Coronary Artery Disease (CAD)
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Author: Steve Leung

Date: 9/21/2018

Indications and Purpose of the Scan: 

In patients with coronary artery disease or ischemic cardiomyopathy, CMR is recommended 

  • To obtain accurate measurements of left and right ventricular size and function
  • To assess likelihood of recovery of function with revascularization
  • To assess presence of left ventricular thrombus
Description:

Coronary artery disease affects a large number of patients, and require long term medical care.  Traditionally, echocardiogram is the major non-invasive modality in assessing the damage caused by myocardial infarctions.  However, CMR has become more utilized due to many of its strengths.

CMR has high interobserver and intraobserver reproducibility of ventricular size and systolic function measurements.1,2  In patients with coronary artery disease, regional wall motion abnormalities can have an impact in 2D echocardiography assessment since method of disc is based on a uniform ellipsoid estimation from 2 and 4 chamber views only. 

One of the most common indication for CMR is viability assessment.  In patients with obstructive coronary artery disease who are planned to undergo revascularization.  With gadolinium based contrast agent (GBCA), CMR with late gadolinium enhancement imaging can assess the transmurality of scar tissue.3 In coronary territories where there is ≤50% transmurality of scar tissue, revascularization has a higher likelihood to improve contractility compared to segments that have >50% transmurality of scar tissue.4,5  In patients with a history of myocardial infarction, the size of late gadolinium enhancement portends to worse prognosis beyond the predictive value of ejection fraction.6

In patients with acute myocardial infarctions, CMR is able to identify various pathologies: myocardial edema (T1 and T2-weighed imaging, T1 and T2 parametric mapping),7 intramyocardial hemorrhage, microvascular obstruction8 and myocardial necrosis (late gadolinium enhancement imaging).  Identification of persistent microvascular obstruction and intramyocardial hemorrhage can predict wall segments that may not recover with revascularization.  Myocardial edema can help identify the area at risk, which would be beneficial in research of medications that can reduce infarct size.

In patients with coronary artery disease, there is a subset of patients who develop left ventricular thrombus.  With GBCA, left ventricular thrombus can be easily detected compared to traditional echocardiography even with echo contrast.9

Why CMR (Specific Advantages):
  • Provide highly reproducible measurements of ventricular size and systolic function1

  •  The only modality that can non-invasively visualize myocardial scar3, myocardial edema (area-at-risk)7, microvascular obstruction, intramyocardial hemorrhage8 due to myocardial infarction

  • Can predict the likelihood of myocardial wall motion recovery after revascularization4,5

  • Provide prognostic information in patients who have coronary artery disease6

  • Assess presence of left ventricular thrombus effectively9

Evidence:
  • Revascularization of dysfunctional segments improved contractility in 66% (411/622) of the segments that have ≤50% transmural scar; whereas <8% (14/182) of dysfunctional segments improve contractility with revascularization when there is >50% transmurality of scar.4,5
  • In a study of 122 revascularized STEMI patients, infarct size was the only significant predictor of adverse outcomes in multivariate analysis.6
  • In a study of 121 patients at risk of developing left ventricular thrombus, contrast enhanced CMR was able to detect thrombus in 24 patients, while contrast enhanced echo identified 14 and non-contrast echo identified 8.9

Contraindications
  • Presence of contraindications for MRI

  • Severe renal failure (eGFR <30) or acute renal failure.

References:

1.      Grothues F, Smith GC, Moon JC, Bellenger NG, Collins P, Klein HU, Pennell DJ. Comparison of interstudy reproducibility of cardiovascular magnetic resonance with two-dimensional echocardiography in normal subjects and in patients with heart failure or left ventricular hypertrophy. Am J Cardiol. 2002;90:29–34

2.      Patel MR, White RD, Abbara S, Bluemke DA, Herfkens RJ, Picard M, Shaw LJ, Silver M, Stillman AE, Udelson J. 2013 ACCF/ACR/ASE/ASNC/SCCT/SCMR Appropriate Utilization of Cardiovascular Imaging in Heart Failure - A Joint Report of the American College of Radiology Appropriateness Criteria Committee and the American College of Cardiology Foundation Appropriate Use Criteria Task Force. J Am Coll Cardiol. 2013 May 28;61(21):2207-31

3.      Kim RJ, Fieno DS, Parrish TB, Harris K, Chen EL, Simonetti O, Bundy J, Finn JP, Klocke FJ, Judd RM. Relationship of MRI delayed contrast enhancement to irreversible injury, infarct age, and contractile function. Circulation. 1999 Nov 9;100(19):1992-2002.

4.      Kim RJ, Wu E, Rafael A, Chen EL, Parker MA, Simonetti O, Klocke FJ, Bonow RO, Judd RM.  The use of contrast-enhanced magnetic resonance imaging to identify reversible myocardial dysfunction. N Engl J Med. 2000 Nov 16;343(20):1445-53.

5.      Selvanayagam JB, Kardos A, Francis JM, Wiesmann F, Petersen SE, Taggart DP, Neubauer S. Value of delayed-enhancement cardiovascular magnetic resonance imaging in predicting myocardial viability after surgical revascularization. Circulation. 2004 Sep 21;110(12):1535-41.

6.      Wu E, Ortiz JT, Tejedor P, Lee DC, Bucciarelli-Ducci C, Kansal P, Carr JC, Holly TA, Lloyd-Jones D, Klocke FJ, Bonow RO.  Infarct Size By Contrast Enhanced Cardiac Magnetic Resonance Is a Stronger Predictor Of Outcomes Than Left Ventricular Ejection Fraction or End-Systolic Volume Index: Prospective Cohort Study.  Heart 2008;94;730-736.

7.      Ugander M, Bagi PS, Oki AJ, Chen B, Hsu LY, Aletras AH, Shah S, Greiser A, Kellman P, Arai AE.  Myocardial Edema as Dected by Pre-Contrast T1 and T2 CMR Delineates Area at Risk Associated with Acute Myocardial Infarction.  J Am Coll Cardiol Img 2012;55:596-603.

8.      Wu KC.  CMR of Microvascular Obstruction and Hemorrhage in Myocardial Infarction.  J Cardiovasc Magn Reson. 2012;14:68

9.      Weinsaft JW, Kim RJ, Ross M, Krauser D, Manoushagian S, LaBounty TM, Cham MD, Min JK, Healy K, Wang Y, Parker M, Roman MJ, Devereux RB.  Contrast-enhanced anatomic imaging as compared to contrast-enhanced tissue characterization for detection of left ventricular thrombus. JACC Cardiovasc Imaging. 2009 Aug;2(8):969-79

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