Impact of Right Atrial Pressure on Fractional Flow Reserve Measurements: Comparison of Fractional Flow Reserve and Myocardial Fractional Flow Reserve in 1,600 Coronary Stenoses.

Objectives: This study sought to assess the impact of a wide range of mean right atrial pressure (Pra) on fractional flow reserve (FFR) measurements.

Background: FFR invasively assesses the ischemic potential of coronary stenoses. FFR is calculated as the ratio of mean distal coronary pressure (Pd) to mean aortic pressure (Pa) during maximal hyperemia. The Pra is considered to have little impact if it is within normal range, so it is neglected in the formula.

Methods: In 1,676 stenoses of 1,235 patients undergoing left-right heart catheterization for ischemic (642 [52%]) or valvular heart disease (593 [48%]), the authors compared the FFR values calculated without accounting for Pra (FFR= Pd/Pa) to the corresponding myocardial fractional flow reserve (FFRmyo) values accounting for Pra (FFRmyo = Pd - Pra/Pa - Pra).

Results: The median Pra was 7 (interquartile range [IQR]: 5 to 10) mm Hg with a maximum of 27 mm Hg. The correlation and agreement between FFR and FFRmyo was excellent (R(2) = 0.987; slope 1.096 ± 0.003). The median FFR (0.85; IQR: 0.78 to 0.91) was slightly but statistically significantly higher than the median FFRmyo (0.83; IQR: 0.76 to 0.90; p < 0.001) with a median difference of 0.01 (IQR: 0.01 to 0.02). Values of FFR above the cutoff of 0.80 provided an FFRmyo ≤0.80 in 110 (9%) stenoses. No FFR value above 0.80 provided an FFRmyo ≤0.75.

Conclusions: The difference between FFR and FFRmyo was minimal even in patients with markedly increased Pra. FFR values above the gray zone (i.e., >0.80) did not yield values below the gray zone (i.e., ≤0.75) in any case, which suggests that the impact of right atrial pressure on FFR measurement is indeed negligible.