Coronary Microvascular Spasm as the Underlying Cause of the Angiographic Slow Flow Phenomenon

Pharmacological coronary spasm provocative testing in clinical practice: A French Coronary Atheroma and Interventional Cardiology Group (GACI) position paper

Vasospastic angina, also described as Prinzmetal angina, was first described as a variant form of angina at rest with transient ST-segment elevation; it is common and present in many clinical scenarios, including chronic and acute coronary syndromes, sudden cardiac death, arrhythmia and syncope. However, vasospastic angina remains underdiagnosed, and provocative tests are rarely performed. The gold-standard diagnostic approach uses invasive coronary angiography to induce coronary spasm using ergonovine, methylergonovine or acetylcholine as provocative stimuli. The lack of uniform protocol decreases the use and performance of these tests, accounting for vasospastic angina underestimation. This position paper from the French Coronary Atheroma and Interventional Cardiology Group (GACI) aims to review the indications for provocative tests, the testing conditions, drug protocols and positivity criteria.

Pathophysiology and Diagnosis of Coronary Functional Abnormalities

Approximately one-half of patients undergoing diagnostic coronary angiography for angina have no significant coronary atherosclerotic stenosis. This clinical condition has recently been described as ischaemia with non-obstructive coronary arteries (INOCA). Coronary functional abnormalities are central to the pathogenesis of INOCA, including epicardial coronary spasm and coronary microvascular dysfunction composed of a variable combination of increased vasoconstrictive reactivity and/or reduced vasodilator function. During the last decade - in INOCA patients in particular - evidence for the prognostic impact of coronary functional abnormalities has accumulated and various non-invasive and invasive diagnostic techniques have enabled the evaluation of coronary vasomotor function in a comprehensive manner. In this review, the authors briefly summarise the recent advances in the understanding of pathophysiology and diagnosis of epicardial coronary artery spasm and coronary microvascular dysfunction.

Invasive Diagnosis of Coronary Functional Disorders Causing Angina Pectoris

Coronary vasomotion disorders represent a frequent cause of angina and/or dyspnoea in patients with non-obstructed coronary arteries. The highly sophisticated interplay of vasodilatation and vasoconstriction can be assessed in an interventional diagnostic procedure. Established parameters characterising adequate vasodilatation are coronary blood flow at rest, and, after drug-induced vasodilation, coronary flow reserve, and microvascular resistance (hyperaemic microvascular resistance, index of microcirculatory resistance). An increased vasoconstrictive potential is diagnosed by provocation testing with acetylcholine or ergonovine. This enables a diagnosis of coronary epicardial and/or microvascular spasm. Ischaemia associated with microvascular spasm can be confirmed by ischaemic ECG changes and the measurement of lactate concentrations in the coronary sinus. Although interventional diagnostic procedures are helpful for determining the mechanism of the angina, which may be the key to successful medical treatment, they are still neither widely accepted nor applied in many medical centres. This article summarises currently well-established invasive methods for the diagnosis of coronary functional disorders causing angina pectoris.