Flow-function mismatch in patients with chest pain and normal coronary arteries: a cardiovascular magnetic resonance stress tagging study

Background: Matching between regional flow and myocardial function is a pathophysiological hallmark of normal and ischemic myocardium, but only few and conflicting data are available in patients with chest pain and normal coronary arteries. Cardiovascular magnetic resonance (CMR) allows a simultaneous and quantitative assessment of flow and function during stress. Aim: to simultaneously assess coronary flow and myocardial function matching in patients with chest pain and normal coronary arteries. Methods: we enrolled 16 patients (7 males, age = 63±5) with typical chest pain, angiographically smooth coronary arteries, no inducible vasospasm and normal resting left ventricular function. All underwent dipyridamole (D, 0.84 mg/kg) MRI with simultaneous assessment of perfusion reserve index (PRI, calculated as the ratio between D and rest upslope) and wall strain (systolic lengthening, E1,%, and shortening, E2,%) by tagging. A 16 segment model of the left ventricular was adopted. Results: The 224 LV segments were divided into 3 groups, based upon the segmental transmural PRI response: I, lowest tertile (PRI between 0.74 and 1.84); II=middle tertile (PRI between 1.86 and 2.63); III=highest tertile (PRI between 2.66 and 11.45). The group with highest flow had tendentially lower E1 stress value (I = -12.3±4.1; II = -11.1±5; III = -10.8±3.6, p=ns) but significantly lowest E2 stress value (I = 36±20; II = 28±15; III = 27±16, p= 0.02 I vs II and p<0.01 I vs III). There was a weak correlation between transmural PRI and E2 (r = 0.15, p=0.02). The correlation was absent when only subendocardial (E1: r = 0.09; E2: r= 0.02, p=ns) or subepicardial PRI (E1: r = 0.09, p=ns; E2: r = 0.11, p=0.09) were considered. Conclusions: Patients with chest pain and normal coronary arteries show a peculiar mismatch between regional coronary flow and segmental function, with a "paradoxical" supernormal function in segments with lowest increase in flow. This is a clue to a possible metabolic or cellular uncoupling between flow and function as the central defect in these patients.