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Elizabeth A. Buzney, IV Gillian Lieberman, MD July 2002 Imaging the Coronary Arteries Elizabeth A. Buzney Harvard Medical School, Year IV Gillian Lieberman, MD From http://www.animatedsoftware.com/ascodesc/hartdesc.htm Elizabeth A. Buzney, IV Gillian Lieberman, MD Our Patient, Mr. G. • • • • • 68 year-old male 1 year of chest pain with exertion Pain resolves with 1 nitroglycerin tablet Denies symptoms of heart failure Father had MI in 50’s • Suspect stable angina 2 Elizabeth A. Buzney, IV Gillian Lieberman, MD Coronary Artery Imaging Modalities • • • • • • • • Plane film Stress EKG Stress Echocardiogram Nuclear imaging Angiography EBCT (Electron beam CT) IVUS (Intravascular Ultrasound) MRA 3 Elizabeth A. Buzney, IV Gillian Lieberman, MD Cardiac Imaging Modalities • • • • • • • • Plane film Stress EKG Stress Echocardiogram Nuclear imaging Angiography EBCT (Electron beam CT) IVUS (Intravascular Ultrasound) MRA 4 Elizabeth A. Buzney, IV Gillian Lieberman, MD First Imaging Modality: Nuclear Imaging 5 Elizabeth A. Buzney, IV Gillian Lieberman, MD Principles of Nuclear Imaging • Areas of the heart with severe stenosis are always maximally vasodilated in order to increase perfusion • Areas without stenosis are not vasodilated at rest • When stimulated, normal vessels vasodilate, stealing blood away from tissue with stenotic vessels • Therefore, stenotic areas appear black on perfusion studies after stress or vasodilation 6 Elizabeth A. Buzney, IV Gillian Lieberman, MD Principles of Nuclear Imaging, Continued • Since stress causes vasodilation, vasodilation is often used as a proxy for stress during nuclear imaging studies 7 Elizabeth A. Buzney, IV Gillian Lieberman, MD Choosing a Nuclear Imaging Study • Exercise or pharmacologic stressor? • Thallium or Sesta-MIBI? 8 Elizabeth A. Buzney, IV Gillian Lieberman, MD Choosing a “Stressor” • 3 “pharmacologic stressors:” adenosine, dipyridimole, dobutamine • Beware: adenosine causes bronchospasm; avoid in COPD or asthma Exercise Dobutamine Dipyridamole inhibits breakdown Inotropy Adenosine * Vasodilation 9 Elizabeth A. Buzney, IV Gillian Lieberman, MD The “Best” Stress Exercise Stress • Best approximate of the patient’s expected realistic physical stress. • Higher specificity for clinically significant CAD. • More than just a physiologic marker. Pharmacologic Stress • Best for patients who cannot exercise (arthritis, CVA, amputation, pulm dz, deconditioning). • Higher sensitivity for anatomic CAD in those unlikely to perform maximally on exercise stress. 10 Elizabeth A. Buzney, IV Gillian Lieberman, MD Thallium vs. MIBI Thallium-201 • Potassium analog • Half-life: 74 hours • Whole body radiation dose: 0.20 rads/mCi Technetium-99m SestaMIBI • Hydrophilic cation • Half-life: 6 hours • Whole body radiation dose: 0.02 rads/mCi 11 Elizabeth A. Buzney, IV Gillian Lieberman, MD Thallium vs. MIBI, continued Thallium-201 • Uptake depends on ATPase Æ best measure of cell viability Technetium-99m SestaMIBI • Uptake depends on cell membranes with intact electrochemical gradient Æ only fair measure of viability • Does not redistribute • Redistributes over 2-12 hours into all viable cells • Measures perfusion and • Measures viability only insofar as cells are perfused viability independently 12 Elizabeth A. Buzney, IV Gillian Lieberman, MD Limitations of Nuclear Imaging • 10-25% of non-reversible defects found to be viable upon reperfusion • Artifact often due