Optical coherence tomography as a tool for percutaneous coronary interventions

Dextran or Saline Can Replace Contrast for Intravascular Optical Coherence Tomography in Lower Extremity Arteries

PURPOSE

To examine the hypothesis that alternative flush media could be used for lower extremity optical coherence tomography (OCT) imaging in long lesions that would normally require excessive use of contrast.

METHODS

The OPTical Imaging Measurement of Intravascular Solution Efficacy (OPTIMISE) trial was a single-center, prospective study (ClinicalTrials.gov identifier NCT01743872) that enrolled 23 patients (mean age 68±11 years; 14 men) undergoing endovascular intervention involving the superficial femoral artery. Four flush media (heparinized saline, dextran, carbon dioxide, and contrast) were used in succession in random order for each image pullback. Quality was defined as ≥270° visualization of vessel wall layers from each axial image. Mean proportions (± standard deviation) of image quality for each flush medium were assessed using 1-way analysis of variance and are reported with the 95% confidence intervals (CI).

RESULTS

Four OCT catheters failed, leaving 19 patients who completed the OCT imaging protocol; from this cohort, 51 highest quality runs were selected for analysis. Average vessel diameter was 3.99±1.01 mm. OCT imaging allowed 10- to 15-μm resolution of the lumen border, with diminishing quality as vessel diameter increased. Plaque characterization revealed fibrotic lesions. Mean proportions of image quality were dextran 87.2%±12% (95% CI 0.81 to 0.94), heparinized saline 74.3%±24.8% (95% CI 0.66 to 0.93), contrast 70.1%±30.5% (95% CI 0.52 to 0.88), and carbon dioxide 10.0%±10.4% (95% CI 0.00 to 0.26). Dextran, saline, and contrast provided better quality than carbon dioxide (p<0.001).

CONCLUSION

OCT is feasible in peripheral vessels <5 mm in diameter. Dextran or saline flush media can allow lesion characterization, avoiding iodinated contrast. Carbon dioxide is inadequate for peripheral OCT imaging. Axial imaging may aid in enhancing durability of peripheral endovascular interventions.

Nonangiographic assessment of coronary artery disease: a practical approach to optical coherence tomography and fractional flow reserve

In an era of increased scrutiny of the appropriateness and safety of revascularization, interventional cardiologists must evolve by adding key tools to their armamentarium. This review highlights the utility of optical coherence tomography and fractional flow reserve in the catheterization lab and provides a practical guide for using these technologies during coronary intervention in various lesion subsets. We propose that fractional flow reserve informs the decision to intervene and optical coherence tomography guides the optimization of the outcome.

Optical coherence tomography guided PCI - initial experience at Apollo Health City, Jubilee Hills, Hyderabad

Background

The capability of OCT to examine the structure of the arterial wall before or after PCI is superior to those of other imaging modalities. Therefore the application of OCT during PCI seems logical and has the potential to enhance our performance during the PCI procedures.

Methods

OCT was performed in fifty-two patients out of which, 45 patients underwent PCI. Out of these 45 patients, in 25 patients both pre and post PCI OCT assessment was done. In 20 patients only post PCI OCT assessment was done. In seven patients PCI was not done due to nonsignificant obstruction, these seven patients were not included in final analysis.

Results

Over all OCT leads to management changes in 65% of the time it was used. Alteration of stent length was done in 56% of the cases when evaluated pre PCI. Alteration of stent diameter was done in 36% cases when evaluated pre PCI. Treatment of malapposition was done in 24% of total cases. Further balloon dilatation for vessel expansion was done in 15% of total cases. In one case left main stenting was done after proximal edge dissection.

Conclusion

OCT makes better visualization of plaque, thrombus, stent malapposition, dissection, plaque prolapse and helps in optimization of PCI results. More extensive, long-term studies will be needed to assess the prognostic implications of these findings.

