Culprit segments identified by optical coherence tomography in patients with acute myocardial infarction: two case reports
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- Sato, D., Koga, S., Yasunaga, T. et al. Cardiovasc Interv and Ther (2012) 27: 47. doi:10.1007/s12928-011-0081-0
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The high resolution of optical coherence tomography (OCT) provides detailed information about coronary plaque morphology, which enables the mechanism of acute myocardial infarction to be evaluated. We describe two patients with acute myocardial infarction in whom culprit segments were identified by OCT, but not by either coronary angiography or intravascular ultrasound.
KeywordsAcute myocardial infarctionOptical coherence tomographyPlaque ruptureThrombusUlcer
Optical coherence tomography (OCT) is a new intravascular imaging modality with higher resolution (10–20 μm) than intravascular ultrasound (IVUS).
We describe two patients with acute myocardial infarction in whom OCT provided useful intracoronary information for detecting culprit lesions and understanding the mechanism of onset.
Optical coherence tomography is a novel invasive imaging method that can assess coronary plaque morphology at a resolution of 10–20 μm, which is about tenfold higher than that of IVUS. This method has emerged as a promising tool for assessing patients with acute coronary syndrome and for detecting key features of plaques including thin-cap fibroatheroma, plaque rupture and thrombus in such patients .
In case 1, OCT revealed ruptured plaque at the LAD–MSB bifurcation and a flap-like mass in the LAD side of the LAD–MSB bifurcation. We regarded this flap-like mass as thrombus. Thrombi on OCT are defined as masses protruding into a vessel lumen discontinuously from the surface of the vessel wall . Intracoronary thrombi can be accurately identified by OCT . Thrombus detected by OCT can present in various forms, but flap-like thrombi such as those in the present case are rare. Prati et al.  also described a flap-like thrombus, but the present case was unusual as the flap was rather large. The features of thrombi can be distinguished by OCT. Red thrombi consist mainly of red blood cells and OCT images are characterized by high-backscattering protrusions with signal-free shadowing . White thrombi consist mainly of platelets and white blood cells, and are characterized by signal-rich, low backscattering billowing projections that protrude into the lumen . In reality, thrombi are rarely all white or all red and mixed thrombi are common. Whether the flap-like thrombus in the present case was red or white thrombus was unclear. When ulcerated or ruptured plaques present with thrombus on OCT, the lesion can generally be defined as being culprit . Thus, OCT was helpful in locating the culprit lesion in the LAD side of the LAD–MSB bifurcation during the acute phase of the disease in this patient. In fact, this notion was supported by CAG findings during the chronic phase.
An occlusion of the DB and TIMI-3 grade flow in the main vessel of the LAD was confirmed by CAG in case 2. These findings indicated that the DB was the culprit vessel whereas OCT confirmed an ulcer with thrombi in the LAD at the origin of the DB. Thus, the OCT findings indicated that the culprit lesion was in fact ulcerated plaque in the LAD, not the DB. Furthermore, microvessel formation in the inner plaque near the ulcer was also detected by OCT. Neovascularization in atherosclerotic plaques is associated with plaque vulnerability  and the high resolution of OCT allows direct visualization of plaque neovascularization in vivo . Microvessels in plaque are generally considered to appear on OCT as thin black holes with a diameter of 50–100 mm in at least 3–4 consecutive frames in pull-back images . The presence of such microvessels in the inner plaque near the ulcer also supported our conclusion that the culprit lesion was ulcerated plaque in the LAD.
Thus, OCT in addition to CAG and IVUS can provide detailed intracoronary information. Combinations of these imaging modalities would be more helpful and increase reliability for detecting culprit lesions, and for understanding the mechanisms of acute coronary syndrome onset.