Chapter 36 IVUS versus OCT: Relative Merits and Drawbacks

Transcription

1 Chapter 36 IVUS versus OCT: Relative Merits and Drawbacks GAGANDEEP SINGH HARI RAJ TOMAR BHAWANI SHANKAR Intracoronary imaging modalities have helped us in having better understanding of coronary artery disease (CAD) and percutaneous coronary intervention (PCI). Intravascular ultrasound (IVUS) has contributed significantly to latest PCI techniques. Optical coherence tomography (OCT) has further enhanced our knowledge as it has 10 times higher resolution and 40 times faster imaging acquisition. Second generation of OCT uses Fourier or frequency domain (FD) detection technology in which a monochromatic source emits light which is swept across wavelengths between 1250 and 1350 nm and there is fixed reference mirror. High viscous fluids like contrast are used to purge blood from vessel and image acquisition is done rapidly 1. This contrasts with earlier time domain (TD) technology in which a fixed light source and a moving reference mirror was used, taking more time and it also required balloon occlusion of proximal artery. TECHNICAL COMPARISON BETWEEN IVUS AND OCT 2,3 IVUS FD-OCT Source of image Ultrasound Near infrared light Axial resolution (microns) Lateral resolution (microns) Tissue penetration (mm) Frame rate (frames/s) Pullback speed (mm/s) Blood clearance Not required Contrast ml ADVANTAGE OF INTRACORONARY IMAGING Both IVUS and OCT provide tomographic views of the coronary artery. Before PCI, they help to identify relevant measurements as lesion length, minimal luminal area (MLA), proximal and distal reference locations and diameters. This information is useful in deciding stent size. Post-PCI, they help to assess stent expansion, apposition and procedural complications as edge dissection, plaque prolapse and geographical miss. They help in better understanding of mechanisms of stent failure (thrombosis and restenosis) that may be missed using coronary angiography alone. ADVANTAGES OF IVUS For more than two decades, IVUS is the most used and reliable intracoronary imaging modality to guide stenting, especially in complex lesions including left main stenting, chronic total occlusions (CTO), coverage of ostial lesions and bifurcation lesions. ASSESSMENT OF INTERMEDIATE LEFT MAIN CORONARY ARTERY (LMCA) LESION AND LMCA STENTING Deferring of revascularization in patients with LMCA lesions is safe 4, if IVUS MLA is more than 6.0 mm 2. In Korean patients, 4.8 mm 2 is a better MLA cut-off than 6.0 mm 2 in LMCA lesions 5. IVUS must be performed from both the left circumflex (LCX) and left anterior descending (LAD) till the LMCA ostium to assess the MLA within the LMCA and the disease at the LAD and LCX ostium. Single stent cross-over technique from LMCA to LAD is associated with FFR 0.8, if MLA is more than 4.0 mm 2 291

