The benefits of optical coherence tomography in the cath lab

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Kevin Croce

Kevin Croce, director, Chronic Total Occlusion and Complex Percutaneous Coronary Intervention Program at Brigham and Women’s Hospital, Harvard Medical School, Boston, USA, discusses the use of optical coherence tomography (OCT), and considers its benefits over other imaging methods.

How does OCT work, and what is its benefit over other imaging methods?

Optical coherence tomography (OCT) is an intravascular imaging modality that utilises near-infrared light to generate high resolution images of coronary arteries. Like intravascular ultrasound (IVUS), OCT provides information about intravascular anatomy that far exceeds the level of detail obtained from conventional contrast cineangiography. OCT generates in vivo images of coronary arteries and deployed stents with up to 10μm of spatial resolution compared to the lower 100- to 200-μm resolution of IVUS. The ultrahigh resolution of OCT enables automated measurement of lumen area, and current OCT systems co-register the OCT images with the angiogram. Co-registration and automated lumen assessment provide a high resolution 4-dimensional artery visualisation of the angiogram, the OCT lumen cross section co-registered to the angiogram, a graphical plot of the lumen area and, the longitudinal artery structure (Figure 1).

Does use of OCT lead to different outcomes compared to angiography and why?

Compared to angiography alone, OCT-guided percutaneous coronary intervention (PCI) results in greater stent expansion, less residual stenosis, and a better residual fractional flow reserve (FFR)1. Larger stents and higher FFR values would be predicted to lead to improved outcomes following PCI. Registry studies show lower mortality for OCT guided PCI compared to IVUS-guided and angiogram-guided PCI2. The Illumien IV study, which is randomising patients to angiogram versus angiogram plus OCT guided PCI, is currently enrolling to evaluate the impact of OCT on adverse events in a group of patients at risk for target vessel revascularisation and stent failure3.

What data is available to demonstrate its efficacy?

In addition to the investigations noted above, in the LightLab OCT study, physicians improved their assessment of potential blockages as a result of using OCT, which better informed the choice of stent size and optimal stent deployment. Recent data from LightLab demonstrates that OCT changes diagnosis and decision-making during PCI 88% of the time compared to an angiography-based strategy. Importantly, when calcium was present in LightLab cases, OCT prompted escalation in vessel preparation strategy to a non-compliant balloon, specialty balloon, or atherectomy 47% percent of the time4.

Figure 1: OCT User Interface. Pre-PCI OCT showing 1-dimensional information (Panel A). Angiogram with white square curser (black arrow) denoting location of co-registered cross-sectional OCT image (Panel B). (Panel C) Graphical representation of the artery lumen area. White arrow points to line marker that shows location of co-registered angiogram and cross-sectional OCT image. (Panel D) Longitudinal artery view (Panel C) Graphical representation of the artery lumen area. White arrow points to line marker that shows location of co-registered angiogram and cross-sectional OCT image. (Panel D) Longitudinal artery view

How steep is the learning curve for using OCT?

OCT image acquisition and image interpretation are easy to learn. Recent development of a standardised “MLD MAX” OCT PCI optimisation workflow, that was applied in the LightLab programme, has made the process of learning and teaching OCT much easier. MLD MAX is an acronym for the prescriptive OCT workflow that utilises (1) a pre-PCI OCT run to define lesion morphology and to determine stent length and diameter and (2) a post-PCI OCT run to address medial dissections, and to optimise stent apposition and expansion. PCI operators become comfortable with the MLD MAX OCT workflow after about ten cases, and the OCT workflow is greatly facilitated by computer automated measurements of lumen size and stent expansion.

Can you provide examples where OCT has been of particular benefit?

Randomised intravascular imaging studies show reduction in major adverse cardiovascular events in both complex PCI and all-comer PCI populations5,6. One would presume that like other intravascular imaging modalities, OCT will broadly benefit all PCI patients, but this will need to be confirmed in clinical studies. Importantly, the number needed to treat for intravascular imaging guided PCI is predicted to be very favourable for complex PCI (long stents, chronic total occlusion, bifurcation) and for cases where clinical factors such as acute coronary syndromes and/or diabetes increase risk of target vessel revascularization. We find that the high resolution of OCT provides tremendous value when treating complex anatomy, bifurcations, and in stent restenosis.

Are there limitations of using OCT, and how could these be overcome?

