OCT5 compared to TD-OCT. This multicenter study was performed as a pre-approval study for Food and Drug Administration (FDA) clearance, in order to evaluate the effectiveness and safety of the newly developed FD-OCT for imaging intracoronary stents.
Study population. The multicenter study included 3 medical centers and was conducted from November 2008 to July 2009. The inclusion criteria were adult (age >18 years) patients with stable angina or acute coronary syndrome (ACS) who were undergoing percutaneous coronary intervention (PCI) with a single stent.
Clinical exclusion criteria were serious co-morbid conditions (malignancy, inflammatory disease), previous coronary artery bypass graft surgery in the target vessel, New York Heart Association class III or IV heart failure, left ventricular ejection fraction <30%, ACS within 24 hours before the index procedure, hemodynamic or electrical instability, and renal insufficiency (serum creatinine ≥1.8 mg/dL). The lesion-specific exclusion criteria were lesions with multiple stents, stent diameters <2.0 mm or >3.5 mm, ostial lesions, lesions containing large thrombus, and heavily calcified or highly tortuous vessels. The study protocol was approved by the institutional review board and ethics committee at each participating institution, and written informed consent was obtained from all participating patients.
Image acquisition. Femoral approach was used in all patients for coronary angiograms, PCI and OCT imaging. Weight-adjusted, unfractionated heparin (institution M and institution S) or bivalirudin (institution C) was given for anticoagulation. After the placement of the guiding catheter (6 Fr) into the coronary ostium, a standard PCI guidewire was advanced into the coronary artery in the conventional manner. Following the placement of an FDA-approved intracoronary stent, FD-OCT imaging was performed.
FD-OCT system and catheter. The FD-OCT system (C7 System; LightLab Imaging, Inc/St Jude Medical) consists of a computer console containing the data acquisition board, an imaging engine, and a patient interface unit that connects to the intravascular OCT catheter (RX Image wire II; LightLab Imaging, Inc/St Jude Medical), In this study, the 2.7 Fr rapid-exchange catheter was advanced over a 0.014˝ coronary guidewire through a 6 Fr guide catheter. The imaging lens of the catheter was positioned distal to the stent. After catheter placement, a cardiovascular injection pump was used to deliver contrast medium through the guide catheter at a rate of 4 mL/s. An average of 14 cc of contrast medium was used for each run. The optical fiber of the catheter was automatically pulled back at a rate of 20 mm/s for 2.5 seconds.
Image analysis. Images were digitally stored and submitted to the core laboratory for offline analysis. OCT images were analyzed by two independent observers who were blinded to the procedure and patient information. Each OCT pullback was analyzed every 1 mm to measure the overall length of the pullback containing clear cross-sectional images.
A recent analysis of a large stent implantation database has demonstrated that 90% of implanted coronary stents have a length less than 24 mm.7,8 Based on this statistic, our study selected a performance target of 24 mm for the median length of clear imaging within an OCT pullback. The clear imaging length (CIL, in millimeters) is the cumulative sum of clear image segment frames (CIF). The CIF was defined as an OCT cross-sectional image frame with a visible boundary between the lumen and the vessel wall along a continuous arc of at least 270° around the center of the lumen (Figure 1A). In addition, length of stent that was visible within the CIL was identified. Clear stent length (CSL) was defined as the total stent length (in millimeters) visualized within the CIL (Figure 1B).
Additional features including presence of stent edge dissection, malapposition, and tissue prolapse were recorded during analysis (Figure 2). Stent edge dissection was defined as a linear rim of tissue clearly separated from the vessel wall or the adjacent stent struts at the stent edge.9 Malapposition was noted when the distance from the center of the superficial reflection in stent strut to the leading edge of the vessel wall was greater than the sum of strut thickness plus polymer.9 Tissue prolapse was defined as the presence of tissue between stent struts protruding into the lumen with a circular arc connecting adjacent struts.
Primary endpoint. The primary endpoint was to achieve a median clear image length of more than 24 mm to demonstrate diagnostic effectiveness. The safety endpoint was assessed by the incidence of serious procedural or postprocedural adverse events, including angina pectoris, ST-segment changes, or arterial spasm persisting despite treatment, ventricular arrhythmias, coronary artery dissection, intracoronary thrombus, periprocedural myocardial infarction, or death.
Secondary endpoints. The CSL was evaluated to examine the completeness of stent length that could be visualized during imaging. Changes in intracoronary microstructures including edge dissection, tissue prolapse, and malapposition were documented to represent the additional diagnostic feasibility.
Intraobserver and interobserver variabilities. CIL was evaluated by two independent observers to assess interobserver variability. CIL measurement was repeated by each observer at least 4 weeks after the initial evaluation to assess intraobserver variablity. When there was discordance between observers, a consensus reading was obtained.
Statistical analysis. Continuous variables were reported as the mean and standard deviation (SD) or the median and interquartile range based on their normal distribution. Categorical variables were expressed as the number or frequency of occurrence.
The baseline characteristics are shown in Table 1. The majority of patients had stable angina with preserved left ventricular function. A total of 52 OCT image pullbacks from 47 patients were performed. The total number of frames evaluated in this study was 10,195 (2039 mm), and the total stent length analyzed was 733.3 mm (7388 struts). The target vessel was the left anterior descending coronary artery in 20 patients, the left circumflex artery in 8 patients and the right coronary artery in 19 patients.