Hot Line - Improving selection of patients for invasive coronary testing

In patients with suspected coronary artery disease (CAD) at coronary computed tomography angiography (CTA), ESC guidelines recommend verification of myocardial ischaemia by myocardial perfusion imaging (MPI) prior to the use of invasive coronary angiography (ICA),¹ which should reduce patient risk and treatment costs. However, the most effective MPI technique to use in this setting has yet to be established.

In a Hot Line session yesterday, Professor Morten Bottcher (Aarhus University - Aarhus, Denmark) presented results from the Dan-NICAD 2 trial, directly comparing the diagnostic performances of 3T cardiac magnetic resonance (CMR) and ⁸²Rubidium positron emission tomography (Rb-PET) in patients with suspected obstructive stenosis at coronary CTA.

In the trial, patients with CTA stenosis suggestive of obstructive CAD (>50% diameter in vessels >2 mm diameter) received both adenosine-stress CMR and Rb-PET, and subsequently underwent ICA fractional flow reserve (ICA-FFR). Haemodynamically obstructive CAD was defined as ICA with FFR ≤0.80 or >90% diameter stenosis by visual assessment. Among 1,732 consecutive patients (mean age 59 years, 57% men), 445 (26%) had suspected stenosis on coronary CTA and 372 of these completed both CMR and Rb-PET. ICA-FFR-determined haemodynamically obstructive CAD was identified in 44.1% of these patients.

There was no difference between the sensitivities for CMR (59%; 95% CI 51 to 67) and Rb-PET (64%; 95% CI 56 to 71) (p=0.21) nor between the specificities (84%; 95% CI 78 to 89 and 89%; 95% CI 84 to 93, respectively; p=0.08).

The positive predictive value (CMR 76% versus Rb-PET 79%) and negative predictive value (CMR 73% versus Rb-PET 75%) were similar for the two techniques. Overall accuracy was slightly higher for Rb-PET compared with CMR (78% versus 73%, respectively; p=0.03). Classification of patients with high-risk disease (left main or three-vessel disease) as abnormal was achieved more frequently with Rb-PET (30/31, 96.8%) than with CMR (24/31, 77.4%) (p=0.03). Both modalities had high sensitivity for severe stenoses with >70% diameter stenosis: CMR 83% (95% CI 72 to 91) and Rb-PET 89% (95% CI 79 to 95).

Commenting on the results, Prof. Bottcher says, “Less than half of the patients (44%) with suspected CAD on coronary CTA had obstructive CAD confirmed with ICA-FFR. CMR stress and PET stress had comparably moderate sensitivities and high specificities to predict the FFR results. A perfusion test approach therefore seems safe as almost all patients with serious disease (high-grade stenoses, left main and three-vessel disease) were diagnosed. But the modest sensitivities to predict low FFR mean that there was often a discrepancy between these advanced perfusion results and the invasive FFR.”

He concludes, “The accuracy of coronary CTA needs to improve so that more patients without obstructive CAD avoid further investigations. This might be achieved through better CT image quality and perhaps by more advanced image analyses like non-invasive FFR estimation and photon counting systems. Perfusion techniques could also be improved, for example by using quantitative measurements of perfusion with CMR or ¹⁵O-water PET systems.”