Measurement of in vivo myocardial microcirculatory function with electron beam CT

Purpose: The purpose of this work was to examine the capability of electron beam CT (EBCT) to characterize responses of recruitable (capillaries and s mall arterioles) compared with nonrecruitable (small to large arterioles) m yocardial microvessels to vasoactive substances. Method: 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 admin istration of either NG-monomethyl-L-arginine (L-NMMA), nitroglycerin, adeno sine, or saline. Plotting the relationship of BV and F provided values for the recruitable and nonrecruitable microvascular transit times and BV allot ment. Results: Nitroglycerin increased nonrecruitable BV by 84.5 +/- 7.4%, wherea s 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% decr ease only in the recruitable BV. In the control group, no changes were obse rved. Conclusion: Characteristic responses of different-size myocardial microvess els may be inferred with EBCT, which provides a unique opportunity to portr ay intramyocardial microcirculatory function noninvasively.