Coronary flow capacity: concept, promises, and challenges

Abstract

The vasodilator capacity of the coronary circulation is an important diagnostic and prognostic characteristic, and its accurate assessment is therefore an important frontier. The coronary flow capacity (CFC) concept was introduced to overcome the limitations associated with the use of coronary flow reserve (CFR) for this purpose, which are related to the sensitivity of CFR to physiological alterations in systemic and coronary hemodynamics. CFC was developed from positron emission tomography, and was subsequently extrapolated to invasive coronary physiology. These studies suggest that CFC is a robust framework for the identification of clinically relevant coronary flow abnormalities, and improves identification of patients at risk for adverse events over the use of CFR alone. This Review will discuss the concept of CFC, its promises in the setting of ischaemic heart disease, and its challenges both in theoretical and practical terms.

Keywords: Coronary flow; Coronary flow capacity; Coronary flow reserve; Vasodilator reserve capacity.

Fig. 1

The coronary flow capacity concept derived from positron emission tomography on the basis of a scatter plot of CFR versus absolute stress flow. As coronary flow reserve (CFR) equals stress flow divided by rest flow, a 2-dimensional plot comprehensively captures the flow characteristics of the coronary circulation. Reproduced from Johnson and Gould [11], with permission

Fig. 2

Individual patient data incorporated into the coronary flow capacity concept. The captured rest and stress flow, and coronary flow reserve can be displayed within the coronary flow capacity scatter plot, and can be incorporated into a graphical map of the left ventricle. Reproduced from Johnson and Gould [11], with permission

Fig. 3

Since coronary flow reserve (CFR) equals hyperemic to baseline average peak flow velocity (hAPV), a 2-dimensional map of CFR versus hAPV comprehensively describes the invasive flow characteristics of the coronary vasculature under investigation. Within this concept, four clinically meaningful categories are defined (coded with different colors in the graph) based on well-validated invasive CFR cut-off values and the corresponding hAPV percentiles. See “Doppler flow velocity derived coronary flow capacity” section for details. Reproduced from van de Hoef et al. [12], with permission

Fig. 4

Identification of severely reduced CFC by CFR. A large proportion of patients with moderately to normal coronary flow capacity presented abnormal CFR values. CFC coronary flow capacity, CFR coronary flow reserve. (Adapted from van de Hoef et al. [12], with permission)