Different Mechanisms of Ischemic Adaptation to Repeated Coronary Occlusion in Patients With and Without Recruitable Collateral Circulation

Objectives. The aim of this study was to investigate the interaction between ischemic preconditioning (IP) and collateral recruitment (CR) during ischemic adaptation in patients. Background. The mechanism of ischemic adaptation still remains controversial in humans. Methods. The clinical, electrocardiographic, hemodynamic and echocardiographic responses to three 150-s occlusions of the left anterior descending coronary artery were assessed in relation to CR in 18 patients with effort angin undergoing elective percutaneous transluminal coronary angioplasty. Results. During the first occlusion, recruitable collateral circulation (RCC) to the occluded myocardium was detected by myocardial contrast echocardiography in 6 patients (Group C) and was not seen in 12 (Group N). In Group N, all patients manifested signs of severe ischemi during each inflation. However, their symptoms and ST segment shift significantly decreased from the first to the third occlusions, suggesting the occurrence of IP. The elevation of mean pulmonary artery pressure and deterioration of anterior wall motion were comparable between the first and the third occlusions in Group N. In contrast, myocardial ischemi was significantly less marked during occlusion in Group C than in Group N, and no preconditioning effect was observed. The extent of RCC did not differ between the first and the third occlusions in each group. Conclusions. Both IP and CR may play independent roles in ischemic adaptation in humans. With RCC, myocardial ischemi was greatly reduced. Without RCC, preconditioning clinically and electrocardiographically lessened myocardial ischemi but failed to preserve left ventricular function.