Coronary Microvascular Function is Correlated With Peak Exercise Capacity in Patients With Unexplained Cardiac Exertion Symptoms and Non-obstructive Coronary Artery Disease

Introduction: Coronary microvascular dysfunction (CMD) is prevalent in symptomatic patients with no obstructive coronary artery disease. We postulated that exercise capacity and cardiac output augmentation in response to exercise are linked to coronary microvascular function in this patient population.Methods: Fifty-one consecutive patients with unexplained cardiac exertion symptoms, non-obstructive coronary artery disease on angiography (<50% stenosis), and normal left ventricular ejection fraction (>50%) who underwent concurrent clinically indicated coronary reactivity testing and invasive cardiopulmonary exercise testing (CPEX) were included. Microvascular function was assessed by coronary flow reserve (CFR; hyperemic/resting flow) in response to intracoronary adenosine injection. Cardiac output (CO) was calculated at rest and peak exercise using Fick’s formula. CO limitation was defined as a measured (peak CO - resting CO) <80% than the expected [6*absolute ΔVO2 (Peak VO2-Rest VO2) increase in CO in L/min]. The relationship between CFR, maximal exercise capacity, and CO augmentation at peak exercise was explored.Results: Patients were 56.6±10.5 years old and 73% were females. CFR had a modest positive correlation with measured increase in CO (r=0.42; P=0.003) (Fig 1A), and with maximal ergometric exercise capacity [in Watts/Kg] (Pearson’s r=0.33, P=0.02) (Fig 1B). Patients with, vs. without impaired cardiac limitations during exercise, had significantly lower CFR levels (2.6±0.5 vs 3.1±0.7; P=0.01) (Fig 2).Conclusion: Impaired coronary microvascular function is associated with lower peak exercise capacity and reduced cardiac output augmentation in response to exercise, underscoring the functional ramification of CMD in symptomatic patients.