to hibernating myocardium (viable but chronically hypoperfused tissue) • Hibernating myocardium may be revealed by thallium reinjection under non-stress conditions • PET scan best reveals hibernating myocardium: high glucose uptake relative to perfusion 13 Elizabeth A. Buzney, IV Gillian Lieberman, MD Reading Defects on Nuclear Imaging Studies • Reversible defect: Ischemia • Non-reversible defect: Infarct or hibernating myocardium 14 Elizabeth A. Buzney, IV Gillian Lieberman, MD Mr. G’s Stress Test • Since Mr. G. was able to exercise, he decided to have an exercise stress test using a Modified Bruce Protocol 15 Elizabeth A. Buzney, IV Gillian Lieberman, MD What are the Bruce Protocols? • Treadmill programs where the METS (determined by grade and mph) change every 3 minutes Stage METS Activity Modified 1 3 Cooking Modified 2 4 Light gardening Modified 3 = Regular 1 5 Washing clothes, sex Regular 2 Regular 3 Regular 4 Regular 5 7 10 13 16 Carrying suitcase Running 16 Elizabeth A. Buzney, IV Gillian Lieberman, MD Mr. G’s Stress Test at the BIDMC Thallium injection Imaging Exercise/stress MIBI Imaging Stress EKG injection at point of From: www.greaterthings.com/Books/ClintonAIDS/ From: www.dis-tenet.com/Procedures/nuclear-cardiology.htm maximal HR From: www.perduecreative.com/ fun.html 17 Elizabeth A. Buzney, IV Gillian Lieberman, MD Mr. G’s Stress Test • Exercised 6.5 minutes on a modified Bruce protocol • Stress EKG showed 1-2mm EKG changes inferolaterally • Had 9/10 chest pain during exercise 18 Elizabeth A. Buzney, IV Gillian Lieberman, MD So How Did Mr. G. Do? • 6.5 min on modified Bruce – washing clothes • Achieved only 74% of maximal heart rate • Should achieve 80-85% maximal heart rate for a good stress test 19 Elizabeth A. Buzney, IV Gillian Lieberman, MD Reading Nuclear Imaging Scans RV LV Base Apex Short axis Vertical; Oblique sagittal Apex Base From http://brighamrad.harvard.edu/education/ online/Cardiac/anatomic-orient.html Horizontal; Oblique transaxial From Braunwald: Heart Disease: Cardiovascular Medicine, 6th ed., 2001, Fig. 9-6 20 Elizabeth A. Buzney, IV Gillian Lieberman, MD Coronary Artery Territories on Nuclear Imaging From http://brighamrad.harvard.edu/education/ online/Cardiac/coronary-artery-territory.html 21 Elizabeth A. Buzney, IV Gillian Lieberman, MD Mr. G’s MIBI Moderate reversible anterior defect Severe reversible apical defect From BIDMC PACS From http://brighamrad.harvard.edu/education/ online/Cardiac/anatomic-orient.html 22 Elizabeth A. Buzney, IV Gillian Lieberman, MD Another example: Patient II Severe reversible defect in inferior region From http://brighamrad.harvard.edu/education/ online/Cardiac/coronary-artery-territory.html From BIDMC PACS 23 Elizabeth A. Buzney, IV Gillian Lieberman, MD Last example: Patient III Severe reversible defect in lateral region From http://brighamrad.harvard.edu/education/ online/Cardiac/coronary-artery-territory.html From BIDMC PACS 24 Elizabeth A. Buzney, IV Gillian Lieberman, MD And patient III after CABG… Lateral defect has partially resolved! From BIDMC PACS 25 Elizabeth A. Buzney, IV Gillian Lieberman, MD Back to Mr. G… • Anterior and apical defects: LAD region stenoses • Reversibility suggests ischemia • These regions are still viable and might benefit from cardiac catheterization Mr. G. goes to cardiac catherization! 