How to measure coronary collateral function?

By Thorsten Reffelmann

The optimal method for quantitation of coronary collateral blood flow remains a matter of discussion. Various angiographic indices as well as flow- and pressure-derived parameters are currently used. The “gold standard” appears to be the pressure-derived collateral blood flow index, primarily based on intracoronary pressure distal to an occluded balloon.

However, only dynamic blood flow, not static pressure, brings oxygen and substrates to the heart, and high static intracoronary pressures distal to the occluded balloon may be measured when nearly no collateral flow exists due to impeded outflow toward an obstructed microvasculature.

“Wash-out collaterometry,” as the clearance of contrast-medium distal to the occluded balloon, was proposed as a flow-based quantitation of collateral function by Seiler et al in 2001.1 Here, the number of heart beats was counted until approximately half the length of an occluded epicardial vessel was cleared of a radiographic contrast medium.

In our paper, we tried to apply this method to the principles of thermodilution: an intracoronary flush of room-temperature saline should evoke an intracoronary temperature drop. The velocity of the rise in temperature back to normal value should be in direct relation to the existent blood flow. In a fully occluded artery (using, for example, balloon occlusion), this would be equal to collateral blood flow.

Starting with this idea, a miniature model with a system of plastic tubes and pumps was set up, simulating coronary flow, pressure, and collateral flow. Using a thermo-pressure wire and the RADI-analyzer system, we confirmed our expectations of an exponential temperature rise after a room-temperature flush of saline during balloon occlusion with the slope of the temperature rise being related to experimental collateral flow.

Inspired by these promising results, a clinical study in 26 patients with coronary artery disease was conducted, in which we measured temperature curves after an intracoronary bolus of room-temperature saline and subsequent balloon occlusion. The interested reader may be referred to our article to see whether these measurements keep the promise of a “novel flow-based” parameter of collateral flow.

Reference

  1. Seiler C, Billinger M, Fleisch M, Meier B. Washout collaterometry: a new method of assessing collaterals using angiographic contrast clearance during coronary occlusion. Heart. 2001;86:540-546.

 

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