Is optical coherence tomography effective in imaging intravascular thrombus?
Sponsored by St. Jude Medical
Intravascular optical coherence tomography (OCT) is an imaging modality with high tomographic imaging resolution (approximately 10 μm) that is approximately 10 times greater than its clinical alternative, intravascular ultrasound (IVUS).1,2 Recent work showed the feasibility and safety of using OCT in patients undergoing percutaneous coronary intervention (PCI).3,4
While OCT identifies most of the intravascular architectural features as seen with IVUS,2,5 OCT also provides several additional morphologic details that aid in detailed plaque characterization.5 For example, OCT is superior to IVUS and angioscopy in detecting thrombus, and it has the unique ability to characterize intracoronary thrombi as either red (red blood cell–rich thrombus) or white (platelet-rich thrombus).
Because red blood cells scatter and attenuate the OCT signal, red thrombus is visualized on OCT as a high-backscattering intravascular globular mass with significant signal attenuation that causes shadowing.6 Thrombus, on the other hand, appears as a mass with low attenuation, allowing visualization of vascular structures behind the thrombus. The figure shows examples of the characteristics of red and white thrombi on OCT.
Although the ability to identify and characterize thrombus using OCT is an advance over other imaging modalities, the clinical implications of this information remain unclear. In the setting of PCI, angiographically obvious intracoronary thrombus is a known risk factor for adverse cardiovascular events;7 however, at high resolution, thrombus is a very common finding on OCT after PCI.
Further quantification and characterization of intracoronary thrombus using OCT may effectively risk stratify patients undergoing PCI and may guide antithrombotic therapy. The ongoing Massachusetts General Hospital OCT Registry, an international collaborative effort that will include 3,000 patients, may ultimately answer questions regarding the impact of thrombus burden and characteristics on patient outcomes.
Sammy Elmariah, MD, MPH, and Ik-Kyung Jang, MD, PhD, are with the Cardiology Division, Massachusetts General Hospital, Harvard Medical School in Boston, Massachusetts. Dr. Jang may be reached at (617) 726-9226; firstname.lastname@example.org.