Author + information
- Received April 7, 2015
- Revision received July 20, 2015
- Accepted August 19, 2015
- Published online July 1, 2016.
- Kyeong Ho Yun, MDa,
- Gary S. Mintz, MDb,
- Bernhard Witzenbichler, MDc,
- Shinji Inaba, MDb,d,
- Takehisa Shimizu, MD, PhDb,d,
- D. Christopher Metzger, MDe,
- Michael J. Rinaldi, MDf,
- Ernest L. Mazzaferri Jr., MDg,
- Peter L. Duffy, MD, MMMh,
- Giora Weisz, MDb,d,i,
- Thomas D. Stuckey, MDj,
- Bruce R. Brodie, MDj,
- Ajay J. Kirtane, MD, SMb,d,
- Gregg W. Stone, MDb,d and
- Akiko Maehara, MDb,d,∗ ()
- aWonkwang University Hospital, Iksan, South Korea
- bCardiovascular Research Foundation, New York, New York
- cHelios Amper-Klinikum, Dachau, Germany
- dColumbia University Medical Center, New York, New York
- eWellmont CVA Heart Institute, Kingsport, Tennessee
- fSanger Heart & Vascular Institute/Carolinas HealthCare System, Charlotte, North Carolina
- gThe Ohio State University Wexner Medical Center, Columbus, Ohio
- hReid Heart Center, FirstHealth of the Carolinas, Pinehurst, North Carolina
- iShaare Zedek Medical Center, Jerusalem, Israel
- jLeBauer Cardiovascular Research Foundation/Cone Health, Greensboro, North Carolina
- ↵∗Reprint requests and correspondence:
Dr. Akiko Maehara, Cardiovascular Research Foundation, 111 East 59th Street, 12th Floor, New York, New York 10022.
Objectives This study evaluated the relationship between platelet reactivity and plaque morphology using grayscale and radiofrequency intravascular ultrasound (IVUS) virtual histology (VH).
Background Recent studies have reported that high on-treatment platelet reactivity (HPR) is associated with higher plaque volume and the presence of multivessel disease; however, the association between HPR and plaque morphology has not been evaluated.
Methods The ADAPT-DES (Dual AntiPlatelet Therapy With Drug Eluting Stents) intravascular ultrasound substudy was a prospective, multicenter, observational study of 8,582 patients undergoing percutaneous coronary intervention with drug-eluting stents in whom platelet reactivity on clopidogrel was assessed routinely. The current analysis included 909 culprit lesions from 773 patients with pre-intervention grayscale IVUS and IVUS-VH. HPR was defined as platelet reactivity >208 P2Y12 reaction unit in point-of-care P2Y12 testing by the VerifyNow assay, measured during steady-state platelet inhibition in patients receiving an antiplatelet agent.
Results HPR was associated with 3-vessel coronary artery disease (31.0% vs. 24.4%; p = 0.04). The incidence of fibroatheroma was higher in patients with HPR than those without HPR (77.1% vs. 68.9%; p = 0.01). The HPR group had larger percent plaque and media volume (plaque and media/external elastic membrane volume: 58.1% [95% confidence interval (CI): 57.1% to 59.0%] vs. 56.6% [95% CI: 55.8% to 57.5%]; p = 0.03) and plaque burden at the minimum lumen site (76.7% [95% CI: 75.7% to 77.8%] vs. 75.0% [95% CI: 74.0% to 76.0%]; p = 0.02). Despite a similar prevalence of attenuated plaque, patients with HPR had longer culprit lesion attenuated plaque length (8.0 [95% CI: 7.0 to 9.1] mm vs. 6.5 [95% CI: 5.9 to 7.1] mm; p = 0.01). On multivariate analysis, the presence of angiographic calcium (odds ratio [OR]: 1.85: 95% CI: 1.33 to 2.56; p = 0.0002) and HPR (OR: 1.45; 95% CI: 1.05 to 2.01; p = 0.02) were independent predictors for a culprit lesion fibroatheroma.
