Reassessment of myocardIAL Bridge TOwards PeRsOnalized Medicine: RIALTO PRO

TRIAL PROCEDURES Once MB is angiographically detected, eligible and consenting patients will be randomly assigned in a 1:1 ratio to receive a "standard approach" or a "full-physiology approach" during index CA.

Index coronary angiography Coronary angiography will be performed through a radial or femoral approach. Unfractionated heparin (initial weight-adjusted intravenous bolus of 50-70 IU/kg, with repeat boluses to achieve an activated clotting time ∼250) will be administered in all patients. To fully expose all segments of the coronary arteries, at least 2 perpendicular projections for the right coronary artery (RCA) and 4 projections for the LAD will be taken. Intracoronary nitrates can be used (depending on blood pressure and, in any case, at the discretion of the Investigator) to increase the angiographic sensitivity in detecting the "milking effect".

Physiological epicardial and microvascular assessment MB hemodynamic assessment will be performed using a diagnostic guidewire placed in the index vessel. Intravenous heparin (50-70 U/kg) should be administered to achieve therapeutic anticoagulation (activated clotting time ∼250 s). The innovative Abbott PressureWire™ X Guidewire will be used to measure pressure and temperature. The guidewire's wireless measurements are connected to an advanced platform (Coroventis‡ CoroFlow‡ Cardiovascular System) to measure physiological indices. Abbott's PressureWire™ X Guidewire and Coroventis‡ CoroFlow‡ Cardiovascular System are, nowadays, the only solution for the cath lab able to assess both epicardial vessel (i.e., FFR< 0.80) and microcirculation (i.e., CFR< 2.0 and IMR≥ 25).

Epicardial assessment will include:

• Resting Pd/Pa (n.v. > 0.92)
• FFR after intravenous adenosine administration (n.v. > 0.80)
• RFR (n.v. > 0.89)
• FFR after intravenous dobutamine administration (n.v. > 0.75) FFR is defined as the mean distal pressure (Pd)/mean aortic pressure (Pa) across MB during maximal hyperemia, achieved by administration of intravenous (140 μg/kg/min) or intracoronary bolus (up to 200 µg) of adenosine. Pd/Pa was automatically calculated by current computational software as the ratio found in the pressure recording. A cut-off of 0.80 will be used to detect hemodynamic relevance. Inotropic stimulation to exalt the hemodynamic significance of MB will be performed with intravenous dobutamine infusion, in case of a negative functional assessment (Pd/Pa> 0.92, FFR> 0.80, RFR> 0.89). The infusion will be started at 5 μg/kg/min and increased by 5μg/kg/min every 5 minutes up to 20 μg/kg/min or until the patient develops symptoms or clear evidence of ischemia. An intravenous infusion of 1 mg atropine will be administered if the patient will not experience symptoms or signs of myocardial ischemia with 20 μg/kg/min of dobutamine infusion. An intravenous bolus of β-blocker (i.e., metoprolol 5 mg) will be administered at the end of the procedure to antagonize the effects of dobutamine.