A ''Twilight Period'' of coronary perfusion: The risk of intraoperative infarction in surgery for main left coronary obstruction

This study investigates the significance of an intraoperative period of low coronary perfusion pressure which may lead to ischemia, infarction, or both, in patients undergoing coronary bypass surgery for tight left main obstruction. ''Twilight Period'' (TP) was defined as the time interval from initiation of cardiopulmonary bypass to implementation of cold cardioplegia. Fifty-four patients with main left coronary obstruction (>50%) were divided in three groups: Group I (20), TP<5 minutes; Group II (15), TP=5-15 minutes; and Group III (19), TP>15 minutes. Monitoring parameters included: systemic perfusion pressure during TP, perfusion flows, length of TP, time of ischemia, myocardial temperatures during ischemia, postoperative CK-MB level, EKG-detectable infarction, and postoperative therapeutic support requirements. Results: Intraoperative myocardial infarction by EKG was 0% in Group I, 7% in Group II, and 26.3% in Group III; mortality was 0%, 0%, and 15.7%, respectively. CK-MB values were 18±3.2 IU, Group I; 18.3±2.5 IU, Group II; and 49.4±10.3 IU, Group III. Group I vs. III: P 0.01. Levels of postoperative support: Level A, <12 hours; Level B, 12-36 hours; and Level C, >36 hours. Intra-aortic balloon pump (IABP) was considered Level C. In Group I, 75% (15/20) fell in Level A; 15% (3/20) in Level B and 10% (2/20) in Level C. In Group II, 60% (9/15) fell in Level A; 26.7% (4/15) in Level B; and 13% (2/15) in Level C. In Group III, 36.8% (7/19) fell in Level A; 15.8% (3/19) in Level B; and 47.4% (9/19) in Level C. Six patients, all in Group III, required IABP; 3 of them died (15.7%). When the TP is more than 15 minutes, the incidence of intraoperative myocardial infarction definitely increases.