As soon as the so-called Fractional flow reserve (FFR) measurement of coronary stenoses had established itself as the new standard, it may already be phasing out, at least in the management of stable angina pectoris: A new study shows that a stress-perfusion MRI scans are similarly effective and avoids unnecessary cardiac catheter examinations.
For patients with stable angina pectoris, two diagnostic procedures are available today to find the cause of the symptoms (usually a blocked coronary artery): On the one hand, an invasive cardiac catheter examination can be performed in which the fractional flow reserve (FFR) of narrowed coronary vessels is measured. If this is less than 0.8, revascularization of the corresponding vessel is indicated. An alternative is the stress perfusion MRI, in which the administration of a vasodilator (typically adenosine) triggers a controlled angina pectoris symptomatology.
The simultaneous injection of a contrast agent allows ischemic areas in the heart to be detected. If the ischemic area is at least 6%, coronary angiography is usually indicated. The advantage of MRI is obvious: it is non-invasive and prevents unnecessary cardiac catheterization. However, it is questionable whether dangerous stenoses can be overlooked. A study recently published in the New England Journal of Medicine compared both procedures and provides answers.
A total of 918 patients from 16 centers worldwide suffering from stable angina pectoris participated in the MR-INFORM study. In addition, the subjects had to bring at least two cardiovascular risk factors or alternatively a positive ergometry. Patients with heart failure, cardiac arrhythmias, previous bypass surgery or moderate renal failure were excluded from the study. All study participants were randomized for further diagnosis: One half received a cardiac catheter with FFR diagnosis, the other half underwent a stress perfusion MRI. If a relevant stenosis was detected (FFR < 0.8 or ischemia in at least 6% of the myocardium), coronary angiography was performed with the option of revascularization. Subsequently, all 918 patients were monitored for one year to determine whether the non-invasive MRI diagnosis differed from the invasive FFR diagnosis in terms of the primary outcome (death, myocardial infarction, or cardiac revascularization).
A total of 48.7% of the patients in the MRI group were suspected of having treatment-requiring stenosis, which was confirmed in the subsequent coronary angiography in 40.5% of the patients. In the FFR group, 45.9% of the patients were diagnosed with stenoses requiring treatment - so there was no difference between the two treatment arms (P = 0.11). In the FFR group, however, the stenoses were subsequently revascularized much more frequently, either by percutaneous transluminal coronary angioplasty (PTCA) or bypass surgery (45.0% vs. 35.7%, P = 0.005).
In the one-year follow-up period, 3.6% of patients from the MRI group and 3.7% from the FFR group achieved the primary outcome. Thus, there was approximately the same number of deaths, myocardial infarction, and revascularization in both groups. There were also no differences between the treatment arms (P = 0.21) with regard to the number of patients who were free of any angina pectoris symptoms after 12 months (49.2% in the MRI group and 43.8% in the FFR group).
Data from the MR-INFORM study show that stable angina pectoris can be assessed as well with cardiac stress perfusion MRI as with FFR. The event rates in the one-year follow-up period were identical. This is not really a big surprise: Previous studies have shown that revascularization with stable angina pectoris has no major effect on survival or recurrence of heart attacks.
Therefore, when two compared methods are used to determine an indication for revascularization, similar outcomes can be expected. The important finding of this study lies elsewhere: Compared to the FFR patients, the patients from the MRI group received significantly fewer cardiac catheters (48% vs. 97%) and invasive revascularizations (36% vs. 45%) - with the same clinical outcome. Simply put, this means that expensive cardiac catheter interventions could be avoided in favor of cheaper, non-invasive MRIs. Based on the study results, it is quite possible that cardiac MRI will replace the diagnostic cardiac catheter in the first-line assessment of stable angina pectoris in the future.
Source:
Nagel E et al. Magnetic Resonance Perfusion or Fractional Flow Reserve in Coronary Disease. N Engl J Med 2019; 380:2418-2428. June 20, 2019.