26 Elizabeth A. Buzney, IV Gillian Lieberman, MD Second Imaging Modality: Cardiac Catheterization 27 Elizabeth A. Buzney, IV Gillian Lieberman, MD Indications for Cardiac Catheterization • Gold standard for identification of CAD when noninvasive imaging modalities are equivocal • Assessment of disease extent for interventional therapy (angioplasty or surgery) 28 Elizabeth A. Buzney, IV Gillian Lieberman, MD Risks for Coronary Catheterization • • • • • • Rare (<0.1%) risk of MI, CVA or death Risk increased if: emergency, acute MI, unstable Allergic reactions (0.37%) Arrhythmia (0.38%) Vascular occlusion (0.43%) Contrast medium-induced renal failure (3-7%) 29 Elizabeth A. Buzney, IV Gillian Lieberman, MD Mr. G’s Coronary Catheterization • • • • Fasting Conscious sedation 5000U IV Heparin Percutaneous catheter into R femoral artery, advanced under fluoroscopy • Iodine-containing radio-opaque dye injected into coronary arteries • Digital acquisition of x-ray images 30 Elizabeth A. Buzney, IV Gillian Lieberman, MD Mr. G.’s Catheterization Results • 99% stenosis of proximal LAD and first diagonal branch • 80% stenosis of RCA 31 Elizabeth A. Buzney, IV Gillian Lieberman, MD Mr. G’s catheterization: Left main artery disease Left main Circumflex Diagonal Defects Catheter LAD From BIDMC Coronary Catheterization Lab 32 Elizabeth A. Buzney, IV Gillian Lieberman, MD Mr. G’s catheterization: Intermediate step in repair LAD has been stented, but diagonal has been completely occluded in the process From BIDMC Coronary Catheterization Lab 33 Elizabeth A. Buzney, IV Gillian Lieberman, MD Mr. G’s catheterization: Left main repair completed Stent has been placed in diagonal From BIDMC Coronary Catheterization Lab 34 Elizabeth A. Buzney, IV Gillian Lieberman, MD Mr. G’s catheterization: Right coronary artery repair From BIDMC Coronary Catheterization Lab RCA defect …here corrected with stent 35 Elizabeth A. Buzney, IV Gillian Lieberman, MD Coronary Angiography vs. IVUS: Angiographic underestimation of disease Catheter Atheroma Lumen Adapted from Nissen SE, Yock P. Circulation.2001; 103:604-616 Courtesy of Dr. Clouse, BIDMC 36 Elizabeth A. Buzney, IV Gillian Lieberman, MD Third Imaging Modality: EBCT (Electron-Beam CT) 37 Elizabeth A. Buzney, IV Gillian Lieberman, MD What Is EBCT? • Also known as Ultrafast CT (UFCT) • Electron stream is aimed onto tungsten rings which focus the electrons to generate xrays • Moving xray tube is eliminated • Entire heart imaged in one breathhold Æ eliminates blurring 38 Elizabeth A. Buzney, IV Gillian Lieberman, MD How Can EBCT Image the Coronary Arteries? • Noninvasive coronary angiography • Assessment of myocardial perfusion • Calcium deposit detection 39 Elizabeth A. Buzney, IV Gillian Lieberman, MD EBCT Coronary Angiography • Uses intravenous contrast • Sensitivity of 77-82% and specificity of 92% for detecting luminal stenoses of >50% • Limitations: - inadequate image quality - requires breathold - requires contrast • Still undergoing refinement 40 Elizabeth A. Buzney, IV Gillian Lieberman, MD EBCT Coronary Angiography Patient IV LAD Imaging Soft plaque within LAD 3D reconstruction Pulm. trunk LCX Aorta Obtuse Marginal 1 LV LA Courtesy of Dr. Clouse, BIDMC LAD LV 41 Elizabeth A. Buzney, IV Gillian Lieberman, MD EBCT Calcium Detection • Highly controversial means of visualizing calcium within the coronary arteries • Non-contrast CT • Not covered by insurance • $400.00 at BIDMC • Patients are given a calcium score: estimate of total artery calcification by volume and by arterial location (age/sex –related) 42 Elizabeth A. Buzney, IV Gillian Lieberman, MD Coronary