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Cardiac MRI is more accurate at confirming or ruling out coronary heart disease than stress myocardial perfusion imaging with single-photon emission CT (SPECT), researchers found in a prospective real-world trial.

Sensitivity was significantly better with cardiac MRI than with SPECT at 86.5% versus 66.5% (P<0.0001), John P. Greenwood, PhD, of the University of Leeds, England, and colleagues reported online in The Lancet.

The same was true for negative predictive value at 90.5% with the magnetic resonance technique compared with 79.1% with SPECT (P<0.0001) in the study comparing these imaging methods against gold standard x-ray coronary angiography.

The SPECT approach has become the most widely used test for assessing myocardial ischemia but has some drawbacks, including exposure to ionizing radiation, the researchers pointed out.

"These findings support the wider adoption of cardiovascular magnetic resonance for coronary heart disease diagnosis and its inclusion in evidence-based clinical management guidelines," they argued in the paper.

But not so fast, countered Robert O. Bonow, MD, of Northwestern University in Chicago, in an accompanying commentary.

Better diagnostic accuracy has to be balanced against cost and availability issues with cardiac MRI, he noted.

Moreover, it remains to be seen whether more accurate diagnosis actually improves patient outcomes, Bonow added.

"Diagnosis of coronary artery disease alone is not sufficient to determine the need for revascularization," he wrote. "To show value, advances in imaging must be coupled with enhanced patient well-being or a reduction in unnecessary downstream testing and procedures."

The Clinical Evaluation of MAgnetic Resonance imaging in Coronary heart disease (CE-MARC) study included 752 patients with suspected angina pectoris and at least one cardiovascular risk factor who agreed to get all three diagnostic tests:

• Cardiac MRI, which included rest and adenosine stress perfusion, cine imaging, late gadolinium enhancement
• SPECT imaging, which included gated adenosine stress and rest using 99mTc tetrofosmin
• Invasive x-ray coronary angiography

Overall, 39% of the patients showed significant coronary heart disease on angiography.

Unlike sensitivity and negative predictive value, other measures of diagnostic accuracy didn't differ significantly between the noninvasive imaging methods, though numerically higher with cardiac MRI.

Specificity was 83.4% with cardiac MRI compared with 82.6% with SPECT (P=0.916).

Positive predictive value was 77.2% with cardiac MRI versus 71.4% with SPECT (P=0.061).

Even when leaving the coronary artery MR images out of the picture, the other MR imaging parameters still yielded significantly better sensitivity and negative predictive value (both P<0.0001), and the difference in positive predictive value became significant compared with SPECT (P=0.01), likely because of a reduction in false positives, according to the researchers.

"Because coronary angiography using cardiovascular magnetic resonance is neither universally available nor feasible for all patients, it is noteworthy that the relative diagnostic accuracy of [cardiac MRI] was not diminished when the noninvasive coronary angiographic data were eliminated from the analysis," Bonow noted in the commentary.

The advantage of stress perfusion cardiac MRI was seen in diagnosing both single and multivessel coronary artery disease compared with SPECT, with area under the curve values of 0.87 versus 0.71 and 0.91 versus 0.77 (P<0.0001 for both).

Greenwood's group cautioned that their comparison results need to be "considered in the context of published SPECT data, which are heterogeneous for population, radioisotope tracer, mode of stress, and protocol."

Also, the study design with patients prospectively recruited before any other imaging and getting angiography regardless of clinical intention may have boosted the number of false negatives for both noninvasive imaging methods, though arguably more realistic.

Limitations also included a possible lack of generalizability from the homogeneous group of white Northern Europeans without prior bypass surgery studied and that all patients were seen at a single center with high cardiac MRI and SPECT imaging volume.

From the American Heart Association: