Imaging Coronary Artery Histology

For years, patients have been under the misconception that a coronary intervention of a coronary stenosis was “preventing an impending heart attack.” As cardiologists, we know better. In stable coronary artery disease, when we perform a coronary intervention, we do not know if the target site is going to evolve into a ruptured plaque and result in acute coronary syndrome. Prediction and prevention of an acute coronary syndrome is what the patient wants and what we have been striving for years but with much frustration. We know the characteristics of a vulnerable plaque (a large plaque burden with positive remodeling, a large lipid core with a thin fibrous cap, and evidence of macrophage infiltration, to name a few) but remain handicapped in our ability to find an imaging modality that can reliably identify which plaques will indeed rupture and which will not. Inability to foresee which one of the multiple ruptured plaques would cause an acute coronary syndrome further complicates the task of prediction.Article see p 384Virtual histology (VH) intravascular ultrasound (IVUS) has been an exciting step forward for intracoronary ultrasound. The technology uses a proprietary algorithm that assesses the returning ultrasound signal to seek information about plaque morphology. Conventional gray-scale ultrasound relies on the amplitude (or strength) of the returning radiofrequency signal to provide gross classification of morphology (hard, soft, and calcified). Simply stated, a hard or calcified surface will reflect more ultrasound back to the transducer so it will appear brighter (or whiter) on the screen. More advanced quantification of the radiofrequency signal, before postprocessing (used to form a better image), is the basis for integrated backscatter–IVUS. Integrated backscatter–IVUS has been used primarily by investigators in Japan to successfully study several aspects of plaque characterization.1,2 VH-IVUS also uses the amplitude information but adds …