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OCT in Spontaneous Coronary Artery Dissection
Study Questions:
Is spontaneous coronary artery dissection (SCAD) caused by primary microvessel hemorrhage within the vessel wall through: i) an assessment of indirect measures of false lumen (FL) pressurization from fenestrated and nonfenestrated cases; ii) assessment of vasa vasorum density, and iii) an analysis of the light attenuation characteristics of the FL contents using optical coherence tomography (OCT) intravascular imaging?
Methods:
A total of 65 SCAD patients (68 vessels) with OCT imaging performed as part of routine clinical care were included. Images were classified by the absence or presence of a connection (fenestration) between the true lumen (TL) and FL. Indexed measures of TL stenosis, external elastic lamina (EEL) area, FL area, and light attenuation of the FL were assessed. Vasa vasorum density of SCAD cases was compared with control non-SCAD myocardial infarction cases.
Results:
Five patients in this cohort had confirmed fibromuscular dysplasia (FMD). There were no connective tissue disorders and two documented cases of inflammatory conditions. There was no significant difference in vessel affected between SCAD types. In nonfenestrated cases, there was significantly larger expansion of the EEL area (9.1% vs. -1.9%, p < 0.05), and a larger FL area (73.6% vs 53.2%, p < 0.05) in dissected segments. The FL contents were heterogeneous but less light-attenuating than whole blood or thrombus. SCAD was not associated with increased vasa vasorum density in the acute phase but evidence of neovascularization as part of a late healing response was noted.
Conclusions:
These observational data suggest that the absence of a fenestration leads to an increased FL pressure and compression of the TL. While vasa vasorum may still be implicated in pathogenesis, increased vasa vasorum density could be an epiphenomenon of vascular healing.
Perspective:
As the authors point out, OCT imaging in this study was not protocol driven but conducted as part of routine clinical care, and potential selection bias should be considered. Nonetheless, this is the largest OCT imaging series in SCAD patients reported thus far. Interestingly, lack of fenestration was associated with FL pressurization and evidence of neovascularization was noted as part of a late healing response. Furthermore, the FL contents have light attenuation characteristics lower than either whole blood or thrombus but with a high degree of heterogeneity consistent with organizing thrombus. Overall, these findings offer much needed initial insight on anatomical characteristics of SCAD. Further investigation is needed before OCT can be used for clinical decision making in patients with SCAD.
Keywords: Acute Coronary Syndrome, Constriction, Pathologic, Coronary Vessel Anomalies, Diagnostic Imaging, Dissection, Fibromuscular Dysplasia, Myocardial Infarction, Thrombosis, Tomography, Optical Coherence, Vasa Vasorum, Vascular Diseases
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