CMR May Help Evaluate Nonculprit Lesions in STEMI Patients

Cardiac magnetic resonance (CMR) imaging holds up fairly well to fractional flow reserve (FFR) measurements when it comes to looking for hemodynamically significant nonculprit lesions in STEMI patients who have already undergone primary PCI, new data show.

Visual analysis of CMR perfusion images had a diagnostic accuracy of 71% when compared with FFR, indicating “moderate-to-good agreement,” according to Henk Everaars, MD (Amsterdam University Medical Centers, the Netherlands), one of the study’s lead authors. More time-consuming semiquantitative or fully quantitative assessment of the perfusion images performed similarly.

“CMR and FFR are both valuable approaches for treating a nonculprit lesion after STEMI,” Everaars told TCTMD. “And I think it’s important for physicians to realize that there is some discordance with these techniques, but we don’t know how this discordance translates into clinical outcomes. That’s something we should look at. I think at the moment neither strategy is wrong, so you’re good to go with either one.”

The study, with lead authors Everaars and Nina van der Hoeven, MD (Amsterdam University Medical Centers), was published online September 18, 2019, ahead of print in JACC: Cardiovascular Imaging.

REDUCE-MVI Substudy

Though CMR has emerged as a tool for evaluating suspected obstructive coronary disease, FFR is considered the gold standard approach for identifying hemodynamically significant lesions in need of revascularization. The two modalities have been reported to have strong correlation in patients with stable CAD, but less is known about how they agree in the post-STEMI setting.

The REDUCE-MVI trial, which compared ticagrelor and prasugrel for the prevention of microvascular injury after primary PCI, provided the opportunity to explore this issue. In this substudy, the investigators looked at 77 patients (mean age 60 years; 86% men) who had undergone primary PCI, had at least one intermediate nonculprit lesion (diameter stenosis 50-90%), and who underwent CMR and invasive coronary angiography with FFR measurements about a month after the initial intervention.

Hemodynamically obstructive nonculprit lesions—defined by an FFR of 0.80 or less—were found in 40% of patients.

Although there was moderate-to-good correlation between CMR and FFR measurements for identifying such lesions, some disagreement remained. Everaars explained that “some of the discordance is not due to failure of either technique, but just reflects simple physiology.” That is, the two modalities are measuring somewhat different things—FFR measures the hyperemic pressure gradient in the epicardial coronary arteries, whereas CMR assesses both epicardial and microvascular disease. “We know that, especially in STEMI patients, microvascular disease plays an important role also in nonculprit vascular territories,” Everaars said. “So this might also explain a significant amount of the disagreement between CMR and FFR.”

The investigators also examined whether assessing the myocardial perfusion images with a fully quantitative analysis versus a semiquantitative or visual analysis would improve the diagnostic performance of CMR, and they found that it did not.

Senior author Robin Nijveldt, MD, PhD (Radboud UMC, Nijmegen, the Netherlands), said that’s important “because there are a few studies now going on that stress the fact that you should do quantification of stress perfusion results, which means that it costs a little bit more effort to get your results.” This study, on the other hand, shows “that a more simple approach of visual assessment is not inferior to a full quantitative approach,” he added.

What Does This Mean for Practice?

Nijveldt said it remains unknown what impact the discrepancy between CMR and FFR in terms of identifying functionally significant nonculprit lesions that are suitable for revascularization might have on patient outcomes because randomized trials comparing the two strategies have not been completed. He noted that one trial, iMODERN, which is comparing instantaneous wave-free ratio (iFR)-guided intervention of nonculprit lesions during the initial PCI in patients with STEMI with a deferred strategy guided by CMR, is underway and should provide some answers.

In the meantime, Nijveldt said, both CMR and FFR are options depending on the situation and timing. CMR has the advantage of being noninvasive and providing additional information beyond whether lesions are ischemic, including LV function, infarct size, and valve stenosis and leakages. “So you get a full report of the patient’s status at that time and you don’t need to do any invasive or echocardiographic follow-up if you do just one CMR,” he said.

On the other hand, he said, FFR might have an advantage if its use allows for revascularization of all significant nonculprit lesions at the time of primary PCI, avoiding the need for a patient to return 4 to 6 weeks later for additional assessment and intervention. “That could be a potential benefit for FFR or iFR measurements of the nonculprit lesion [if] you can treat everything in one session,” said Nijveldt.

A potential obstacle for wider use of CMR for the evaluation of nonculprit lesions in the United States specifically, Nijveldt pointed out, is that adoption of the technology has lagged behind other parts of the world, including Europe.

This study doesn’t seem likely to close that gap, as one US commentator, Bina Ahmed, MD (Dartmouth-Hitchcock Medical Center, Lebanon, NH), said that “the sensitivity and specificity correlations [between CMR and FFR] were not as high as we’d like them to be.”

For now, these residual nonculprit lesions should be managed with FFR-guided PCI, said Ahmed, who noted that this study “is great for hypothesis generation.”

The main advantage for a CMR-guided approach would be the avoidance of additional invasive procedures, Ahmed said. “If you could find a way to identify lesions just using MRI that either do not need revascularization or they do need revascularization, it would further refine who you send for additional procedures and potential PCI.”

Ahmed is not sure a CMR-guided approach is “ready for prime time,” but she said “we need data like this to help better our understanding of these intermediate lesions in patients—especially patients who’ve come in for STEMI—who’ve had their culprit artery treated [and] what is the best way to manage the intermediate leftover lesions. And so I think the study definitely adds to our ability and thoughts and ideas about how to evaluate those types of lesions, and maybe one day cardiac MRI will be able to provide us a direction in terms of who we need to revascularize and who we are comfortable just treating with medications.”

Photo Credit: Henk Everaars