Stress CMR for CAD Matches Prognostic Utility of More Established Techniques

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Stress cardiac magnetic resonance (CMR) imaging has excellent prognostic utility, according to a study scheduled to be published online May 28, 2013, ahead of print in the Journal of the American College of Cardiology. Patients showing ischemia on the test subsequently experience increased risks of both MI and cardiovascular death.

The findings were previously presented at the 2013 American College of Cardiology Scientific Session/i2 Summit in San Francisco, CA.

Investigators led by Michael Salerno, MD, PhD, of the University of Virginia Health System (Charlottesville, VA), conducted a meta-analysis of 19 studies that reported use of stress CMR imaging to assess myocardial ischemia in 11,636 patients with known or suspected CAD. Adenosine was the stress agent used in 14 of 19 studies, while 4 employed dobutamine and 1 used both.

Negative Test Linked to Low Risk of Future Events

At a mean follow-up of 32 months, patients with ischemia on stress CMR had higher incidences of MI and/or cardiovascular death than patients with a negative study (table 1).

Table 1. Outcomes for Positive vs. Negative Stress CMR

P < 0.00001 for all.

Additionally, patients with a positive stress CMR also had higher annualized event rates than those with negative tests (table 2).

Table 2. Annualized Event Rates

Meta-regression analysis was performed to determine whether any clinical variables were linked to adverse outcomes; only prior MI was associated with an increased incidence of combined cardiovascular outcomes (P < 0.04).

Presence of late gadolinium enhancement (LGE) also was associated with worse prognosis for the combined outcome of cardiovascular death and MI (OR 3.82; 95% CI 2.56 to 5.71; P < 0.00001) and cardiovascular death (OR 2.71; 95% CI 1.66 to 4.41; P < 0.0001), with a trend toward a higher incidence of MI (OR 3.29; 95% CI 0.55 to 19.76; P = 0.19).

Underutilization, Excellent Discriminatory Ability

In an e-mail communication with TCTMD, Dr. Salerno said CMR is currently underutilized for evaluation of CAD due to “limited distribution of the clinical expertise and lack of knowledge of the utility of the technique.” He stressed, however, that among its main advantages is that it can be performed in under an hour, and it provides comprehensive information about heart function and myocardial scarring.

Additionally, he said new advances in CMR are further improving spatial resolution and “significant progress has been made toward providing a quantitative assessment of myocardial perfusion, which can currently only be performed using PET.”

In an editorial accompanying the study, Raymond H. Chan, MD, MPH, and Warren J. Manning, MD, both of Harvard Medical School (Boston, MA), write that CMR provides “a comprehensive cardiovascular evaluation in 1 session previously available only by combining multiple modalities.” They say the test also offers superior spatial resolution in the assessment of ischemia, function, and structure of both ventricles and valves, and it can directly characterize viability of ischemic tissue, thereby providing information as to whether a patient is likely to benefit from catheterization and/or revascularization.

The meta-analysis “supports the excellent discriminatory ability of stress CMR with or without LGE to risk stratify patients with known or suspected CAD,” Drs. Chan and Manning comment.

However, they note that while odds ratios quantify the risks of cumulative events at the end of follow up, there is no indication of how risks may vary over the course of that time frame. It remains to be seen how prognostic information from stress CMR should be used to guide management of CAD patients, “particularly in an era where novel strategies such as FFR-guided revascularization show promise,” they add.

Drs. Chan and Manning also note several limitations of the meta-analysis including:

• Heterogeneity between the study populations
• Variable definitions of positive CMR
• Quantification of ischemia as a dichotomous rather than a continuous variable
• Small number of studies that examined relative incremental predictive value of combinations of parameters obtained during stress CMR
• Limited generalizability of data

For stress CMR or any modality to become a preferred test, it must do more than make a correct diagnosis. Rather, it “needs to accurately identify low risk patients who will not benefit from downstream testing, in effect acting as a ‘gatekeeper’ for other invasive and non-invasive tests and procedures,” Drs. Chan and Manning say. “Furthermore, once negative, repeat testing in the near term should not be required.”

Comparable to Nuclear, Echocardiography Studies

According to Dr. Salerno, the data suggest that stress CMR is at least as accurate, if not more accurate than currently used stress imaging modalities.

“It is comforting to know that even in populations which are intermediate risk for CAD, patients with a normal stress perfusion study and/or lack of myocardial scar by late enhancement imaging have very low risk of cardiac death or myocardial infarction less than 1% per year,” he said. “This is similar to nuclear and echo imaging.”

However, Dr. Salerno concluded that prospective comparative effectiveness studies comparing CMR to other stress modalities will be needed to show that the high diagnostic accuracy and strong prognostic data can impact patient outcomes and provide incremental benefit compared to the more established stress testing modalities.

Study Details

Patients were aged 63 ± 12 years, and 63% were male. The weighted mean LVEF was 61 ± 12%.

Source:

1. Lipinski MJ, McVey CM, Berger JS, et al. Prognostic value of stress cardiac magnetic resonance imaging in patients with known or suspected coronary artery disease: A systematic review and meta-analysis. J Am Coll Cardiol. 2013;Epub ahead of print.
2. Chan RH, Manning WJ. Stress CMR—It’s time to trust the magnetic crystal ball [editorial]. J Am Coll Cardiol. 2013;Epub ahead of print.

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