2 292 SECTION IV Interventional Cardiology and a plaque burden is less than 50% at the LCX ostium 6. Poststenting IVUS helps to detect proper lesion coverage, stent apposition and optimal stent expansion. Assessment of stent expansion with MLA must be done at level of LMCA (optimal MLA 8 mm 2 ), polygon of confluence ( 7 mm 2 ), ostium of LAD ( 6 mm 2), ostium of LCX ( 5 mm 2 ) 7. LCX ostium is the most common site of stent underexpansion. In two-stent strategy, restenosis is most common at sites with underexpansion than at sites without underexpansion (24.1% vs. 5.4%, P.001). ASSESSMENT OF AORTO-OSTIAL LESIONS By measuring plaque burden, IVUS helps in planning proper lesion coverage at aorto-ostial locations. PRE-PCI ASSESSMENT OF CALCIFIED LESIONS IVUS helps to identify calcium deposits which predispose to stent underexpansion. If the arc and length of calcium are severe, there is more likelihood of stent underexpansion. Such heavily calcified segments predispose to extensive dissections and occasionally stent fractures. This information may help the operator in timely deciding for plaque modification. IVUS-GUIDED CTO-PCI IVUS is helpful to find entrance to CTO if positioned into proximal side branch. By positioning IVUS in subintimal space, IVUS-guided wiring helps in penetrating from subintimal space to true lumen. In retrograde approach of CTO opening, when doing reverse CART (controlled antegrade and reterograde subintimal tracking), IVUS helps to assess position of antegrade and retrograde wires in intima or subintima and thus guides in decision-making. Unlike OCT, IVUS can acquire images even in absence of flow and thus avoid intracoronary injectioninduced propagation of dissections and subintimal space. IVUS-GUIDED STENT PLACEMENT AND THE SUPPORTIVE EVIDENCE IVUS has greater penetration and thus helps in obtaining proper media-to-media dimension. This information helps in deciding stent size. IVUS can calculate exact plaque burden. The landing zones of stent shall have minimum plaque burden. In cases of ostial lesions, IVUS helps to determine whether to cover aorto-ostial junction. IVUS guidance leads to better stent expansion and larger poststenting areas. Bare-metal stents (BMS): Meta-analysis of the randomized angiographic versus IVUS-guided BMS implantation trials showed that IVUS reduced restenosis and repeat revascularization, but not death or myocardial infarction 8. Drug-eluting stents (DES): Meta-analysis by Zhang et al. including 3 RCTs and 17 registry studies including 29,068 patients showed that IVUSguided DES implantation was associated with a reduction in MACE including mortality, myocardial infarction, stent thrombosis and repeat revascularization 9. IVUS PREDICTORS OF EARLY STENT THROMBOSIS OR OF IN-STENT RESTENOSIS Stent underexpansion or small lumen area caused by thrombus protrusion are the predisposing factors. The presence of significant dissections or plaque burden at edges is also predictor of early stent thrombosis or of in-stent restenosis. Surprisingly acute stent malapposition is not a risk factor, if the stent is properly expanded. DRAWBACKS OF IVUS 1. In tight lesions, IVUS catheter can occlude lumen, and low pullback speed can lead to myocardial ischaemia. 2. Grey scale IVUS has limitations in assessing tissue composition. Various radiofrequency-ivus technologies have been developed to improve plaque characterization. But for PCI optimization, data are lacking to indicate that these newer technologies further improve acute or long-term patient outcomes. 3. IVUS cannot measure calcium thickness, which may be an important limit to stent expansion. 4. IVUS cannot accurately assess stent malapposition, edge dissection, tissue prolapse, thrombus and endothelial coverage of struts. ADVANTAGES OF OCT OCT has 10 times better resolution and so it can clearly visualize the surface of vessel lumen. There is high rate of data acquisition and so can be performed rapidly. It gives high quality longitudinal view, threedimensional vessel reconstruction and can be coregistered with coronary angiogram.

3 Chapter 36 IVUS versus OCT: Relative Merits and Drawbacks 293 PLAQUE CHARACTERIZATION Plaques can be characterized as fibrous (high reflectivity, low signal attenuation), lipid rich (low reflectivity, high signal attenuation) or calcific (heterogeneous area, high or low reflectivity, low signal attenuation) 10, 11 ( Fig. 36-1). OCT has advantage to assess width of calcium plaque. It can also distinguish red thrombus (red blood cells rich, signal rich, high attenuation) from white thrombus (white blood cells and platelet rich, signal rich, low attenuation) 12 ( Fig. 36-2). PLAQUE VULNERABILITY High resolution of OCT helps in identifying plaques which are prone to rupture. The features associated with plaque vulnerability on OCT are thin fibrous caps, large lipid cores, microchannels, macrophage infiltration, superficial spotty calcification and cholesterol crystals 13. Thin-cap fibroatheroma is defined as lipid-rich plaque with an overlying fibrous cap less than 65 microns. Lipid-rich plaque occupies two or more quadrants of the cross-sectional image. Microchannels are small black holes within a plaque microns in diameter and seen in at least three consecutive frames on pullback. Macrophage accumulations are linear series of signal-rich spots with high signal attenuation. Spotty calcium refers to calcium deposits with an arc 90. Cholesterol crystals are identified as thin, linear, signal-rich structures with low signal attenuation ( Fig. 36-3). PATHOPHYSIOLOGY OF ACUTE CORONARY SYNDROME (ACS) ACS occurs mostly because of coronary thrombosis associated with plaque rupture (60%), plaque erosion (36%) and less commonly calcified nodules (4%) 14. OCT identifies plaque rupture as fibrous cap A. Fibrous B. Lipid C. Calcific Figure Optical coherence tomography images of various coronary plaques with different composition. (Reprinted from: Ong, D. S., Jang, I. K. (2015). Fundamentals of optical coherence tomography image acquisition and interpretation. Interventional Cardiology Clinics, 4, ; with permission from Elsevier.) A. Red thrombus B. White thrombus Figure Optical coherence tomography images of red (high attenuation) and white thrombus (low attenuation). (Reprinted from: Ong, D. S., Jang, I. K. (2015). Fundamentals of optical coherence tomography image acquisition and interpretation. Interventional Cardiology Clinics, 4, ; with permission from Elsevier.)

