The potential of RF backscattered IVUS data and multidetector-row computed tomography images for tissue characterization of human coronary atherosclerotic plaques

Intravascular imaging of coronary calcification and its clinical implications

Calcium impacts the natural history and treatment of coronary artery disease in many ways. Intravascular imaging studies, mostly intravascular ultrasound, but more recently studies using optical coherence tomography, have been instrumental in increasing our understanding of the relationship between calcium and coronary atherosclerosis, the predictors, the natural history of this relationship, and the impact on treatment. On one hand, stable coronary lesions are associated with more calcium than unstable lesions; and the amount of calcium may affect the success of percutaneous coronary intervention. On the other hand, calcium correlates with plaque burden; unstable lesions are associated with focal calcium deposits; and calcific nodules are one of the morphologies of vulnerable plaque. This review focuses on more than 20 years of intravascular imaging studies of the relationship between calcium and coronary atherosclerosis.

Regression of coronary atherosclerosis: Current evidence and future perspectives

Coronary atherosclerosis has been considered a chronic disease characterized by ongoing progression in response to systemic risk factors and local pro-atherogenic stimuli. As our understanding of the pathobiological mechanisms implicated in atherogenesis and plaque progression is evolving, effective treatment strategies have been developed that led to substantial reduction of the clinical manifestations and acute complications of coronary atherosclerotic disease. More recently, intracoronary imaging modalities have enabled detailed in vivo quantification and characterization of coronary atherosclerotic plaque, serial evaluation of atherosclerotic changes over time, and assessment of vascular responses to effective anti-atherosclerotic medications. The use of intracoronary imaging modalities has demonstrated that intensive lipid lowering can halt plaque progression and may even result in regression of coronary atheroma when the highest doses of the most potent statins are used. While current evidence indicates the feasibility of atheroma regression and of reversal of presumed high-risk plaque characteristics in response to intensive anti-atherosclerotic therapies, these changes of plaque size and composition are modest and their clinical implications remain largely elusive. Growing interest has focused on achieving more pronounced regression of coronary plaque using novel anti-atherosclerotic medications, and more importantly on elucidating ways toward clinical translation of favorable changes of plaque anatomy into more favorable clinical outcomes for our patients.

Prognostic implications of nonobstructive coronary plaques in patients with non-ST-segment elevation myocardial infarction: a multidetector computed tomography study

OBJECTIVES

We sought to determine whether the amount of noncalcified plaque (NCP) in nonobstructive coronary lesions as detected by multidetector computed tomography (MDCT) was a predictor of future coronary events.

BACKGROUND

Patients presenting with non-ST-segment elevation myocardial infarction (NSTEMI) frequently have multiple coronary plaques, which may be detected with MDCT.

METHODS

We included 312 consecutive patients presenting with NSTEMI, who underwent 64-slice MDCT coronary angiography and coronary artery calcium scoring before invasive coronary angiography. All patients were treated according to current guidelines based on an invasive treatment approach. Quantitative measurements of plaque composition and volume were performed by MDCT in all nonobstructive coronary lesions. The endpoint was cardiac death, acute coronary syndrome, or symptom-driven revascularization.

RESULTS

After a median follow-up of 16 months, 23 patients had suffered a cardiac event. Age, male sex, and diabetes mellitus were all associated with an increasing amount of NCP. In a multivariate regression analysis for events, the total amount of NCP in nonobstructive lesions was independently associated with an increased hazard ratio (1.18/100-mm(3) plaque volume increase, p = 0.01). Contrary to this, neither Agatston score nor the amount of calcium in nonobstructive lesions was associated with an increased risk.

CONCLUSIONS

Multidetector computed tomography plaque imaging identified patients at increased risk of recurrent coronary events after NSTEMI by measuring the total amount of NCP in nonobstructive lesions. The amount of calcified plaque was not associated with an increased risk.

Relationship between tissue characterization with 40 MHz intravascular ultrasound imaging and 64-slice computed tomography

BACKGROUND

Identification of coronary plaque composition is important for selecting the treatment strategy, and 64-slice computed tomography (CT) is a noninvasive method of characterizing atherosclerotic plaques. However, the correlation between plaque characteristics detected by CT and intravascular ultrasound (IVUS) is not clear. A 40 MHz IVUS imaging system (iMap-IVUS) has recently been developed to evaluate plaque composition. The aim of this study was to compare iMap-IVUS with 64-slice CT angiography for the characterization of non-calcified coronary plaques.

METHODS AND RESULTS

Both 64-slice CT angiography and iMap-IVUS were performed in 19 patients (38 plaques). CT values were measured as Hounsfield units (HU) in circular regions of interest (ROI) drawn on the plaques. The iMap-IVUS system analyzed coronary plaques as fibrotic, lipidic, necrotic, or calcified tissue based on the radiofrequency spectrum. A positive correlation was found between CT values and the percentage of fibrotic plaque (r=0.34, p=0.036) or calcified plaque (r=0.40, p=0.011). Conversely, a negative correlation was found between CT values and the percentage of lipidic plaque (r=-0.41, p=0.01), or necrotic plaque (r=-0.41, p=0.01).

CONCLUSIONS

Good correlations were observed between the characteristics of non-calcified plaque determined by iMap-IVUS and the CT values of plaque detected by 64-slice CT scanning.

Systemic markers of inflammation are associated with cardiac allograft vasculopathy and an increased intimal inflammatory component

We evaluated an extensive profile of clinical variables and immune markers to assess the inflammatory milieu associated with cardiac allograft vasculopathy (CAV) assessed by intravascular ultrasound (IVUS) and virtual histology (VH). In total, 101 heart transplant (HTx) recipients were included and underwent IVUS/VH examination and measurement of plasma C-reactive protein (CRP), soluble tumor necrosis factor receptor-1, interleukin-6, osteoprotegerin, soluble gp130, von Willebrand factor, vascular cell adhesion molecule-1 (VCAM-1) and neopterin. Mean Maximal Intimal Thickness (MIT) was 0.61 +/- 0.19 mm and mean fibrotic, fibrofatty, dense calcified and necrotic core components were 55 +/- 15, 14 +/- 10, 15 +/- 13 and 17 +/- 9%, respectively. In multivariate analysis, CRP > 1.5 mg/L (OR 4.6, p < 0.01), VCAM-1 > 391 ng/mL (adjusted OR 3.2, p = 0.04) and neopterin > 7.7 nmol/L (OR 3.8, p = 0.02) were independently associated with MIT > 0.5 mm. Similarly, CRP > 1.5 mg/L (OR 3.7, p < 0.01) and VCAM-1 > 391 (OR 2.7, p = 0.04) were independently associated with an increased intimal inflammatory component (dense calcified/necrotic core component > 30%). Advanced CAV is associated with elevated CRP, VCAM-1 and neopterin and the two former biomarkers are also associated with an increased intimal inflammatory component. Forthcoming studies should clarify if routine measurements of these markers can accurately identify HTx recipients at risk of developing advanced CAV and vulnerable lesions.