Background—Small drifts in intracoronary pressure measurements (±2 mmHg) can affect stenosis categorization using
pressure indices. This has not previously been assessed for fractional flow reserve (FFR), instantaneous wave-free ratio
(iFR), and whole-cycle distal pressure/proximal pressure (Pd/Pa) indices.
Methods and Results—Four hundred forty seven stenoses were assessed with FFR, iFR, and whole-cycle Pd/Pa. Cut point
values for significance were predefined as ≤0.8, <0.90, and <0.93, respectively. Pressure wire drift was simulated by
offsetting the distal coronary pressure trace by ±2 mmHg. FFR, iFR, and whole-cycle Pd/Pa indices were recalculated
and stenosis misclassification quantified. Median (±median absolute deviation) values for FFR, iFR, and whole-cycle Pd/
Pa were 0.81 (±0.11), 0.90 (±0.07), and 0.93 (±0.06), respectively. 34.6% (155), 50.1% (224), and 62.2% (278) of values
lay within ±0.05 U of the cut point for FFR, iFR, and whole-cycle Pd/Pa, respectively. With ±2 mmHg pressure wire drift,
21% (94), 25% (110), and 33% (148) of the study population were misclassified with FFR, iFR, and whole-cycle Pd/Pa,
respectively. Both FFR and iFR had significantly lower misclassification than whole-cycle Pd/Pa (P<0.001). There was
no statistically significant difference between the diagnostic performance of FFR and iFR (P=0.125).
Conclusions—In a substantial proportion of cases, small amounts of pressure wire drift are enough to cause
stenoses to change classification. Whole-cycle Pd/Pa is more vulnerable to such reclassification than FFR and iFR.