Relation between coronary 'steal' and contractile function at rest in collateral-dependent myocardium of humans with ischemic heart disease

Background - We tested the hypothesis that rest asynergy in collateral- dependent myocardium correlates with coronary steal. Methods and Results - PET with [¹³N]ammonia measured myocardial blood flow and flow reserve in 15 patients with symptomatic chronic ischemic heart disease. Coronary angiography assessed stenosis severity and collateral blood supply. Echocardiography or contrast ventriculography evaluated regional wall motion. Collateral-dependent segments with normal flow at rest and supplied by coronary vessels having ≤50% diameter stenosis were studied. Steal was defined as a decline in myocardial blood flow with adenosine ≥0.15 mL · min^-1 · g^-1 versus rest. Blood flow at rest in asynergic, collateral- dependent segments with steal (1.15±0.35 mL · min^-1 · g^-1) exceeded (P<0.0001) that of asynergic segments without steal (0.81±0.24) and those with normal contraction (0.77±0.18). Although the flow reserve ratio of segments with normal contraction (1.8±0.8) exceeded that of asynergic ones with (0.6±0.1) or without (1.3±0.4) steal, overlap was great. Correlation between basal contraction and flow reserve ratio in collateral-dependent myocardium was significant but weak (r=0.45, P<0.001). However, segments demonstrating 'steal' with adenosine manifested asynergy in 22 of 23 collateral-dependent segments versus 24 of 39 nonsteal segments (χ²=7.10, P<0.01). Conclusions - Although myocardial flow reserve in collateral- dependent segments with normal contraction exceeded that of asynergic segments, overlap was great. However, in patients with angina or congestive heart failure, left ventricular segments demonstrating steal with adenosine almost always exhibit asynergy at rest. Thus, coronary steal may play an important role in the pathogenesis of chronic contractile impairment at rest, whereas simple reduction of flow reserve may be less important in selected patients.