CT Imaging of Atherosclerotic Plaque William Stanford MD Professor-Emeritus Radiology University of Iowa College of Medicine Iowa City, IA
PREVALENCE OF CARDIOVASCULAR DISEASE In 2006 there were 80 million individuals who had suffered some form of cardiovascular disease Of these 16,800,000 were victims of angina and heart attacks Cardiovascular disease caused 864,500 deaths in 2005 and is the leading cause of death in the United States today 17.5% of heart attack victims were under 65 Economic loss $475.3 billion (est.) 2009 2009 Heart & Stroke Facts. American Heart Association
Coronary Artery Disease eath Rates/Sudden Death: Not uncommon for CAD to remain silent until a major catastrophic event occurs Yearly 310,000 Individuals die of CAD without being hospitalized 64% Women and 50% men dying suddenly from CAD had no previous symptoms Afro-American death rates were higher than Caucasian American Heart Assn 2009
Coronary Artery Disease mpact of Imaging Imaging modalities that have the potential to Identify coronary atherosclerotic plaque and especially vulnerable plaque are extremely important in evaluating CV disease Multidetector CT advanced technology is playing an increasingly important role in identifying coronary atherosclerotic plaque
Pathogenesis of Coronary Atherosclerosis Davies Atlas CAD
Imaging Modalities for Vulnerable Plaque Imaging Modalities for Vulnerable Plaque ultidectector CT---Advantanges Can detect luminal stenosis, evaluate coronary wall anatomy & composition and detect calcification alcification: Important in identifying and defining the extent of atherosclerotic burden however the absence of calcification does not negate the absence of CAD laque Composition: Can differentiate between soft, intermediate and calcified plaques laque Remodeling: Can evaluate plaque remodeling. Positive remodeling believed to be associated w/ plaque vulnerability
Coronary Calcium Protocol epresentative Protocol Scanner Type: Dual source Siemens Somatom Definition scanner Collimation; 2 x 32 x 0.6mm Rotation Time: 0.2sec Tube voltage 120kVp 150mAs Acquisition: Prospective gating Phase cardiac cycle 60-75% RR interval Radiation dose 4.25mGy Slice acquisition 1.2mm Reconstructed slice thickness 3mm Medication: No contrast Beta blockers to achieve HR <65 bpm Nitroglycerine sublingual
Coronary Calcification-- --Summary a++ as an Indicator of Obstructive Disease Sensitivity 89%, Specificity 75% Budoff et al. Circulation 2006;114:1761-91 rediction of Cardiac Events MDCT Ca++ was an independent predictor of mortality in a study of 10,377asymptomatic individuals followed over 5 years. Mortality in individuals w/ a Ca++ score of <10 was 99% vs a 95% in individuals w/ a Ca++ score >1000 (p<0.001) Shaw et al. Radiology 2003;228:8266-33 Mortality data on 25,253 asymptomatic individuals referred for Ca++ screening and followed over a 10 years period showed a 99% survival for a Ca++ score of 0 vs an 88% survival for a Ca++ score >1000 Budoff et al. JACC 2007;49:1860-70 urrent Thinking: Coronary Ca++ can add incremental value the predictability for cardiac events. Ca++ is helpful in the evaluation of individuals at intermediate risk. The absence of Ca++ does not negate the presence of non-calcified plaque
CT Angiography Protocol epresentative Protocol Scanner Type: Dual source Siemens Somatom Definition scanner Collimation; 2 x 32 x 0.6mm Rotation Time: 0.33sec Pitch 0.2 0.46 adapted to HR Tube voltage 120kVp 340mAs Acquisition: Dose modulation Radiation dose 22.51 mgy Slice acquisition 0.6mm Reconstructed slice thickness 0.75mm Medication: Contrast Isovue 370mg/ml Contrast administration 5ml/sec Contrast delivery: 3 phase (contrast, 50-50, saline) Beta blockers To achieve HR <65 bpm Nitroglycerine Sublingual
CT Angiographic Obstruction MDCT 64 CTA Imaging in evaluating obstruction in ER patients vs enzyme elevation, perfusion scintigraphy and/or conventional angiography Sensitivity 100% Specificity 92% Pos. Pred. Value 87% Neg. Pred. Value 100% Rubinshtein et al. Am. J. Cardiol; 2007;99:925-929
Characteristics of Vulnerable Plaque Non-occlusive plaques have lipid cores which are more prone to rupture. Conversely, fibrous plaques have a higher content of smooth muscle cells & collagen with relatively little lipid content and have less chance to rupture Pathological Characteristics Vulnerable Plaques Thin Fibrous Cap Large Lipid Pool Macrophages in or around fibrous cap (inflammation) Plaque rupture occurs more frequenty in proximal and mid-coronary artery locations
CT Imaging Atherosclerotic Plaque Purpose: Evaluate vulnerable plaque composition in pts w/ known CAD. Plaques classified by MDCT as noncalcified, mixed, calcified & by IVUS as necrotic core, fibrous, fibro-fatty, calcific. Vulnerable plaque defined as necrotic core component > 10%, no fibrous cap, Ca++ >5%, remodel index >1.05. Results: MDCT plaques: non-calcified in 22; mixed in 56. In unstable angina pts mixed plaques present in 76% vs 38% in stable angina pts IVUS: Necrotic core present in 14% mixed vs 7.5% in noncalcified plaques, fibrous tissue present in 59 vs 67%. Accuracy: Vulnerable plaque: MDCT PPV 77%, NPV 54%, Accuracy 59%. Conclusions: CT correlates w/ IVUS in mixed plaque but is not good enough to support its use in vulnerable plaque detection. Sarno et al. Eurointervention. 2008;4:318-23
CT Imaging Atherosclerotic Plaque urpose: Compare plaque composition in stable and unstable angina pts. -- MDCT 64 CTA in 110 unstable pts vs 189 stable pts. esults: Unstable pts had more non-ca++ plaques than mixed Ca++ plaques. (Odds ratio 1.3.) and for % relative culprit plaque (Odds ratio 1.06 ). No significant relationships between spotty Ca ++ and remodeling index. onclusion: Large non-ca++ culprit plaques are found more frequently in unstable than stable anginal pts. Meijs et al. Am J. Cardiol. 2009;140:305-11
CT Imaging of Atherosclerotic Plaque ummary MDCT is currently the most effective non-invasive imaging modality; IVUS is the most effective invasive imaging modality MDCT Ca++ provides a good estimation plaque burden & adds incremental value to conventional risk factors but can miss the presence of soft plaque CTA is excellent for stenosis and adds incremental value to Ca++ imaging. It is increasingly important in soft plaque assessment Soft Plaques w/ thin fibrous caps are often the culprit lesions and are more prone to rupture; conversely hard calcified plaques are more stable Conventional angiography while excellent at accessing stenosis does not image the arterial wall