Cardiac MRI Improves Culprit Lesion Identification in NSTEMI

Patrice Wendling

April 30, 2019

Upfront delayed-enhancement cardiac magnetic resonance (DE-CMR) imaging identifies a different or new culprit lesion than standard angiography in nearly one in three patients presenting with non-ST-segment elevation myocardial infarction (NSTEMI), prospective findings suggest.

The study showed that the infarct-related-artery (IRA) could not be identified by invasive coronary angiography in 37% of 114 patients with NSTEMI.

DE-CMR, however, identified the IRA in 60% of these patients and led to a new nonischemic diagnosis in a further 19%.

In the remaining 72 patients whose IRA was picked up by angiography, DE-CMR found hyperenhancement consistent with MI in a different territory in 14%. Another 10 patients (12.5%) were deemed to have a nonischemic diagnosis, including myocarditis in seven, Takotsubo cardiomyopathy in one, and amyloidosis in one.

For the entire population, DE-CMR significantly increased IRA identification vs coronary angiography (72% vs 63%; P < .01), driven primarily by those without significant coronary artery disease (CAD; 54% vs 22%; P < .01).

Overall, DE-CMR led to a new IRA diagnosis in 35 patients, a nonischemic diagnosis in 17, or either in 52 patients, although the 95% confidence interval was wide, at 37% to 55%.

"The main findings are that identification of the IRA by coronary angiography is challenging, and DE-CMR may lead to a new diagnosis or elucidate a new nonischemic etiology in nearly half the cohort," the authors report April 30 in Circulation: Cardiovascular Interventions.

Speaking about the study with | Medscape Cardiology, Deepak Bhatt, MD, executive director of interventional cardiology programs at Brigham and Women's Hospital, Boston, said: "It's extremely interesting, very eye-opening, very insightful, and I think will be of great interest to clinical cardiologists and to interventional cardiologists."

"A lot of times people with NSTEMI have multivessel disease and it's hard to know if the culprit vessel is the one we're really going after," he said. "Now if someone is doing a complete revascularization, it might matter a little bit less. But it just goes to show that what we think is the culprit artery in NSTEMI oftentimes based on angiography when more sensitive testing, such as MR is done, it turns out we were wrong."

Implications for Revascularization

Multivessel disease is present on angiography in about 50% to 60% of patients presenting with NSTEMI and was found in 80% of patients with a different IRA by DE-CMR in the study.

Challenges in identifying the IRA may in part explain conflicting evidence and recommendations regarding whether culprit artery-only or multivessel revascularization is best for patients with NSTEMI, the authors suggest.

"It may be that we're looking at this wrong," lead author John F. Heitner, MD, New York Presbyterian-Brooklyn Methodist Hospital, told | Medscape Cardiology. "Perhaps the reason why multivessel works is because you're more apt to get the right vessel and I think it could be that if you did the MRI first, then single-vessel might be the way to go. So I think there are a lot of ramifications based on this study."

Of the 55 patients who underwent revascularization, 15 patients (27%) had revascularization solely to non-IRA territories as determined by DE-CMR. Eleven had a different IRA identified by DE-CMR than the coronary artery or arteries that were revascularized and four had a nonischemic diagnosis of myocarditis or Takotsubo cardiomyopathy as the reason for hospital admission.

"For me, the most compelling thing here is that one out of every four patients who got revascularized had a stent placed to an artery that had no infarct by MRI. And I would go further and say one out of every five patients really had it to the wrong artery," Heitner said. "To me, I think that has huge, huge implications."

Nevertheless, he said, it would be a big leap to say that every patient with NSTEMI should have a cardiac MRI based on the study, but its findings merit a large randomized controlled trial utilizing MRI before angiography. "Because if the results come out the way this preliminary study shows, then clearly I think you're talking about a complete change in the way we manage non-STEMI patients, in that they really should have MRIs done beforehand."

CMR was performed a median of 1.1 days after admission and angiography performed a median of 4 hours after CMR. Clinical teams and interventional cardiologists were blinded to the results of the DE-CMR scans, which were interpreted by a core lab blinded to clinical and angiographic data.

In all, investigators enrolled 118 patients from New York, the Duke Cardiovascular Magnetic Resonance Center in Durham, North Carolina, and the Maastricht University Medical Center in the Netherlands. Two patients withdrew consent and two had pulmonary embolism on CMR and did not undergo angiography.

The data for revascularization in NSTEMI are quite strong, as are the guidelines supporting its use as part of an early invasive strategy, observed Bhatt. But those results, which in general are showing that an early invasive strategy is better than medical therapy, could be made even better if cardiologists had a higher certainty that the lesions they're stenting are in fact the ones that caused the acute coronary syndrome (ACS) the patient came in with.

"So it could really improve the interventional management of ACS by a huge amount," Bhatt said. "Obviously, what I just said would need to be tested in prospective randomized trials, but this study sure provides some encouragement for doing those type of trials."

Bhatt also pointed out the sizeable portion of patients in the study who had a noncoronary cause for their ACS.

"I think most cardiologists already know that that occurs, that not all patients that come in with ACS are due to plaque rupture in the coronary arteries," he said. "But still, just to have a way of making that diagnosis somewhat definitely could be really clinically useful, especially as we're talking more and more about other causes of acute coronary syndrome and troponin elevation."

The study shows CMR is quite useful and "if it weren't for cost and logistics, I'd say why not get it just as a matter of routine. But obviously there are cost and logistics issues, so more data are needed to sort out exactly how to integrate MR into ACS treatment equipoise."

Ischemia Testing

Reached for comment, Christopher Kramer, MD, medical director, Cardiovascular Imaging Center, University of Virginia Health System, Charlottesville, said: "It's an important addition to the literature that cardiac MR does well at identifying the real culprit artery. But in terms of, does this really move the needle on management, does this mean that every patient with an NSTEMI is going to get a late gadolinium-enhanced [LGE] cardiac MR. No, I don't think that's the answer here."

He noted that there have been a number of studies in the literature, including meta-analyses, showing that MRI is the right test in patients with normal coronary arteries and that the differential generally includes myocarditis, Takosubo or stress cardiomyopathy, as well as an infarct, in the patient who doesn't have obstructive coronary artery disease (CAD). However, many of the so-called misidentified arteries in the study were in patients with multivessel disease.

"I think MI in normal coronary arteries is an absolutely fabulous indication for cardiac MR," Kramer said. "I think every patient with an MI and normal coronary arteries should have a cardiac MR. No question in my mind about that. As to using LGE to decide which artery to revascularize, that I have an argument with. I think there you need ischemia testing, not just infarct detection."

Given the absence of a "truth standard" for the correct identification of the IRA, it's possible DE-CMR was incorrect in some patients; however, all patients with infarction by DE-CMR showed only a single infarct, the authors note.

Heitner reports no relevant conflicts of interest; senior author Raymond J. Kim is an inventor on a US patent on a delayed-enhancement MRI owned by Northwestern University . Kramer and Bhatt report no relevant conflicts of interest.

Circ Cardiovasc Interv. Published online April 30, 2019. Abstract

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