Cardiac MRI to determine Myocardium Viability before revascularization
Even severely dysfunctional myocardium in patients with coronary artery disease may show functional improvement after revascularization. Recent literature is showing that Cardiac MRI (CMR) is superior to low-dose dobutamine echocardiography and thallium-SPECT for viability imaging.
The whole concept of viability on Cardiac MRI is based on the fact that all infarcts enhance vividly 10-15 minutes after intravenous contrast administration. Cardiac MRI shows the transmural extent of the infarct very reliably. It tells you that:
"white is dead" (All infarcts irrespective of age enhance)
In areas of hypokinesia, if there is a rim of "black" or non-infarcted myocardium that is not contracting well, it indicates the presence of hibernating myocardium, which is likely to improve after revascularization of the artery supplying that particular territory.
Viability imaging reliably allows identification of areas of hibernation and viable or non-viable myocardium. All infarcts irrespective of age enhance.
The percentage involvement of the myocardial wall thickness by an infarct determines viability. Involvement of the myocardium by more than 50% usually implies that there will be no improvement after revascularization And similarly, less than 25% involvement of the myocardium by infarction usually implies that there is an 80% chance of improvement after revascularization.
Read article CMR in Myocardial Viability (Reference: Bhavin Jankharia: CMR in Myocardial Viability. The Internet Journal of Cardiology. 2004. Volume 2 Number 2.)
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