Artery Calcification Patient V RV RCA RA AA LV LA LAD DA From BIDMC PACS 43 Elizabeth A. Buzney, IV Gillian Lieberman, MD Examples of Coronary Artery Scans Patient VI No calcification Patient VII Patient VIII Moderate calcification Significant calcification Images courtesy of HeartScan San Francisco Courtesy of Dr. Clouse, BIDMC 44 Elizabeth A. Buzney, IV Gillian Lieberman, MD Coronary Calcification Detection • • • • Advantages 150,000 Americans/yr die from first MI All other tests designed to detect disease when patient is symptomatic (70-90% lumenal stenosis) EBCT detects calcification with 20% lumenal stenosis Coronary Ca++ more Se and Sp than cholesterol for CAD death prediction Questions • Yes, 90% of plaques contain Ca++,BUT does calcification predict clinically significant plaques? • Yes, EBCT detects plaques that do not impede flow, BUT do these plaques provide significant risk? • Does “plaque burden” add to Framingham risk score (CAD prediction)? 45 Elizabeth A. Buzney, IV Gillian Lieberman, MD Current recommendations for EBCT • Negative EBCT: Good predictor for clean coronaries • Positive EBCT: – 85% Se and 49% Sp for diagnosis of angiographic CAD (vs. 85% and 91% for MIBI) ++ – Greater Ca = greater likelihood of occlusive CAD – BUT no 1:1 relationship – AND findings may not be site specific – Total calcium underestimates total plaque burden ++ – High Ca score may mean high MI risk in 2-5yrs 46 Elizabeth A. Buzney, IV Gillian Lieberman, MD References • • • • • • • • • Arad Y, Spadaro LA, Goodman K, Lledo-Perez A, Sherman S, Lerner G, Guerci AD. Predictive value of EBCT of the coronary arteries: 19-month follow-up of 1173 asymptomatic subjects. Circulation 1996; 93: 1951-53. Braunwald E, editor-in-chief, Zipes DP, Libby P. Heart Disease: A Textbook of Cardiovascular Medicine, 6th ed. W. B. Saunders Company: Philadelphia, 2001. Cerqueira MD and Lawrence A. Nuclear cardiology update. Radiologic Clinics of North America 2001; 39: 931946. Donohoe KJ and Van den Abbeele AD. Teaching Atlas of Nuclear Medicine. Thieme Medical Publishers: New York, 2000. He ZX, Hedrick TD, Pratt CM, Verani MS, Aquino V, Roberts R, Mahmarian JJ. Severity of coronary artery calcification by EBCT predicts silent myocardial ischemia. Circulation 2000; 101: 244-251. Mazur W, Nagueh SF. Myocardial viability: recent developments in detection and clinical significance. Current Opinion in Cardiology 2001; 16: 277-81. O'Rourke RA, Brundage BH, Froelicher VF, Greenland P, Grundy SM, Hachamovitch R, Pohost GM, Shaw LJ, Weintraub WS, Winters WL Jr, Forrester JS, Douglas PS, Faxon DP, Fisher JD, Gregoratos G, Hochman JS, Hutter AM Jr, Kaul S, Wolk MJ. American College of Cardiology/American Heart Association Expert Consensus document on electron-beam computed tomography for the diagnosis and prognosis of coronary artery disease. Circulation 2000; 102: 126-40. San Roman JA, Vilacota I, Castillo JA, Rollan MJ, Hernandez M, Peral V, Garcimartin I, de la Torre MM, Fernandez-Aviles F. Selection of the optimal stress test for the diagnosis of coronary artery disease. Heart 1998; 80: 370-376. Schelbert HR. 18F-deoxyglucose and the assessment of myocardial viability. Seminars in Nuclear Medicine 2002; 32: 60-69. 47 Elizabeth A. Buzney, IV Gillian Lieberman, MD Acknowledgements Dan Saurborn, MD Melvin Clouse, MD Kevin Donohoe, MD Thomas Tu, MD Sven Paulin, MD Bertrand d’Othee, MD Eric Niendorf, MD Gillian Lieberman, MD Pamela Lepkowski Larry Barbaras and Cara Lyn D’amour 48