Measurement of In Vivo Myocardial Microcirculatory Function with Electron Beam CT

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Abstract
The purpose of this work was to examine the capability of electron beam CT (EBCT) to characterize responses to recruitable (capillaries and small arterioles) compared with nonrecruitable (small to large arterioles) myocardial microvessels to vasoactive substances. Myocardial perfusion (F) and total intramyocardial blood volume (BV) of the anterior cardiac wall were quantitated in 36 pigs, using EBCT and intravenous contrast agent injections, before and after intracoronary administration of either NG-monomethyl-L-arginine (L-NMMA), nitroglycerin, adenosine, or saline. Plotting the relationship of BV and F provided values for the recruitable and nonrecruitable microvascular transit times and BV allotment. Nitroglycerin increased nonrecruitable BV by 84.5 ± 7.4%, whereas adenosine increased both recruitable and nonrecruitable microvascular BV (47.1 ± 18.9 and 66.0 ± 10.9%, respectively). L-NMMA led to a 25.1% decrease only in the recruitable BV. In the control group, no changes were observed. Characteristic responses of different-size myocardial microvessels may be inferred with EBCT, which provides a unique opportunity to portray intramyocardial microcirculatory function noninvasively.