In this segment of the 'Cath Lab Guide to Coronary Reactivity Testing', Dr Robert Jay Widmer (The McKinney Heart Hospital, US) demonstrates an intracoronary acetylcholine protocol using low-dose (20µg) and higher-dose (100µg) infusions. He outlines preparation of the solution from ophthalmic vials, its dilution, and the technique for slow intra-coronary injection over 1–2 minutes.

Dr Widmer highlights the importance of continuous monitoring for ECG changes, heart block, hemodynamic instability, or symptom reproduction, and explains how to differentiate epicardial from microvascular spasm when angiography appears normal. In this case, the patient shows no chest pain, no ECG changes, and preserved epicardial caliber at both doses—findings consistent with a negative spasm test.
 

Key learning points:

• Step-by-step guidance for safe preparation and administration of intracoronary acetylcholine, including test dosing and hemodynamic monitoring.
• Diagnostic distinctions between epicardial and microvascular spasm, and the role of symptom reproduction in interpretation.
• How to assess a normal acetylcholine response and its management implications regarding calcium channel blocker or nitrate use.