Courtesy of Dr. Guillermo Migliaro.

Fractional flow reserve (FFR) is the radio of two flows expressed as the ratio of two pressures ─ distal pressure across stenosis (Pd) to aortic pressure (pa) ─ obtained only under maximal coronary hyperemia, which is a state of drug induced maximal vasodilation.

The gold standard to create maximal hyperemia is intravenous adenosine administration which, because of time and cost constraints, has been replaced by intracoronary adenosine administration. However, the presence of adverse events associated to the administration of adenosine, or other vasodilators, has led to the introduction of other indices that do not require the administration of any drugs, such as the instant wave-free ratio (iFR).

iFR measures coronary pressure during diastole, namely 25% after the dicrotic notch on the aortic tracing until 5 milliseconds before systole.  During this period, microvascular resistance is minimal and constant (a similar state to that of hyperemia), similar to that obtained with resting Pd/Pa, and in linear correlation with FFR.

On the other hand, previous studies showed that conventional contrast media, routinely used for angiographies and FFR, is able to induce hyperemia, although inferior to adenosine induced hyperemia.

The RINASCI study, which included 80 patients with 104 intermediate lesions, showed FFR measured after the first 10 seconds of radiographic contrast medium administration (cFFR) has a close correlation with FFR, and is superior to both iFR and resting Pd/Pa in predicting FFR.

The MEMENTO study was a multicenter retrospective pooled analysis of the accuracy of cFFR in predicting FFR at large scale in the real world in lesions requiring invasive functional assessment.

It included 1,026 coronary stenoses from 10 centers in 4 European countries.

Resting Pd/Pa and cFFR were significantly higher than FFR (0.93±0.05 vs 0.87±0.08 vs 0.84±0.08; p<0.001). There was strong correlation and close agreement between cFFR and FFR (r=0.90, p<001 and 95% CI of disagreement from -0.042 to 0.11). ROC curve analyzis showed excellent accuracy (89%) for a cFFR cutoff value of 0.85 to predict FFR value ≤ 0.80, area under the curve 0.90 (95% CI 0.94-0.96), significantly better than the one observed for resting Pd/Pa.

Conclusion

The study concludes that cFFR accurately predicts the functional significance of stenoses. This could help avoid or limit adenosine administration in most lesions and, therefore, save time and money.

The study proposes a diagnostic algorithm to intervene lesions presenting cFFR ≤ 0.83 and differ those presenting cFFR ≥ 0.89. With cFFR between 0.84 and 0.88, we should retest with FFR and adenosine.

Editorial Comment

As limitations, note that the study leaves lesion selection to the operator’s criterion, without defining inclusion criteria. There was not standard protocol to obtain hyperemia (neither the dosage nor the adenosine administration route were defined).

It remains unclear whether hyperemia could vary according to the different contrast media involved, ionic vs. non-ionic, or with the same media osmolality. iFR was not compared against cFFR.

However, this is a very interesting study presenting conclusions that could change, and even simplify, our daily practice.

Courtesy of Dr. Guillermo Migliaro. German Hospital, Buenos Aires, Argentina.

Original Title: The Multicenter Evaluation of the Accuracy of the Contrast Medium Induced Pd/pa Ratio in Predicting FFR (MEMENTO-FFR) study.

Reference: Leone A et al. Eurointervention 2016;12:708-715

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