The invasive assessment of coronary atherosclerosis and stents using optical coherence tomography: a clinical update

Ischaemic heart disease (IHD) remains one of the leading causes of death. Atherosclerosis has been intensely researched given the IHD prevalence and the financial impacts on healthcare systems. More recently, in vivo characterisation of coronary atherosclerotic plaque and tissue responses following stent implantation in a coronary artery has been made possible by a novel technology called optical coherence tomography (OCT). OCT is a light-based, invasive, intracoronary imaging modality long applied to the field of ophthalmology and now in clinical use worldwide. It gives a unique view of within the coronary artery using near-infrared light with a resolution of 15 microns, 10 times higher than other invasive coronary imaging techniques like intravascular ultrasound. The technology is being adopted to comprehensively detect features that make plaques 'vulnerable' (eg, large lipid pool, thin, fibrous-cap atheroma), whether stents are implanted optimally within the artery, and visualise the small layers of tissue that form over stent metal surfaces over time, which in turn may provide surrogate markers for long-term stent safety and help guide the optimal duration of dual antiplatelet therapy, a topic of big discussion at the current point of time.

Intracoronary optical diagnostics current status, limitations, and potential

Optical coherence tomography (OCT), is a novel intravascular imaging modality analogous to intravascular ultrasound but uses light instead of sound. This review details the background, development, and status of current investigation using OCT, and discusses advantages, limitations, and likely future developments. It provides indications for possible future clinical use, and places OCT in the context of current intravascular imaging in what is a rapidly changing field of investigation.

Current status of optical coherence tomography

Optical coherence tomography (OCT) is a novel imaging technology based on low-coherence interferometry that use near-infrared light in real-time, and allows cross-sectional in-situ visualization of the vessel wall at the microscopic level. OCT provides 10-fold higher resolution than intravascular ultrasound which is currently the most used modality for intra-coronary imaging. OCT offers the obvious advantages when characterizing precise plaque microstructure and distinguishing various type of plaques. OCT is also being assessed for its potential role in the understanding of neointimal coverage, vascular healing and the progression of atherosclerosis in coronary vasculature after stenting on the micron scale. These unique capabilities could be helpful in guiding coronary management and interventions. Recent improvement in next generation OCT technology, such as frequency-domain OCT, will allow for a simple imaging procedure, providing more useful information and complementing other modalities on both clinical and research applications for the cardiologists.

Optical coherence tomography-current technology and applications in clinical and biomedical research

Optical coherence tomography (OCT) is a noninvasive imaging technique that provides real-time two- and three-dimensional images of scattering samples with micrometer resolution. By mapping the local reflectivity, OCT visualizes the morphology of the sample. In addition, functional properties such as birefringence, motion, or the distributions of certain substances can be detected with high spatial resolution. Its main field of application is biomedical imaging and diagnostics. In ophthalmology, OCT is accepted as a clinical standard for diagnosing and monitoring the treatment of a number of retinal diseases, and OCT is becoming an important instrument for clinical cardiology. New applications are emerging in various medical fields, such as early-stage cancer detection, surgical guidance, and the early diagnosis of musculoskeletal diseases. OCT has also proven its value as a tool for developmental biology. The number of companies involved in manufacturing OCT systems has increased substantially during the last few years (especially due to its success in opthalmology), and this technology can be expected to continue to spread into various fields of application.

Optical coherence tomography: its value in intravascular diagnosis today

Optical coherence tomography is a recently developed high-resolution intravascular diagnostic technique. Initially, it was mainly used for characterizing atherosclerotic plaque because it served a number of functions, from identifying plaque with high lipid content to detecting macrophage accumulation, both of which are associated with plaque instability. Currently, there is growing interest in the value of optical coherence tomography in the area of coronary intervention, where the technique offers significant advantages over more widespread intravascular diagnostic techniques such as intravascular ultrasound: its higher resolution means that the vessel lumen diameter can be measured more precisely, periprocedural complications such microdissection of the coronary artery can be detected, stent apposition relative to the vessel wall can be optimized, neointimal hyperplasia can be detected after stent implantation, and neointimal thickness can be measured. It would therefore appear to be a very useful technique for interventional cardiologists. This review article considers the technical details of the technique and its applications, and compares it with other intravascular diagnostic techniques.

