Optical Coherence Tomography for Imaging of Coronary Arteries

This evidence review was created in February 2012 and has been updated periodically with literature reviews of the MEDLINE database, most recently through January 5, 2015.

Optical coherence tomography (OCT) is intended as an alternative to intravascular ultrasound (IVUS) for imaging the coronary arteries. Therefore, the most relevant type of studies for evaluating the utility of OCT includes a head-to-head comparison between OCT and IVUS. These studies are limited by the lack of a true criterion standard for intravascular imaging but can permit comparison of the frequency and type of findings for the 2 types of imaging. Single-arm case series of OCT provide less useful information. Results from case series can characterize the findings obtained from OCT, use these findings to predict future events, and provide important information on adverse events. However, case series provide limited data on the comparative efficacy of OCT and IVUS.

Population Reference No. 1 Policy Statement

Technical Performance of OCT

The reliability of OCT findings was examined by Gonzalo et al.⁴ They used a second-generation, frequency-domain optical coherence tomography (FD-OCT) and evaluated the reproducibility of OCT findings according to the interstudy, interobserver, and intraobserver variability. Overall, the reproducibility of the OCT findings was high. The reproducibility of stent features such as edge dissection, tissue prolapse, intrastent dissection, and stent malapposition was 100% (k=1.0). Plaque characteristics also had high reproducibility, with k values for interstudy, interobserver, and intraobserver variability of 0.92, 0.82, and 0.95, respectively.

Fedele et al evaluated the reproducibility of OCT lumen and length measurements.⁵ In this study, OCT measurements were taken twice at intervals of 5 minutes in 25 patients undergoing coronary angiography. Per-segment and per-frame analyses showed high correlation for interobserver, intraobserver, and intrapullback comparisons for lumen area and length (R≥0.95, p<0.001 for all correlations), indicating excellent reproducibility. Similarly, Jamil et al reported good interstudy correlation for FD-OCT in an evaluation of both stented and native coronary arteries in 18 patients undergoing PCI (R²=0.99, p<0.001 for mean lumen area and minimal lumen area for repeat evaluations of the same coronary lesion).⁶ Liu et al reported good intra- and interobserver reliability for stent length measurements, along with high correlation between OCT and IVUS for stent length measurements in 77 patients undergoing PCI with stenting.⁷

In contrast, Brugaletta et al demonstrated a higher level of variability in inter- and intraobserver measurements of stent strut coverage with FD-OCT, with k values of 0.32 to 0.4 for interobserver measurements, depending on the OCT zoom setting, and 0.6 to 0.75 for intraobserver measurements.⁸ Stent strut coverage assessment is less standardized than other measures of vessel plaques or stents, so increased variability in measurements may be expected but should be considered in studies that use FD-OCT to measure stent strut coverage.

Identification, Risk Stratification, and Treatment of the “Vulnerable Plaque”

A number of studies have compared OCT with IVUS for evaluation of the vulnerable plaque. One of the earliest of these studies was reported by Jang et al in 2002.⁹ They compared the findings of 42 coronary plaques in 10 patients who underwent angiography, IVUS, and OCT. OCT had higher axial resolution (13

mm) than IVUS (98 mm). All fibrous plaques, microcalcifications, and echolucent areas identified by IVUS were also imaged by OCT. There were additional cases of echolucent regions and intimal hyperplasia imaged with OCT but not IVUS.

Kubo et al compared OCT and IVUS for identifying and classifying vulnerable plaques.¹⁰ A total of 96 target lesions were examined by both OCT and IVUS, and the presence of a “vulnerable plaque” was made using standard definitions for each procedure. OCT identified 18 vulnerable plaques as evidenced by thin fibrous caps of less than 65 µm. IVUS identified 16 plaques, for a sensitivity of 89% compared with OCT. IVUS also identified an additional 11 lesions as vulnerable not meeting the criteria by OCT. These were assumed to be false-positive IVUS results, resulting in a specificity for IVUS of 86%.

Miyamoto et al studied 81 coronary lesions with a plaque burden of greater than 40%.¹¹ IVUS and OCT gave somewhat different profiles of plaque characteristics. Vulnerable plaques identified by OCT had a larger plaque burden, more positive remodeling, and less fibrous plaque than IVUS.

