Enter Your Email Address to Receive a
Copy of MedicExhange Member Demograhpics

The role of Cardiac Magnetic Resonance Imaging ( CMR ) in patients with acute and chronic myocardial infarction (MI) was reviewed by American College of Cardiology.

According to the review, MI is a leading cause of morbidity and mortality for which a broad range of ever-changing therapeutic and diagnostic options are available. Outcomes are directly related to MI size. Similarly, diagnostic tests for detection of MI are also dependent on a critical mass of involved myocardium for detection. Current recommendations suggest a combination of electrocardiographic, enzymatic, and imaging techniques including CMR, echocardiography, and radionuclide imaging to establish the diagnosis.

CMR is a multi-technique imaging modality dependent on both hardware and software for acquisition. Acquisition software can be modified with different pulse sequences to obtain different unique and nonoverlapping data. A comprehensive CMR exam will include multiple pulse sequences designed to define cardiac anatomy and blood flow and to detect thrombus, infarction, perfusion, etc. Many CMR artifacts are specific to the pulse sequence utilized and, as such, will not be present on all images.

Commonly used CMR techniques include cine imaging for cardiac function, determination of ventricular volumes, and left ventricular mass as well as valvular morphology. CMR determined chamber size and mass are highly accurate and reproducible. Other CMR techniques include specific imaging for acute myocardial injury as well as perfusion imaging at stress and with rest, the review says.

Use of gadolinium contrast for delayed imaging is a highly specific marker of MI. Gadolinium is excluded from normal, active myocytes and is sequestered in the interstitium. As such, when detected late after injection, it is a marker of nonviable areas of myocardium, but is not necessarily specific for ischemic heart disease.

The specific pattern of late gadolinium enhancement may allow a more specific diagnosis. The effects of coronary occlusion, typically spread in a wavefront from the endocardium to the epicardium and a matching pattern of gadolinium hyperenhancement, may be specific for the effects of coronary occlusion. Other diseases, such as acute myocarditis, present with patchy or mid-myocardial enhancement.

The spatial resolution of delayed enhancement (DE)-CMR is exceptionally high and in the clinical setting allows detection of MI involving as little as 1 g of myocardium. In comparison, wall motion abnormalities detected with echocardiography or other techniques will be dependent on a threshold of subendocardial involvement, and SPECT imaging may require >10 g of myocardial involvement before an abnormality is reliably detected.

In addition to detecting both acute and chronic MI, CMR may be useful for detecting complications such as aneurysm formulation, right ventricular involvement, pericarditis, and left ventricular thrombus.

Using DE-CMR as a marker for MI, a substantial number of clinically and electrocardiographically silent MIs are detected. DE-CMR detects 2-3 times more clinically occult MIs than does an electrocardiogram.

Because of the high spatial resolution and reproducibility of CMR for detecting and quantifying MI, it may serve as an accurate endpoint for clinical trials in which reduction in myocardial size rather than mortality is a surrogate endpoint. It has implications for allowing reduced sample size to be used in clinical trials.

Source: ACC

You can get more details about Cardiology & its related topics from our Cardiology User Group.