How should I treat a complex Post-CABG patient?

BACKGROUND

A 69 year old man was admitted with unstable angina (Class IIB). He had a history of chronic renal impairment, diabetes mellitus, hypertension and coronary bypass surgery in 1997 (LIMA graft to the LAD anf diagonal branch, saphenous vein grafts to the RCA and first marginal branch of LCx.

INVESTIGATION

Coronary angiography.

DIAGNOSIS

Unstable angina (Class IIB). Occlusion of the LCx and RCA. Functionally occluded LIMA on the LAD and diagonal branch. Diffuse disease of the LAD with two significant lesions at the LAD-first diagonal and mid-distal LAD.

TREATMENT

Revascularisation.

The initial extent of malapposition in ST-elevation myocardial infarction treated with drug-eluting stent: the usefulness of optical coherence tomography

PURPOSE

The aim of this study is to identify the extent of initial malapposition using optical coherence tomography (OCT) in ST-elevation myocardial infarctions (STEMI) treated with different types of drug-eluting stents (DES).

MATERIALS AND METHODS

Twenty four STEMI patients that underwent primary percutaneous coronary intervention (PCI) were enrolled. The OCT and intravascular ultrasound (IVUS) were performed within 72 hours after the primary PCI. Distances between the endo-luminal surface of the strut reflection and the vessel wall and the extent of malapposition were measured and analyzed.

RESULTS

Sirolimus-eluting stents (SES), paclitaxel-eluting stents (PES) and zotarolimus-eluting stents (ZES) were deployed in 7 patients (29%), 7 patients (29%) and 10 patients (42%). In total, 4951 struts in 620 mm single-stent segments were analyzed (1463 struts in SES, 1522 in PES, and 1966 in ZES). In strut analysis by OCT, the incidence of malapposition was 17 % (860/4951) and in stent analysis by IVUS, malapposition rate was 21% (5/24). The malapposition rate of strut level using OCT in 5 patients who had malapposition in IVUS was significantly higher than the 19 of those who had not (32 +/- 5% vs. 12 +/- 6%, p = 0.001). In addition, the frequency of malapposition was also significantly different (28% in SES, 11% in PES, 10% in ZES, p = 0.001). The use of SES was an independent predictor of malapposed struts.

CONCLUSION

The incidence of malapposition using OCT was quite prevalent in STEMI after primary PCI with DES implantation and SES has especially higher rates of malapposition compared to other DESs.

Use of an oxygen-carrying blood substitute to improve intravascular optical coherence tomography imaging

Optical coherence tomography (OCT) is a catheter-based imaging technology with powerful resolution capable of identifying vulnerable plaques and guiding coronary intervention. However, a significant limitation of intravascular OCT imaging is its attenuation by blood. We propose that the use of an oxygen-carrying blood substitute could potentially optimize OCT image quality. Surgical isolation of the descending thoracic aorta of six rabbits is performed, followed by intravascular OCT imaging of the abdominal aorta. Perfluorodecalin (PFD) is oxygenated using a bubble-through technique with 100% oxygen. OCT imaging is performed and compared using three different flushing modalities: PFD; saline; and blood. OCT imaging of the rabbit abdominal aorta is successful in all of the subjects. In each of the six studied subjects, flushing with PFD consistently provides dramatically better imaging of the vessel wall tissue structures. OCT image quality is highly dependent on the ability of the flushing modality to remove blood from the imaging field. From this proof-of-concept study, we demonstrate that endovascular flushing with an oxygen-carrying blood substitute (PFD) is optically superior to saline flushing for intravascular imaging.

