CMR is superior to SPECT for CAD detection

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Perfusion-cardiac MR (CMR) is a valuable alternative to SPECT for coronary artery disease (CAD) detection showing equal performance in the head-to-head comparison, according to a MR-IMPACT trial published in the February issue of the European Heart Journal.

Juerg Schwitter, MD, of the division of cardiology at the University Hospital Zurich in Germany, and colleagues set out to determine in a multicentre, multivendor trial the diagnostic performance for perfusion-CMR in comparison with coronary x-ray angiography (CXA) and SPECT.

The investigators conducted the double-blind, randomized, phase II clinical trial at 18 centers in Europe and the United States.

Of the 241 patients enrolled during 12 months, 234 entered the safety analysis (patients dosed), and evaluable CXA and correctly performed perfusion-CMR studies were available in 228 patients, the authors wrote. Since three patients had no SPECT study, 225 patients were available for the perfusion-CMR vs. SPECT comparison.

The researchers said that CAD was defined as diameter stenosis ≥50 percent on quantitative CXA. Five CMR and eight SPECT studies (of 225 complete studies) were excluded from analyses due to inadequate quality (three blinded readers scored per modality).

The comparison of CMR vs. SPECT was based on receiver operating characteristic (ROC) analysis, the authors said. Perfusion-CMR at the optimal CM dose (0.1 mmol/kg) had similar performance as SPECT, if only the SPECT studies of the 42 patients with this dose were considered [area under ROC curve (AUC): 0.86 ± 0.06 vs. 0.75 ± 0.09 for SPECT]. However, the researchers found that diagnostic performance of perfusion-CMR was better vs. the entire SPECT population of 212 patients (AUC: 0.67 ± 0.05).

In their discussion, the authors noted that early detection of myocardial perfusion abnormalities is crucial for an optimal management of patients with suspected CAD and could potentially reduce the rate of fatal myocardial infarctions. In this trial, a high diagnostic performance of perfusion-CMR for the detection of CAD in ≥2 mm coronary vessels was found at a CM dose of 0.1 mmol/kg, which was equal to SPECT in the head-to-head comparison. At this CM dose, the diagnostic performance of perfusion-CMR was superior vs. SPECT imaging when comparing with all 212 SPECT studies, i.e. gated and ungated SPECT combined, according to Schwitter and colleagues.

MR-IMPACT is the largest multi-center perfusion-CMR study performed so far, and even more important, it also evaluates its test performance in a multi-vendor design, which is expected to reflect true diagnostic performance of widely applied perfusion-CMR more appropriately than single centre, single vendor studies, the authors wrote.

For their limitations, the investigators noted that gated-SPECT was not available in approximately half of patients, and perfusion-CMR did not outperform gated-SPECT with regard to CAD detection.

Overall, Schwitter and colleagues found that comparing perfusion-CMR with the entire SPECT population suggests CMR superiority over SPECT, which warrants further evaluation in larger trials.