Conclusions HPR was associated with increased culprit lesion atherosclerotic burden and adverse plaque morphology among patients undergoing percutaneous coronary intervention. Platelet reactivity might be associated with not only blood clot formation, but also severity of atherosclerosis. (Assessment of Dual AntiPlatelet Therapy With Drug Eluting Stents [ADAPT-DES]; NCT00638794)
Dual antiplatelet therapy including a platelet P2Y12 receptor inhibitor is the cornerstone of coronary artery disease management and secondary prevention, especially after drug-eluting stent implantation. Recently, P2Y12 receptor inhibitor nonresponsiveness, characterized as high on-treatment platelet reactivity (HPR), has been recognized to correlate with adverse events after acute coronary syndromes (ACS) and percutaneous coronary intervention (PCI) (1–4). Platelet activation and aggregation in response to endothelial injury—namely, plaque rupture—is responsible for intracoronary thrombosis leading to ACS and, in particular, to acute myocardial infarction (MI); however, increasing evidence suggests that platelets are also important mediators of inflammation and play a central role in atherogenesis itself (5,6). Therefore, HPR may not only be associated with MI or stent thrombosis, but also may be associated with increased coronary atherosclerotic burden or unstable plaque morphology. Recent angiographic and intravascular ultrasound (IVUS) studies have reported that HPR is associated with multivessel disease and greater plaque volume (7,8); however, plaque morphology has not been evaluated. In the present study, we evaluated the relationship between platelet reactivity and plaque morphology (as well as overall plaque burden) using grayscale and radiofrequency IVUS virtual histology (VH) in patients enrolled in the ADAPT-DES (Assessment From the Dual AntiPlatelet Therapy With Drug-Eluting Stents) study.
Study design and protocol
In the ADAPT-DES study, consecutive patients at 11 U.S. and German sites successfully treated with 1 or more U.S. Food and Drug Administration- or CE mark-approved drug-eluting stent were eligible for enrollment, regardless of patient or lesion complexity. The only exclusion criteria were the occurrence of a major complication during the procedure or before platelet function testing or planned bypass surgery after PCI. The primary endpoint was definite or probable stent thrombosis according to the Academic Research Consortium definitions (9). The study has been described in detail previously (10). Procedural IVUS use was at operator discretion; however, when IVUS was used, the patients were enrolled in a pre-specified IVUS substudy, and the operator was required to report the timing of IVUS imaging (pre-intervention, post-stent, post-adjunct balloon inflation, and so on) and how the IVUS information influenced the procedure. The study was approved by the institutional review board at each participating center, and all eligible patients signed informed, written consent.
Assessment of platelet reactivity
Platelet reactivity after successful PCI was assessed by VerifyNow P2Y12 assays (Accumetrics, San Diego, California). Clopidogrel was given as either: 1) a dose of 600 mg at least 6 h before VerifyNow testing; 2) a dose of 300 mg at least 12 h before VerifyNow testing; or 3) a dose of 75 mg or more for at least 5 days before VerifyNow testing. If eptifibatide or tirofiban were used during the PCI, a 24-h washout period was required before VerifyNow testing. A 10-day washout period was required if abciximab was used; thus, no patients receiving abciximab were enrolled. VerifyNow P2Y12 baseline reactivity, P2Y12 reaction unit (PRU), and P2Y12 percent inhibition were measured as platelet function. In the ADAPT-DES study, HPR has been defined as a high level of platelet reactivity (>208 PRU) that is measured during steady state platelet inhibition in patients receiving an antiplatelet agent (10,11).