Uemura et al (2012) prospectively evaluated the ability of OCT to predict the natural history of coronary plaques.¹² This cohort study enrolled 53 patients, with 69 nonobstructing coronary plaques, who had undergone both PCI and OCT. A second coronary angiogram was performed at a mean follow-up of 7 months to assess progression of plaques. Thirteen (18.8%) of 69 lesions showed progression on angiography at follow-up. There were several plaque characteristics defined by OCT that were predictive of progression, while the luminal diameter of the stenoses was not predictive. The factors found more frequently in lesions that progressed were intimal laceration (61.5% vs 8.9%, p<0.01), microchannel images (76.9% vs 14.3%, p<0.01), lipid pools (100% vs 60.7%, p=0.02), thin-cap fibroatheroma (76.9% vs 14.3%, p<0.01), macrophage images (61.5% vs 14.3%, p<0.01), and intraluminal thrombi (30.8% vs 1.8%, p<0.01). On regression analysis, the presence of fine-cap atheroma and microchannel images were strong predictors of progression (odds ratios, »20).

Another prospective cohort study that evaluated OCT in predicting the natural history of plaques was published in 2012 by Uemura et al.¹² This study enrolled 53 consecutive patients undergoing PCI and followed them for 7 months, at which time angiography was repeated. Of the 69 total obstructing lesions, 13 showed evidence of progression while 56 did not. OCT parameters predictive of progression were intimal laceration (61.5% vs 8.9%, p<0.01), presence of microchannels (76.9% vs 14.3%, p<0.01), lipid pools (100% vs 60.7%, p=0.02), macrophage images (61.5% vs 14.3%, p<0.01), and intraluminal thrombi (30.8% vs 1.8%, p<0.01).

Cross-sectional studies of risk stratification by OCT have also been published. In these studies, angiography is performed once, and characteristics of the plaque as defined by OCT are correlated with plaque rupture and/or other angiography findings. Yonetsu et al performed a cross-sectional study of 266 coronary plaques identified on angiography.¹³ A reliable measure of cap thickness was obtained in 188 (70.7%) of 266 patients. The thickness of the fibrous cap was an independent predictor of plaque rupture, and the optimal cutoff for predicting plaque rupture was estimated to be less than 67 µm.

Guo et al performed a cross-sectional study to evaluate characteristics of coronary plaques associated with coronary artery thrombosis.¹⁴ They included 42 patients with coronary artery plaque rupture detected by OCT during evaluation of 216 native coronary artery lesions among 170 patients. Plaques were divided into those with and without thrombus, which occurred in 64% of coronary plaques. Ruptured plaques with thrombus had significantly thinner fibrous caps (57 µm) than those without thrombus (96 µm; p=0.008).

Jia et al used data from a multicenter registry of patients who had undergone OCT of coronary arteries to characterize the morphologic features of the culprit coronary plaques in ACS.¹⁵ They included 126 patients with ACS who underwent preintervention OCT imaging. Plaques were defined by OCT as having plaque rupture (disrupted fibrous cap with underlying lipid), as a OCT-calcified nodule (disrupted fibrous cap with underlying calcium), as an OCT-erosion (intact fibrous cap), or other, and the category of culprit plaque pathology was compared with clinical and angiographic outcomes. The authors found significant differences in age, presentation with non-ST-segmented elevation ACS, and vessel diameter across different types of plaque. Given these differences, the study suggested that different types of plaque features may be caused by different underlying pathologies and warrant different treatment approaches; however, on its own, this study is insufficient to determine changes in treatment that would occur based on OCT results.

Gamou et al conducted a cross-sectional study of the association between OCT-determined coronary plaque morphology and deteriorated coronary flow after stent in 126 subjects undergoing stenting, 44 with ACS and 82 with stable angina pectoris.¹⁶ Patients were divided into the deteriorated flow group (n=21) and the reflow group (n=105) based on deterioration of Thrombolysis in Myocardial Infarction (TIMI) flow grade on angiography after mechanical dilatation. There were significant differences in the presence of reflow based on presentation (ACS vs stable angina; p<0.000). The presence of thrombus or thin-cap fibroatheroma on OCT was associated with deteriorated flow on angiography for patients with both ACS and stable angina. In multivariable modeling, thin-cap fibroatheroma was independently predictive of deteriorated flow (hazard ratio, 12.32; 95% confidence interval, CI, 3.02 to 50.31; p<0.000).

In another study evaluating characteristics of high-risk coronary plaques, Galon et al compared plaque characteristics for nonculprit coronary plaques in patients with ST-elevation myocardial infarction (STEMI) compared with those with stable angina pectoris.¹⁷ The study included 67 patients, 30 with STEMI and 37 with stable angina who underwent OCT evaluation after stent implantation. Compared with plaques in patients with stable angina, coronary plaques in STEMI patients had more surface area for thin-cap fibroatheroma (0.43 mm² vs 0.15 mm²; p=0.011), thinner minimum fibrous cap thickness (31.63 µm vs

47.27          µm; p=0.012), greater fractional luminal area for thin-cap fibroatheroma (1.65% vs 0.74%; p=0.046), and greater macrophage index (0.022% vs 0.015%; p<0.01).

