Stress Testing and Cardiac Magnetic Resonance

Coronary artery disease is a major cause of morbidity and mortality in the United States. Currently, the presence of physiologically significant coronary disease is most commonly diagnosed using non-invasive imaging tests such as a nuclear stress test or an echo stress test. Unfortunately, nuclear stress tests require the use of ionizing radiation and have a limited spatial resolution. On the other hand, echo stress tests are dependent of adequate imaging windows. Adenosine stress testing combined with cardiac magnetic resonance (CMR) is a rapidly evolving technique for diagnosing significant coronary disease. It does not use ionizing radiation and has excellent image quality. In a recent meta-analysis of 14 studies with a total of 1,183 patients, the sensitivity and specificity of stress CMR for detecting significant coronary disease was 91% and 81%. Additionally, 2 studies have shown that patients with a normal stress CMR study have a <1% risk of having a cardiovascular event during the ensuing year. Another important advantage to stress CMR is the ability to fully quantify myocardial blood flow which may improve the diagnostic accuracy of stress CMR. In addition to perfusion imaging, CMR can directly visualize the coronary arteries, detect extremely small myocardial infarctions, and precisely measure the left ventricular function.

Although adenosine stress CMR is a rapidly maturing test, several important challenges exist. First, many patients find it difficult to tolerate the common side effects of adenosine in the confined space of the MRI scanner. Secondly, many patients under the influence of adenosine and its side effects cannot adequately hold their breath during image acquisition making image interpretation more difficult and quantitative analysis very time consuming. Finally, because adenosine must be continuously infused during a contrast-enhanced stress CMR, 2 separate intravenous (I.V.) catheters are needed. Most of the undesirable effects of adenosine are mediated through the adenosine A(2B) and A(3) receptors; where as, its desired vasodilator effects are mediated through the A(2A) receptor. The FDA recently approved an adenosine A(2A) receptor specific stress testing agent called regadenoson which is administered as a 10 second bolus and has an improved side effect and safety profile when compared to adenosine. With its improved tolerability and ease of use, regadenoson is a more ideal stress testing agent to use with CMR.

The purpose of this study is to determine whether a comprehensive regadenoson stress cardiac magnetic resonance study which includes myocardial perfusion imaging, optimized coronary imaging, and myocardial scar imaging provides incremental prognostic information over a clinical evaluation that includes nuclear stress testing.