Identification of Reversible Myocardial Dysfunction with MRI
Particularly exciting is the ability of delayed post contrast MR imaging to determine if poorly contracting myocardium (heart muscle) is due to infarction (Dead muscle due to heart attack) or viable but ischemic (hibernating) myocardium. This has particular utility in determining if revascularization with coronary bypass will benefit the patient. Contrary to infarcted myocardium, poorly functioning or hibernating myocardium can improve its function and contractility if the blood supply is increased with cardiac bypass surgery. Conversely, bypassing to a region of infarcted myocardium will have no benefit. Thus, the identification of infarcted myocardiuim, and differentiating it from viable, poorly functioning ischemic myocardium can enhance treatment decisions and potentially improve patient outcome.
Kim, et al, demonstrated this in a landmark New England Journal of Medicine study (link to abstract: http://content.nejm.org/cgi/content/abstract/343/20/1445). Delayed contrast-enhanced cardiac MRI was found to be predictive of functional recovery of myocardium following coronary artery bypass. A strong inverse correlation was made regarding the amount of infarcted myocardium with the potential for the recovery of wall motion after coronary bypass. Kim found that a greater than 75% transmural extent of infarct demonstrated at MRI was predictive of lack of recovery of that muscle following bypass.
Thus, MRI can be used to assess risks and benefits of coronary bypass surgery in certain subsets of patients. Potential subsets of patients who may benefit from MRI include patients with:
- Known or suspected prior MI (myocardial infarction)
- Abnormal dobutamine/stress echocardiography
- Ischemic cardiomyopathy
- Some patients with fixed thallium or sestamibi defects
Other studies have shown this MRI technique to be of similar sensitivity to PET imaging for the same purpose. However, MRI has an advantage over PET because of improved spatial resolution, the ability to determine the depth of the infarct, and the ability to perform a global, dynamic left ventricular functional evaluation at the time of the MRI.
Case example of delayed enhancement of infarct, abnormal wall motion:
Feasibility of delayed contrast enhanced technique:
Relationship of MRI delayed contrast enhancement to irreversible injury, infarct age, and contractile function.
Additional clinical trials:
The Use of Contrast-Enhanced Magnetic Resonance Imaging to Identify Reversible Myocardial Dysfunction
Multimodality MR imaging assessment of myocardial viability: combination of first-pass and late contrast enhancement to wall motion dynamics and comparison with FDG PET-initial experience.
Evaluation of myocardial viability with contrast-enhanced magnetic resonance imaging--comparison of the late enhancement technique with positron emission tomography
Accuracy of contrast-enhanced magnetic resonance imaging in predicting improvement of regional myocardial function in patients after acute myocardial infarction.