在评价缺血性心脏病中的作用

The Role Of CT And MRI In The Management Of Ischemic Heart Disease Patricia Nguyen, MD Division of Cardiovascular Medicine Stanford University The Great Wall International Congress of Cardiology Diagnosis Of Subclinical Atherosclerosis: The Asymptomatic Patient Subclinical Atherosclerosis And Early Abnormalities Of Structure And Function Subclinical Atherosclerosis (Higher Risk) Functional Abnormalities Structural Abnormalities Coronary Artery Calcium Score Is Predictive Of Death And MI Greenland, P. et al. ACC/AHA Expert Consensus, JACC, 2007 Higher CACS, higher event rates *f/u 3-5 years Coronary Artery Calcium Score Improves Risk Stratification Over Framingham Risk Score CACS 400 = CHD Equivalent (10 year risk 20%) Greenland P, ACC/AHA Expert Consensus, JACC, 2007 Can We Do Better Than CACS? CT exposes patients to radiation Calcification appears relatively late Very late in women and young tend not to have Ca ? Significance of progression Progression more related to baseline CACS Ca related to healed not vulnerable plaque Unclear if statin improves Ca 10% inter-scan variability Functional defects appear years earlier and improvement can occur as early as 2 weeks post Rx Vascular Function Testing Assessment of arterial response to chemical or physical stimuli known to cause vasoreactivity Endothelial-dependent: Ach, shear stress, cold pressor Endothelial-independent: NTG, adenosine Measurement in diameter, CSA, velocity, or resistance Normal: Dilation Abnormal: Impaired Dilation, No Response, Constriction Coronary and peripheral arteries XRA, MRI, U/S (brachial artery) Impaired Vasoreactivity To Endothelial Dependent And Independent Stimuli Is Associated With CV Events Schachinger V, Circulation 2000 147 pts referred for XRA for chest pain or single vessel PCI 43% had no angiographic evidence of CAD All significant after multivariate analysis (RF, atherosclerosis on XRA) More CVD Events With Impaired Vasodilation during 7 Year Follow-Up Schachinger, Circulation 2000 MRI Assessment Of Vascular Function Acquire long and short axis images at baseline Choose most linear segment of artery for short axis images to yield most circular cross section Give stimulus then reacquire high resolution images at “peak” effect of stimulus Measure % change in CSA in response to the stimulus CSA Post-Stimulus CSA BL - CSA BL % Vasodilation = Pre Nitro Post Nitro Feasibility Study Of MRI Assessment To determine if MRI can quantify changes in epicardial size in response to NTG 12 pts undergoing XRA (6 CAD, 6 Tx) and 20 healthy controls 0.4 mg sl NTG with minimal systemic effects Excellent correlation of lumen area w/ XRA: r = 0.98 Terashima, JACC, 2005 Tx Intra-observer variability 3 2% (r=0.99) Inter-observer variability 5 5% (r=0.96) Nl MRI NTG Vasodilation Impaired In DM And ESRD Pre Nitro Post Nitro Nl ESRD 25.6% 17.8% 19.8% 14.8% 15% 75% stenosis occlusion Lewis B, JACC 2007 In-Stent Restenosis Neointimal hyperplasia without significant stenosis Complete stent occlusion Oncel D, Am. J. Roentgenol 2008 Dx Of High Grade Lesions: CT Angiography XRA remains the gold standard Indicated only if intermediate pretest probability and if ACS: enzymes and ECG must be negative Chest pain syndrome/Chronic ischemic dz (ECG un- interpretable, cannot exercise or equivocal stress test) Evaluation of new onset heart failure Not recommended for in stent restenosis Radiation dose is 5 to 13 mSv (1 yr background radiation) and 100 cc of contrast required MR Coronary Angiography Promising But Complex Acquisition With Lower Spatial Resolution Diagnosis And Risk Assessment In The Symptomatic Patient : Functional Imaging by MRI MRI Assessment Of Resting Function Is “Gold Standard” MRI Stress Perfusion: Areas With Significant Stenosis Enhance Less And More Slowly Stress Rest Sensitivity, Specificity And Accuracy n Sensitivity Specificity Accuracy Schwitter (2001) 48 87 85 - Nagel (2003) 84 88 90 89 Wolf (2004) 99 93 75 85 MRI Perfusion Alternative To Stress Echo On A Case by Case Basis Comparable sensitivity and specificity for stress echo and MRI perfusion Due to cost, versatility and patient comfort, stress echo is preferred If image quality impaired in echo, MRI perfusion is a good alternative Abnormal Microvascular Function In Syndrome X Painting, NEJM, 2002 Guiding Revascularization Post MI And Prognosis: Myocardial Viability MRI Assessment Of Viability Infarct (Gd) Normal Imaging Sequence (SE, FSE, GRE) -Normal myocardium signal is null (dark) -Infarct has partially recovered (bright) TI Gd is injected. Wait 10 - 15min. Gd accumulates in infarcted tissue A 180 RF pulse inverts all the spins. Tissues return to nl at different rates. At time TI, imaging sequence begins. 180 Inversion Pulse Low Chance Of Recovery If Delayed Enhancement 75% Kim, R et al, NEJM 2000 No hyperenhancement =78% segments improved Only 1 out of 58 segments improved if hyperenhancement 75% Less certain outcome for segments between 25-50% Same relationship in segments with most dysfunction Recent studies have also shown increased areas of DE indicates worse prognosis Delayed Enhancement Compared To Available Techniques Comparable sensitivity to DBA echo but slightly lower specificity MRI preferred in patients with severe baseline hypokinesis Comparable sensitivity and specificity to PET and SPECT Ability to detect small, subendocardial infarcts better than PET or SPECT MRI Detects Small Infarcts Better Than SPECT Ibrahim T, JACC 2007 Microvascular Obstruction After AMI Is Marker Of Poor Prognosis Wu KC, Circulation 1998 Comprehensive Evaluation Of Patient With Ischemic Cardiomyopathy MRI Delayed Enhancement As Alternative to DBA Echo On A Cas