Optical coherence tomography (OCT) has been increasingly used in clinical practice as a guide during percutaneous coronary intervention (PCI) . Prior to stent implantation, OCT can provide accurate measurements of the minimal lumen area, the distal and proximal reference areas, and lesion length. The accuracy of the OCT measurements has been established by the ex vivo lumen diameter assessment of Plexiglas phantoms [1]. The minimal lumen area (MLA) measured by OCT in vivo was slightly smaller than intravascular ultrasound (IVUS)-MLA, but the correlation between the two measurements was highly significant (r = 0.82; p < 0.001) [2]. OCT showed excellent reproducibility for both the lumen area and the lesion length measurements with low intraobserver, interobserver, and interpullback variability [3, 4]. Fully automatic computer-assisted lumen contour detection in OCT images has been shown to represent a reliable tool for in vivo assessment of stented coronary vessels [5, 6]. These preprocedural measurements can help select stent and balloon sizes.

OCT is particularly useful during challenging procedures, such as calcified lesions, bifurcation, and unprotected left main (ULM) PCI . OCT imaging can help characterize lesion morphology and select treatment strategy based on plaque characteristics. It is being proposed that lipid-rich lesions may be amenable to medical therapy and resolution of luminal obstruction verified by improved fractional flow reserve (FFR) [7]. PCI of calcified lesions has been associated with lower rates of procedural success and higher rates of subsequent adverse cardiovascular events [8]. Because of reduction in vessel wall compliance, calcified lesions have higher risks of stent underexpansion and malapposition and acute postprocedural complications such as dissection and perforation. Development of atheroablation techniques, in particular rotational and orbital atherectomy, significantly improved the success rate of calcified lesion PCI. OCT allows measurements of calcification size and depth and their precise location within the lesion, which might help select the appropriate atheroablation technique.

Treatment of coronary artery bifurcation lesions remains a challenging area in interventional cardiology despite major advances in bifurcation stenting approach [9, 10]. Side branch (SB) occlusion can result in vessel closure and ischemia, leading to increased incidence of periprocedural myocardial infarction (MI) and even cardiac deaths after PCI [11]. Provisional stenting remains the main approach to treatment of bifurcation lesions; however, it may result in significant narrowing of the SB ostium after main vessel stenting. High-resolution OCT imaging can characterize SB stenosis before and after stenting, select appropriate treatment strategy, and evaluate the effects of SB treatment. Three-dimensional OCT reconstruction provides a unique opportunity to assess the true morphology of the main and side vessels [12]. Preprocedure assessment of bifurcation lesion morphology with OCT can help identify SBs with a high risk of occlusion. The presence of large lipid plaque in the proximal segment of the main vessel (MV) has been shown to be an independent OCT predictor of SB stenosis severity after MV stenting [13, 14].

Coronary artery bypass graft (CABG) surgery has historically been the treatment of choice for patients with unprotected left main coronary artery (LMCA) disease. However, with the introduction of drug-eluting stents (DESs), selected patients with unprotected LMCAs have been increasingly treated with PCI [15, 16]. A recent pilot trial demonstrated the safety and feasibility of frequency-domain OCT for unprotected left main PCI [17]. Compared to IVUS, OCT provided a similar assessment of lumen and stent dimensions but was more sensitive in detecting malapposition and edge dissections.

Finally, OCT imaging before stenting can provide patient risk stratification for periprocedural MI, since OCT-derived thin-cap fibroatheroma and evidence of plaque rupture have been associated with elevation of post-PCI myocardial necrosis markers [18, 19]. Compared to plaque burden by intravascular ultrasound (IVUS) and plaque lipid content by near infrared spectroscopy (NIRS), OCT fibrous cap thickness was the most important independent predictor of periprocedural MI in a recent multimodality imaging study [20].