Grayscale and IVUS-HS image acquisition
Pre- and post-PCI grayscale and IVUS-VH were performed using a synthetic aperture array, 20 MHz, 3.2-Fr catheter (Eagle Eye, Volcano Corporation, Rancho Cordova, California) after intracoronary nitroglycerin. The IVUS catheter was advanced distal to the treated lesion, and pulled backed to the aorto-ostial junction using an R-100 (Volcano Corporation) motorized catheter pullback device (0.5 mm/s). During pullback, grayscale IVUS was recorded, raw radiofrequency data were captured at the top of the R-wave, and reconstruction of the color-coded map by a IVUS-VH data recorder was performed (s5, Volcano Corporation). IVUS studies were archived onto DVD. Using computerized planimetry software (echoPlaque, INDEC Systems Inc, Santa Clara, California) for contouring and data output, off-line grayscale, and IVUS-VH analyses of all imaged segments were performed prospectively at an independent IVUS core laboratory (Cardiovascular Research Foundation, New York, New York) that was blinded to the clinical events.
Grayscale and IVUS-VH analysis before PCI
External elastic membrane (EEM) and lumen borders were contoured for each slice. Quantitative IVUS measurements included EEM, lumen, plaque and media (P&M) (EEM minus lumen) cross-sectional area and plaque burden (P&M divided by EEM). Volumes were calculated using Simpson’s rule and also reported as normalized area (volume divided by length). IVUS-VH plaque components were color coded as dense calcium (white), necrotic core (red), fibrofatty (light green), or fibrous tissue (dark green) and reported as percentages of total plaque volume. A culprit lesion was defined as the segment that was stented and was identified by comparing the pre- and post-PCI IVUS images. The slice with the minimum lumen cross-sectional area was identified and assessed.
Pre-PCI qualitative grayscale IVUS morphology included plaque rupture (intraplaque cavity that communicated with the lumen with an overlying residual fibrous cap fragment), attenuated plaque (ultrasound attenuation of deeper arterial structures despite the absence of bright calcium), and calcified nodule (irregular and protruding convex shape of calcium). Using IVUS-VH a fibroatheroma was defined as >10% confluent necrotic core (spotty red color was not considered as confluent necrotic core) (12).
Categorical variables were summarized using percentages and counts and were compared using chi-square tests or the Fisher exact test where appropriate. Continuous variables were shown as median and first and third quartiles and compared using the Wilcoxon rank sum test. For lesion-level data, a model with a generalized estimating equation approach was used to compensate for potential cluster effects of multiple lesions in the same patient and presented as least square means with 95% confidence intervals. Baseline variables considered clinically relevant were evaluated by univariate logistic regression model, and parameters with p < 0.10 were entered into the multivariate logistic regression models. Statistical analyses were performed using SAS version 9.1.3 (SAS Institute, Cary, North Carolina); p < 0.05 was considered significant for all analyses.
From July 2008 to September 2010, 8,582 patients were enrolled in ADAPT-DES among whom 2,064 patients were enrolled into the pre-specified IVUS substudy. Pre-PCI grayscale and IVUS-VH images in de novo (not previously treated) native coronary arteries were available in 909 culprit lesions from 773 patients to assess the underlying morphology. Patient characteristics according to HPR (PRU >208) are described in Table 1. HPR was observed more commonly in elderly patients, female patients, and in patients with versus without diabetes mellitus. The incidence of ACS and 3-vessel coronary artery disease was higher in patients with HRP than those without HPR. HPR was associated with high body mass index, a history of heart failure, and a low left ventricular ejection fraction.
Grayscale and IVUS-VH analysis
Grayscale and IVUS-VH findings in the culprit lesions are shown in Table 2. In the volumetric and minimal lumen area site analyses, the HPR group had a larger percent P&M volume (P&M volume/EEM volume) and plaque burden at the minimal lumen area site. Patients with HPR had longer culprit lesion attenuated plaque length despite a similar prevalence of attenuated plaque. The prevalence of culprit lesion plaque rupture was similar in the 2 groups. The prevalence of a fibroatheroma was higher in patients with HPR than those with no HPR (77.1% vs. 68.9%; p = 0.01). Conversely, the prevalence of pathologic intimal thickening was higher in patients without HPR.
