MICROVASCULAR DYSFUNCTION IN COLLATERAL-DEPENDENT MYOCARDIUM

Objectives. The aim of this study was to evaluate myocardial blood how regulation in collateral-dependent myocardium of patients with corona ry artery disease. Background. Despite great clinical relevance, perfu sion correlates of collateral circulation in humans have rarely been e stimated by quantitative methods at rest and during stress. Methods. N ineteen patients with angina and isolated occlusion of the left anteri or descending (n = 14) or left circumflex (n = 5) coronary artery were evaluated. Using positron emission tomography and nitrogen-13 ammonia , we obtained flow measurements at baseline, during atrial pacing-indu ced tachycardia and after intravenous administration of dipyridamole ( 0.56 mg/kg body weight over 4 min). Flow values in collateral-dependen t and remote areas were compared with values in 13 normal subjects. Re sults. Flow at rest was similar in collateralized and remote myocardiu m (0.61 +/- 0.11 vs. 0.63 +/- 0.17 ml/min per g, mean a 1 SD), and bot h values were lower than normal (1.00 +/- 0.20 ml/min per g, p < 0.01) . During pacing, blood flow increased to 0.83 +/- 0.25 and 1.11 +/- 0. 39 ml/min per g in collateral-dependent and remote areas, respectively (p < 0.05 vs. baseline); both values were lower than normal (1.86 +/- 0.61 ml/min per g, p < 0.01). Dipyridamole induced a further increase in perfusion in remote areas (1.36 +/- 0.57 ml/min per g, p < 0.01 vs , pacing) but not in collateral dependent regions (0.93 +/- 0.37 ml/mi n per g, p = NS vs. pacing); again, both values were lower (p < 0.01) than normal (3.46 +/- 0.78 ml/min per g). Dipyridamole how in collater al dependent myocardium was slightly lower in patients with poorly dev eloped than in those with well developed collateral channels (0.75 +/- 0.29 vs. 1.06 +/- 0.38 ml/min per g, respectively, p = 0.06); however , the former showed higher flow inhomogeneity (collateral/control how ratio 0.58 +/- 0.10 vs. 0.81 +/- 0.22, respectively, p < 0.02). A line ar direct correlation was observed between how reserve of collateral d ependent and remote regions (r = 0.83, p < 0.01). Conclusions. Despite rest hypoperfusion, collateral-dependent myocardium maintains a vasod ilator reserve that is almost fully utilized during increases in oxyge n consumption. A global microvascular disorder might hamper adaptation to chronic coronary occlusion.