Timing of Hyperemia in IMR Testing with Acetylcholine

Standardized Protocol Sequence

• The European Society of Cardiology recommends performing ACh testing first with incremental doses to assess endothelium-dependent vasodilation and test for vasospasm 1, 2, 3
• The administration of ACh should be stopped immediately if coronary vasospasm is induced at any dose, and continuous Doppler flow monitoring, 12-lead ECG, and symptom monitoring should occur throughout 1, 2, 3
• The European Society of Cardiology suggests administering intracoronary nitroglycerine after completing ACh testing to reverse any vasospastic effects and allow assessment of endothelium-independent epicardial coronary vasodilation 1, 2, 3, 4
• Hyperemia induction for IMR measurement should be performed at the end of the procedure using adenosine, which induces maximal hyperemia for measuring IMR and CFR 1, 2, 3, 4, 5

Critical Rationale for This Sequence

• The European Society of Cardiology states that ACh is an endothelium-dependent vasodilator that tests for vasospasm and endothelial dysfunction, while adenosine is an endothelium-independent vasodilator that induces maximal hyperemia for structural microvascular assessment 1, 2, 3, 4, 6, 7

Alternative Hyperemic Agent

• If adenosine is contraindicated, the European Society of Cardiology recommends using papaverine for hyperemia induction, though it carries risk of polymorphic ventricular tachycardia requiring precautionary measures 2, 4