Download this article's Factoid (PDF & PPT for Gold Subscribers)

Cardiac magnetic resonance (CMR) imaging may provide valuable prognostic information in patients with coronary artery disease (CAD), according to a literature review published online January 29, 2014, ahead of print in the Journal of the American College of Cardiology. However, the CMR features that predict future events vary with patients’ CAD status.

Drawing on databases through February 25, 2013, investigators led by Hamza El Aidi, MD, of University Medical Center Utrecht (Utrecht, The Netherlands), evaluated the association between CMR findings and hard outcomes (all-cause mortality, cardiac death, cardiac transplantation, and/or MI) or MACE (as defined by the individual trials) in 27 studies of patients with a recent (within 2 weeks) MI and 29 studies of patients with suspected or known CAD (total n = 25,497).

Predictors Differ Based on CAD Status

In the recent MI category, no inference could be drawn about the prognostic value of CMR findings for hard events because the 5 studies (n = 1,223) that looked at those endpoints did not meet the authors’ criteria for significance. In the 27 studies (n = 5,057) that looked at the link between CMR findings and MACE, LVEF was an independent predictor in multivariable analysis in more than half of the studies (adjusted HR range: 1.03-1.05 per 1% LVEF decrease). There was insufficient evidence to determine whether microvascular obstruction and infarct size were also independent CMR predictors.

As for patients with suspected or known CAD, 24 studies (n = 18,212) evaluated the association between CMR findings and hard events. Of the CMR findings assessed in the required number of patients and studies, the following parameters were important independent predictors:

• Inducible wall motion abnormality (adjusted HR range: 1.87-2.99)
• Inducible perfusion defects (adjusted HR range: 3.02-3.77)
• LVEF (adjusted HR range: 0.72-0.82 per 10% increase)
• Presence of infarct (adjusted HR range: 2.82-9.43)

For both inducible wall motion abnormality and inducible perfusion defects, the risk of a hard event increased with the number of segments involved.

Of the 18 studies (n = 12,847) that evaluated the prognostic value of CMR features for MACE (n = 1,859) and met the threshold for significance, the following were independent predictors:

• Inducible perfusion defects (adjusted HR range: 1.76-3.21)
• Presence or extent of infarct size (adjusted HR range: 1.04-5.98)

Did Revascularization Skew Findings?

The authors acknowledge that in practice CMR exams are performed primarily to guide clinical decision-making and not to assess future risk. “If a patient is found to have abnormal perfusion or wall motion abnormalities, physicians will generally refer them for revascularization,” they note, adding that this practice may have affected subsequent patient outcomes and thus assessment of prognostic value.

In a telephone interview with TCTMD, Victor A. Ferrari, MD, of the Penn Heart and Vascular Center (Philadelphia, PA), said the study’s inclusion of over 25,000 patients “speaks to the fact that we are gaining momentum in the effort to determine the specific prognostic value of CMR.”

In particular, the study underscores that LVEF “continues to maintain its importance as a prognostic indicator despite variability due to loading conditions and inotropic states,” he noted. The ability of CMR to measure LVEF and its changes over time more accurately and reproducibly than other imaging techniques “gives us more confidence going forward,” Dr. Ferrari added.

Reason for Greater Impact of Perfusion Abnormality Unclear

In an accompanying editorial, Ilan Gottlieb, MD, PhD, and Gabriel Camargo, MD, both of the National Institute of Cardiology (Rio de Janeiro, Brazil), say an important message of the study is that perfusion abnormalities appear to have greater prognostic impact than wall motion abnormality, although the reason for this is unclear and deserves further investigation.

Dr. Ferrari conjectured that because wall motion may be due to mechanical impairment, when infarcted tissue tethers normal tissue its prognostic import may be overestimated in some studies.

The paper also confirms the strong predictive power of CMR late gadolinium enhancement (LGE), which assesses myocardial necrosis and fibrosis, Drs. Gottlieb and Camargo write. Determination of scar burden is important in assessing whether patients are likely to experience arrhythmias and how best to treat them, Dr. Ferrari added.

Recent-MI Results ‘Confusing’

Drs. Gottlieb and Camargo call the findings regarding recent-MI patients confusing. “Theoretically, infarct size (as seen by CMR LGE) should be [more closely] related to prognosis than acute LVEF,” they say, but the current study finds that LVEF is a multivariable predictor of outcomes while infarct size is not. In fact, CMR provided no prognostic information regarding future hard events in these patients, “which is very unlikely, both due to physiological reasons, and also given that there is ample evidence that LVEF measured by echocardiography is related to hard events in the [ACS] setting,” they point out, adding that the reason may be the investigators’ “somewhat arbitrary” standard for sufficient evidence from which to draw conclusions.

This discordance “brings into the light the urgent need of CMR studies in the acute MI setting. It would also be interesting to understand how all CMR variables combined interact with the prognostic models, especially using individual patient data meta-analyses,” the editorial concludes.

Dr. Ferrari cited CMR’s ability to detect smaller degrees of subendocardial ischemia and clinically unrecognized infarction in diabetic patients as additional areas in which clinicians may profit from employing the modality by prescribing more aggressive treatment.

“The take-home message is that we don’t yet have a large enough body of data to adjudicate some of the parameters that CMR provides,” he said, noting that head-to-head comparisons with other techniques are required to ensure that CMR provides incremental prognostic information in a cost-effective manner.

Study Details

The number of patients in the underlying studies ranged from 44 and 2,194, with a mean age ranging from 52 to 67 years and a follow-up duration between 6 and 74 months.

Individual CMR results were considered independent prognostic findings when they were assessed in at least 3 studies that included a summed total of more than 1,000 patients.

 

---

Sources:
1. El Aidi H, Adams A, Moons KGM, et al. Cardiac magnetic resonance imaging findings and the risk of cardiovascular events in patients with recent myocardial infarction or suspected or known coronary artery disease: A systematic review of prognostic studies. J Am Coll Cardiol. 2014;Epub ahead of print.

2. Gottlieb I, Camargo G. Is cardiac magnetic resonance one of cardiology’s magic crystal balls? J Am Coll Cardiol. 2014;Epub ahead of print.

 

 

Related Stories:

• Early Data Show Clinical Value of Cardiac MR Imaging
• New AHA Guidelines for Noninvasive CT and MR Coronary Angiography
• Mixed IMPACT for Cardiac MRI: More Sensitive Than SPECT, But Less Specific