Wykrzykowska et al reported initial results of a pilot randomized controlled trial (RCT) that treated high- risk plaques with a nitinol self-expanding vShield device.¹⁸ High-risk plaques were defined as the presence of a thin-cap fibroatheroma on OCT examination. Twenty-three patients were randomized to vShield (n=13) or medical therapy (n=10). At 6-month follow-up, there were no dissections or plaque ruptures after shield placement. There were no device-related adverse events at 6 months for patients treated with vShield. Mean stent area increased by 9% at 6-month follow-up. This small pilot RCT demonstrated the feasibility of identifying patients with vulnerable plaque by OCT and treating with a vShield device.

Section Summary: Identification, Risk Stratification, and Treatment of the “Vulnerable Plaque”

OCT can be used to evaluate morphologic features of atherosclerotic plaques and to risk-stratify plaques by their likelihood of rupture. Limited evidence from studies comparing OCT with IVUS has indicated that OCT picks up more abnormalities than IVUS and is probably more accurate in classifying plaques as high risk. Because of the lack of a true criterion standard, the sensitivity and specificity of OCT for this purpose cannot be determined with certainty. Some experts consider OCT to be the criterion standard and compare other tests with OCT.

Although OCT may be more accurate than other imaging modalities, its clinical utility is uncertain. It is not clear which patients should be assessed for a high-risk plaque, nor is it clear whether changes in management should occur as a result of testing. One clinical trial has used OCT to select patients for treatment of vulnerable plaques, but no outcome data have been reported yet. Therefore, the evidence is not sufficient to determine the effect of OCT on health outcomes when used to assess coronary atherosclerotic plaques.

Summary of Evidence

Optical coherence tomography (OCT) has some advantages over intravascular ultrasound (IVUS) for imaging coronary arteries. It has a higher resolution and provides greater detail for accessible structures compared with IVUS. Case series have demonstrated that OCT can be performed with a high success rate and few complications. Head-to-head comparisons of OCT and IVUS have reported that OCT picks up additional abnormalities not detected by IVUS, implying that OCT is a more sensitive test than IVUS.

Population Reference No. 2 Policy Statement

Adjunctive Treatment as Part of PCIs

Several studies have demonstrated that the use of IVUS as an adjunct to PCI results in improved outcomes.^19-21 The 2001 guidelines from the American College of Cardiology and American Heart Association for use of IVUS as an adjunct to PCI²² included the following:

1.       “Assessment of the adequacy of deployment of coronary stents, including the extent of stent apposition and determination of the minimum luminal diameter within the stent….

2.       Determination of the mechanism of stent restenosis … and to enable selection of appropriate therapy…

4. Assessment of a suboptimal angiographic result following PCI….

6.       Establish presence and distribution of coronary calcium in patients for whom adjunctive rotational atherectomy is contemplated….

7.       Determination of plaque location and circumferential distribution for guidance of directional coronary atherectomy….”

OCT as an Adjunct to PCI: Comparisons With IVUS

One randomized trial and a number of nonrandomized comparative studies have compared OCT with IVUS as an adjunct to PCIs. Habara et al performed a small open-label RCT comparing OCT with IVUS in 70 patients undergoing stent implantation.²³ Outcomes were primarily measures of optimal stent deployment, such mean stent area and stent expansion immediately postprocedure. There were no significant differences on most procedural and stent-related outcomes measures. However, several IVUS outcomes were superior. Mean stent area was greater for IVUS than for OCT (8.7±2.4 mm vs 7.5±2.5 mm, p<0.05); the percent focal (80.3±13.4% vs 64.7%±13.7%) and diffuse stent expansion was greater for the IVUS group (98.8%±16.5% vs 84.2%±15.8%; both p<0.05); and the frequency of distal edge stenosis was lower for the IVUS group (22.9% vs 2.9%, p<0.005). These results suggested IVUS achieved optimal stent deployment compared with OCT.

