Regional myocardial shortening in relation to graft-reactive hyperemia and flow after coronary bypass surgery

Extent of regional shortening of myocardium in areas newly perfused by bypass grafting was determined in 56 patients by a new technique employing 4 to 6 radiopaque markers sutured in pairs to the epicardium near the coronary anastomosis. Paradoxical systolic expansion (PSE) was manifest in 16 regions (a 12% incidence) during the follow-up period, and 6 of these showed spontaneous remisson. All cases of PSE were in the region of the left anterior descending artery. Correlation between graft flow measured during operation and regional shortening during the postoperative period revealed that the development of PSE could not be predicted from the hemodynamic measurements. In the majority of cases postoperative myocardial infarction could also be excluded as an explanation. At 1 yr after operation most grafts were patent in PSE regions but collaterals, apparent preoperatively, could not be visualized. Excluding PSE, shortening fraction (ratio of shortening to maximum marker separation) for all graft regions at 1 wk was 9.8%; 1 mth, 12.8%; 3 mth, 13.3%; and 6 mth, 13.9%. Average graft flow was 56 ml per min and average reactive hyperemia was 25% with 37% of grafts showing no response. For those regions that did not develop PSE there was a positive correlation between shortening fraction and flow that became significant (null hypothesis: r=0) when reactive hyperemia exceeded 20%. Correlation was greatest at 1 wk and 1 mth, but became insignificant at 6 mth. These results are consistent with a simple interpretation of reactive hyperemia, i.e. that graft-reactive hyperemia is related to the dependence of viable tissue on the functioning of the graft.