The near-infrared light utilised for OCT is scattered by red blood cells and therefore, OCT imaging requires transient blood clearing during image acquisition. Blood clearance is typically done with contrast injection and thus historically, OCT has required increased use of contrast. OCT imaging techniques that use saline are in development, but currently, angiographic co-registration enables OCT to be done simultaneously with angiography. The MLD MAX workflow, which was employed in the LightLab study, utilises a co-registered OCT run done at the time of angiography to decrease contrast utilisation. In many cases, the high-resolution OCT data also negates the need for multiple orthogonal angiogram views that are employed to improve the diagnostic accuracy of low resolution angiography.

How does OCT compare to other techniques on cost?          

In most healthcare facilities, OCT cost is equivalent to other intravascular imaging technologies.

Do you see OCT being in wide usage in cath labs?

Intravascular imaging clearly improves outcomes in PCI patients, and meta-analyses and large registry studies strongly suggest that intravascular imaging dramatically reduces mortality following PCI2,7,8. With the overwhelming data that intravascular imaging benefits patients, it is only a matter of time until technologies like OCT become synonymous with high quality PCI9. As studies like LightLab demonstrate how OCT streamlines workflow and improves decision making, and anticipated studies such as Illumien IV further validate the clinical impact of OCT, OCT should become a routine part of PCI procedures in the near future.

What else you would like to share about LightLab?

LightLab is continuing through multiple phases looking at decision making, efficiency, and application of OCT to complex PCI. In the next few months, we are excited to share new data on the tremendous impact of OCT on treatment of in-stent restenosis, and in the mid-term, we will publish the effect of the MLD MAX OCT workflow on procedure efficiency evaluating parameters such as procedure time, number angiographic runs, and contrast utilisation.

References:

  1. Meneveau N, Souteyrand G, Motreff P et al. Optical coherence tomography to optimize results of percutaneous coronary intervention in patients with non-ST-elevation acute coronary syndrome: results of the multicenter, randomized DOCTORS study. Circulation 2016; 134: 906–917.
  2. Jones DA, Rathod KS, Koganti S et al. Angiography alone versus angiography plus optical coherence tomography to guide percutaneous coronary intervention: outcomes from the pan-London PCI cohort. JACC Cardiovasc Interv 2018; 11: 1313–1321.
  3. Ali Z, Landmesser U, Karimi Galougahi K et al. Optical coherence tomography-guided coronary stent implantation compared to angiography: a multicenter randomized trial in PCI—design and rationale of ILUMIEN IV: OPTIMAL PCI. EuroIntervention 2020.
  4. Bezerra HG. Analysis of changes in decision-making process during optical coherence tomography-guided percutaneous coronary interventions: Insights from the LightLab Initiative. EuroPCR 2020 presentation.
  5. Hong SJ, Kim BK, Shin DH et al. Effect of intravascular ultrasound-guided vs. angiography-guided everolimus-eluting stent implantation: the IVUS-XPL randomized clinical trial. JAMA 2015; 314: 2155–2163.
  6. Zhang J, Gao X, Kan J et al. Intravascular ultrasound versus angiography-guided drug-eluting stent implantation: the ULTIMATE trial. J Am Coll Cardiol 2018; 72: 3126–3137.
  7. Darmoch F, Alraies MC, Al-Khadra Y et al. Intravascular ultrasound imaging-guided versus coronary angiography-guided percutaneous coronary intervention: a systematic review and meta-analysis. J Am Heart Assoc 2020; 9: e013678.
  8. Choi KH, Song YB, Lee JM et al. Impact of intravascular ultrasound-guided percutaneous coronary intervention on long-term clinical outcomes in patients undergoing complex procedures. JACC Cardiovasc Interv 2019; 12: 607–620.
  9. Klein LW, Anderson HV, Rao SV. Performance metrics to improve quality in contemporary percutaneous coronary intervention practice. JAMA Cardiol 2020.

Kevin Croce is director of the Chronic Total Occlusion Complex PCI Program, Brigham and Women’s Hospital, Harvard Medical School, Boston, USA.

Disclosures Croce has received grant/research support from Abbott, Takeda, Teleflex, CSI, consulting fees from Abbott, Biotronik, Philips, Abiomed, CSI, Takeda and Cordis, and is a major stock shareholder in Dyad Medical.


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