Quantitative flow ratio for the functional assessment of extracranial internal carotid artery stenosis.

BACKGROUND: In asymptomatic patients presenting with significant internal carotid artery (ICA) stenoses undergoing endovascular revascularization, a selective angiography before stenting (CAS) is required. Sometimes, angiographic findings could be discordant from non-invasive assessment and a tool able to evaluate functional relevance of the stenosis could be of value. We sought to evaluate the usefulness of quantitative flow ratio (QFR) as angiography-based tool for functional assessment of ICA stenoses. METHODS: We prospectively enrolled 50 asymptomatic patients undergoing CAS. Peak systolic velocity (PSV, cm/s) assessed at color Doppler echocardiography was used to identify significant stenoses (PSV >125 cm/s). At angiography, assessment of ICA stenosis was obtained visually (%DSVISUAL) and according NASCET criteria (%DSNASCET). Stenoses were considered significant if >60%. After exclusion of 20 vessels, QFR, area stenosis (AS, %) and minimal lumen area (MLA, mm2) were obtained in the remaining 80 vessels. RESULTS: At linear regression analysis, QFR significantly correlated with PSV (r2=0.52, P<0.001) as well as with %DSNASCET (r2=0.68, P<0.001) and %DSVISUAL (r2=0.71, P<0.001). Using PSV as reference, QFR showed good accuracy to predict functionally significant stenosis (AUC=0.98, P<0.001) with a cut-off value of 0.93. As compared with %DSNASCET and %DSVISUAL, QFR showed a significantly higher accuracy (61% vs. 73% vs. 94%, respectively; P<0.05), sensitivity (43% vs. 61% vs. 93%, respectively; P<0.05) and negative predictive value (46% vs. 51% vs. 85%, respectively; P<0.05) for detecting hemodynamically significant ICA stenoses. CONCLUSIONS: This study suggest the potential benefit of adopting QFR for functional assessment of extracranial ICA stenoses. These data should be validated in larger studies.

Invasive Assessment of Coronary Microcirculation: A State-of-the-Art Review.

A significant proportion of patients presenting with signs and symptoms of myocardial ischemia have no "significant" epicardial disease; thereby, the assessment of coronary microcirculation gained an important role in improving diagnosis and guiding therapy. In fact, coronary microvascular dysfunction (CMD) could be found in a large proportion of these patients, supporting both symptoms and signs of myocardial ischemia. However, CMD represents a diagnostic challenge for two main reasons: (1) the small dimension of the coronary microvasculature prevents direct angiographic visualization, and (2) despite the availability of specific diagnostic tools, they remain invasive and underused in the current clinical practice. For these reasons, CMD remains underdiagnosed, and most of the patients remain with no specific treatment and quality-of-life-limiting symptoms. Of note, recent evidence suggests that a "full physiology" approach for the assessment of the whole coronary vasculature may offer a significant benefit in terms of symptom improvement among patients presenting with ischemia and non-obstructive coronary artery disease. We analyze the pathophysiology of coronary microvascular dysfunction, providing the readers with a guide for the invasive assessment of coronary microcirculation, together with the available evidence supporting its use in clinical practice.