The role of optical coherence tomography in vascular medicine

Optical coherence tomography (OCT) is an emerging imaging modality that provides high-resolution, microstructural information on atherosclerotic plaques in biological systems. Intracoronary OCT can identify thin-cap fibroatheroma and other vulnerable plaques that may be responsible for acute coronary events. These characteristics make OCT helpful in guiding coronary management and interventions, including stent apposition and early identification of procedure-related complications. OCT is being assessed for its potential role in carotid plaque characterization and in the diagnosis of peripheral arterial atherosclerosis. Its current use in studying carotid and cerebral vasculature and in the diagnosis of peripheral arterial diseases is limited and ill defined, but it is finding increasing application in these areas. Its performance can be further improved by increasing the signal to noise ratio and by using dynamic focus tracking techniques. It can potentially be used to monitor the progression and regression of atherosclerosis in the coronary, cerebral and peripheral vasculature. New indications for its use in vascular medicine are emerging as its technology continues to improve over time.

Assessment with optical coherence tomography of a new strategy for bifurcational lesion treatment: the Tryton Side-Branch Stent

The Tryton-Side Branch Stent (Tryton Medical, Inc., Newton, MA, USA) is a dedicated stent designed to provide complete carinal coverage of bifurcational lesions. After implantation of a 18 mm cobalt chromium Tryton stent from the left circumflex into the obtuse marginal branch, recrossing with an everolimus eluting Promus stent and final kissing balloon dilatation, optical coherence tomography (OCT) (LightLab Imaging Inc., Westford, MA, USA) was performed with a non-occlusive technique with motorized pullback (3 mm/s) during continuous pump injection of iso-osmolar contrast, in both LCx and OM1. OCT imaging showed good strut apposition at the level of the carina, with full coverage and no stent protrusion at the ostium of the side branch. Few malapposed struts were present in the proximal main vessel in the segment of stent superimposition, with a maximal separation from to the vessel wall of 160 microm. The implantation of the Tryton-Side Branch Stent allowed full coverage of the side branch ostium with uniform apposition of the stent struts at the level of the carina assessed by OCT.

Thrombus causes fluctuations in arterial drug delivery from intravascular stents

Arterial drug concentrations determine local toxicity. As such the emergent safety concerns surrounding drug-eluting stents mandate an investigation of the factors contributing to fluctuations in arterial drug uptake. Drug-eluting stents were implanted into porcine coronary arteries, arterial drug uptake was followed and modeled using 2-dimensional computational drug transport. Arterial drug uptake in vivo occurred faster than predicted by free drug diffusion, thus an alternate, mechanism for rapid transport has been proposed involving carrier-mediated transport. Though there was minimal variation in vivo in release kinetics from stent to stent, arterial drug deposition varied by up to 114% two weeks after stent implantation. The extent of adherent mural thrombus also fluctuated by 113% within 3 days after implantation. The computational drug transport model predicted that focal and diffuse thrombi elevate arterial drug deposition in proportion to the thrombus size by reducing drug washout subsequently increasing local drug availability. Fluctuations in arterial drug uptake are commonly reported. We now explain that variable peristrut thrombus can explain such observations even in the face of a narrow range of drug release from the stent. The mural thrombus effects on arterial drug deposition may be circumvented by forcing slow, rate limiting arterial transport that cannot be further hindered by mural thrombus.

Neointimal coverage of bare-metal and sirolimus-eluting stents evaluated with optical coherence tomography

OBJECTIVE

To analyse the neointimal coverage of sirolimus-eluting stent (SES) and bare-metal stent (BMS) visualised in vivo by optical coherence tomography (OCT).

METHODS

OCT images were obtained in 26 coronary vessels of 24 patients at 5-93 months after SES or BMS deployment. The short-term BMS group (BMS1) consisted of eight BMS in seven patients at 5-10 months of follow-up, the long-term BMS group (BMS2) consisted of six BMS in six patients at 23-93 months of follow-up, and the SES group (SES) consisted of 13 SES in 10 patients at 6-12 months of follow-up. The strut apposition, strut coverage and mean maximal and minimal neointimal thicknesses (NIT) for both BMS groups and SES were compared.

