Diagnostic Considerations for FFR and iFR in Severe Aortic Stenosis

Guideline Recommendations and Diagnostic Performance

• The European Society of Cardiology recommends FFR or iFR for intermediate stenoses (40-90% diameter) to guide revascularization decisions, with both indices being Class I, Level A recommendations for assessing hemodynamic significance when non-invasive tests are inconclusive 1
• However, these guideline recommendations were not specifically validated in severe AS populations 1

Comparative Diagnostic Accuracy and Outcome Concerns

• Meta-analyses show a 2% absolute increase in all-cause mortality at 5 years with iFR-guided management compared to FFR, though not specifically in AS populations 1
• This mortality difference was not associated with increased MI or revascularization rates 1
• The iFR has a theoretical advantage of not requiring adenosine, eliminating hyperemic agent contraindications 1

Reliability of Physiology Testing in Severe Aortic Stenosis

Key Physiological Concerns in Severe AS

• Coronary flow reserve (CFR) is reduced in patients with severe aortic stenosis, even with normal coronary arteries, due to myocardial hypertrophy and abnormal microvascular function, according to the American Heart Association 2
• FFR assumptions may be violated in severe aortic stenosis because the calculation assumes constant minimal microvascular resistance during hyperemia, but the condition causes heterogeneous microcirculatory responses, as stated by the American College of Cardiology 2