4 294 SECTION IV Interventional Cardiology A. TCFA B. Lipid-rich plaque C. Microchannels D. Macrophages E. Spotty calcium F. Cholesterol crystal Figure Characteristics of vulnerable plaque on optical coherence tomography. (Reprinted from: Ong, D. S., Jang, I. K. (2015) Fundamentals of optical coherence tomography image acquisition and interpretation. Interventional Cardiology Clinics, 4, ; with permission from Elsevier.) discontinuity with underlying lipid core and cavity formation within the plaque. On OCT, definite plaque erosion is absence of fibrous cap discontinuity and presence of thrombus attached to an intact or visualized plaque. On OCT, calcified nodules are lesions with fibrous cap disruption with underlying calcified plaque (protruding calcification, superficial A. Plaque rupture calcium or the presence of significant calcium adjacent to the lesion) (Fig. 36-4). PCI PLANNING OCT helps in mapping culprit lesions. By identifying vessel size, lesion length and disease-free landing B. Plaque erosion C. Calcified nodule Figure Optical coherence tomography images of various pathophysiological events leading to acute coronary syndrome. (Reprinted from: Ong, D. S., Jang, I. K. (2015). Fundamentals of optical coherence tomography image acquisition and interpretation. Interventional Cardiology Clinics, 4, ; with permission from Elsevier.)

5 Chapter 36 IVUS versus OCT: Relative Merits and Drawbacks 295 zones, it helps to decide stent size and length. In non-st elevation myocardial infarction cases, if OCT shows that size of lipid arc is more, there is more chance of no-reflow phenomenon and poor myocardial blush (angle of lipid more than 180 ). CALCIFIED LESIONS IVUS gives fair assessment of calcified plaques and guides treatment decisions but OCT may be a better imaging modality in calcified lesions as light can penetrate calcium fully and can evaluate the circumferential and axial extent of calcium 15. IVUS can only visualize the superficial arc of calcium, as the ultrasound waves get reflected. After stenting, OCT helps in better assessment of underexpansion and malapposition in calcified lesions. BIFURCATION LESIONS OCT with its high-resolution images provides useful information about atheroma distribution and type of carina. Previously, IVUS studies have shown that carina shift is more important than plaque shift as a cause of side branch occlusion. The presence of eyebrow sign (spikey carina on longitudinal reconstruction) leads to more carinal shift and side branch compromise after main vessel stenting. Three-dimensional rendering of OCT images and fly-through views help in better understanding of bifurcation lesion. After stenting, OCT can guide in accurate side branch rewiring through struts and avoiding distortion of stent. BIORESORBABLE SCAFFOLD (BRS) IMPLANTATION OCT because of its ability to clearly visualize the stent struts played a major role in development of BRS technology. It helped in understanding the natural course of BRS after implantation. Light is not attenuated by polymeric struts, struts are transparent and there is full visualization of vessel structure behind scaffold ( Fig ). As there is less radial force of BRS, knowledge of plaque constituents and lesion preparation is very important. Proper sizing is essential, as there is reduced BRS expandability and postdilation must be within 0.5 mm of stent diameter. BRS implantation with OCT guidance shall lead to aggressive lesion dilation, correct sizing and high-pressure postdilations. Such approach even in highly complex lesions leads to similar lumen area, residual stenosis and malapposition as second-generation metallic stents 16. OCT Figure Well-apposed polymeric struts of BRS, no light attenuation and full visualization of vessel structure behind the scaffold. has limitation to assess extent of scaffold degradation, as it cannot distinguish between polylactide polymer and provisional matrix of proteoglycan formed after degradation ( Fig. 36-6). POSTSTENT ASSESSMENT IVUS and OCT are similar to study stent expansion, as they can quantify poststent lumen area. OCT has the advantage of automatically determining the Figure Fully endothelialized struts of BRS at follow-up.

