MRI could set stage for directing unrecognized myocardial infarction treatment
A prospective study investigating the use of MRI to detect clinically unrecognized myocardial infarctions (UMIs) has laid the groundwork to determine if these findings have a different pathogenesis than recognized myocardial infarctions (RMIs). According to research published this month in Radiology, if long-term follow-up proves this hypothesis true, a patient who presents with UMI may require different care and treatment than one who has had an RMI.
“It has recently been observed that the presence and extent of unrecognized myocardial scars at MR imaging are strong predictors of major adverse cardiac events, including cardiac death, in patients suspected of having coronary artery disease but without a history of myocardial infarction (MI),” stated the authors of the study conducted at Uppsala University Hospital in Sweden.
The researchers, which included personnel from the pharmaceutical company AstraZeneca, prospectively performed whole-body MR angiography (MRA) and cardiac MR imaging on a sample of patients recruited from the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study. All patients in the researcher’s study were recruited for participation at 70 years of age. A cohort of 248 patients (123 women and 125 men) made up the final study group.
“The subjects were grouped on the basis of late-enhancement MR imaging findings: 188 had no MI scar, 49 had a UMI, and 11 had an RMI,” the authors wrote.
Imaging was performed with a 1.5-Tesla Gyroscan Intera (Philips Medical Systems) MR system using a standard quadrature body coil for MRA and a standard sensitivity-encoding cardiac coil for cardiac imaging. The patients were injected with gadodiamide (Omniscan, GE Healthcare) and whole-body MRA was performed in four stations with a 3-cm overlap between the stations, according to the researchers.
“After the whole-body MRA, cardiac late-enhancement images were acquired by using a three-dimensional inversion-recovery gradient-echo sequence that covered the entire heart in short- and long-axis views,” the scientists wrote.
The whole-body MRA images were assessed by one researcher for atherosclerosis. The team established a criterion of significant atherosclerosis for any assessable vessel that presented with luminal narrowing of 50 percent or greater. The late-enhancement cardiac images were analyzed by two researchers who used subendocardial involvement as a criterion for identification of MI scars.


Left: Anteroposterior maximum intensity projection of whole-body MR angiogram (repetition time msec/echo time msec, 2.5/0.94; flip angle, 30°; acquired voxel size, 1.76 x 1.76 x 4.0 mm reconstructed to 0.88 x 0.88 x 2.0 mm) shows significant atherosclerosis in left anterior tibial artery (arrow).

Right: Cardiac late-enhancement MR images (approximately 3.6 [shortest]/approximately 1.8 [shortest]; flip angle, 15°; acquired voxel size, 1.56 x 2.81 x 10 mm reconstructed to 1.56 x 1.56 x 5 mm; individually set inversion time) in same subject demonstrate RMI (arrows) in free lateral wall of left ventricle. Image and caption courtesy of the Radiological Society of North America.

The team found that 85 percent of the UMIs and 73 percent of the RMIs were located within one to four inferolateral segments of the left ventricle. The researchers noted that the findings that the UMIs were not associated with significant atherosclerosis in the rest of the body or with traditional risk factors for heart disease.
“Neither the prevalence of significant atherosclerosis at whole-body MRA nor the intima-media thickness, C-reactive protein level, or Framingham risk score differed significantly between the group without MI scars and the UMI group, but these prevalence rates were all significantly increased in the RMI group compared with those in the group without MI scars,” the authors wrote.
The researchers observed that the study may have been limited by in that they did not include the coronary arteries in their imaging and that the parameters selected to indicate an atherosclerotic pathogenesis of MRI-detected UMI may have been too coarse compared with the sensitivity of late-enhancement MRI. They also noted that the RMI group in the study consisted of a small number (11) of patients.
Although the study was not definitive, the results were intriguing enough that the researchers have committed to a 5-year follow-up of the same cohort to gather information on the prognosis of UMIs and whether UMIs and RMIs have the same pathogenesis. The results of this follow-up hold significant implications for patient care.
If the UMIs have a different pathogenesis than RMIs, then patients with UMI detected via MRI may require different care and treatment than those patients with RMI. If both types of MI turn out to have the same pathogenesis, a case can be made for utilizing MRI as a cardiac screening technology.
“If UMIs are caused by atherosclerosis, but manifest at an earlier stage of disease than conventional methods are able to depict, MRI then could be useful as a method for depicting early atherosclerosis,” the authors wrote.