Comparing Diastolic Hyperemia-Free Ratio (DFR) and Instantaneous Wave-Free Ratio (iFR) in Cardiac Catheterization

The main difference between Diastolic Hyperemia-Free Ratio (DFR) and Instantaneous Wave-Free Ratio (iFR) in cardiac catheterization relates to how they measure coronary artery pressure gradients:

Instantaneous Wave-Free Ratio (iFR)
iFR isolates a specific period in diastole called the “wave-free period” to measure pressure gradients:

• Measures the ratio of distal coronary pressure to aortic pressure during the wave-free period in diastole
• During this period, competing forces affecting coronary flow are quiescent
• Pressure and flow are considered to be linearly related during this time
• Does not require administration of vasodilators like adenosine

Diastolic Hyperemia-Free Ratio (DFR)
DFR measures pressure gradients throughout the entire diastolic period:

• Calculates the ratio of distal coronary to aortic pressure over the full diastolic phase
• Does not isolate a specific “wave-free” period
• Also does not require vasodilator administration

The key distinction is that iFR focuses on a particular wave-free window in diastole, while DFR considers the entire diastolic period.

Similarities
Both iFR and DFR:

• Are resting indices that do not require pharmacological vasodilation
• Aim to assess the hemodynamic significance of coronary artery stenoses
• Can be used to guide decisions about coronary revascularization
• Have shown similar diagnostic accuracy compared to Fractional Flow Reserve (FFR) in clinical studies

Recent research suggests DFR and iFR may provide numerically similar results in practice. Both offer potential advantages over FFR by avoiding the need for adenosine administration, which can cause patient discomfort and prolong procedure times.

In summary, while iFR and DFR use slightly different measurement approaches, they represent similar efforts to assess coronary physiology without inducing hyperemia, providing alternatives to traditional FFR for evaluating the functional significance of coronary artery lesions during cardiac catheterization.

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