Study Finds MR Superior to SPECT, But Clinical Role Is “Uncertain” Reply

Authors of a new study published online in the Lancet state that multiparametric cardiovascular magnetic resonance (CMR) is superior to single-photon emission computed tomography (SPECT) in patients with suspected coronary heart disease (CHD). But at least one expert states that the future role of the technique in clinical practice remains “uncertain.”

John Greenwood and colleagues compared the diagnostic accuracy of CMR and SPECT in 752 patients with suspected CHD. All the patients also underwent invasive x-ray angiography. The investigators calculated the sensitivity, specificity, positive predictive value (PPV), and the negative predictive value (NPV) of the two tests.

CMR:

  • sensitivity: 86·5% (CI 81·8–90·1)
  • specificity: 83·4% (79·5–86·7)
  • PPV: 77·2%, (72·1–81·6)
  • NPV: 90·5% (87·1–93·0)

SPECT:

  • sensitivity: 66·5% (CI 60·4–72·1)
  • specificity 82·6% (78·5–86·1)
  • PPV: 71·4% (65·3–76·9)
  • NPV: 79·1% (74·8–82·8)

In comparing the two tests the authors reported a highly significant difference in sensitivity and NPV  (p<0·0001 for both), but the differences were not significant for specificity (p=0·916) and PPV (p=0·061).

The authors conclude that the findings “support the wider adoption of CMR for the diagnosis and management of stable coronary heart disease patients.”

But in an accompanying comment, Robert Bonow writes that the future role of CMR is “uncertain”:

Enhanced diagnostic accuracy of CMR must be balanced against availability and cost-effectiveness, and there is a need for evidence of measurable improvements in patient outcomes. Diagnosis of coronary artery disease alone is not sufficient to determine the need for revascularisation. To show value, advances in imaging must be coupled with enhanced patient well-being or a reduction in unnecessary downstream testing and procedures.

Here is the press release from the Lancet:

Study shows new imaging technique to be superior to standard SPECT scans for diagnosis of coronary artery disease

In recent years, modern imaging tests have replaced exercise treadmill testing to diagnose coronary artery disease, with single-photon emission computed tomography (SPECT) being the most common, although accuracy varies and patients are exposed to ionising radiation. But a study published Online First by The Lancet shows that a more modern method— multiparametric cardiovascular magnetic resonance (CMR)—is superior to SPECT and should be more widely adopted. TheArticle is by Dr John Greenwood, University of Leeds, UK and Leeds General Infirmary, UK and colleagues.

All non-invasive imaging tests have their limitations. For SPECT this includes patient and staff exposure to ionizing radiation and limited spatial resolution of the images. For CMR, the test takes a little longer and some patients who are claustrophobic or have implanted devices (e.g. pacemakers) are not suitable. However, CMR is considered very safe and is becoming more widely available.

In this prospective trial, patients with suspected angina pectoris and at least one cardiovascular risk factor were scheduled for CMR, SPECT, and invasive x-ray coronary angiography. Of the 752 recruited patients, 39% had significant CHD as identified by x-ray angiography. For multiparametric CMR the sensitivity* was 87%, specificity 83%, positive predictive value 77%, and negative predictive value 90%. The sensitivity of SPECT was 66%, specificity 83%, positive predictive value 71%, and negative predictive value 79%. The sensitivity and negative predictive value of CMR and SPECT differed significantly statistically but specificity and positive predictive value did not.

The authors say that the study shows CMR should be included in all evidence-based clinical management guidelines. They conclude: “CE-MARC is the largest, prospective, real world assessment of CMR. The findings of CE-MARC support the wider adoption of CMR for the diagnosis and management of stable coronary heart disease patients, in view of the growing concern of the cancer risk associated with medical-source ionising radiation.”

In a linked Comment, Dr Robert O BonowCenter for Cardiovascular Innovation, Northwestern University Feinberg School of Medicine, Chicago, IL, USA, says: “Enhanced diagnostic accuracy of CMR must be balanced against availability and cost-effectiveness, and there is a need for evidence of measurable improvements in patient outcomes.”

He concludes: “The explosive growth of cardiovascular technology in the second half of the 20th century coincided with a remarkable decrease in coronary mortality in the same period. However, whether diagnostic imaging had a role in these improved outcomes is unclear. What is clear is that use of imaging has increased more rapidly than any other component of medical care. Research is now sorely needed to show that the appropriate use of these resources can further improve patient outcomes.”

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