technique [84]. The overall rate of malapposed struts was significantly higher in the lesions treated with angiography‐guided PCI than in those undergoing OCT‐guided PCI [84].
The position where the guidewire re‐crosses the stent struts into the side branch (i.e. proximal, mid, or distal cell) has been demonstrated to be one of the most important factors driving full strut apposition and larger lumen in the side branch ostium after balloon dilatation. Crossing into the side branch through a proximal cell provides no scaffolding of the side branch ostium and leaves many struts unapposed near the carina, reducing the strut‐free side branch ostial area. It has been suggested to use OCT to confirm re‐crossing the wire through the most distal cell of the main vessel stent in order to efficiently widen the opening at the side branch ostium [85]. The feasibility and effectiveness of OCT‐guided stent re‐crossing compared with angiography guidance have been evaluated in 52 patients [86]. The OCT‐guided group showed a significantly lower number of malapposed stent struts, especially in the quadrants toward the side branch ostium (9 vs 42%, p <0.0001).
Three‐dimensional (3D) reconstruction of OCT images is also potentially useful to better understand wire positioning and lumen expansion in bifurcation stenting [87–91]. The clinical application of high quality off‐line 3D‐OCT to optimize side branch opening by identifying the configuration of overhanging struts in front of the side branch ostium according to the presence of the link between hoops at the carina and the appropriate distal cell for the re‐crossing position has been evaluated in 22 patients [92]. This study showed that 3D‐ OCT confirmation of the re‐crossing into the jailed side branch is feasible during PCI and helps to achieve distal rewiring and favorable stent positioning against the side branch ostium, leading to reduction in incomplete strut apposition and potentially better clinical outcomes [76]. Finally, OCT has also been used to assess the procedural success of dedicated side branch stents compared with conventional strategies [93].
Calcified lesions still represent a major challenge for PCI resulting in difficulties to cross lesions, to advance and expand balloons and stents and to identify a plaque free landing zone for safe stent placement, impeding an optimal result (see Figure 9.6). Angiography is limited in its ability to determine the extent and type of calcium present in a lesion. Characterization of the calcific burden is crucial in determining if treatment with an ablative device is needed to adequately achieve full stent optimization. Furthermore, intravascular imaging helps to identify the correct landing zones so as to minimize the risk of edge dissections. OCT clearly defines the calcium morphology into three distinct categories: deep, superficial or nodular. Stent under‐expansion in heavily calcified lesions is associated with a high rate of target vessel failure and future ischemic events.
Figure 9.6a OCT cross‐section demonstrates a protruding nodule with an MLA of 12.95mm2. The OCT cross‐section is co‐registered with the angiogram in the upper, left corner (red arrow in the left image).
Figure 9.6b OCT of the proximal LAD revealed a lesion with an MLA of 3.55mm2, despite a mild angiographic appearance.
Figure 9.6c OCT proximal to the bifurcation demonstrates a calcified lesion with >270° arc of superficial calcium with a protruding nodule. Calcium thickness measures 0.72mm.
Figure 9.6d OCT at the bifurcation of the LAD and 1st diagonal branch. It is important to note the location of bifurcations on the co‐registered angiogram to assist in precise stent implantation.
Figure 9.6e OCT following stent implantation demonstrating optimal stent expansion. In the longitudinal profile of Panel B, stent rendering has been activated. Final angiogram is shown on the right panel.
Dedicated devices to approach coronary calcific lesions include rotational and orbital atherectomy (RA‐OA), but because of their complexity, these methods are used in a small minority of the patients in need [94]. Cutting and scoring balloons offer possible alternatives but their deliverability and effectiveness are suboptimal and they achieved inferior results in a recent randomized trial against RA. Intravascular lithotripsy (IVL) has the potential to overcome some of the limitations of the aforementioned tools. Characterization of the longitudinal and circumferential calcium distribution with OCT plays a pivotal role in the identification of calcified lesion requiring dedicated treatment devices. OCT analysis is highly accurate in assessing calcium including thickness, a clear advantage over IVUS where shadowing helps to detect calcium at first glance but precludes assessment of other features. Calcium thickness is an important determinant of calcium fracture with PCI [95]. Superficial calcium can be stratified based on the calcium‐volume index (CVI) score, integrating the depth, length, and arc of calcium. If the depth is >0.5mm, the length is >5mm and the arc is >180°, ablative therapy using rotational atherectomy, orbital atherectomy, intravascular lithotripsy, or excimer laser atherectomy therapies should be considered. While OCT may miss some deep calcium due to limited penetration, this may not be a clinically relevant limitation since superficial calcium is the true obstacle to expansion. Nodular calcium is distinctly difficult to treat for a myriad of reasons. These lesions often do not yield to traditional balloon techniques, as it is common for the balloon to only expand on the non‐calcified side of the wall leaving the nodule untreated. The other component is that they often behave like a thin cap fibroatheroma and become unstable with platelet aggregation causing further complications. OCT can detect more reliably the presence of calcium fractures after IVL or atherectomy because of its greater resolution. Occasionally, there will be instances where the OCT catheter is unable to cross a calcified lesion and pre‐treatment is necessary. In these circumstances it is imperative to understand that prior to deploying a stent, OCT should be performed after lesion preparation to accurately assess fracture and vessel dimensions, ensuring full stent expansion. In our experience the application of a standardized algorithm with intravascular imaging guidance, mainly OCT, of IVL facilitated second generation DES expansion delivers excellent immediate lumen expansion and patient outcome [96].
For chronic total occlusions, there is a relative contraindication to inject contrast at high speed and pressure before wire crossing or if the wire has followed a possible subintimal position because of the risk of inducing a dangerous distal dissection. IVUS is definitely preferable to confirm the intraluminal position of the wire distally and in the occlusion body and decide the length of the stented segment and its size. After stenting, however, OCT can also be used to detect distal dissections, double channels, distal plaques and, especially, stent expansion and strut apposition.
Long lesions are often at risk of suboptimal expansion, side branch compromise, slow flow and high restenosis rates when a full metal jacket approach is used. OCT can identify relatively healthy segment where a stent can be spared and exclude nasty deep dissections at the edges after stent implantation. The long tip of the prior generation OCT catheters can create difficulties during imaging of very distal segments
