How does invasive FFR differ from instantaneous wave-free ratio (iFR)?

How does invasive FFR differ from instantaneous wave-free ratio (iFR)?

• A. FFR uses pharmacologic hyperemia to measure pressure during maximal hyperemia; iFR measures pressure ratio at rest without hyperemia.
• B. They are identical in measurement approach.
• C. FFR uses rest without hyperemia; iFR uses pharmacologic hyperemia.
• D. iFR uses hyperemia; FFR uses rest.

Answer: (A)

Invasive FFR and iFR both assess whether a coronary narrowing significantly limits blood flow, but they handle the resistance of the microcirculation differently. FFR relies on pharmacologic hyperemia to create maximal vasodilation, which lowers microvascular resistance and reveals how much pressure is dropped across the lesion when blood flow demand is high. This means the distal-to-proximal pressure ratio is measured during maximal hyperemia and used to gauge physiological significance. iFR, on the other hand, measures during rest, exploiting a natural period in diastole when microvascular resistance is relatively constant and low—the wave-free period—so no vasodilator is used. The pressure ratio is taken during that rest window to estimate the impact of the stenosis without inducing hyperemia. That difference is what makes the statement about using pharmacologic hyperemia for FFR and measuring at rest without hyperemia for iFR the best answer. The other options either imply identical measurement approaches or invert which method uses hyperemia.

Invasive FFR and iFR both assess whether a coronary narrowing significantly limits blood flow, but they handle the resistance of the microcirculation differently. FFR relies on pharmacologic hyperemia to create maximal vasodilation, which lowers microvascular resistance and reveals how much pressure is dropped across the lesion when blood flow demand is high. This means the distal-to-proximal pressure ratio is measured during maximal hyperemia and used to gauge physiological significance.

iFR, on the other hand, measures during rest, exploiting a natural period in diastole when microvascular resistance is relatively constant and low—the wave-free period—so no vasodilator is used. The pressure ratio is taken during that rest window to estimate the impact of the stenosis without inducing hyperemia.

That difference is what makes the statement about using pharmacologic hyperemia for FFR and measuring at rest without hyperemia for iFR the best answer. The other options either imply identical measurement approaches or invert which method uses hyperemia.