Letter by de Araújo Gonçalves et al Regarding Article, “Invasive Evaluation of Patients With Angina in the Absence of Obstructive Coronary Artery Disease”
Authors: Pedro de Araújo Gonçalves, Mauro Echavarria-Pinto, Hector M. Garcia-Garcia
Journal: Circulation (2015)

The elegant study of Lee et al 1 adds to the growing body of recent evidence that underlines the importance of nonobstructive causes of ischemic heart disease.We would very much appreciate the authors' views on the following aspects of their work.First, we find polarity between the high coronary flow reserve (CFR; 4.11±1.70)observed in the left anterior descending artery and the cardiovascular risk profile and the notably high prevalence (72%) of abnormal stress tests in the study population.Although CFR has been criticized for a higher hemodynamic dependence, the observed CFR values coincide with those of normal control subjects and healthy volunteers. 2 This contrasts with the clinical profile and high prevalence of predisposing risk factors (patients in whom CFR normally averages 2.8±1.39 6 ) and even likely suggests a "supranormal" CFR in distant territories-such as that observed in athletes-in those patients in whom stress tests were abnormal, provided that the reported CFR and abnormal stress test region matched the left anterior descending artery territory.Could the authors please comment and offer a tentative explanation for the positive stress tests given the preserved flow supply?Moreover, we are puzzled by the poor correlation between CFR and index of microcirculatory resistance (IMR) observed in vessels with intermediate stenosis, considering that both CFR and IMR are partly investigating microcirculatory function. 3By evaluating vessels with normal epicardial conductance (by fractional flow reserve), this study offers a great opportunity to address the relationship between CFR and IMR under ideal conditions (absence of epicardial disease) for both indexes.Could the authors please further describe the observed relationship between CFR and IMR?Finally, we believe that the definition of microvascular dysfunction based on IMR ≥25 U is pragmatic but can be challenged in patients in whom CFR is frankly normal (as in many of the present study), given the preserved flow supply and, most remarkably, the wealth of data linking a normal CFR with a very low risk of adverse events at the long term. 2 Bridging is a very frequent finding in both computed tomographic angiography and autopsy studies and is still a matter of debate in terms of its clinical implications because many of the cases might be only innocent bystanders.In a recent computed tomographic angiography study evaluating the long-term outcome of patients with chest pain, those with myocardial bridging had a rather uneventful outcome, with an adverse cardiac event rate similar to that of patients without this feature, over a follow-up of >6 years. 4In addition, if the presence of myocardial bridging could explain symptoms or myocardial ischemia, it would be expected that the depth (with >2 mm considered deep bridging) and length of the tunneled segments could have some influence on this outcome.This was not reported in the study of Lee et al, 1 but other authors failed to demonstrate a correlation of the depth and length of the myocardial bridge to either the presence of ischemia 5 or patient outcomes. 4Thus, it is not reasonable to assume that patient symptoms could be explained in all cases by the presence of this very common feature.