A matched comparison of patients undergoing angiography alone versus angiography plus OCT was published by Prati et al in 2012.²⁴ A total of 335 patients were treated with OCT as an adjunct to angiography and PCI; they were matched with 335 patients undergoing PCI without adjunct OCT. The primary end point was the 1-year rate of cardiac death or MI. In 34.7% of cases in the OCT group, additional findings on OCT led to changes in management. Patients in the OCT group had a lower rate of death or MI at 1 year, even after multivariate analysis with propensity-matching (odds ratio, 0.49; 95% CI, 0.25 to 0.96; p=0.037).

Yamaguchi et al studied 76 patients from 8 medical centers who were undergoing angiography and possible PCI.²⁵ Both IVUS and OCT were performed in a single target lesion selected for a native coronary artery with a visible plaque less than 99% of lumen diameter. Procedural success was 97.3% for OCT and 94.5% for IVUS. There were 5 cases in which the smaller OCT catheter could cross a tight stenosis where the IVUS catheter could not. No deaths or major complications were reported. Minimal lumen diameter was highly correlated between the 2 modalities (r=0.91, p<0.001). Visibility of the lumen border was superior with OCT, with poor visibility reported for 6.1% of OCT images compared with 17.3% by IVUS (p<0.001).

Kawamori et al reported on 18 patients undergoing stenting who had both OCT and IVUS performed.²⁶ The lumen area of the culprit vessel was smaller on OCT images compared with IVUS. OCT was more sensitive in identifying instances of stent malapposition (30%) than IVUS (5%; p=0.04). OCT also picked up more cases with stent edge dissection (10% vs 0%) and stent thrombosis (15% vs 5%). These results were interpreted as demonstrating the higher resolution and greater detail obtained with OCT compared with IVUS.

Bezerra et al compared IVUS with both frequency-domain (FD) and time-domain (TD) OCT in stented and unstented vessels.²⁷ The authors included 100 matched FD-OCT and IVUS evaluations in 56 nonstented and 44 stented vessels and 127 matched TD-OCT and IVUS evaluations in stented vessels, all in 187 patients who were undergoing PCIs in several trials. The results from evaluations of stented vessels follow. The authors included comparisons between 44 matched FD-OCT and IVUS evaluations and 127 matched TD-OCT and IVUS evaluations in stented vessels.²⁷ In the immediate post-PCI stent evaluations, tissue protrusion and malapposition areas were significantly larger by FD-OCT compared with IVUS (for tissue protrusion, OCT-IVUS difference of 0.16 mm², p<0.001; for malapposition areas, OCT-IVUS difference of 0.24 mm², p=0.017). Acute malapposition rates were 96.2% with FD-OCT compared with 42.3% with IVUS (k=0.241, p<0.001). However, measurements of mean area were larger for IVUS than for FD-OCT (OCT-IVUS difference, -0.50 mm², p=0.002). For follow-up of stented vessels, compared with IVUS, FD-OCT detected smaller minimal stent lumen areas (3.39 mm² vs 4.38 mm², p<0.001) and a greater neointimal hyperplasia area (1.66 mm² vs 1.03 mm², p<0.001). Similar findings were seen when TD-OCT was compared with IVUS. These results corroborated other studies’ findings that FD-OCT may be associated with greater detail resolution than IVUS in assessing coronary artery stents. The direction of the difference in immediate post-PCI stent area measurements between FD-OCT and IVUS measurements were counter to authors’ expectations; on reevaluation of imaging; they determined that patients with post-PCI imaging had more calcification than those who had follow-up imaging, and hypothesized that calcification may have affected detection of the stent-liminal interface on immediate postprocedure IVUS images.

Sohn et al compared detection rates for tissue prolapse after drug-eluting stent implantation between OCT and IVUS among 38 patients undergoing stent placement for coronary artery disease.²⁸ Tissue prolapse was detected in 38 (95%) of 40 lesions on OCT compared with 18 (45%) of 40 lesions on IVUS. Thirty patients were followed clinically for 2 years postprocedure, during which time 1 case of sudden cardiac death occurred, but no cases of MI, target vessel revascularization, or stent thrombosis. The clinical significance of the OCT detection rate is unclear given that the presence of tissue prolapse did not correlate with major cardiac adverse events during follow-up. In a study with similar cardiac adverse events findings, Sugiyama et al compared tissue prolapse measurements on OCT with stent morphologic characteristics among 178 native coronary lesions in patients undergoing PCI with stent placement.²⁹ Although higher degrees of tissue prolapse on OCT were associated with the presence of thin-cap fibroatheroma, there was no association between the presence of tissue prolapse and clinical events during 9 months of follow-up.

