Despite remarkable advances in procedural techniques during the past decades, coronary bifurcation lesions, which account for approximately 10–20% of all PCIs, remain a challenge [8]. The application of 3D OCT rendering has allowed visualization of bifurcation lesions in detail not achieved by any imaging diagnostic modalities including 2D OCT. Recently, through 3D OCT image analysis of human bifurcation lesions, Farooq et al. reported that there is a variability of carina structure according to takeoff angle of side branch (SB): perpendicular (e.g., septal, mid-distal diagonal, and obtuse marginal branch) vs. parallel takeoff (e.g., proximal diagonal, right ventricular branch). They suggested that stenting across SBs with parallel takeoff is more susceptible to the carina shift rather than SBs with perpendicular takeoff [9]. This study highlights the potential role of 3D OCT in enhancing our understanding of the complex coronary anatomy and the effect of PCI on adjacent structure.

Accurate sizing of SB is crucial to circumvent SB injury during PCI with final kissing ballooning. It is well known that angiographic appearance of SB ostium after stent crossover is inconclusive [10]. According to a recent report using 3D cut-plane analysis, it is feasible to determine an accurate SB ostial diameter in a single OCT imaging of the main branch, by correcting the misalignment errors between pullback direction (main branch) and SB centerline [11]. This method could be utilizable in catheterization laboratory because it reduces the need for burdensome SB rewiring and additional pullback. Meanwhile, during the provisional stenting with kissing balloon inflation, it is recommended to rewire SB via a distal cell (Fig. 19.2a, a*, b, b*) because, otherwise, there remain large unopposed struts at the carina (Fig. 19.2c, c*, d, d*), which potentially cause disturbance in shear flow, delay in re-endothelialization, and thrombosis [8, 12]. 3D OCT is expected to provide an intuitive and accurate imaging guidance to ensure distal cell recrossing (Fig. 19.2).

As clinical trials failed to demonstrate the benefits of routine kissing ballooning in bifurcation lesions [13, 14], jailed SB is usually left untreated unless indicated (e.g., SB flow compromise, SB dissection, etc.). However , significant alterations of SB ostium morphology during strut coverage still warrant further investigation regarding the natural course of jailed SB [15, 16]. 3D OCT could offer unique opportunity for visualization of anatomical modifications occurring at the SB ostium (Fig. 19.3, left panel). Indeed, serial 3D demonstration of jailed SB has shown that overhanging struts may serve as a focus for excessive neointima formation and thrombosis, suggesting the potential mechanism regarding delayed SB compromise [15]. Theoretically, the use of a bioresorbable vascular scaffold could be a solution to this issue because restoration of normal bifurcation anatomy can be expected after full biodegradation [17]. In this regard, there is an attempt to categorize jailed SB according to 3D morphology to elucidate the fate of scaffold during bioresorption (Fig. 19.3, right panel) [18]. Application of 3D OCT will help to clarify the roles of stent design, strut-tissue interaction, and optimized PCI on long-term patency of jailed SB.

Coronary stent fracture is an important cause of late stent failure associated with major adverse cardiovascular outcome [19]. However, even with the use of current Fourier domain OCT, it is challenging to accurately identify fracture sites in a small mesh-like structure. In particular, newer-generation open-cell design stent exhibits nonuniform strut allocation on cross-sectional images (Fig. 19.4, left lower panel), and conventional 2D OCT criteria for stent fracture (e.g., lack of circumferential stent strut) appear to be inconclusive [20, 21]. Volumetric 3D OCT offers significant advantages over other imaging modalities in terms of accurate delineation of 3D configuration (Fig. 19.4).

The quality and spatial accuracy of 3D-rendered images are hampered by cardiac motion and under-sampling (still only 12% of the lumen is sampled with current Fourier domain OCT, Fig. 19.5 b, d) [22, 23]. Recent progress of ultrahigh-speed OCT, a novel method that achieves a 5–10 times faster imaging speed, enables more accurate assessment of stent configuration by sampling larger data during a short period of diastole, an optimal phase for coronary imaging [24]. As ultrahigh-speed 3D OCT enables high-fidelity, motion-free imaging, it seems to be promising for more precise evaluation of stent integrity (Fig. 19.5 a, c).

With the introduction of the first commercial 3D-rendering technology, 3D OCT is now finding its way into interventional practice. Further studies are warranted to determine whether the beneficial advantages outlined above will translate into improved clinical outcomes.

Coronary plaque rupture is a dynamic biological process driven by chronic maladaptive immune response against subendothelial lipoproteins, which involves growth of lipid-enriched necrotic core, increases of inflammation and protease activities, and thinning of fibrous cap by gradual loss of collagen and smooth muscle cell [25, 26]. Despite the clinical need to predict future coronary events, current structural imaging alone does not estimate rupture risk enough to guide clinical decisions [27]. This concise overview will address recent advances in biological cardiovascular imaging for the assessment of plaque vulnerability, focusing specifically on multimodal integrative imaging approaches combined with OCT (Table 19.1).