6 296 SECTION IV Interventional Cardiology reference vessel size and the minimal stent area. But with IVUS, the operator has to select the crosssection in which underexpansion is suspected and then do the measurement. More than 30% underexpansion on OCT (compared with reference lumen area) or more than 20% underexpansion on QCA needs intervention. Stent underexpansion and malapposition are common in patients with extensive coronary calcification undergoing PCI. IVUS has limitation in assessment of heavily calcified lesions, as there is poor penetration by ultrasound because of reflection. IVUS can assess only the superficial arc of calcium but OCT can assess the width of calcium ( Fig ). OCT is superior to IVUS in the detection of stent underexpansion and malapposition in patients with extensive calcification. OCT is better than IVUS to detect tissue protrusion (58% vs. 20%, P.001), stent-edge dissection (40% vs. 16%, P.005) and stent malapposition (47% vs. 8%, P.001) 17. Significant malapposition is defined as more than 200 microns in axial plane and in 5 consecutive frames ( Fig ). Many IVUS and OCT studies indicate that if stent malapposition is not associated with stent underexpansion, the incidence of stent thrombosis and subsequent restenosis is not increased. Operators shall not overreact to edge dissections because of increased sensitivity of OCT. Edge dissection that is 180 in less than five frames is considered minor and requires no intervention ( Fig ). In the presence of intramural haematoma, an additional stent should be placed to seal the dissection to avoid vessel collapse. Flow-limiting edge dissections, thrombus and tissue protrusions should be treated. The use of OCT after PCI leads to further interventions in 35% 55% of the target vessels 18, 19. In CL-OPCI study, 1-year clinical outcomes in 335 patients with OCT guidance were compared with a matched control group undergoing PCI with angiographic guidance alone. After adjustments, OCTguided PCI was associated with a lower risk of cardiac death or MI (odds ratio, 0.49; P.037) 20. ASSESSMENT OF NEOINTIMAL HYPERPLASIA AND CAUSES OF STENT FAILURE OCT helps in interpreting various mechanisms associated with stent failure such as uncovered struts, stent underexpansion, stent fracture and neointimal A B C Figure Calcium assessment on OCT and IVUS. Calcium on IVUS is measured as superficial arc. IVUS is unable to assess depth because of acoustic shadowing. (Courtesy: Bezerra, H. Expert Analysis ACC June 2016.) D

