A novel flow-based parameter of collateral function assessed by intracoronary thermodilution

Currently, many methods for quantitation of coronary collateral function are based on intracoronary pressure measurements distal of an occluded balloon, which do not fully account for the dynamic nature of collateral flow. Therefore, a flow-based parameter of coronary collateral function based upon principles of thermodilution was evaluated.

In 26 patients with a high-grade coronary artery stenosis, intracoronary hemodynamics were analyzed by the RadiAnalyzer system (St Jude Medical), including fractional flow reserve (FFR), index of microcirculatory resistance (IMR), and the pressure-based collateral flow index (CFI) during balloon occlusion and hyperemia (intravenous adenosine). Moreover, immediately after an intracoronary bolus of room-temperature saline, the balloon was occluded and the intracoronary temperature distal to the balloon was analyzed over time. The slope of the temperature-time curve was calculated after logarithmic transformation as an index of collateral blood flow (CBFI).

The coefficient of variation between two measurements of CBFI amounted to 11 ± 2%. In patients with CFI ≥0.25, CBFI amounted to 0.55 ± 0.09, whereas in those with CFI <0.25, CBFI was 0.37 ± 0.03. CBFI correlated significantly with CFI (r = 0.65; P<.001). Interestingly, in the subgroup with IMR below the median (<14.2 mm Hg · s), the slope of the linear regression for CBFI vs CFI was steeper than in individuals with higher IMR, which indicates more effective collateral flow for any given intracoronary pressure distal to the occluded balloon in the group with lower microvascular resistance.

This novel index might be useful as a flow-based index of collateral function, and should be evaluated in further studies.