RESULTS

OCT images were acquired successfully. Significant differences between completely apposed and malapposed stent struts (p<0.0001) and between covered and uncovered stent struts (p<0.0001) were found among the three groups. The mean maximal and minimal NIT in the SES group were all significantly less than those of the BMS1 or BMS2 group, the minimal NIT in the BMS1 group was significantly less than that of the BMS2 but the mean maximal NIT was no significant difference between the BMS1 and BMS2 groups. In an open bifurcation artery, 19 struts visualised by OCT had no discernible coverage or were surrounded by either thrombus or a thick tissue layer.

CONCLUSIONS

OCT imaging can clearly visualise stent apposition and neointimal coverage of stent struts. Incomplete strut apposition and lack of strut coverage occurred with a significantly higher frequency in SES than in BMS. These findings may explain the occurrence of late thrombosis in SES. Optical coherence tomography (OCT) is the optical analogue to ultrasound, measuring the back-reflection of infrared light instead of sound waves. The greatest advantage of OCT is its high resolution, which exceeds that of any currently available in vivo imaging technology. The resolution of catheter-based systems is in the range of 10-20 microm. Furthermore, resolutions as high as 4 microm have been achieved ex vivo with more sophisticated techniques that may be applicable to future catheter-based approaches. The main components of various atheromatous plaques can be identified in OCT images, and have been validated in a histology-controlled study. Several studies have demonstrated the feasibility of OCT imaging in patients undergoing percutaneous coronary intervention (PCI). The aim of the present study was to use OCT to analyse the neointimal coverage of sirolimus-eluting stents (SES), compared with that of bare-metal stents (BMS).

Safety and feasibility of an intravascular optical coherence tomography image wire system in the clinical setting

Optical coherence tomography (OCT) is a fiber-optic technology that enables high-resolution intracoronary imaging. The aim of this study was to evaluate the safety and feasibility of intracoronary imaging with OCT in the clinical setting; 76 patients with coronary artery disease from 8 centers were enrolled. The OCT imaging system (ImageWire, Light Imaging Inc., Westford, Massachusetts) consists of a 0.006 inch fiber-optic core that rotates within a 0.016 inch transparent sheath. OCT imaging was performed during occlusion of the artery with a compliant balloon and continuous flushing. Intravascular ultrasound (IVUS) imaging was performed in the same segments. We assessed the safety and feasibility of the OCT imaging, compared with IVUS. Vessel occlusion time was 48.3 +/- 13.5 seconds and occlusion-balloon pressure was 0.4 +/- 0.1 atmospheres. Flushing with lactated Ringer's solution was performed at a rate of 0.6 +/- 0.4 ml/s. No significant adverse events, including vessel dissection or fatal arrhythmia, were observed. Procedural success rates were 97.3% by OCT and 94.5% by IVUS. The OCT image wire was able to cross 5 of 6 tight lesions that the IVUS catheter was unable to cross. Of the 98 lesions in which both OCT and IVUS were successfully performed, OCT imaging had an advantage over IVUS for visualization of the lumen border. Minimum lumen diameter and area measurements were significantly correlated between OCT and IVUS imaging (r = 0.91, p <0.0001 and r = 0.95, p <0.0001, respectively). In conclusion, this multicenter study demonstrates the safety and feasibility of OCT imaging in the clinical setting.

Assessment of blood vessel mimics with optical coherence tomography

Optical coherence tomography (OCT) is an imaging modality that enables assessment of tissue structural characteristics. Studies have indicated that OCT is a useful method to assess both blood vessel morphology and the response of a vessel to a deployed stent. We evaluated the ability of OCT to visualize the cellular lining of a tissue-engineered blood vessel mimic (BVM) and the response of this lining to a bare metal stent. We develop a side-firing endoscope that obtains intraluminal, longitudinal scans within the sterile bioreactor environment, enabling time-serial assessment. Seventeen BVMs are imaged with the endoscopic OCT system. The BVMs are then evaluated via fluorescence microscopy and/or standard histologic techniques. We determine that (1) the OCT endoscope can be repeatedly inserted without visible damage to the BVM cellular lining, (2) OCT provides a precise measure of cellular lining thickness with good correlation to measurements obtained from histological sections, and (3) OCT is capable of monitoring the accumulation of cellular material in response to a metallic stent. Our studies indicate that OCT is a useful technique for monitoring the BVM cellular lining, and that OCT may facilitate the use of BVMs for early stage device assessment.