7 Chapter 36 IVUS versus OCT: Relative Merits and Drawbacks 297 Figure Significant stent malapposition. as IVUS and was found to be noninferior to IVUS but at same time was not superior to IVUS or angiography guidance 22. DRAWBACKS OF OCT VERSUS IVUS Figure Dissection at distal edge of stent. hyperplasia. The OCT pattern of neointimal tissue in cases of in-stent restenosis is classified as homogenous, heterogenous or layered 21. OCT can provide detailed assessment of in-stent neoatherosclerosis which is common finding for ISR (in-stent restenosis) as well as stent thrombosis ( Fig ). ILUMIEN III: OPTIMIZE PCI study compared OCT with IVUS and coronary angiography to guide stent implantation in a randomized fashion. The primary end point was postangioplasty minimum stent area. OCT gave similar minimum stent areas 1. OCT has shallow tissue penetration. It cannot measure plaque burden which requires visualization of the external elastic membrane. 2. It has limitation to assess aorto-ostial lesions and CTO lesions. 3. The use of contrast in FD-OCT during PCI may cause acute kidney injury which is one of the major causes of in-hospital and long-term morbidity and mortality, more so in patients with pre-existing renal dysfunction. 4. There is lack of clinical OCT data to show improvement in early and long-term clinical outcomes after stenting. CONCLUSION Both IVUS and OCT have their own merits and drawbacks. Because of the basic technical difference in tissue penetration and resolution, they have preferable use in various clinical scenarios. They are more similar than different by providing important information in assisting PCI. The day is not far when combined IVUS-OCT catheter becomes a reality in clinical practice.

8 298 SECTION IV Interventional Cardiology A I I II II B III III IV IV Figure Neointimal hyperplasia and strut coverage are better visualized with OCT. (Reprinted from: Bezerra, H. G., Attizzani, G. F., Sirbu, V., et al. (2013). Optical coherence tomography versus intravascular ultrasound to evaluate coronary artery disease and percutaneous coronary intervention. JACC Cardiovascular Interventions, 6, ; with permission from Elsevier.) REFERENCES 1. Bouma, B. E., Yun, S. H., Vakoc, B. J., Suter, M. J., & Tearney, G. J. ( 2009 ). Fourier-domain optical coherence tomography: Recent advances toward clinical utility. Current Opinion in Biotechnology, 20 ( 1 ), Lowe, H. C., Narula, J., Fujimoto, J. G., & Jang, I. K. ( 2011 ). Intracoronary optical diagnostics current status, limitations, and potential. JACC Cardiovascular Interventions, 4 ( 12 ), Jang, I. K. ( 2011 ). Optical coherence tomography or intravascular ultrasound? JACC Cardiovascular Interventions, 4, de la Torre Hernandez, J. M., Hernández Hernandez, F., Alfonso, F., Rumoroso, J. R., Lopez-Palop, R., Sadaba, M., et al. ( 2011 ). Prospective application of pre-defined intravascular ultrasound criteria for assessment of intermediate left main coronary artery lesions results from the multicenter LITRO study. Journal of the American College of Cardiology, 58, Park, S. J., Ahn, J. M., Kang, S. J., Yoon, S. H., Koo, B. K., Lee, J. Y., et al. ( 2014 ). Intravascular ultrasound-derived minimal lumen area criteria for functionally significant left main coronary artery stenosis. JACC Cardiovascular Interventions, 7, Kang, S. J., Ahn, J. M., Kim, W. J., Lee, J. Y., Park, D. W., Lee, S. W., et al. ( 2014 ). Functional and morphological assessment of side branch after left main coronary artery bifurcation stenting with cross-over technique. Catheterization and Cardiovascular Interventions, 83, Kang, S. J., Ahn, J. M., Song, H., Kim, W. J., Lee, J. Y., Park, D. W., et al. ( 2011 ). Comprehensive intravascular ultrasound assessment of stent area and its impact on restenosis and adverse cardiac events in 403 patients with unprotected left main disease. Circulation Cardiovascular Interventions, 4, Casella, G., Klauss, V., Ottani, F., Siebert, U., Sangiorgio, P., & Bracchetti, D. ( 2003 ). Impact of intravascular ultrasound-guided stenting on long-term clinical outcome: A meta-analysis of available studies comparing intravascular ultrasound-guided and angiographically guided stenting. Catheterization and Cardiovascular Interventions, 59, Zhang, Y. J., Pang, S., Chen, X. Y., Bourantas, C. V., Pan, D. R., Dong, S. J., et al. ( 2015 ). Comparison of intravascular ultrasound guided versus angiography guided drug eluting stent implantation: A systematic review and meta-analysis. BMC Cardiovascular Disorders, 15, Jang, I. K., Bouma, B. E., Kang, D. H., Park, S. J., Park, S. W., Seung, K. B., et al. ( 2002 ). Visualization of coronary atherosclerotic plaques in patients using optical coherence tomography: Comparison with intravascular ultrasound. Journal of the American College of Cardiology, 39, Yabushita, H., Bouma, B. E., Houser, S. L., Aretz, H. T., Jang, I. K., Schlendorf, K. H., et al. ( 2002 ). Characterization of human atherosclerosis by optical coherence tomography. Circulation, 106 ( 13 ),

