In the last decade, stress cardiac magnetic resonance (CMR) imaging has become well-established as an excellent technique for the diagnosis and prognostic stratification of patients with acute or chronic ischemic heart disease.
The main advantages of CMR over other stress techniques relate to the high spatial and temporal resolution (superior to myocardial perfusion scintigraphy), the lack of ionizing radiation, and the high-quality images that are not limited by an echocardiographic window. Stress CMR is diagnostic in more than 97% of cases1 and can be successfully performed and interpreted in 95% of patients with a body mass index ≥ 30. The images allow diagnosis of subendocardial ischemia, nontransmural necrosis, viable myocardium, and dysfunctional myocardium in patients with ischemic heart disease.
Another advantage of stress CRM is its safety and low complication rate. A recent study by Monmeneu et al.,1 which included 11 984 patients, showed a nonsevere complication rate of 1.5% (there were no deaths or infarcts during the test), with 24.8% of patients experiencing minor symptoms. The presence of inducible ischemia was the main presidposing factor for complications during the test.
From a technical point of view, similarly to other pharmacological stress tests, stress CMR is based on the administration of dipyridamole, adenosine, regadenoson, or dobutamine, and the subsequent assessment of perfusion and myocardial contractility. The degree of transmurality of the perfusion defect relates to the severity of the coronary stenosis. Therefore, there is a good correlation between the presence of inducible perfusion defects on stress CMR and a reduction in the fractional flow reserve on conventional angiography.2 Patients with myocardial perfusion defects and inducible segmental wall motion abnormalities have a higher rate of complications at follow-up. Therefore, these are the patients who would benefit most from myocardial reperfusion strategies. Although current experience is still limited, the use of regadenoson as a pharmacological stressor offers an excellent diagnostic accuracy for coronary artery disease (93% sensitivity and 89% specificity) without increasing the rate of complications.3
One of the most recent technical advances is exercise stress CMR with an MR-compatible treadmill. A multicenter study demonstrated that exercise stress CMR has a specificity of 99%, a negative predictive value of 96%, and strong agreement (¿ = 0.82) with invasive coronary angiography.4
In patients with no previous history of ischemic heart disease and an intermediate pretest probability of coronary artery disease, stress CMR has a diagnostic accuracy for coronary disease similar to those of other currently-used imaging tests. Stress CMR has lower sensitivity than computed tomography but higher specificity than other methods.5 From a prognostic point of view, the presence of myocardial necrosis detected on late enhancement sequences, with associated reversible myocardial perfusion defects, in patients with known ischemic heart disease predisposes them to higher cardiovascular mortality and infarction and complication rates at follow-up. Therefore, a positive stress CMR can effect changes in treatment in up to 70% of patients studied.6 A recent study demonstrated that the main factors to determine treatment changes are the presence of inducible ischemia, the patient's age, and the absence of known coronary artery disease. In addition, this technique is an excellent aid in the decision to perform revascularization in a patient with chronic coronary occlusion. In this clinical context, revascularization in patients with inducible ischemia on stress CMR is associated with clinical improvement of ventricular volumes and systolic function.
In conclusion, it is fair to say that stress CMR has become established as an excellent investigation for assessing patients with suspected or known coronary artery disease. The test is free from ionizing radiation and is highly safe. Although only preliminary results are available, it is likely that in the future, exercise stress testing (with the additional functional and physical information it offers) may no longer be an intrinsic limitation of the technique.