After adjusting for clinical variables, the presence of any angiographic calcium and HPR were independent predictors for a fibroatheroma (Table 3).
This study demonstrates that HPR is associated with a greater atherosclerotic plaque burden and worse plaque morphology, especially in culprit lesions in patients undergoing PCI. Compared with patients without HPR, those with HPR exhibited a higher prevalence of culprit lesion fibroatheroma. Previous studies have suggested that HPR was related to extent of coronary artery atherosclerotic disease (7,8). Our grayscale and IVUS-VH findings confirm these reported observations and extended the relationship of HPR to worse plaque morphology.
HPR has been defined as a high level of platelet reactivity that is measured during steady-state platelet inhibition in patients receiving an antiplatelet agent (12). Several mechanisms have been described for the suboptimal response to clopidogrel, including genetic, cellular, and clinical factors (13,14). Increased platelet reactivity has been observed more commonly in specific clinical scenarios such as ACS, increased body mass index, diabetes mellitus, and renal insufficiency (13); these results were also seen in our current study. Although diabetes mellitus, renal insufficiency, and body mass index were not independent predictors for fibroatheroma in our multivariate analysis, there were significant differences according to PRU that might have contributed to the frequency of fibroatheroma in the HPR group. In addition, both diabetes mellitus and renal insufficiency play a significant role in arterial calcification. Therefore, the process of atherosclerotic vascular disease such as endothelial injury as observed in certain clinical situations (e.g., diabetes mellitus) or plaque rupture in ACS could lead to functional platelet abnormalities and increased platelet reactivity (8,14).
In the current study, HPR was associated with greater atherosclerotic burden. The incidence of 3-vessel disease was greater in patients with HPR, and percent P&M volume in the entire lesion as well as plaque burden at the minimal lumen area site were also greater in culprit lesions in patients with HPR. Previous studies have reported a relationship between plaque rupture, especially recurrent plaque ruptures, and culprit lesion plaque burden. Mann et al. (15) reported that repeated silent ruptures that heal were the cause of progressive and worsening luminal compromise. Similarly, Burke et al. (16) reported that plaque burden and percent luminal narrowing increased with the number of previous ruptures and that percent luminal narrowing was greater for acute compared to healed ruptures. A pathologic study by Finn et al. (17) reported that 65% of lesions with a plaque burden of >50% had pathologic plaque rupture, and 42% contained a thin-cap fibroatheroma; conversely, 35% of lesions with a plaque burden of <50% had plaque rupture and 57% had a thin-cap fibroatheroma. Therefore, it is possible that increased platelet reactivity may potentiate arterial thrombosis at the time of rupture, thereby driving inflammation and atherosclerotic lesion progression.
The present study also demonstrated that HPR was associated with worse plaque morphology, especially attenuated plaque length and fibroatheroma morphology. Attenuated plaque, especially superficial echo attenuation, has been reported as evidence of a fibroatheroma containing a large necrotic core (18). Recent clinical studies have shown that attenuated plaques were associated with ST-segment elevation MI and periprocedural myonecrosis or no-reflow in patients with coronary artery disease undergoing PCI (19–21). In particular, Wu et al. (19) and Shiono et al. (21) correlated the amount of attenuated plaque, especially reflected in its length, with adverse events after stent implantation.
Activated platelets promote endothelial adhesion of neutrophils and monocytes (22). In addition, activated platelets are associated with expression of adhesion molecules, oxidation of low-density lipoprotein, and smooth muscle cell proliferation (23). These processes may lead to foam cell development and accelerated atherogenesis and development of a fibroatheroma that is associated with poor outcomes. A previous PROSPECT (Providing Regional Observations to Study Predictors of Events in the Coronary Tree) substudy reported that patients with 1 or more fibroatheromas had a 12.9% frequency of adverse events during 3-year follow-up, whereas those without a fibroatheroma had only a 3.7% event rate (24). Similar results were reported by the VIVA (VH-IVUS in Vulnerable Atherosclerosis) investigators (25). Attenuated plaque was also associated with adverse events.
