Effects of previous myocardial infarction on measurements of reactive hyperemia and the coronary vascular reserve

The measurement of coronary vascular reserve by the reactive hyperemic response to ischemia has been advocated as a practical method of assessing the physiologic significance of coronary stenoses. Because the concept of measuring coronary blood flow during maximal vasodilation assumes a normal arteriolar network and viable myocardium, the presence of previous myocardial infarction may cause a significant decrease in the coronary reserve unrelated to the severity of a coronary stenosis itself. To determine the potential importance of this effect, rest and hyperemic coronary blood flow were measured in 14 dogs in the regions subtended by the left anterior descending and left circumflex coronary arteries. One hour occlusion of the left anterior descending artery followed by reperfusion was performed in 10 dogs; the 4 remaining dogs in which no occlusion was performed served as control animals (group 3).One week later, rest and hyperemic blood flow measurements were repeated in all 14 dogs. Of the 10 dogs undergoing left anterior descending artery occlusion, 5 had a large infarct (group 1) and 5 had a small infarct (group 2). In group 1 in the 1 week study, both the coronary reserve in the left anterior descending artery zone and the ratio of the coronary reserve in this zone and the left circumflex artery zone decreased compared with values before occlusion (from 425 ± 134 to 150 ± 34% and from 1.56 ± 0.40 to 0.68 ± 0.31, respectively; both p = 0.007). These values were also less compared with either group 2 or group 3 at 1 week (364 ± 155% and 1.84 ± 0.86, respectively, in group 2 and 318 ± 75% and 1.17 ± 0.11, respectively, in group 3; both p = 0.02). Thus, a large infarcted region will result in a decreased coronary vascular reserve despite a widely patent epicardial coronary artery