Indications for cardiac MRI vary depending on local referring patterns. The ability of MRI to offer both static and dynamic/cine multi-planar, and global views of both right and left heart chambers, pericardium and aorta offers advantages over echocardiography and other imaging modalities in specific circumstances.

Commonly accepted indications for cardiac MRI include:

• Determination of myocardial viability prior to bypass
• Suspected arrythmogenic right ventricular dysplasia
• Diagnosis of constrictive pericarditis
• Evaluation of suspected cardiac masses
• Comprehensive left ventricular function evaluation in patients with inadequate visualization at echocardiography
• Pre and post operative assessment of congenital heart disease
• Calculation of shunt fractions and cardiac output

Through Turville Bay MRI Centers at St. Mary’s Hospital, the latest commercially available cardiac MR sequences are performed on Siemens 1.5 Tesla Symphony MRI scanners. All cardiac exams are attended and supervised by our radiologists in order to obtain best results.

Advanced and future applications include dobutamine stress MRI and coronary MR angiography.

Please note that patients with arrhythmia or prominent shortness of breath may be poor candidates for MRI. Pacemakers are a strict contraindication for MRI.

Cine MR true-fisp horizontal long axis/4-chamber view (left) and short axis views (right) demonstrate septal hypertrophy, small mitral regurgitation and mild tricuspid regurgitation. These beautiful images demonstrate how cine MRI can perform functional and morphologic cardiac analysis.

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:

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Figure 1: End diastolic (E.D.) and end systolic (E.S.) source images from cine short axis left ventricular MR study at rest demonstrate reduced inferior wall thickening at end systole (asterisk).

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Figure 2: Delayed gadolinium enhanced static MR demonstrates an approximate 50% wall thickness region of delayed high signal (bright) enhancement (delimited by asterisks) representing myocardial infarction. This corresponds to the region of wall motion abnormality demonstrated in figure 1. Arrow indicates enhancing, infarcted papillary muscle.

References:

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.