Acetylcholine coronary vasospastic responses evaluated via a hydrodynamic model

Background Acetylcholine (ACh) provocation testing may identify epicardial or microvascular coronary vasospasm. However, delineation of these diagnoses is difficult in current clinical practice, warranting investigation of physiological changes. Aim To evaluate epicardial and microvascular resistance during ACh provocation using a novel hydrodynamic model. Methods ANOCA (angina with non-obstructive coronary arteries) patients underwent Functional Coronary Angiography (n=48), involving a dual sensor-tipped pressure-doppler flow wire measuring continuous blood flow velocity and coronary pressure during ACh provocation. A hydrodynamic model was developed to evaluate epicardial and microvascular resistances for both pre- and post-ACh administration. Results Consistent with the diagnostic criteria, the model confirms that patients with a clinical diagnosis of epicardial spasm (n=6) exhibited substantial changes in epicardial resistance during ACh provocation (n=4). However, amongst patients with a clinical diagnosis of microvascular spasm (n=25), 64% exhibited only an increased epicardial resistance and thus may be inappropriately classified. Additionally, the model identified a subset of patients with simultaneous increases in both epicardial and microvascular resistance (n=11, 23%). Conclusion Our findings challenge the current evaluation of coronary vasospasm. The contemporary clinical diagnostic criteria for epicardial spasm are supported by an increased epicardial resistance in the model. However, 2/3 of patients clinically diagnosed as microvascular spasm do not have an increased microvascular resistance, but only an increased epicardial resistance. Moreover, of those with an increased microvascular resistance, most also had an increased epicardial resistance, i.e. a combined phenotype representing a novel diagnostic entity.