9 Chapter 36 IVUS versus OCT: Relative Merits and Drawbacks Kume, T., Akasaka, T., Kawamoto, T., Ogasawara, Y., Watanabe, N., Toyota, E., et al. ( 2006 ). Assessment of coronary arterial thrombus by optical coherence tomography. American Journal of Cardiology, 97 ( 12 ), Kato, K., Yasutake, M., Yonetsu, T., Kim, S. J., Xing, L., Kratlian, C. M., et al. ( 2011 ). Intracoronary imaging modalities for vulnerable plaques. Journal of Nippon Medical School, 78 ( 6 ), Virmani, R., Kolodgie, F. D., Burke, A. P., Farb, A., & Schwartz, S. M. ( 2000 ). Lessons from sudden coronary death: A comprehensive morphological classification scheme for atherosclerotic lesions. Arteriosclerosis, Thrombosis, and Vascular Biology, 20 ( 5 ), Kume, T., Okura, H., Kawamoto, T., Yamada, R., Miyamoto, Y., Hayashida, A., et al. ( 2011 ). Assessment of the coronary calcification by optical coherence tomography. EuroIntervention, 6 ( 6 ), Mattesini, A., Secco, G. G., Dall Ara, G., Ghione, M., Rama- Merchan, J. C., Lupi, A., et al. ( 2014 ). ABSORB biodegradable stents versus second-generation metal stents: A comparison study of 100 complex lesions treated under OCT guidance. JACC Cardiovascular Interventions, 7, Kubo, T., Imanishi, T., Kitabata, H., Kuroi, A., Ueno, S., Yamano, T., et al. ( 2008 ). Comparison of vascular response after sirolimus-eluting stent implantation between unstable angina pectoris and stable angina pectoris: A serial optical coherence tomography study. JACC Cardiovascular Imaging, 1, Stefano, G. T., Bezerra, H. G., Mehanna, E., Yamamoto, H., Fujino, Y., Wang, W., et al. ( 2013 ). Unrestricted utilization of frequency domain optical coherence tomography in coronary interventions. International Journal of Cardiovascular Imaging, 29, Viceconte, N., Chan, P. H., Barrero, E. A., Ghilencea, L., Lindsay, A., Foin, N., et al. ( 2013 ). Frequency domain optical coherence tomography for guidance of coronary stenting. International Journal of Cardiology, 1, Prati, F., Di Vito, L., Biondi-Zoccai, G., Occhipinti, M., La Manna, A., Tamburino, C., et al. ( 2012 ). Angiography alone versus angiography plus optical coherence tomography to guide decision-making during percutaneous coronary intervention: The centro per la lotta contro l infarto-optimisation of percutaneous coronary intervention (CLI-OPCI) study. EuroIntervention, 8, Gonzalo, N., Serruys, P. W., Okamura, T., van Beusekom, H. M., Garcia-Garcia, H. M., van Soest, G., et al. ( 2009 ). Optical coherence tomography patterns of stent restenosis. American Heart Journal, 158, Ali, Z. A., Maehara, A., Généreux, P., Shlofmitz, R. A., Fabbiocchi, F., Nazif, T. M., et al. ( 2016 ). Optical coherence tomography compared with intravascular ultrasound and with angiography to guide coronary stent implantation (ILUMIEN III: OPTIMIZE PCI): A randomised controlled trial. Lancet, 388,

10