Cardiac MRI is a very powerful diagnostic tool and one of the most valuable techniques available to image the heart, says Samer Sayyed, MD, cardiologist at The Nebraska Medical Center and assistant professor of Internal Medicine at the University of Nebraska Medical Center (UNMC).
“Cardiac MRI goes beyond just analyzing the structure of the heart, but can also provide accurate quantitative assessment of bi-ventricular and valvular function, shunt fraction, myocardial perfusion, viability and scarring, as well as angiography of the pulmonary and systemic vasculature, all while avoiding the use of ionizing radiation or contrast agents that are toxic to the kidney,” he says.
First line cardiac diagnostic studies generally involve an electrocardiogram and/or an echocardiogram. A cardiac MRI study is appropriate when other tests are inconclusive, or when additional information about a patient’s cardiac condition is required to develop a more accurate diagnosis or management plan, notes Dr. Sayyed.
To get the most value from an MRI, the exact indication for ordering the test needs to be provided so the study can be tailored to effectively answer the clinical questions at hand, says Dr. Sayyed. “The study itself can take anywhere from 30 minutes to over an hour sometimes,” he says, “therefore, time is of the essence, and it is not a test to be performed in emergency situations.”
Some of the primary indications for cardiac MRI include:
- Assessment of cardiac structure and function when other techniques are insufficient or ineffective
- Evaluation of valvular structure and function
- Cardiac stress testing
- Assessment of myocardial viability prior to revascularization
- Ischemic and non-ischemic cardiomyopathy such as hypertrophic cardiomyopathy, sarcoidosis, amyloidosis, and hemochromatosis.
- Cardiac masses or thrombi
- Complex congenital heart disease
- Aortic and pulmonary angiography for aneurysms/dissection even for those who can’t receive contrast
- Complex intra and extra cardiac shunts
- Arrhythmogenic right ventricular dysplasia
- Pericardial disease such as acute pericardial inflammation and pericardial constriction
A comprehensive list of appropriate, uncertain, and inappropriate indications for cardiac MRI has been published by the Journal of the American College of Cardiology in 2006, says Dr. Sayyed.
It should also be noted that the contrast agents used for cardiac MRI are very different from those used for CT scans, says Dr. Sayyed. A CT scan uses an iodine-based agent whereas a cardiac MRI uses a gadolinium-based agent. The iodine agent can be toxic to the kidneys. The gadolinium-based agent, on the other hand, is not nephrotoxic and can be given to a larger group of patients, even those with moderate kidney disease. However, it should not be used on those patients with severe kidney disease. Even in those with a contraindication for contrast, there are ways to perform non-contrast enhanced MRI angiography with high image quality, notes Dr. Sayyed.
Because cardiac MRI uses magnetic fields, patients with implanted ferromagnetic material such as pacemakers, nerve stimulators or have a history of welding may not be eligible for this test. Obese and claustrophobic patients may also be unable to fit within the magnet, or tolerate being confined within its bore for the duration of the study. Despite these few limitations, MRI remains the gold standard noninvasive method of evaluating a wide array of cardiovascular diseases.