Breet et al. (26) reported that a HPR (PRU cutoff of 236) was associated with an increased rate of MI (hazard ratio [HR]: 2.96), but not stent thrombosis or death. A recent meta-analysis also demonstrated that a PRU of ≥230 was associated with long-term cardiovascular events after PCI, including stent thrombosis (HR: 3.11), death (HR: 2.04), and MI (HR: 1.66) (27). The overall ADAPT-DES study confirmed that a PRU of >208 was strongly related to stent thrombosis (adjusted HR: 2.49) and MI (adjusted HR: 1.42) during 1-year follow-up (10). Thus, a HPR is associated not only with blood clot formation, but also with unstable plaque morphology as shown in the current analysis, irrespective of a specific PRU cutoff.
IVUS use was per operator discretion, and IVUS was not performed in all coronary arteries in all patients. We did not assess more global measures of atherosclerotic burden, and some selection bias was expected. Platelet reactivity was assessed at only a single time point at a relatively late stage in the development of atherosclerotic disease. IVUS-VH phenotype classification depends on subjective assessments of plaque morphology that may vary between observers; however, fibroatheroma was assessed by a >10% necrotic core, and the amount of necrotic core was automated output and was not interpreted. Our study demonstrated only correlative association; the cause-and-effect relationship between platelet reactivity and plaque morphology remains speculative.
In this ADAPT-DES substudy, we demonstrated that HPR was associated with increased atherosclerotic burden and worse plaque morphology. Further studies are required to define the causal mechanisms between platelet reactivity and development and progression of atherosclerosis and whether this may be a contributing factor in future cardiovascular events.
COMPETENCY IN MEDICAL KNOWLEDGE: Relationship between HPR and stent thrombosis and myocardial infarction is well-known. This study demonstrated that HPR is associated with increased culprit lesion atherosclerotic burden and adverse plaque morphology among patients undergoing percutaneous coronary intervention.
TRANSLATIONAL OUTLOOK: The cause-and-effect relationship between platelet reactivity and plaque morphology remains speculative. Further studies are required to define the causal mechanisms between platelet reactivity and development and progression of atherosclerosis and whether this may be a contributing factor in future cardiovascular events.
Dr. Yun has received speaking honoraria from AstraZeneca Korea. Dr. Mintz has received grant support from Volcano Corporation; and is a consultant for Volcano Corporation, Boston Scientific, InfraReDx. Dr. Witzenbichler is a consultant for Volcano. Dr. Shimizu has received grant funding from Japan Heart Foundation and Bayer Yakuhin Research Grant Abroad. Dr. Metzger is a consultant for Abbott Vascular, Cordis, IDEV, Medtronic, and Volcano. Dr. Rinaldi is a consultant for Abbott, Boston Scientific, and St. Jude Medical. Dr. Duffy has received speaker honoraria from Volcano. Dr. Stuckey is on the advisory board for Boston Scientific; has received speaker honoraria from Boston Scientific and Eli Lilly/Daiichi-Sankyo. Dr. Kirtane has received institutional research grants to Columbia University from Boston Scientific, Medtronic, Abbott Vascular, Abiomed, St. Jude Medical, Vascular Dynamics, and Eli Lilly. Dr. Maehara has received grant support from Boston Scientific; is a consultant for Boston Scientific, ACIST Medical Systems; and has received speaker fees from St. Jude Medical.
David J. Moliterno, MD, served as Guest Editor for this paper.
- Abbreviations and Acronyms
- acute coronary syndromes
- external elastic membrane
- high on-treatment platelet reactivity
- hazard ratio
- intravascular ultrasound
- myocardial infarction
- plaque and media
- percutaneous coronary intervention
- P2Y12 reaction unit
- virtual histology
- Received April 7, 2015.
- Revision received July 20, 2015.
- Accepted August 19, 2015.
- American College of Cardiology Foundation
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