PHARMACOLOGICAL STRESS-INDUCED REGIONAL MYOCARDIAL BLOOD-FLOW HETEROGENEITY AND LEFT-VENTRICULAR WALL THICKENING ABNORMALITY - COMPARISON OF INTRAVENOUS ADENOSINE WITH DIPYRIDAMOLE IN A MODEL OF CRITICAL CORONARY STENOSIS

Variations in reported sensitivity of myocardial perfusion scans or wa ll motion abnormalities during pharmacologic stress with intravenous a denosine and dipyridamole may be caused by differences in myocardial o xygen demand or myocardial blood flow redistribution induced by each a gent. To investigate the physiologic correlates of functional abnormal ities during pharmacologic stress testing, regional myocardial blood f low (radiolabeled microsphere technique) and left ventricular segmenta l wall thickening (quantitative two-dimensional echocardiography) were measured in 9 dogs with an open chest model of critical stenosis of t he left circumflex coronary artery. Data were obtained at baseline and peak drug infusion for intravenous adenosine (0.42 mg/kg over a 3-min ute period) and for intravenous dipyridamole (0.56 mg/kg over a 4-minu te period). Adenosine and dipyridamole induced regional flow abnormali ty in 7 (77%) of 9 dogs. Myocardial segments with decreased endocardia l/epicardial flow ratio were similar for both agents (2.9 +/- 1.8 vs 2 .7 +/- 1.3, p = [NS]). Segments with myocardial flow heterogeneity (ra tio of endocardial flow to control left anterior descending/left circu mflex endocardial flow) were similar for both agents (2.7 +/- 0.9 vs 2 .3 +/- 1.0, p = NS). Adenosine-induced wall thickening abnormality (77 % vs 55% with dipyridamole) correlated with regional flow abnormality. Significantly lower mean arterial pressure (53 +/- 1.7 mm Hg vs 64 +/ - 1.9 mm Hg, p < 0.01) and more prolonged drug effect (18 +/- 6.4 min vs 3 +/- 1.4 min, p < 0.001) were seen for dipyridamole compared with adenosine. Adenosine induces regional flow abnormality similar to dipy ridamole but with less hemodynamic perturbation, and adenosine-induced wall thickening abnormality more closely parallels regional flow abno rmality.