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

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

• A. iFR uses rest without pharmacologic vasodilation; FFR uses hyperemia.
• B. FFR uses rest without pharmacologic vasodilation; iFR uses pharmacologic hyperemia.
• C. iFR uses hyperemia; FFR uses rest.
• D. They are identical in measurement approach.

Answer: (A)

Instantaneous wave-free ratio (iFR) is measured at rest, during a specific wave-free period in diastole when microvascular resistance is naturally low and stable, so no pharmacologic vasodilator is used. Invasive FFR, on the other hand, requires inducing maximal hyperemia with a vasodilator (such as adenosine) to minimize and standardize microvascular resistance, which allows the pressure drop across a stenosis to reflect its true impact under those hyperemic conditions. In other words, iFR compares distal and proximal pressures at rest without vasodilators, while FFR compares them during maximal hyperemia. This distinction is why iFR is described as resting and hyperemia-free, whereas FFR relies on hyperemia to unmask the stenosis’s effect.

Instantaneous wave-free ratio (iFR) is measured at rest, during a specific wave-free period in diastole when microvascular resistance is naturally low and stable, so no pharmacologic vasodilator is used. Invasive FFR, on the other hand, requires inducing maximal hyperemia with a vasodilator (such as adenosine) to minimize and standardize microvascular resistance, which allows the pressure drop across a stenosis to reflect its true impact under those hyperemic conditions. In other words, iFR compares distal and proximal pressures at rest without vasodilators, while FFR compares them during maximal hyperemia. This distinction is why iFR is described as resting and hyperemia-free, whereas FFR relies on hyperemia to unmask the stenosis’s effect.