Increased dose of adenosine and the relationship between the resting full-cycle ratio and fractional flow reserve

Intermediate coronary artery stenosis can be evaluated with fractional flow reserve (FFR) and resting full-cycle ratio (RFR) to determine if the stenosis is functionally significant. However, RFR and FFR have shown discordance in around 20% of examinations. One explanation could be that maximal hyperemia was not achieved during adenosine infusion. The aim was to investigate if increased doses of adenosine would reduce FFR further, and if the agreement between RFR and FFR would improve.

Two hundred patients underwent physiological assessment of an intermediate stenosis with RFR and FFR at 140 µg/kg/min (FFR₁₄₀) and 200 µg/kg/min (FFR₂₀₀) of adenosine infusion. The microcirculation function was assessed using the index of microvascular resistance (IMR).

Median RFR was 0.89 (interquartile range [IQR] 0.85-0.93). Median FFR decreased significantly during increased adenosine doses: FFR₁₄₀ = 0.85 (IQR 0.77-0.90) versus FFR₂₀₀ = 0.82 (IQR 0.75-0.87), p < 0.001. Reduction in FFR during increased adenosine doses was higher in patients with IMR ≥ 24 (FFR₁₄₀ 0.85 [IQR 0.78-0.92] versus FFR₂₀₀ 0.82 [IQR 0.75-0.86], p < 0.001) compared to patients with IMR < 24 (FFR₁₄₀ 0.83 [IQR 0.77-0.89] versus FFR₂₀₀ 0.81 [IQR 0.75-0.87], p < 0.001) with an absolute difference of -0.03 (-0.05, -0.01) versus -0.01 (-0.02, 0.0), p < 0.001. Area under the curve (AUC) of RFR compared to FFR₁₄₀ was 0.88 (95 % confidence interval [CI] 0.84-0.93), and for FFR_200, AUC was 0.88 (CI: 0.84-0.93).

Increased doses of adenosine significantly reduced FFR values, whereas the correlation agreement between RFR and FFR was not improved.