Minimally invasive evaluation of coronary microvascular function by electron beam computed tomography

Background-We previously demonstrated that in vivo electron-beam computed t omography (EBCT)-based indicator-dilution methods provide an estimate of in tramyocardial blood volume (BV) and perfusion (F), which relate as BV=aF+b rootF, where a characterizes the recruitable (exchange) and b the nonrecrui table (conduit) component of the myocardial microcirculation, In the presen t study, we compared BV and F with intracoronary Doppler ultrasound-based c oronary blood flow (CBF) as a method for detecting and quantifying differen tial responses of these microvascular components to vasoactive drugs in nor mal (control) and hypercholesterolemic (HC) pigs. Methods and Results-BV and F values were obtained from contrast-enhanced EB CT studies in 14 HC and 14 control pigs, BV, F, and CBF values were obtaine d at baseline (intracoronary infusion of saline) and after 5 minutes each o f intracoronary infusion of adenosine (100 mug . k(-1) . min(-1)) and nitro glycerin (40 mu Lg/min). BV and CBF reserves in response to adenosine were attenuated in HC pigs compared with controls (90+/-36% versus 127+/-42%, P< 0.03, and 485+/-18'% versus 688+/- 160%, P<0.01, respectiveIy). The relatio nship between BV and F showed consistently lower recruitable BV in HC versu s control pigs. Nonrecruitable BV reserve in response to adenosine was atte nuated in HC compared with controls (77+/-20% versus 135+/-28%, P<0.001). O ur findings are consistent with HC-induced impairment of intramyocardial re sistance vessel function. Conclusions--EBCT technology allows minimally invasive evaluation of intram yocardial microcirculatory function and permits assessment of microvascular BV distribution in different functional components. This method may be of value in evaluating the coronary microcirculation in pathophysiological sta tes such as hypercholesterolemia.