Ann et al compared detection rates for edge dissection after drug-eluting stent implantation between angiography, IVUS, and OCT among 58 patients who underwent balloon-expandable stent placement.³⁰ Stent edge dissection was detected in 24 (24%) of 100 stent edges on OCT imaging compared with 3 (3%) of 100 of stent edges on angiography and 4 (4%) of 100 stent edges on IVUS. Over 1-year follow- up, 1 patient with an edge dissection showed an angiographic in-stent restenosis; no cases of death, MI, target lesion revascularization, or stent thrombosis occurred.

Evaluation of Treatment Pathways Using OCT-Assisted PCI

A small body of literature has addressed whether a treatment pathway guided by OCT measurements is feasible or leads to improvements in outcomes. One potential role for OCT-guided therapy is in the use of repeat OCT measurements in the acute setting for guiding treatment decisions for patients with ACS who have undergone revascularization, particularly those with large thrombus burden who have undergone thrombus aspiration. OCT may be useful in these patients in determining the need for stent placement postthrombus aspiration, based on the size and appearance of any residual clot. Controlled trials of OCT- assisted PCI versus a standard approach are needed to determine whether OCT-guided PCI improves outcomes.

Two uncontrolled studies of OCT-guided PCI were identified. Souteyrand et al conducted a prospective observational cohort study to evaluate outcomes for invasive treatment decisions guided by OCT in patients with ACS with a large thrombus burden.³¹ Based on results of OCT, 63 (62.4%) patients underwent stenting, while the remainder was managed medically. Over 12 months of follow-up, no sudden deaths or MIs occurred.

Cervinka et al reported results of a pilot study assessing whether OCT guidance could guide intervention during primary PCI, with the goal of avoiding balloon angioplasty and stenting.³² The study included 100 patients with STEMI who underwent thrombus aspiration followed by OCT. Based on OCT imaging, 20 patients were treated with thrombus aspiration only. At follow-up angiography 1 week postprocedure, all 20 treated with thrombus aspiration had a “normal vessel” without significant stenosis or evidence of nonobstructive thin-cap fibroatheroma. No major adverse clinical events occurred at 30-day, 9-month, or 12-month follow-ups in either group.

These uncontrolled studies have demonstrated the feasibility of an OCT-guided approach to stent placement following thrombus aspiration. However, this evidence does not permit conclusions whether OCT-guided treatment decisions improve outcomes better than standard approaches, given the lack of control groups. Further high-quality comparative trials are needed.

Section Summary: Adjunctive Treatment as Part of PCIs

The evidence on use of OCT as an adjunct to PCI consists of 1 small RCT and several nonrandomized studies that compared the results of OCT with IVUS as an adjunct to PCI to evaluate stent placement, along with several nonrandomized studies that assessed the feasibility of an OCT-guided treatment strategy of deferred stenting. Because of the lack of a true criterion standard, it is not possible to determine the accuracy of OCT for detecting abnormalities of stent placement with certainty. Available studies have reported that OCT picks up more abnormalities than IVUS, including abnormalities such as stent malapposition that lead to changes in management. The single RCT comparing OCT with IVUS did not report any advantage of OCT over IVUS and, in fact, IVUS was superior to OCT on a number of outcome measures. Overall, the evidence is limited and insufficient to determine the degree of improvement with OCT or the clinical significance of this improvement. As a result, it is not possible to determine whether OCT improves health outcomes when used as an adjunct to PCI.

Summary of Evidence

As an adjunct to percutaneous coronary intervention (PCI), OCT may improve on the ability of IVUS to pick up clinically relevant abnormalities, and this may lead to changes in management. A single small randomized controlled trial did not report any advantage of OCT over IVUS for achieving optimal stent placement. Several noncomparative studies have addressed whether an OCT-guided treatment strategy involving deferred stenting is feasible. However, no comparative studies have been conducted to demonstrate improved clinical outcomes with such a strategy. Overall, the current evidence is limited and includes relatively small numbers of patients who have been evaluated by OCT. As a result, it is not possible to determine the degree of improvement with OCT, or the clinical significance of this improvement. Therefore, the use of OCT as an adjunct to PCI is considered investigational.

Population Reference No. 3 Policy Statement

Follow-Up Evaluation After Stent Placement

A large number of studies have used OCT as a research tool, primarily for coronary stenting. OCT is used to assess the degree of neoendothelial coverage of the stent within the first year of placement. Stent coverage is considered an important intermediate outcome, because it has been shown to be predictive of clinical outcomes for patients undergoing stenting. Other studies have used OCT as a tool to evaluate edge dissections after coronary stenting.³³ These types of studies do not provide relevant information on the clinical utility of OCT and will therefore not be discussed further.

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