A Novel Hydrodynamic Approach for the Evaluation of Microvascular Resistance during Provocative Spasm Testing

Introduction: Intracoronary acetylcholine provocative testing is the gold standard method for the assessment of epicardial and/or microvascular spasm, with the latter diagnosed when there are acetylcholine (ACh)-induced chest pain and ischaemic electrocardiogram changes in the absence of epicardial spasm. While epicardial spasm can be visualised, microvascular spasm cannot and remains a presumed diagnosis. Methods: This article describes a hydrodynamic model developed to calculate the epicardial and microvascular resistances for both pre- and post-ACh administration. The model is based on the concept of two resistances (epicardial and microvascular) located in a series arrangement. The epicardial resistance is obtained as a hydraulic resistance, accounting for the friction resistance between the coronary blood flow and the arterial walls. The microvascular resistance is calculated by subtracting the epicardial resistance from the ratio of the pressure and flow measured using coronary guidewire-based techniques. Conclusion: This novel methodology provides key insights into the physiological characteristics of epicardial and microvascular spasm during ACh provocation testing. Further clinical validation is required to explore the clinical utility of this methodology.