The purpose of this study is to determine the diagnostic performances of iodine contrast medium and resting conditions to predict fractional flow reserve (FFR). Reference FFR will be measured using standard adenosine. We hypothesize that contrast FFR will offer superior diagnostic agreement compared to resting conditions.

We are conducting a diagnostic accuracy study. The reference standard is adenosine-derived FFR. The diagnostic tests undergoing evaluation are resting conditions and hyperemia induced by intracoronary injection of contrast medium. While all these tests give a continuous result, we will apply binary cutoffs for comparison to FFR≤0.8 as the reference standard. Subjects will be selected prospectively from consecutive patients undergoing FFR assessment for standard clinical indications. The paired comparative design means that each patient will undergo resting (baseline), post-contrast, and adenosine-derived measurements. To enhance test integrity, all pressure recordings will be analyzed in a central physiology core laboratory blinded to clinical data and recruiting site.

Inclusion Criteria:

• Age 18 years or older.
• Undergoing FFR assessment for standard clinical indications.
• Ability to understand and willingness to sign a written informed consent.

Exclusion Criteria:

• Prior coronary artery bypass grafting (CABG).
• Extremely tortuous or calcified coronary arteries precluding intracoronary physiologic measurements. Operators may exclude subtotal or similar high-grade lesions, which in their judgment may be threatened by pressure wire placement.
• Known severe left ventricular hypertrophy (septal wall thickness at echocardiography of >13 mm).
• Inability to receive adenosine (for example, severe reactive airway disease, marked hypotension, or advanced atrioventricular block without pacemaker).
• Recent (within 3 weeks prior to cardiac catheterization) ST-segment elevation myocardial infarction (STEMI) in any arterial distribution (not specifically target lesion).
• Culprit lesions (based on clinical judgment of the operator) for either STEMI or non-STEMI cannot be included.
• Severe cardiomyopathy (ejection fraction <30%).
• Renal insufficiency such that an additional 12 to 20 mL of contrast would, in the opinion of the operator, pose unwarranted risk to the patient.

Patients undergoing FFR assessment for standard clinical indications