Clinical applications of optical coherence tomography

Rupture of vulnerable plaque (VP) is responsible for most coronary events. Optical coherence tomography (OCT) is a high-resolution imaging method that allows excellent characterization of atherosclerotic plaque. While this technique is limited by the need to interrupt blood flow and a shallow depth of penetration, its resolution is an order of magnitude greater than possible with intravascular ultrasound (IVUS), and it has demonstrated better sensitivity and specificity for accurately determining plaque composition. Early in vitro and in vivo experiences have affirmed the excellent quality of these images making it an attractive technology for the analysis of VP. Its high resolution likely renders it the best imaging modality currently available for the evaluation of proper stent deployment and of intracoronary pathology in the setting of percutaneous coronary interventions (PCI). Our institution is currently involved in a multicenter trial to evaluate the effectiveness of OCT when compared to IVUS in this setting. Ongoing technological improvements aim to permit rapid scanning which should alleviate its current major limitation of needing to scan in a blood-free space. OCT is a promising new technology in the evaluation of atherosclerotic plaque and coronary microstructure.

Comparison of nonuniform rotational distortion between mechanical IVUS and OCT using a phantom model

Optical coherence tomography (OCT) is an optical analog of mechanical intravascular ultrasound (M-IVUS) with much higher spatial resolution. However, no data exist regarding the nonuniform rotational distortion (NURD) with OCT. The aim of the study was to investigate whether OCT generates less NURD relative to M-IVUS. A coronary artery phantom model was constructed with a rubber ring (3.68 mm in diameter), located at the distal end of the phantom. This model was also composed of eight equally spaced steel wires and an additional marker-wire. Two types of vascular phantoms were used, mild curve (90 degrees ) and acute curve (near 180 degrees ). Subsequent M-IVUS (n = 6) and OCT (n = 6) imaging was performed. Eight angles between eight wires, except the marker-wire, were measured from each image. These angles, measured with M-IVUS and OCT, were compared with those of high-resolution optical photography as a gold standard. The average in angle differences was significantly smaller in OCT compared with M-IVUS in the mild curve model (3.2 +/- 1.0 degrees vs, 6.9 +/- 2.1 degrees , p < 0.01). Compared with the latter model, the average in angle differences was exaggerated in the acute curve model with M-IVUS (9.1 +/- 0.9 degrees vs. 6.9 +/- 2.1 degrees , p < 0.05) but not with OCT (3.5 +/- 0.8 degrees vs. 3.2 +/- 1.0 degrees , p= not significant). OCT generates significantly less NURD compared with M-IVUS, especially in tortuous situation.

Technology Insight: optical coherence tomography--current status and future development

The understanding of concepts in coronary artery disease, such as the vulnerable or high-risk plaque, which accounts for many acute coronary events arising from non-flow-limiting coronary lesions, has advanced remarkably. Although coronary angiography is an established imaging technique for visualizing atherosclerotic disease, it is limited by its two-dimensional imaging aspect and a low sensitivity for identifying lesions in the presence of positive remodeling and diffuse disease. Moreover, coronary atherosclerotic plaques cannot be characterized. Although intravascular ultrasound is currently the most commonly employed adjunctive method to better define lesions, it is limited by low resolution. The development of new technologies for improved coronary plaque characterization has, thus, been desired. Optical coherence tomography is a developing technique that uses near-infrared light for the cross-sectional visualization of the vessel wall at the microscopic level. It enables excellent resolution of coronary architecture and precise characterization of plaque architecture. Quantification of macrophages within the plaque is also possible. These capabilities allow precise identification of the most common type of vulnerable plaque, the thin-cap fibroatheroma. Here, we discuss results from clinical studies which indicate that optical coherence tomography is a promising imaging technique for improved characterization of the coronary atherosclerotic plaque.