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February 2004 Case of the Month |
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History: 65 year old male with history of high blood pressure and diabetes who underwent a recent hospitalization for myocardial infarction. Patient returned two weeks later for a cardiac MRI viability evaluation.
Compiled by: Gregory J. Fenzl, D.O.
Technique:
(A.) Post gadolinium (15 minute delayed) T1 weighted short axis images of the left ventricle (Image #1)
(B.) Cine data set obtained using the balanced fast field echo sequence (Movie)
(C.) Companion Case: Short and vertical long axis T1 weighted delayed post gadolinium images through the left ventricle.
(Images #2 and #3)
Companion Case
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Image #2 |
Image #3 |
Findings:
Case #1
Diffuse hyper enhancement of the inferior and portions of the inferior lateral walls of the left ventricle compatible with myocardial infarction. Cine images reveal an akinetic segment within the inferior basilar wall of the left ventricle corroborating the findings seen on the post gadolinium enhanced viability sequence.
Case #2
Short axis and vertical long axis delayed post gadolinium images through the left ventricle demonstrate a thin rind of hyper enhancement along the inferior lateral basilar wall of the left ventricle compatible with subendocardial infarction. Cine images (not provided) demonstrate mild hypo kinesis within the involved segment.
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Discussion:
Patients with ischemic cardiomyopathy often have extensive coronary artery disease and reduced left ventricular function due to myocardial scar or hibernation. In order to plan therapeutic revascularization strategies, it is essential to distinguish dysfunctional, but viable (hibernating/stunned) myocardium from nonviable myocardial scar (infarction). Cardiac MRI not only accomplishes this goal, but its excellent spatial resolution and contrast capabilities allows for direct visualization of subendocardial and transmural areas of nonviable tissue.
Viable myocardium may recover function if the cause of the dysfunction is corrected; non-viable myocardium will not. Armed with this information, physicians would be able to identify those patients with coronary artery disease and left ventricular dysfunction that could benefit from more aggressive revascularization strategies.
Myocardial viability imaging with MRI is performed after I.V. administration of gadolinium contrast (0.2 mmol/kg) injected over 20 seconds; imaging begins after 10-15 minutes). Nonviable (infarcted) myocardium enhances on delayed contrast images. Stunned or hibernating myocardium is viable and will not enhance, but will have abnormal contractility. Stunned myocardium is viable tissue that demonstrates abnormal function after an ischemic event and the abnormal function is reversible once reperfusion ensues. Hibernating myocardium is viable tissue that is in an altered hypo metabolic state due to chronic ischemia. It will demonstrate abnormal function, however, once adequate perfusion ensues normal function will return.
PET (positron-emission tomography) is considered by many to be the “gold standard” for assessment of myocardial viability. Klein et al compared the extent and location of hyper enhancement by MRI with nonviable tissue as defined by PET in 167 patients with chronic ischemic heart failure. They found a sensitivity and specificity of cardiac MRI to be 0.83 and 0.88 respectively for detecting any defect (transmural or nontransmural). These results closely correlate with that of PET for determination of extent of scar tissue. The difference, however, is that cardiac MRI provides superior spatial resolution.1
The limitations of MRI involve claustrophobic patients, patients with permanent pacemakers/internal cardioverter-defibrillators, or other implanted devices which can have their function affected or altered by the magnet.
References:
1. Klein C., Nekolla SG, Bengel FM, et al.
Assessment of myocardial viability with contrast-enhanced magnetic resonance imaging comparison with positron emission tomography. Circulation 2002; 105:
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